BRPI0919505A2 - solar grade silicon production from silicon dioxide - Google Patents

Abstract

Method for the production of pure silicon, formulation, reactor and / or electrodes, device and use of silicon oxide in the production of silicon The present invention relates to a complete method for the production of pure silicon which is suitable for use as a silicon. solar-grade, comprising reducing a silicon oxide, purified by acid precipitation from an aqueous solution of a silicon oxide dissolved in an aqueous phase, using one or more sources of pure carbon, the purified silicon oxide being obtained, in particular, by precipitation of a silicon oxide dissolved in an aqueous phase in an acidifier. The invention also relates to a formulation containing an activator and a device for producing silicon, a reactor and electrodes.

Description

Descriptive Report of the Invention Patent for METHOD FOR THE PRODUCTION OF PURE SILICON, FORMULATION, REACTOR AND / OR ELECTRODES, DEVICE AND USE OF SILICON OXIDE IN THE PRODUCTION OF SILICON

The present invention relates to a complete method for the production of pure silicon, which is suitable as solar grade silicon, comprising the reduction of a silicon oxide, purified by acid precipitation of the aqueous solution of a silicon oxide dissolved in phase aqueous, with one or more sources of pure carbon, in particular the purified silicon oxide is obtained by precipitation of a silicon oxide dissolved in an aqueous phase in an acidifying agent. The invention also relates to a formulation containing an activator, and a device for the production of silicon, a reactor and electrodes.

The proportion of photovoltaic cells in global electricity generation has been steadily increasing for some years. To further increase market share, it is essential that the costs of producing photovoltaic cells are reduced and their efficiency is increased.

Costs for high purity silicon (solar grade silicon) are an important cost factor in the production of photovoltaic cells. On an industrial scale, this is normally produced by the Siemens process, which was developed over 50 years ago. In this process, silicon is first reacted with hydrogen chloride gas at 300 to 350 ° C in a fluidized bed reactor for trichlorosilanes (silicochloroform). After expensive distillation steps, in a reversal of the above reaction, the trichlorosilanes are thermally decomposed again at 1000 to 1200 ° C in the presence of hydrogen on heated silicon rods of very high purity. Elemental silicon grows on the stems and the released hydrogen chloride is recycled. Silicon tetrachloride is produced as a by-product; this is converted into trichlorosilanes and recycled to the process or is burned in an oxygen flame to pyrogenic silicic acid.

A chlorine-free alternative to the above process is the decomposition of monosilanes, which can also be obtained from

2/114 elements and decompose again after a purification step on heated surfaces or when passed through fluidized bed reactors. Examples of this are given in WO 2005/118474 A1.

Another known method for the production of silicon is the reduction of silicon dioxide in the presence of carbon according to the following reaction equation (Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 23, pages 721-748, 5th edition, 1993 VCH Weinheim).

SiO ₂ + 2 C -> Si + 2 CO

For this reaction to occur, very high temperatures, preferably above 1700 ° C, are necessary, which can be achieved, for example, in arc furnaces. Despite the high temperatures, this reaction starts very slowly, and then also proceeds at a low rate. Due to the associated long reaction times, this method is both energy-intensive and cost-intensive.

If silicon is to be used in solar applications, the silicon produced in particular must meet high purity requirements. Even contamination of the initial compounds in mg / kg (ppm range), (pg / kg) ppb to ppt range is uncomfortable in this field of application.

Due to their electronic properties, the elements of groups III and V of the periodic system are especially disturbing, so that for these elements, the limit values of contamination in silicon are particularly low. For phosphorus and pentavalent arsenic, for example, doping resulting from silicon produced as a type n semiconductor is problematic. Trivalent boron also leads to undesirable doping of the produced silicon, so that a p-type semiconductor is obtained. For example, there is a solar grade silicon (Si _sg ) with a purity of 99.999% (five nines) or 99.9999% (six nines). Silicon suitable for semiconductor production (electronic grade silicon, Si and _g ) requires even higher purity. For these reasons, even metallurgical silicon from the reaction of silicon oxide with carbon must meet high purity requirements, in order to minimize subsequent expensive purification steps due to embedded halogenated compounds, such as boron trichloride, in

3/114 halosilanes for the production of silicon (Si _sg or Si _eg ). Contamination with compounds containing boron causes particular difficulties, because boron has a distribution coefficient of 0.8 in molten silicon and in solid phase and therefore can hardly be separated from silicon longer by zone melting (DE 2546957 A1).

In general, methods for producing silicon from silicon oxide are known in the prior art. Thus, DE 29 45141 C2 describes the reduction of porous SiO ₂ glasses in an arc. The carbon particles necessary for the reduction can be introduced into the porous glass. The silicon obtained by the disclosed method is suitable in a boron content of less than 1 ppm for the production of semiconductor components. DE 33 10828 A1 takes the approach of decomposing halogenated silanes into solid aluminum. This certainly ensures a low boron content, but the aluminum content of the obtained silicon is higher and the energy consumption of the process is appreciable due to the need for electrolytic recycling of the aluminum chloride that forms.

DE 30 13 319 discloses a method for producing silicon of a specified purity, starting from silicon dioxide and a reducing agent containing carbon, such as carbon black, determining the maximum phosphorus and boron contents. The carbon containing reducing agent was used in the form of pellets with a high purity binder, such as starch.

WO 2007/106860 A1 describes a method for the production of silicon, in which aqueous sodium silicate is left over ion exchangers for boron separation, to obtain purified sodium silicate without aqueous boron. Next, the silicon dioxide is precipitated from the purified aqueous phase. This method has the disadvantage that mainly only boron and phosphorus impurities are eliminated from sodium silicate. In order to obtain sufficiently pure solar grade silicon, it is in particular also necessary to remove metallic impurities. For this purpose, WO 2007 / 106860A1 proposes the use of additional ion exchange columns in the process. This leads, however, to a very expensive process with low space-time performance.

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In order to produce silicon of a grade suitable for solar cell production, it is generally necessary to use silicon dioxide with a purity of at least 99.99% by weight. The concentration of impurities, such as boron and phosphorus, should not exceed 1 ppm. Admittedly, it is possible to use natural resources, such as high quality quartz, as starting material for high purity silicon dioxide, but due to their natural limitation they are only available in limited quantities for industrial mass production. In addition, based on economic aspects, it is too expensive to purchase. What the methods described above have in common is that they are very expensive and / or energy-intensive, so there is a high demand for less expensive, more efficient methods for producing solar grade silicon.

Therefore, there is a requirement for the production of high purity silicon dioxide from readily available, economical silicates. Methods are known in which a flux is added to a silicon-containing material, such as silica sand or feldspar, and the mixture is melted. A fiber-like silicate glass is pulled from the melt and is leached with an acid, with the formation of powdery porous silicon dioxide (SiO ₂ ) (DE 31 23 009). For the production of high-purity silicon dioxide by leaching, the glass mass is restricted to that which can be leached easily, and aluminum oxide and alkaline earth metal salts must also be added as glass ingredients to silicon dioxide. A serious disadvantage is the need for subsequent removal of metals with the exception of silicon dioxide.

A method is also known in which a silica gel is obtained by reacting an alkaline silicate (which is generally known as soluble glass or soluble silicate) with an acid (see, for example, JG Vail, Soluble Silicates (ACS Monograph Series) , Reinhold, New York, 1952, Vol. 2, p. 549). This silica gel leads as a rule to a SiO ₂ with a purity of approximately 99.5% by weight, in any case, the content of impurities, such as boron, phosphorus, iron and / or aluminum is too high for this dioxide silicon is used for the production of grade silicon

5/114 solar. As silicate solutions are available in very large quantities as a very economical raw material, in the past there has been no lack of attempts to produce high purity SiO ₂ from silicate solutions. Accordingly, US 4,973,462 describes processes in which the highly viscous soluble glass was converted at low pH value of the reaction solution with an acidifying agent to SiO ₂ . This SiO ₂ was then filtered, washed with water, resuspended in a mixture of acid, water and a chelating agent, filtered and washed several times. A similar method was described in JP02-311310, but in this case a chelating agent has already been added to the precipitation reaction. These two methods have the disadvantage that they include a very complicated processing procedure. In addition, it has been found that the precipitate obtained is sometimes difficult to filter. Finally, there are additional costs for the chelating agent and its separation from silicon dioxide.

The aim of the invention was to provide a complete method for the production of solar grade silicon, which is economical on an industrial scale, with a reduced number of process stages, and can be carried out advantageously using non-pre-purified silicates or silicon dioxides ordinary materials, preferably as starting materials and production of purified silicon oxide. Another objective was to develop a reactor and electrodes, which on the one hand allow economical processing, and on the other hand suppress diffusion-dependent contamination with boron from plant components at high temperatures.

An additional objective within the context of the complete method was to provide a new method for the production of high purity silicon dioxide which has at least some disadvantages of the methods of the prior art mentioned above only in reduced form, if at all.

Additional objectives that are not specifically mentioned will become clear from the general context of the description in the following examples and claims. These objectives are achieved by the method described in the description, the examples and claims, the method steps described in this and the products and intermediates described in this.

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It has surprisingly been found that an economical method of producing pure silicon, which is suitable as solar grade silicon or is suitable for the production of solar grade silicon, can be provided by reducing a purified silicon dioxide with one or more sources of pure carbon, the purified silicon dioxide being obtained by precipitation in an acidifying agent, in particular by reacting at least one aqueous solution of a silicon oxide dissolved in an aqueous phase with at least one acidifying agent under acidic conditions.

According to the invention, precipitation takes place in an acidifying agent to which silicon oxide, dissolved in an aqueous phase, is added, and forms the resulting precipitation suspension. The precipitation suspension is kept acidic during the addition and / or precipitation of silicon oxide.

The objective is achieved by the complete method described in detail in the description, the examples, the figures and the claims that follow for the production of pure silicon and by the method components described herein.

The invention therefore relates to a method for the production of pure silicon, more particularly solar grade silicon or a silicon suitable for the production of solar grade silicon, comprising the reduction of silicon dioxide, purified by precipitation of the aqueous solution, with one or more sources of pure carbon, in which precipitation takes place from an aqueous solution of silicon dioxide dissolved in an aqueous phase in an acidifying agent, especially in the acidic pH range, and the suspension The resulting precipitation rate is maintained permanently at an acidic pH.

It has been found that silicon dioxides, more particularly silicon dioxide purified by acidic precipitation, can be used not only as a raw material for the reaction with the carbon source to supply silicon, but that they can also be used in the production of the source carbon or reaction accelerators or reactor materials.

In addition, it has been found that carbohydrates are particularly

7/114 suitable as the second preferred starting material, for example, carbon source, in the context of the present invention. These carbohydrates can serve as the carbon source or as one of the carbon sources in different component stages of the method, but they can also be used to produce activators or reactor materials. Carbohydrates have the particular advantage that they are available globally, have very low values for boron and phosphorus impurities, and, being a renewable raw material, constitute an ecologically viable carbon source.

The present invention therefore also relates to a method according to claim 1, in which carbon from carbon source is obtained by pyrolysis of carbohydrates in a component step of the method, using S1O2, especially a carbon dioxide silicon purified by acidic precipitation, as a defoaming agent in pyrolysis.

The present invention further relates to a method according to claim 1, in which the high purity silicon carbide is prepared from silicon dioxide and carbohydrates in a component step of the method, and this silicon carbide is preferably used for one or more of the following purposes:

a) for coating reactor components

b) for the production of electrodes for the blast furnace process

c) as a carbon source for the reaction with silicon dioxide purified by acidic precipitation

d) as a reaction accelerator for the reaction of another carbon source with 0 silicon dioxide purified by acidic precipitation.

Finally, the present invention relates to an especially preferred reactor for performing the process according to the invention.

In a very specific method variant of the present invention, only silicon dioxide purified by aqueous media and sugar is used in the complete method.

The method according to the invention is described in detail below:

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Definitions

Precipitation or precipitation processes mean, with respect to the present invention, the reaction of at least one aqueous solution of a silicon oxide dissolved in an aqueous phase with at least one acidifying agent under the conditions more precisely defined in the rest of the description, even if the slight reaction to the formation, from primary particles, of aggregates and agglomerates - with respect to the usual definition of precipitated silicic acids - or of a three-dimensional network - with respect to the usual definition of silica gels. In other words, high purity SiO ₂ particles according to the invention can assume a gel-like structure or a precipitated silicic acid structure or even some other structure.

Silicon dioxide purified by aqueous solution precipitation means silicon dioxide which is obtained by a method in which the reaction regime in the reaction of an acidifying agent and a silicate and subsequent washing steps with acidifying agents and / or solutions aqueous acidifying agents and / or water, preferably demineralized water, reach a total content of aluminum, boron, calcium, iron, nickel, phosphorus, titanium and zinc in silicon dioxide below 10 ppm by weight, and the total impurities aluminum, boron, calcium, iron, nickel, phosphorus, titanium and zinc in silicon dioxide below the total impurities present in educts and water. In other words, precipitation is conducted in such a way that the aforementioned impurities in the educts and washing media remain as far as possible in the aqueous phase and are not transferred to silicon dioxide. In a specific embodiment of the present invention, silicon dioxide purified by precipitation from the aqueous solution means that the commercially available technical acidifying agent is reacted with commercially available technical silicate solution, and the reaction and washing steps are conducted such that, despite of the non-pre-purified educts, a high purity silicon dioxide is obtained.

Pure or high purity silicon means silicon with a profile

9/114 of impurezaz as given below:

The. Aluminum less than or equal to 5 ppm or between 5 ppm and 0.0001 ppt, in particular between 3 ppm and 0.0001 ppt, preferably between 0.8 ppm and 0.0001 ppt, especially preferably between 0.6 ppm and 0, 0001 ppt, even better between 0.1 ppm and 0.0001 ppt, most especially, preferably between 0.01 ppm and 0.0001 ppt and even more preferably 1 ppb to 0.0001 ppt,

B. Boron below 10 ppm to 0.0001 ppt, in particular in the range of 5 ppm to 0.0001 ppt, preferably in the range of 3 ppm to 0.0001 ppt or especially preferably in the range of 10 ppb to 0.0001 ppt, up to more preferably in the range of 1 ppb to 0.0001 ppt

ç. Calcium less than or equal to 2 ppm, preferably between 2 ppm and 0.0001 ppt, in particular between 0.3 ppm and 0.0001 ppt, preferably between 0.01 ppm and 0.0001 ppt, especially preferably between 1 ppb and 0 , 0001 ppt,

d. Iron less than or equal to 20 ppm, preferably between 10 ppm and 0.0001 ppt, in particular between 0.6 ppm and 0.0001 ppt, preferably between 0.05 ppm and 0.0001 ppt, especially preferably between 0.01 ppm and 0.0001 ppt, and most especially, preferably between 1 ppb to 0.0001 ppt;

and. Nickel less than or equal to 10 ppm, preferably between 5 ppm and 0.0001 ppt, in particular between 0.5 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, especially preferably between 0.01 ppm and 0.0001 ppt, and most especially between 1 ppb and 0.0001 ppt

f. Phosphorus less than 10 ppm at 0.0001 ppt, preferably between 5 ppm and 0.0001 ppt, in particular less than 3 ppm at 0.0001 ppt, preferably between 10 ppb and 0.0001 ppt and most especially, preferably between 1 ppb and 0.0001 ppt

g. Titanium less than or equal to 2 ppm, preferably less than or equal to 1 ppm at 0.0001 ppt, in particular between 0.6 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, especially preferably between 0 , 01 ppm and 0.0001 ppt, and most especially, preferably between 1 ppb and 0.0001 ppt

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H. Zinc less than or equal to 3 ppm, preferably less than or equal to 1 ppm at 0.0001 ppt, in particular between 0.3 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, especially preferably between 0 , 01 ppm and 0.0001 ppt and most especially, preferably between 1 ppb and 0.0001 ppt, and a purity in the region of the detection limit can be pointed out for each element, and the total contamination with the elements mentioned above must be less than 100 ppm by weight, preferably less than 10 ppm by weight, especially preferably less than 5 ppm by weight on silicon as a product of the direct method from melting.

Especially preferably, the pure silicon obtained is suitable as solar grade silicon.

A purified, pure or high-purity silicon oxide, in particular silicon dioxide, is characterized in that content of:

The. Aluminum is preferably less than or equal to 5 ppm or between 5 ppm and 0.0001 ppt, in particular between 3 ppm and 0.0001 ppt, preferably between 0.8 ppm and 0.0001 ppt, especially preferably between 0.6 ppm and 0.0001 ppt, even better between 0.1 ppm and 0.0001 ppt, most especially, preferably between 0.01 ppm and 0.0001 ppt and even more preferably 1 ppb at 0.0001 ppt,

B. Boron is below 10 ppm to 0.0001 ppt, in particular in the range of 5 ppm to 0.0001 ppt, preferably in the range of 3 ppm to 0.0001 ppt or especially preferably in the range of 10 ppb to 0.0001 ppt, even more preferably in the range of 1 ppb to 0.0001 ppt

ç. Calcium is less than or equal to 2 ppm, preferably between 2 ppm and 0.0001 ppt, in particular between 0.3 ppm and 0.0001 ppt, preferably between 0.01 ppm and 0.0001 ppt, especially preferably between 1 ppb and 0.0001 ppt,

d. Iron is less than or equal to 20 ppm, preferably between 10 ppm and 0.0001 ppt, in particular between 0.6 ppm and 0.0001 ppt, preferably between 0.05 ppm and 0.0001 ppt, especially preferably between 0.01 ppm and 0.0001 ppt, and most especially, preferably between 1 ppb to

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0.0001 ppt;

and. Nickel is less than or equal to 10 ppm, preferably between 5 ppm and 0.0001 ppt, in particular between 0.5 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, especially preferably between 0.01 ppm and 0.0001 ppt, and most especially between 1 ppb and 0.0001 ppt

f. Phosphorus is less than 10 ppm to 0.0001 ppt, preferably between 5 ppm and 0.0001 ppt, in particular less than 3 ppm to 0.0001 ppt, preferably between 10 ppb and 0.0001 ppt and most especially, preferably between in between

1 ppb and 0.0001 ppt

g. Titanium is less than or equal to 2 ppm, preferably less than or equal to 1 ppm at 0.0001 ppt, in particular between 0.6 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, especially preferably between 0.01 ppm and 0.0001 ppt, and most especially, preferably between 1 ppb and 0.0001 ppt

H. Zinc is less than or equal to 3 ppm, preferably less than or equal to 1 ppm at 0.0001 ppt, in particular between 0.3 ppm and 0.0001 ppt, preferably between 0.1 ppm and 0.0001 ppt, especially preferably between 0.01 ppm and 0.0001 ppt and most especially, preferably between 1 ppb and 0.0001 ppt, and that the total of the aforementioned impurities plus sodium and potassium is less than 10, preferably less than 5 ppm, especially preferably less than 4 ppm, very especially preferably less than 3 ppm, especially preferably 0.5 to 3 ppm and very especially, preferably 1 ppm to 3 ppm. And a purity in the region of the detection limit can be pointed out for each element.

Pure or high-purity silicon carbide means a silicon carbide which may, with the exception of silicon carbide, optionally also have carbon and silicon oxide, such as Si _y O _z with y = 30 1.0 to 20 and z = 0 , 1 to 2.0, in particular as matrix C and / or matrix SiO ₂ or matrix Si _y O _z with y = 1.0 to 20 and z = 0.1 to 2.0, and optionally small amounts of silicon. High purity silicon carbide preferably

12/114 means a corresponding silicon carbide with a passivation layer comprising silicon dioxide. High purity silicon carbide can also mean a high purity composition that contains or consists of silicon carbide, carbon, silicon oxide and optionally small amounts of silicon, and the high purity silicon carbide or the high purity composition has in particular an impurity profile for boron and phosphorus below 100 ppm of boron, in particular between 10 ppm and 0.001 ppt, and for phosphorus, below 200 ppm, in particular between 20 ppm and 0.001 ppt of phosphorus, in particular has a total impurity profile for boron, phosphorus, arsenic, aluminum, iron, sodium, potassium, nickel, chromium below 100 ppm by weight, preferably below 10 ppm by weight, especially preferably below 5 ppm by weight in relation to the composition high-purity complete or high-purity silicon carbide.

The impurity profile of pure silicon carbide, preferably of high purity with boron, phosphorus, arsenic, aluminum, iron, sodium, potassium, nickel, chromium is, for each element, preferably below 5 ppm at 0.01 ppt (in weight), and for high purity silicon carbide in particular below 2.5 ppm to 0.1 ppt. Especially preferably, the silicon carbide obtained by the method according to the invention optionally with carbon and / or Si _y O _z matrices has the following content:

Boron below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Phosphorus below 200 ppm, preferably between 20 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Sodium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 1 ppm to 0.001 ppt and / or

Aluminum below 100 ppm, preferably between 10 ppm and

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0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 1 ppm to 0.001 ppt and / or

Iron below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Chromium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Nickel below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Potassium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Sulfur below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 2 ppm to 0.001 ppt and / or

Barium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 3 ppm to 0.001 ppt and / or

Zinc below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Zirconium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Titanium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and / or

Calcium below 100 ppm, preferably between 10 ppm and

0.001 ppt, especially preferably from 5 ppm to 0.001 ppt or below 0.5 ppm to 0.001 ppt and

14/114 in particular magnesium below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably between 11 ppm and 0.001 ppt and / or copper below 100 ppm, preferably between 10 ppm and 0.001 ppt, especially preferably between 2 ppm and 0.001 ppt, and / or cobalt below 100 ppm, in particular between 10 ppm and 0.001 ppt, especially preferably between 2 ppm and 0.001 ppt, and / or vanadium below 100 ppm, in particular between 10 ppm and 0.001 ppt, preferably between 2 ppm and 0.001 ppt, and / or manganese below 100 ppm, in particular between 10 ppm and 0.001 ppt, preferably between 2 ppm and 0.001 ppt, and / or lead below 100 ppm, in particular between 20 ppm and 0.001 ppt, preferably between 10 ppm and 0.001 ppt, especially preferably between 5 ppm and 0.001 ppt.

An especially preferred pure to high purity silicon carbide or a high purity composition contains or consists of silicon carbide, carbon, silicon oxide and optionally small amounts of silicon, and the high purity silicon carbide or the high composition Purity in particular have an impurity profile of boron, phosphorus, arsenic, aluminum, iron, sodium, potassium, nickel, chromium, sulfur, barium, zirconium, zinc, titanium, calcium, magnesium, copper, chromium, cobalt, zinc, vanadium , manganese and / or lead below 100 ppm of pure silicon carbide, preferably below 20 ppm to 0.001 ppt for high purity silicon carbide, especially preferably between 10 ppm and 0.001 ppt for the complete high purity composition or high purity silicon carbide.

According to the invention, the source of pure carbon, optionally containing at least one carbohydrate, or mixture of carbon sources has the following impurity profile: boron less than 2 [pg / g], phosphorus less than 0.5 [pg / g] and aluminum less than 2 [pg / g], preferably less than or equal to 1 [pg / g], in particular iron less than 60 [pg / g], preferably the iron content is less than 10 [pg / g] g], especially preferably less than 5 [pg / g]. Together, according to the invention it is desirable to use a pure carbon source in which the content of

15/114 impurities, such as boron, phosphorus, aluminum and / or arsenic, are below the respective technically possible limit of detection. Preferably, the pure or other carbon source that optionally comprises at least one carbohydrate, or mixture of carbon sources, has the following impurity profile for boron, phosphorus and aluminum and optionally for iron, sodium, potassium, nickel and / or chromium . Boron (B) contamination is in particular between 5 and 0.000001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably 2 to 0.00001 pg / g, according to the invention below 2 to 0.00001 pg / g. Contamination with phosphorus (P) is in particular between 5 and 0.000001 pg / g, preferably from 3 to 0.00001 pg / g, especially preferably below 1 to 0.00001 pg / g, according to the invention below 0.5 to 0.00001 pg / g. Contamination with iron (Fe) is between 100 and 0.000001 pg / g, in particular between 55 and 0.00001 pg / g, preferably from 2 to 0.00001 pg / g, especially preferably below 1 to 0.00001 pg / g, according to the invention below 0.5 to 0.00001 pg / g. Contamination with sodium (Na) is in particular between 20 and 0.000001 pg / g, preferably from 15 to 0.00001 pg / g, especially preferably below 12 to 0.00001 pg / g, according to the invention below 10 to 0.00001 pg / g. Contamination with potassium (K) is in particular between 30 and 0.000001 pg / g, preferably from 25 to 0.00001 pg / g, especially preferably below 20 to 0.00001 pg / g, according to the invention below 16 to 0.00001 pg / g. Contamination with aluminum (Al) is in particular between 4 and 0.000001 pg / g, preferably from 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1.5 to 0.00001 pg / g. Nickel (Ni) contamination is in particular between 4 and 0.000001 pg / g, preferably from 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1.5 to 0.00001 pg / g. Contamination with chromium (Cr) is in particular between 4 and 0.000001 pg / g, preferably from 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1 to 0.00001 pg / g. Minimal contamination with

16/114 respective elements, especially preferably below 10 ppb or below 1 ppb, is preferred.

General description of the complete method

The complete method comprises the reduction of a silicon dioxide purified by acidic precipitation with a carbon source for the production of solar grade silicon. Suitable carbon sources and method conditions are known to the person skilled in the art, for example, from the aforementioned prior art, especially US 2007/0217988 or US 4,247,528. The content of these published specifications is hereby explicitly incorporated into the subject matter of this patent application.

According to the invention, in the overall method according to the invention for producing pure silicon, precipitation-purified silicon oxide is formulated and reacted together with at least one pure carbon source.

For example, wet or still wet silicon oxide can be formulated, extruded, pelleted, granulated or briquetted together with a pure carbohydrate. This formulation can be dried and can undergo a reduction step for the production of pure silicon or can undergo an offline process step, pyrolysis and / or calcination for the production of pure carbon and / or silicon carbide.

Silicon carbide, in particular high purity silicon carbide optionally comprising or containing a carbon matrix (matrix C) or a silicon oxide matrix and / or optionally infiltrated with silicon can be used in the method according to the invention as an activator and / or as a source of pure carbon.

According to one embodiment, the reduction step for the production of pure silicon consists of reacting the purified silicon oxide, in particular silicon dioxide, with a pure or high-purity silicon carbide, as defined above or below.

In specific embodiments, a silicon carbide and / or silicon, where the silicon carbide can comprise a C matrix and / or a silicon oxide matrix and can be infiltrated with silicon, are added to the

17/114 formulation, and the formulation alternatively

a) comprises purified silicon oxide and at least one source of pure carbon and optionally silicon carbide and optionally silicon and / or

b) comprises purified silicon oxide and optionally silicon carbide and optionally silicon and / or

c) comprises at least one source of pure carbon and optionally silicon carbide and optionally silicon, where the respective formulation may optionally contain binders and where the source of pure carbon may also comprise an activated carbon.

Purified silicon oxide, in particular purified silicon dioxide, such as silicic acid, pure carbon, in particular activated carbon and / or silicon carbide can be added to the process a) as powder, granules and / or as lumps and / or b ) contained in a formulation, for example, in a porous glass, in particular quartz glass, in an extrudate and / or mold, such as pellet or briquette, optionally together with other additives, in particular as a binder and / or as a second and additional carbon source. Activated carbon means a carbon source with fractions of graphite or graphite. The graphite fraction in the carbon source is preferably between 30 and 99% by weight with respect to the carbon source, preferably the graphite fraction is 40 to 99% by weight, especially preferably 50 to 99% by weight.

Suitable methods for forming the formulation, in particular briquetting, such as extrusion, compression, tabletting, pelletizing, granulating and other well-known methods are well known to one skilled in the art.

Other additives can be silicon oxide or a second carbon source, in particular purified rice husks, for example, after washing and / or cooking with HCI, or mixtures of other pure carbon sources, such as sugar, graphite, fiber carbon, and / or as a binder and as a second and additional source of carbon and / or silicon can be resins

18/114 natural or synthetic, such as phenolic resin, functional silanes or siloxanes, technical alkyl celluloses, such as methyl cellulose, polyethylene glycols, polyacrylates and polymethacrylates or mixtures of at least two of the above mentioned compounds. As functional silanes or siloxanes, one can mention, for example, - but not exclusively -: tetraloxysilanes, trialkoxysilanes, alkylsilicates, alkylalkoxysilanes, methacryloxyalkylalkoxysilanes, glycidyloxyalkylalkoxysilanes, polyetheralsylated or less hydrochloride compounds than the above-mentioned hydrochloride or hydrochloride compounds. alkoxy means in particular methoxy, ethoxy, propoxy or butoxy and alkyl or Alkyl represents a mono or divalent alkyl group having 1 to 18 carbon atoms, such as methyl, ethyl, n-propyl, butyl, isobutyl, pentyl, hexyl, heptyl, n- / i-octyl etc .; the following can be listed as examples: tetraethoxysilane, silanol etilsilicato, trimethoxysilane, methyltrimethoxysilane, dimethyldiethoxysilane, trimetilpropoxissilano, ethyltrimethoxysilane, metiletildietoxissilano, n-propyltriethoxysilane, n-Zioctiltrimetoxissilano, propilsilanol, octilsilanóis and corresponding oligomers or condensed oligomers 1-metacriloximetiltrimetoxissilano, 2metacriloxietiltrimetoxissilano, 3-methacryloxypropyltrimethoxysilane, 3metacriloxi isobutiltrimetoxissilano-3-metacriloxipropilmetildialcoxissilano, and corresponding 3metacriloxipropilsilanol or condensed oligomers 3glicidiloxipropiltrimetoxissilano, and corresponding 3-glicidiloxipropilsilanol or condensed or hydrolyzed, or also cocondensados cocondensados cocondensados-based block or at least two of npropiltrietoxissilano number, n / i-octyltriethoxysilane, 3methacryloxypropyltrimethoxysilane, 3-glycidyloxypropyltrimethoxysilane and 3polieterpropyltriethoxysilane.

Said additives can simultaneously perform the function of a Si or C supplier and that of a processing aid, in particular in the formation processes which are well known to one skilled in the art, and / or the function of a binder, in particular of a binder that is substantially heat resistant in the range of AT to

11/194

300 ° C. Preferably, for the production of granules, the powders are sprayed with the binder in aqueous or alcoholic solution and then undergo a formation process, in which drying can be carried out simultaneously, or alternatively drying can also be carried out after formation. So that the process gases that were formed during the reduction to pure silicon can flow well through the formulation, preferably highly porous tablets, pellets or briquettes are formed from the formulations.

The size of the briquettes is preferably in the range of 1 to 10 cm ³ , especially for a 500 kW oven. The size is directly dependent on how the process is conducted. The shapes can be adapted depending on the process and technical aspects, for example, to look like gravel or batten, a batten-shaped briquette that is preferred for feeding through a tube. A gravel can be advantageous in direct feed.

Preferred binders produce substantially dimensionally stable formulations in the temperature range 150 to 300 ° C, and especially preferred binders produce dimensionally stable formulations in the temperature range between 200 and 300 ° C. In certain cases it may also be preferable to produce formulations that can provide substantially dimensionally stable formulations in the temperature range above 300 ° C and up to 800 ° C or higher, especially preferably up to 1400 ° C. These formulations can preferably be used for reduction to pure silicon. High temperature binders are based substantially on the predominant cross-linked substrate of Si-O, substrate generally meaning all components or functional groups of the formulation that can condense with silanol groups.

A preferred formulation comprises silicon carbide and / or activated carbon, for example graphite, or mixtures thereof and another source of pure carbon, for example, thermal black, and the specified heat resistant binders, in particular high temperature binders.

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In general, all solid reagents, such as silicon dioxide, the source of pure carbon and optionally silicon carbide must be used in the process or must be present in the composition in a form that offers the maximum possible surface area for the reaction. According to the invention, a formulation in the form of a briquette is added.

One or more sources of pure carbon, optionally in a mixture, an organic compound of natural origin, a carbohydrate, graphite (activated carbon), coke, coal, carbon black, thermal black, pyrolysed carbohydrate, in particular, pyrolysed sugar, are used as a source of pure carbon in the method according to the invention. Carbon sources, especially in the form of pellets, for example, can be purified by treatment with hot hydrochloric acid solution. In addition, an activator can be added to the method according to the invention. The activator can serve the purpose of a reaction initiator, a reaction accelerator as well as the objective of the carbon source. An activator is pure silicon carbide, silicon carbide infiltrated with silicon, and a pure silicon carbide with a C matrix and / or silicon oxide matrix, for example, a silicon carbide containing carbon fibers.

Alternatively the source of pure carbon consists of the activator, that is, in the method according to the invention the activator is used as the sole carbon source. Due to this measure, the composition of the charge can be more dense, because an equivalent mol of carbon monoxide gas in this step, reduction to silicon, is saved. Therefore, the activator can be used in the method in catalytic amounts up to equimolar amounts in relation to silicon oxide.

According to other alternatives, the activator can be used in a weight ratio of 1000: 1 to 1: 1000 for the pure carbon source, the pure carbon source being calculated without SiC, for example, graphite, carbon black, carbohydrate , coal, coke. Preferably, the carbon source is used in a weight ratio of 1: 100 to 100: 1, especially preferably 1: 100 to 1: 9.

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Reduction of purified silicon oxide with one or more sources of pure carbon and / or the activator can be carried out in an industrial oven, such as an arc furnace, in a thermal reactor, in an induction furnace, rotary kiln and / or in a microwave oven, for example, with fluidized bed and / or rotating tube.

In general, the reaction can be carried out in ordinary industrial furnaces for silicon production, for example, melting furnaces for silicon production, such as metallurgical silicon, or other suitable melting furnaces, for example, induction furnaces. The design of these melting furnaces, especially preferably electric furnaces, which use an electric arc as an energy source, is well known to one skilled in the art. In the case of direct current furnaces, they have a melting electrode and a bottom electrode or as an alternating current furnace, usually three melting electrodes. The arc length is controlled by an electrode controller. Arc furnaces are usually based on a reaction space made of refractory material, at the bottom of which liquid silicon can be used or discharged. The raw materials are loaded on top, where the graphite electrodes for generating the arc are also arranged. These ovens are generally operated at temperatures in the region of 1800 ° C. It is also known to someone skilled in the art that the furnace structure itself should not contribute to contamination of the produced silicon.

According to the invention, reduction of the purified silicon oxide takes place with one or more sources of pure carbon in a reaction space coated with high-purity refractories and optionally using electrodes consisting of high-purity material, as explained below. Ordinary electrodes are made of high-purity graphite and are consumed during the reduction process, so that as a rule they can be repositioned continuously.

The molten or molten silicon according to the invention obtained by the reduction is obtained as pure molten silicon, in particular it is suitable as solar grade silicon or it is suitable for the production of silicon grade

22/114 solar, and optionally is further purified by zone fusion or directional solidification, as is well known to one skilled in the art.

Alternatively or additionally, silicon can be solidified, crushed and crushed fragments can be further classified based on differences in magnetic behavior. In particular, the fraction enriched in impurities as a result of zone melting or directional solidification can then be used for the production of organosilanes. The magnetic classification method is known as such by one skilled in the art. For the magnetic classification of silicon from the reaction of purified silicon oxide and one or more sources of pure carbon, the contents of the full disclosure of WO 03/018207 are made an object of the present patent application, with the modification that silicon fed for magnetic separation comes from the reaction of purified silicon oxide and at least one source of pure carbon. A corresponding magnetic separation of the pure silicon produced according to the invention or a silicon still purified by zone melting of the pure silicon is an object of the invention.

The respective partial process steps that are optionally performed, preferably in combination, for the complete method of pure silicon production, each of which, synergistically, makes a decisive contribution to the economic effectiveness of the complete method, are explained in more detail below .

Description of precipitation-purified silicon oxide production

According to a main aspect of the method for producing pure silicon according to the invention, a purified silicon dioxide from at least one silicate solution is used in the method for the production of pure silicon, in particular solar grade silicon .

The inventors found, surprisingly, that it is possible, through the special process management in precipitation and washing, to produce the purified silicon dioxide, in particular high purity silicon dioxide that can be used for the production of solar grade silicon, simply , without a large number of additional purification steps to

23/114 upstream or downstream and without particular expense on the equipment.

According to the invention, the precipitation of a silicon oxide dissolved in an aqueous phase, in particular completely dissolved silicon oxide, is carried out with an acidifying agent. After reacting the silicon oxide dissolved in the aqueous phase with the acidifying agent, preferably by adding the silicon oxide dissolved in the aqueous phase to the acidifying agent, a suspension of precipitation is obtained.

An important feature of the method is the control of the pH value of silicon dioxide and the reaction media containing silicon dioxide during the various stages of the process for the production of silicon dioxide.

According to the invention, the initial charge and the precipitation suspension, in which the silicon oxide dissolved in the aqueous phase, in particular the soluble glass, is added, preferably dropwise, must always show an acid reaction. Acid means a pH value below 6.5, in particular below 5.0, preferably below 3.5, especially preferably below 2.5, and according to the invention below 2.0 to below 0, 5. It may be desirable to check the pH value to ensure that the pH value does not fluctuate too much in order to obtain reproducible precipitation suspensions. If a constant or substantially constant pH value is desired, then the pH value should only show a range of variation of plus / minus 1.0, in particular plus / minus 0.5, preferably plus / minus 0.2 .

In an especially preferred embodiment of the present invention, the pH value of the precipitation suspension is always kept less than 2, preferably less than 1, especially preferably less than 0.5. In addition, it is preferred if the acid is always present in an excess defined for the alkaline silicate solution, to ensure a pH value of the precipitation suspension of less than 2 at any time.

Without being tied to a particular theory, the inventors are of the view that a very low pH value ensures that charged SiO groups

24/114 negatively non-free are present on the silicon dioxide surface, to which the interfering metal ions can be attached.

At a very low pH value, the surface is even positively charged, so that metal cations are repelled by the silicic acid surface. If these metal ions are eliminated now, as long as the pH value is very low, they can be prevented from being deposited on the surface of the silicon dioxide according to the invention. If the silicic acid surface assumes a positive charge, the silicic acid particles are further prevented from aggregating with the consequent formation of cavities in which impurities can accumulate.

Especially preferably, and therefore as the main aspect, the present invention relates to a precipitation process for the production of purified silicon oxide, in particular high purity silicon dioxide, comprising the following steps

The. Preparation of a feed of an acidifying agent with a pH value of less than 2, preferably less than 1.5, especially preferably less than 1, most especially, preferably less than 0.5

B. Preparation of a silicate solution, where the viscosity in particular, for the production of precipitation-purified silicon oxide, can be advantageously adjusted in defined viscosity ranges, in particular a viscosity of 0.1 to 10000 poises being preferred, and depending of the process parameters this viscosity range - as explained below - can be further extended, depending on other process parameters,

ç. Addition of the silicate solution from step b. to the feed of step a., such that the pH value of the obtained precipitation suspension always remains at a value of less than 2, preferably less than 1.5, especially preferably less than 1 and most especially, preferably between less of 0.5

d. Separation and washing of the obtained silicon dioxide, the washable medium having a pH value of less than 2, preferably less than

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1.5, especially preferably less than 1 and most especially preferably less than 0.5

and. Drying of the obtained silicon dioxide

According to an especially preferred first variant of this method of the main aspect of the present invention, the invention relates to a precipitation process for the production of purified silicon oxide, in particular high purity silicon dioxide, which is carried out with solutions from low to medium viscosity silicate, that is, step b is modified as follows:

B. Preparation of a silicate solution with a viscosity of 0.1 to 2 poises

According to a second, particularly preferred variant of this method of the main aspect of the present invention, the invention relates to a precipitation process for the production of purified silicon oxide, in particular high purity silicon dioxide, which is carried out with solutions of high or very high viscosity silicate, that is, step b is modified as follows:

B. Preparation of a silicate solution with a viscosity of 2 to 100000 poises

In the different variants of the method contained as the main aspect of the present invention, in step a) the feed is prepared from an acidifying agent or an acidifying agent and water in the precipitation vessel. The water is preferably distilled water or deionized water.

In all variants of the method according to the invention, not only the especially preferred embodiments described in detail above, the acidifying agents used can be organic or inorganic acids, preferably mineral acids, especially preferably hydrochloric acid, phosphoric acid, nitric acid, sulfuric acid, chlorosulfonic acid, sulfuryl chloride, perchloric acid, formic acid and / or acetic acid in concentrated or diluted form, or mixtures of the aforementioned acids. The inorganic acids mentioned above are

26/114 especially preferred. Very especially preferred are hydrochloric, preferably 2 to 14 N, especially preferably 2 to 12 N, especially preferably 2 to 10 N, especially p _{re erenc} i f _a | _m being 2 to 7 C , and especially preferably 3 to 6 N, phosphoric acid, preferably 2 to 59 N, especially preferably 2 to 50 N, especially preferably 3 to 40 N, especially preferably 3 to 30 N and very especially, preferably 4 to 20 N, nitric acid, preferably 1 to 24 N, especially preferably 1 to 20 N, very especially, preferably 1 to 15 N, especially preferably 2 to 10 N, sulfuric acid, preferably 1 to 37 N, especially preferably 1 to 30 N, most especially, preferably 2 to 20 N, especially preferably 2 to 10 N. Most especially, preferably, concentrated sulfuric acid is used.

The acidifying agents can be used in a purity that is typically referred to as a technical class. It is clear to the person skilled in the art that diluted or undiluted acidifying agents or mixtures of used acidifying agents must incorporate a minimum level of impurities that do not remain dissolved in the aqueous phase of the precipitation suspension in the method. In each case, the acidifying agents should not have impurities that would precipitate with silicon oxide in acidic precipitation, unless they can be kept in suspension of precipitation by means of complexing agents added or by pH control, or eliminated with the subsequent washing means.

The acidifying agent that is used for precipitation can be the same as also used, for example, in step d, to wash the filter cake.

In a preferred variant of this method, in step a) a peroxide that produces a yellow / orange color with titanium (IV) ions under acidic conditions is added to the feed together with the acidifying agent. Especially preferably it is hydrogen peroxide or potassium peroxodisulfate. The yellow / orange color of the

27/114 reaction can provide a very good indication of the degree of purification during the wash step d.

In fact, titanium was found to be a very persistent contaminant, since it readily binds to silicon dioxide at pH values above 2. The inventors found that when the yellow color in stage d) disappears, as a rule the desired oxide purity Purified silicon, in particular silicon dioxide, has been achieved and from this point on silicon dioxide can be washed with distilled or deionized water until the neutral pH of silicon dioxide is reached. To achieve this peroxide indicator function, it is also possible to add peroxide not in step a., But in step b. to sodium silicate or in step c. like a third material stream. Basically it is also possible to add the peroxide only after step c and before step d. or during step d.

All of the above mentioned variants and mixed forms thereof are covered by the present inventions. However, the variants in which peroxide is added in step a. or b. are preferred, as in this case you can perform another function besides the indicator function. Without being bound by a particular theory, the inventors are of the view that some impurities - in particular containing carbon - can be oxidized by reaction with the peroxide and removed from the reaction solution. Other impurities are converted by oxidation into a more soluble form and can therefore be eliminated. The precipitation process according to the invention therefore has the advantage that it is not necessary to carry out a calcination step, although this is naturally optionally possible.

In all variants of the process according to the invention, the silicon dioxide dissolved in the aqueous phase used is preferably an aqueous silicate solution, especially preferably an alkaline and / or alkaline earth silicate solution, most especially preferably a soluble glass. Such solutions can be obtained commercially, they can be produced by the liquefaction of solid silicate, they can be produced from silicon dioxide and sodium carbonate or, for example,

28/114 example, can be produced by the hydrothermal process directly from silicon dioxide and sodium hydroxide and water at elevated temperature. The hydrothermal process can be preferred over the soda process, because it can result in precipitated silicon dioxide from cleaner. A disadvantage of the hydrothermal process is the limited range of proportions obtainable, for example, the ratio of S1O2 to N2O is up to 2, the preferred proportions being 3 to 4, in addition, the water glasses must as a rule be concentrated according to the process hydrothermal before precipitation. Generally the production of soluble glass as such is known to one skilled in the art.

According to an alternative, an alkaline soluble glass, in particular sodium soluble glass or potassium soluble glass, is optionally filtered and then concentrated if necessary. The filtration of the soluble glass or the aqueous solution of the dissolved silicate, in order to remove solid, undissolved constituents, can be carried out by processes that are known to one skilled in the art and with devices that are known to one skilled in the art.

The silicate solution used preferably has a ratio, that is, a weight ratio of metal oxide to silicon dioxide, from 1.5 to 4.5, preferably from 1.7 to 4.2, especially preferably from 2 to 4, 0.

The precipitation process according to the invention does not use chelating agents or ion exchange columns. Calcination steps of the purified silicon oxide can also be omitted. Therefore, the precipitation process present according to the invention is much simpler and more cost effective than prior art methods. Another advantage of the precipitation process according to the invention is that it can be carried out in conventional equipment.

The use of ion exchangers to purify silicate solutions and / or acidifying agents before precipitation is not necessary, but may be desirable depending on the quality of the aqueous silicate solutions. Therefore, an alkaline silicate solution can also

29/114 be pre-treated according to WO 2007/106860, in order to minimize the content of phosphorus and / or boron previously. For this, the alkaline silicate solution (aqueous phase in which the silicon oxide is dissolved) can be treated with a transition metal, calcium or magnesium, a molybdenum salt or with an ion exchanger modified with molybdate salts to minimize the content phosphorus. Before precipitation according to the method of WO 2007/106860, the alkaline silicate solution can undergo precipitation according to the invention under acidic conditions, in particular at a pH value of less than 2. In the method according to However, preference is given to the use of acidifying agents and silicate solutions that were not treated by means of ion exchangers before precipitation.

In a specific embodiment, a silicate solution can be pretreated as a silica sol according to the methods of EP 0 504467 B1 before the actual acid precipitation according to the invention. To this end, the entire disclosure of EP 0 504 467 B1 is expressly incorporated into the present document. The silica sol obtained by the methods disclosed in EP 0 504 467 B1 is completely dissolved again, preferably after a treatment according to the methods of EP 0 504 467 B1, and then subjected to acid precipitation according to the invention, to obtain purified silicon oxide according to the invention.

The silicate solution preferably has, before acidic precipitation, a silicon dioxide content of, for example, approximately 10% by weight or greater.

In the main aspect of the present invention, a silicate solution, especially a soluble sodium glass, used for acidic precipitation has a viscosity of 0.1 to 10,000 poises, preferably 0.2 to 5000 poises, more preferably 0.3 to 3000 poises, especially preferably 0.4 to 1000 poises (at room temperature, 20 ° C).

In steps b and c of the first preferred variant of the main aspect method, a silicate solution is prepared with a viscosity of 0.1 to 2 poises, preferably 0.2 to 1.9 poises, especially 0.3 to

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1.8 poises and especially preferably 0.4 to 1.6 poises and most especially, preferably 0.5 to 1.5 poises. Mixtures of various silicate solutions can also be used.

In steps b and c of the second preferred variant of the main aspect method, a silicate solution is prepared with a viscosity of 2 to 10,000 poises, preferably 3 to 70,000 poises, especially 4 to 6000 poises, especially preferably 4 to 1000 poises, most especially, preferably 4 to 100 poises and especially preferably 5 to 50 poises.

In step c of the main aspect and two preferred variants of the precipitation process according to the invention, the silicate solution from step b is added to the feed and the silicon dioxide is therefore precipitated. It is necessary to ensure that the acidifying agent is always present in excess. Addition of the silicate solution therefore takes place in such a way that the pH value of the reaction solution is always less than 2, preferably less than 1.5, especially preferably less than 1, very especially preferably less than 0, 5 and especially preferably it is 0.01 to 0.5. Additional acidifying agent can be added if necessary. The temperature of the reaction solution is maintained, during the addition of the silicate solution, from 20 to 95 ° C, preferably 30 to 90 ° C, especially preferably from 40 to 80 ° C, by heating or cooling the precipitation vessel.

The inventors have found that precipitates that can be filtered out particularly easily are obtained if the silicate solution introduces the feed and / or suspension of precipitation in the form of droplets. Therefore, in a preferred embodiment of the present invention, care is taken to ensure that the silicate solution introduces the feed and / or suspension of precipitation in the form of droplets. This, for example, can be achieved by adding the silicate solution dropwise to the feed. This may involve a measuring device disposed outside the feed / precipitation suspension and / or immersed in the

11/31 feeding / precipitation suspension.

In the first particularly preferred variant of the main aspect method, that is, the low viscosity soluble glass method, it was particularly advantageous if the precipitation feed / suspension is set in motion, for example, by agitation or pumping, such that the flow velocity measured in a region that is bounded by half the radius of the precipitation vessel ± 5 cm and the surface of the reaction solution per 10 cm below the reaction surface, is 0.001 to 10 m / s, preferably 0.005 to 8 m / s, especially preferably 0.01 to 5 m / s, quite especially 0.01 to 4 m / s, especially preferably 0.01 to 2 m / s and very especially, preferably between 0.01 to 1 m / s s.

Without being bound by a particular theory, the inventors are of the view that due to the low flow rate, there is very little distribution of the inlet silicate solution immediately after introducing the feed / precipitation suspension. As a result, gelation occurs rapidly in the outer envelope of the droplets of incoming silicate solution or streams of silicate solution, before impurities can be confined within the particles. By selecting the optimum flow rate of the feed / precipitation suspension, it is therefore possible to improve the purity of the product obtained.

By combining an optimized flow rate with the introduction of the silicate solution as far as possible in the form of droplets, this effect can be further enhanced, so that a modality of the method according to the invention, in which the silicate solution is introduced in the form of a droplet in a feed / precipitation suspension at a flow rate, measured in a region d which is bounded by half the radius of the precipitation vessel ± 5 cm and the surface of the reaction solution by 10 cm below the surface of reaction, from 0.001 to 10 m / s, preferably 0.005 to 8 m / s, especially preferably 0.01 to 5 m / s, quite especially 0.01 to 4 m / s, especially preferably 0.01 to 2 m / s very especially,

32/114 preferably between 0.01 to 1 m / s. In this way it is also possible to produce particles of silicon dioxide that can be filtered very easily (see figures 1 and 2). Unlike methods in which there is a high flow rate in the feed / precipitation suspension, very fine particles are formed, said particles are very difficult to filter.

In the second preferred embodiment of the main aspect of the present invention, that is, in the case of using high-viscosity soluble glass, particularly pure and easily filterable precipitates the form as a result of the addition of the silicate solution dropwise. Without being linked to a particular theory, the inventors are of the view that the high viscosity of the silicate solution, together with the pH value, means that after step c) easily filtered precipitate is formed and that there is little if any accumulation of impurities in the internal cavities of the silicon dioxide particles, because due to the high viscosity the droplet form of the silicate solution added dropwise is basically conserved and the droplet is not finely distributed before gelation / crystallization begins on the droplet surface. An alkaline and / or alkaline earth silicate solution can be used as a silicate solution, preferably an alkaline silicate solution, especially preferably sodium silicate solution (soluble glass) and / or potassium silicate is used. Mixtures of various silicate solutions can also be used. Alkaline silicate solutions have the advantage that alkaline ions can be easily separated by washing. Viscosity can be adjusted, for example, by the concentration of commercially available silicate solutions by evaporation, or by dissolving the silicate in water.

As stated above, by properly choosing the viscosity of the silicate solution and / or the stirring speed, the filterability of the particles can be improved, because particles with a special shape are obtained. The present invention therefore relates to purified silicon oxide particles, in particular silicon dioxide particles, preferably with an external diameter of 0.1 to 10 mm, especially

33/114 preferably 0.3 to 9 mm and most especially, preferably between 2 to 8 mm. In a first special embodiment of the present invention, said silicon dioxide particles have an annular shape, that is, they have a hole in the middle (see figure 1a) and their shape, therefore, can be compared to a miniature thread . The ring particles can be substantially round in shape, but also more oval in shape.

In a second special embodiment of the present precipitation process according to the invention, the silicon dioxide particles have a shape that is comparable to a mushroom or jellyfish hat, that is, instead of the screw-shaped particle hole described above , in the middle of the main annular structure there is preferably a thin layer of silicon dioxide, that is, thinner than the annular part, which is covered on one side (see figure 2a), stretched over the inner opening of the ring. If these particles are placed on the base with the covered side down and we examine them vertically from above, the particles correspond to a plate with a covered bottom, a rather massive upper edge, that is, thick and a slightly thinner bottom in the region the dome.

Without being bound by a particular theory, the inventors are of the view that the acidic conditions in the feed / reaction solution together with dropwise addition of the silicate solution, plus the viscosity and flow rate of the feed / precipitation suspension, it has the effect that the droplets of the silicate solution start to gel / precipitate on its surface immediately on contact with the acid, and at the same time the droplet is deformed by the movement of the droplet in the solution / reaction feed. Depending on the reaction conditions, apparently the mushroom-like particles with slower droplet movement, whereas the donut-shaped particles are formed with faster droplet movement.

The present invention also relates to a precipitation process in which, after step c, the silicon dioxide particles previously described in the mushroom cap and thread modalities

34/114 are produced or processed in at least one stage.

The silicon dioxide obtained after precipitation, that is, in the main aspect and the preferred variants of the main aspect such as step c., Are separated into other constituents of the precipitation suspension (in the main aspect and the preferred variants of step d of the main aspect) ). Depending on the filterability of the precipitate, this can be accomplished by conventional filtration techniques known to one skilled in the art, for example, with press filters or rotary filters. In case of precipitates with poor filterability, separation can also be carried out by centrifuging and / or decanting the liquid components of the precipitation suspension.

After separating the supernatant, the precipitate is washed, ensuring, with a suitable washing medium, that the pH of the washable medium during washing, and thus also of the purified silicon oxide, in particular silicon dioxide, is less than 2, preferably less than 1.5, especially preferably less than 1, most especially, preferably 0.5 and especially preferably 0.01 to 0.5.

The washing means may preferably be aqueous solutions of water-soluble organic and / or inorganic acids, for example, the aforementioned acids or fumaric acid, oxalic acid, formic acid, acetic acid or other organic acids known to one skilled in the art, that they themselves do not contribute to the contamination of the purified silicon oxide if they cannot be removed completely with high purity water. Generally, therefore, all water-soluble organic acids, in particular compounds of the elements C, H and O, are preferred both as an acidifying agent and in the washing medium, because they themselves do not contribute to the contamination of the reduction step. subsequent. The acidifying agent used in step a. and c. or mixtures thereof in diluted or undiluted form are preferably used.

The washing medium may, if necessary, also comprise

35/114 a mixture of water and organic solvents. Suitable solvents are high-purity alcohols, such as methanol and ethanol, possible esterification does not interfere with the subsequent reduction to silicon.

The aqueous phase preferably does not contain any organic solvent, such as alcohols, and / or no organic, polymeric substance.

In the method according to the invention, it is not normally necessary to add chelating agents to the precipitation suspension or during purification. However, the present invention also includes methods in which, for the stabilization of acid-soluble metal complexes, a complexing metal agent, such as EDTA, is added to the precipitation suspension or to a washing medium. Therefore, it is optionally possible to add a chelating agent to the washing medium or to stir the precipitated silicon dioxide in a washing medium with a corresponding pH value of less than 2, preferably less than 1.5, especially preferably less than 1, most especially, preferably 0.5 and especially preferably 0.01 to 0.5, containing a chelating agent. Preferably, however, washing with the acidic washing medium is carried out immediately after separation of the precipitated silicon dioxide, without additional steps being carried out.

It is also possible to add a peroxide for color marking, as an indicator of undesirable metallic impurities. For example, hydroperoxide can be added to the precipitation suspension or the washing medium in order to indicate, by color, the presence of titanium impurities. Marking is generally also possible with other organic complexing agents, which in turn do not interfere with the subsequent reduction process. This generally includes all complexing agents based on elements C, H and O, and element N can also be advantageously added to the complexing agent. For example, for the formation of silicon nitride, which advantageously decomposes again in the subsequent process.

Washing is continued until the silicon dioxide is of the desired purity. This can be recognized, for example, when the

36/114 wash suspension contains a peroxide and is no longer visible yellow. If the precipitation process according to the invention is carried out without adding a peroxide that forms a yellow / orange colored compound with Ti (IV) ions, then in each washing step a small sample of the washing suspension can be taken and a corresponding peroxide must be added to it. This process is continued until the sample taken no longer gives a visible yellow / orange color after adding the peroxide. It is necessary to ensure that the pH value of the washing medium and thus also that of the purified silicon oxide, in particular silicon dioxide, up to this point in time is less than 2, preferably less than 1.5, especially preferably less than 1, most especially, preferably 0.5 and especially preferably it is 0.01 to 0.5.

The silicon dioxide thus washed and purified, is still preferably washed with distilled water or deionized water, until the pH value of the silicon dioxide obtained is in the range 4 to 7.5 and / or the conductivity of the wash suspension is less than or equal to 9 pS / cm, preferably less than or equal to 5 pS / cm. This ensures that any acidic residue that adheres to silicon dioxide has been properly removed.

Separation can be carried out with usual measures that are well known to one skilled in the art, such as filtration, decantation, centrifugation and sedimentation, as long as the level of impurity of the precipitates by acid, purified silicon oxide is not aggravated again by these measures.

For precipitates with poor filterability, it may be advantageous to perform washing by having the washing medium draining down into the precipitate in a fine mesh filter basket.

The purified silicon dioxide, in particular high purity silicon dioxide thus obtained, can be further dried and processed. Drying can be carried out by all methods known to one skilled in the art, for example, with band dryers, shelf dryers, drum dryers etc.

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It is recommended to grind dry silicon dioxide, obtain an optimal particle size range for further processing to solar grade silicon. The techniques for optional crushing of silicon dioxide according to the invention are known to one skilled in the art and can be found, for example, in Ullmann, 5th edition, B2, 5-20. Preferably, crushing is carried out in countercurrent fluidized bed mills in order to minimize or avoid contamination of high-purity silicon dioxide with worn metal from the mill walls. The grinding parameters are selected such that the particles obtained have an average particle size d ₅ o of 1 to 100 pm, preferably 3 to 30 pm, especially preferably 5 to 15 pm.

The silicon oxides prepared and purified according to the invention preferably have the impurity profile defined above for purified, pure or high purity silicon dioxide, but they can also have the following amounts of impurities:

The. Aluminum between 0.001 ppm and 5 ppm, preferably 0.01 ppm to 0.2 ppm, especially preferably 0.02 to 0.1, most especially, preferably between 0.05 to 0.8 and especially preferably 0.1 to 0 , 5 ppm,

B. Boron less than 1 ppm, preferably 0.001 ppm to 0.099 ppm, especially preferably 0.001 ppm to 0.09 ppm and very especially, preferably between 0.01 ppm to 0.08 ppm

ç. Calcium less than or equal to 1 ppm, 0.001 ppm to 0.3 ppm, especially preferably 0.01 ppm to 0.3 ppm and most especially, preferably between 0.05 to 0.2 ppm

d. Iron less than or equal to 5 ppm, preferably 0.001 ppm to 3 ppm, especially preferably 0.05 ppm to 3 ppm and most especially, preferably 0.01 to 1 ppm, especially preferably 0.01 ppm to 0.8 ppm and much especially, preferably 0.05 to 0.5 ppm

and. Nickel less than or equal to 1 ppm, preferably 0.001 ppm to 0.8 ppm, especially preferably 0.01 ppm to 0.5 ppm and much

38/114 especially, preferably 0.05 ppm to 0.4 ppm

f. Phosphorus less than 10 ppm, preferably less than 5, especially preferably less than 1, very especially, preferably 0.001 ppm to 0.099 ppm, especially preferably 0.001 ppm to 0.09 ppm and very especially, preferably between 0.01 ppm to 0 .08 ppm

g. Titanium less than or equal to 1 ppm, 0.001 ppm to 0.8 ppm, especially preferably 0.01 ppm to 0.6 ppm and most especially, preferably 0.1 to 0.5 ppm

H. Zinc less than or equal to 1 ppm, preferably 0.001 ppm to 0.8 ppm, especially preferably 0.01 ppm to 0.5 ppm and most especially, preferably 0.05 ppm to 0.3 ppm the sum of the impurities mentioned above plus sodium and potassium being less than 10 ppm, preferably less than 4 ppm, especially preferably less than 3 ppm, most especially, preferably 0.5 to 3 ppm and especially preferably 1 ppm to 3 ppm.

The high-purity silicon dioxides according to the invention can be in the forms of presentation described above, that is, as screw-shaped particles or as mushroom hat-shaped particles or in conventional particle shapes. However, they can also be crushed, compressed to granules or briquettes by methods known to one skilled in the art. If the particles have been crushed, that is, they are in the form of conventional particle, they may preferably have an average particle size d ₅ o from 1 to 100 pm, especially preferably 3 to 30 pm and most especially, preferably 5 to 15 pm . Donut-shaped or mushroom-shaped particles preferably have an average particle size d ₅₀ of 0.1 to 10 mm, especially preferably 0.3 to 9 mm and most especially, preferably 2 to 8 mm.

The purified silicon oxides, in particular high purity silicon dioxides, are further processed according to the invention to pure silicon for high purity silicon for the solar industry, or a portion

39/114 thereof is used alternatively as described below. According to the invention, purified silicon oxides, in particular high purity silicon dioxides, are reacted with a source of pure carbon, such as a high purity carbon, silicon carbide and / or pure sugars.

The method according to the invention does not normally comprise a calcination step for silicon dioxide. However, this does not exclude the possibility that the obtained silicon oxide can be subjected to a thermal post-treatment, in particular calcination treatment, preferably at temperatures between 900 and 2000 C, especially preferably around 1400 ° C, in order to remove nitrogen and sulfur-containing impurities.

The purified silicon oxide obtainable by precipitation according to the invention, in particular the purified silicon dioxide has a content of the elements aluminum, boron, calcium, iron, nickel, phosphorus, titanium and / or zinc each separately or in combination, as defined above and preferably has better filterability.

In an alternative embodiment of the method described above for the production of high purity silicon oxide it is also possible to convert the contaminated silicon oxide into a dissolved form and, for example, to produce a high purity silicon dioxide from this solution by the method above mentioned.

Therefore, the invention also relates to the use of at least one silicon oxide containing impurities for the production of silicon, in particular suitable as solar grade silicon or suitable for the production of solar grade silicon, preferably pure silicon of according to the aforementioned definition, comprising the following steps,

I) converting the silicon oxide containing impurities to a silicate dissolved in an aqueous phase, in particular to an aqueous silicate solution,

II) addition of the silicate dissolved in the aqueous phase, in particular the aqueous silicate solution, to an aqueous, acidic solution, with the impurities remaining in solution, in particular the pH value and / or the

40/114 addition is selected so that as far as possible all impurities remain in solution from the beginning of the addition until the end of the addition, and a precipitate of the purified silicon dioxide is obtained.

Another object is a method by which silicon oxide thus obtained - as described in detail below - in step

III) is converted to silicon in the presence of at least one or more carbon sources and optionally by the addition of an activator.

In particular, step II) is performed according to the above-mentioned account for the production of a precipitation suspension, preferably acid precipitation is carried out in aqueous solution optionally in the presence of pure solvents, with unwanted impurities remaining dissolved in the aqueous acidic solution . The pH value is preferably below pH = 2, as stated above.

An impurity-containing silicon oxide is considered to be a silicon oxide with a boron, phosphorus, aluminum, iron, titanium, sodium and / or potassium content greater than 1000 ppm by weight, in particular greater than 100 ppm by weight, preferably one Silicon oxide is still considered to be contaminated silicon oxide if the total impurity content mentioned above is above 10 ppm by weight.

A silicon oxide containing impurities also means a silicon dioxide with a content of the following elements each individually or in any partial combination or also all together:

The. Aluminum above 6 ppm, in particular above 5.5 ppm, also preferably still above 5 ppm, also especially preferably still above 0.85 ppm and / or

B. Boron above 10 ppm, also preferably still above 5.5 ppm, especially preferably above 3.5, most especially, preferably still above 15 ppb and / or

ç. Calcium above 2 ppm, in particular also above 0.35 ppm, especially preferably above 0.025 ppm and / or

d. Iron above 23 ppm, in particular above 15 ppm,

41/114 preferably still above 0.65 ppm and / or

and. Nickel above 15 ppm, in particular above 5.5 ppm, especially preferably still above 0.055 ppm and / or

f. Phosphorus above 15 ppm, in particular above 5.5 ppm, especially preferably still above 0.1 ppm, or also above 15 ppb and / or

g. Titanium above 2.5 ppm, in particular above 1.5 ppm and / or

H. Zinc above 3.5 ppm, in particular above 1.5 ppm, especially preferably still above 0.35 ppm, and in particular the sum of the aforementioned impurities plus sodium and potassium is greater than 10 ppm, also in particular still above 5 ppm, preferably above 4 ppm, especially preferably above 3 ppm, very especially, preferably between above 1 ppm or also above 0.5 ppm.

Also at a boron content of less than 0.5 ppm, also in particular still below 0.1 ppm and / or a phosphorus content above 1 ppm or also above 0.5 ppm, a silicon oxide is considered as silicon oxide containing impurities if only the content of at least one element selected from the group of aluminum, calcium, iron, nickel, titanium, zinc exceeds the limit stated above.

Silicon oxide purified by all the methods described in detail above, especially high purity silicon dioxide, can be used as a starting material in the additional method according to the invention. It can be used for further conversion to high-purity silicon, ie, reduction step, but it can also be used in a process variant as a high-purity defoaming agent in the production of high-purity carbon. This process variant is described below. Silicon oxide purified by all the processes described in detail above can also be used to produce silicon carbide, which is described below.

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Carbon source production by sugar pyrolysis using silicon oxide as a defoaming agent

In addition to other carbon sources mentioned in this description, preferably the natural carbon sources listed in this description, it is also possible to obtain carbohydrate carbon. To produce high-purity carbon, in this preferred variant (component of the method) of the complete method according to the invention to prepare pure silicon, it is preferable to use a carbon source, especially a pure carbon source, in which carbon is obtained by industrial pyrolysis of at least one carbohydrate 10 or a mixture of carbohydrates, especially crystalline sugar, at an elevated temperature with the addition of silicon oxide.

It has been found, surprisingly, that by adding silicon oxide, preferably SiO ₂ , in particular precipitated silicic acid and / or pyrogenically produced silicic acid, the foaming effect 15 can be suppressed.

Since this step essentially involves the production of pure carbon and only a very small amount of silicon oxide needs to be added, it is not absolutely necessary to use a silicon oxide obtained by the method component described in detail above, 20 although this is preferred to simplify the process. In a variant, for example, the high purity silicon oxide obtained by the component of the method described above can be used in conjunction with a carbon source, especially a pure carbon source, and chlorine for the known reaction to provide halogenated silanes. These silanes can be used to produce ultra-high purity pyrogenic silicic acids.

This industrial process for carbohydrate pyrolysis can be operated simply and economically and without unwanted foaming. In addition, when carrying out the method, only a short caramel phase was observed. In addition, in a preferred embodiment it was advantageous, as it is especially for energy saving (low temperature mode), to reduce the pyrolysis temperature from, for example, 1600 ° C to approximately 700 ° C. The method is advantageously carried out above

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X pyrolysis temperatures from 1300 to 15 ° C ^to C are desirable, Pyrolysis is advantageously performed under protective gas and / or reduced pressure (vacuum). For example, at a pressure of 0.1 kPa to 100 kPa (ambient pressure), in particular from 100 to 1000 kPa. The substances used in particular do not need to be dried in pyrolysis using a microwave oven. Educts can have residual moisture. Advantageously, the pyrolysis equipment used is dried before the pyrolysis begins and purged almost entirely of oxygen by washing with an inert gas, such as nitrogen or Ar or He. Preferably, argon or helium are used. The 10 pyrolysis time is usually between 1 minute and 48 hours, preferably between 174 hours ® 18 hours, in particular between 1/4 hour and 12 hours at the temperature of said pyrolysis, and the heating time to reach the desired pyrolysis temperature can additionally be of the same order, in particular between 1/4 hour and 8 hours.

The method is usually carried out as a batting process;

however, it can also be done continuously.

A C-based pyrolysis product obtained containing charcoal, in particular with fractions of graphite and silicic acid and optionally fractions of other forms of carbon, such as coke, and is especially low in 20 impurities, for example, compounds of B, P , As and Ai. In this way, the pyrolysis product can be used advantageously as a reducing agent in the complete method according to the invention. In particular, based on its conductivity properties, the graphite-containing pyrolysis product can be used in an arc reactor.

The present invention therefore relates to a method for technical, that is, industrial, pyrolysis of a carbohydrate or mixture of carbohydrates at elevated temperature with the addition of silicon oxide, in particular purified silicon oxide,

Preferably monosaccharides are used as a carbohydrate component in pyrolysis, that is, aldoses or ketosis, such as trioses, tetroses, pentoses, hexoses, heptoses, especially glucose and fructose, but also corresponding oligo-and polysaccharides based

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Preferably monosaccharides are used as a carbohydrate component in pyrolysis, that is, aldoses or ketosis, such as trioses, tetroses, pentoses, hexoses, heptoses, especially glucose and fructose, but also corresponding oligo- and polysaccharides based on said monomers, such as lactose , maltose, sucrose, raffinose, - to name just a few or their derivatives - as well as starch, including amylose and amylopectin, glycogens, glucosans and fructosans, - to name just a few polysaccharides. However, all the carbohydrates / sugars described in detail below for the production of SiC can be used in the purities mentioned there.

Optionally the aforementioned carbohydrates can be further purified by a treatment using an ion exchanger, dissolving the carbohydrate in a suitable solvent, advantageously water, passing it through a column packed with an ion exchange resin, preferably an ionic or cationic resin, the resulting solution is concentrated, for example, by removing the solvent fractions by heating - in particular under reduced pressure - and the carbohydrate thereby purified is advantageously obtained in crystalline form, for example, by cooling the solution and subsequently separating the crystalline fractions , for example, by filtration or centrifugation. However, a mixture of at least two of the carbohydrates mentioned above can also be used as a carbohydrate or carbohydrate component in pyrolysis.

Especially preferably, a crystalline sugar that is available in economical quantities is used, a sugar such that it can be obtained, for example, by the crystallization of a solution or a broth from sugar cane or beet in a well-known manner, that is, sugar commercially available crystalline, for example, refined sugar, preferably a crystalline sugar with a substance-specific melting / softening range and an average particle size from 1 pm to 10 cm, especially preferably from 10 pm to 1 cm, in particular from 100 pm at 0.5 cm. The particle size can be

45/114 determined, for example, - but not exclusively - by sieve analysis, TEM, SEM or optical microscopy. It is also possible to use a carbohydrate in dissolved form, for example - but not exclusively in aqueous solution, with the solvent being evaporated readily and more or less quickly before the actual pyrolysis temperature is reached.

The silicon oxide component used in pyrolysis is preferably SiOx with x = 0.5 to 1.5, SiO, SiOj, silicon oxide (hydrate), aqueous or water-containing SiO ₂ , for example, in the form of pyrogenic silicic acid or precipitated, wet, dry or calcined, for example, Aerosil® or Sipernat®, or a silicic acid, sol or gel, porous or dense glass silica, quartz sand, quartz glass fibers, fibers, for example, optics, beads quartz glass, or mixtures of at least two of the above components. Silicic acid with an internal surface of 0.1 to 600 m ² / g, especially preferably 10 to 500 m Ig, in particular 100 to 200 m ² / g, is preferably used for pyrolysis. The internal or specific surface can be determined, for example, by the BET method (DIN ISO 9277). Preferably, silicic acid is used with an average particle size of 10 nm to 51 mm, in particular from 1 to 500 pm. The particle size can also be determined here inter alia by TEM (transmission electron microscopy), SEM (scanning electron microscopy) or optical microscopy. Most preferably, a silicon oxide obtained by the method components described above is used.

The silicic acid used in pyrolysis is advantageously of high purity (99%) to ultra-high (99.9999%), and the total content of impurities, such as compounds of B, P, As and Al, must be advantageously <10 ppm by weight, preferably at 5 ppm by weight, especially preferably - 2 ppm by weight and most especially, preferably 1 to 0.001 ppm by weight. In a special embodiment, the impurity content of the elements mentioned above is <0.5 ppm by weight to 0.0001 ppb by weight. According to the invention, purified silicon oxide is used, that is, acid

46/114 silica which was precipitated at a pH value below 2. Especially preferably, in pyrolysis, a purified silicon oxide, especially high purity silicon oxide, according to the definition given at the beginning of this description is used, and most preferably, silicon dioxide prepared by the purification method according to the invention. Impurities can be determined, for example, - but not exclusively - by ICPMS / OS (coupled induction spectrometry / optical electronic spectrometry) and AAS (atomic absorption spectroscopy) or GDMS (luminescent discharge mass spectrometry).

Thus, during pyrolysis it is possible to use carbohydrate for the antifoaming agent, that is, silicon oxide component, calculated as SiO ₂ , in a weight ratio of 1000: 0.1 to 0.1: 1000. Preferably, the weight ratio of the carbohydrate component to the silicon oxide component can be set at 100: 1 to 1: 100, especially preferably at 50: 1 to 1:50, most especially, preferably at 20: 1 to 1:20 , in particular from 2: 1 to 1: 1.

The equipment used to carry out pyrolysis can be, for example, a vacuum reactor heated by induction, the reactor possibly being made of special steel and, in view of the reaction, covered or coated with a suitable inert substance, for example, with SiC high purity, Si3N3, high purity quartz glass or glassy silica, high purity carbon or graphite.

However, other suitable reaction vessels can also be used, for example, an induction furnace with a vacuum chamber to receive a corresponding reaction crucible.

Pyrolysis is generally performed as follows:

The interior of the reactor and the reaction vessel is properly dried and washed with water with an inert gas, which, for example, can be heated to a temperature between room temperature and 300 ° C. Then the carbohydrate or carbohydrate mixture to be pyrolyzed is fed, together with silicon oxide as a defoaming component, in the

47/114 reaction or reaction vessel of the pyrolysis equipment. The substances used can be intimately mixed previously, degassed under reduced pressure and transferred under protective gas to the prepared reactor. The reactor may already have been slightly preheated. Then the temperature can be increased continuously or in stages to the desired pyrolysis temperature, reducing the pressure so that the gas decomposition products released from the reaction mixture can be carried out as quickly as possible. It is advantageous to avoid defoaming the reaction mixture as far as possible, in particular by adding silicon oxide.

In carrying out the pyrolysis reaction, the pyrolysis product may undergo a post-heat treatment for some time, advantageously at a temperature in the range of 1000 to 1500 ° C. As a rule this provides a pyrolysis product or a composition containing pure to high purity carbon. According to the invention, the pyrolysis product is preferably used as a reducing agent for the production of solar grade silicon in the complete method.

For this, the pyrolysis product can be brought into a defined form with the addition of additional components, in particular with the addition of purified SiO ₂ according to the invention, activators, such as SiC, binders, such as organosilanes, organosiloxanes, carbohydrates, silica gel, natural or synthetic resins, and high purity processing aids, such as pressing, tableting or extrusion aids, such as graphite, bring to a defined shape, for example, by granulation, pelletizing, tabletting, extrusion - to provide just a few examples.

The present invention, therefore, also relates to a pyrolysis composition or product, as obtained after pyrolysis. Therefore, the present invention also relates to a pyrolysis product with a carbon content for silicon oxide (calculated as silicon dioxide) from 400 to 0.1 to 0.4 to 1000, in particular 400: 0.4 at 4:10, preferably from 400: 2 to 4: 1.3, especially preferably from 400: 4 to 40: 7.

In particular, the direct pyrolysis product is characterized by

48/114 its high purity and usability for the production of polycrystalline silicon, in particular solar grade silicon for photovoltaic installations, but also for medical applications.

Said composition (also called pyrolysate or abbreviated pyrolysis product) can be used according to the invention as a raw material in the production of solar grade silicon by reducing S1O2, in particular by reducing the purified silicon oxide, in high temperature, in particular in an arc furnace. According to the invention, the product of the direct method will be used for reaction of purified silicon oxide with a pure carbon source in the method according to the invention.

Alternatively, it is also possible to use the product of the direct method simply and economically as an agent containing C reduction in a method of the determined documents, as can be found, for example, in US 4,247,528, US 4,460,556, US 4,294,811 and WO 15 2007/106860.

The present invention also relates to the use of a composition (pyrolysis product) as a raw material in the production of solar grade silicon by reducing SiO ₂ , in particular by reducing the purified silicon oxide at high temperature, in particular in an arc furnace.

²⁰ Production of high purity SiC from SiO ₂ and its use in the method according to the invention

Another aspect according to the invention of the complete method for the production of pure silicon involves the use of silicon carbide as an activator and / or as a source of pure carbon, in which case the silicon carbide must be a pure silicon carbide . First the production of silicon carbide, in particular for use in the method according to the invention for the production of pure silicon, is thus explained below, and then a method in which the silicon carbide is used as an activator, initiator of reaction, reaction accelerator or also as a source 30 of pure carbon in silicon production.

Generally, silicon carbide can be purchased and / or it can be silicon carbide for recycling or waste product, provided that

49/114 meets the purity requirements of this method. In this way, pure silicon carbide can be obtained by reacting silicon oxide and a carbon source comprising at least one carbohydrate at an elevated temperature and can be used in the method according to the invention, for example, as material for production electrodes or high-purity refractories for coating reactors, in particular the first layer of the reaction space or reactor. This aspect will be explained elsewhere below. Crystalline sugar is preferably used as a carbon source comprising at least one carbohydrate, in particular a source of pure carbon.

According to this partial aspect of the invention, a method is disclosed for the production of pure to high purity silicon carbide and / or silicon carbide / graphite particles by the reaction of silicon oxide, in particular purified silicon oxide, and a carbon source comprising a carbohydrate, in particular carbohydrates, at elevated temperature, in particular a commercial process for producing silicon carbide or for producing compositions containing silicon carbide and isolating the reaction products. In addition, this partial aspect of the invention relates to a pure to high purity silicon carbide, compositions containing the latter, use as a catalyst and use in the production of electrodes or as electrode material and other articles.

According to the partial aspect of the invention, one of its objectives is to produce pure to high-purity silicon carbide from clearly more favorable raw materials, and to overcome the existing disadvantages related to the process of known methods, which separate gases sensitive to hydrolysis and auto-ignition. of silicon carbide.

It was surprisingly found that, by reaction, mixtures of silicon dioxide, in particular of the purified silicon oxide according to the invention, and sugar with subsequent pyrolysis and / or high temperature calcination, depending on the proportion of the mixture, a silicon carbide of high purity in a matrix of carbon and / or silicon carbide in a matrix of silicon dioxide and / or a silicon carbide, comprising

50/114 carbon and / or silicon dioxide in a composition, can be produced cost-effectively. Preferably, silicon carbide is produced in a carbon matrix. In particular, a silicon carbide particle with an external carbon matrix, preferably 5 with a graphite matrix on the internal and / or external surface of the particle, can be obtained.

Silicon carbide can be obtained simply, in pure form, by passive oxidation with air, in particular by removing the carbon oxidatively. Alternatively, the silicon carbide can be further purified and / or separated by purification at high temperatures and optionally under high vacuum. Silicon carbide sublimates at temperatures around 2800 ° C.

Silicon carbide can be obtained in pure form by post-treatment of silicon carbide in a carbon matrix by passive oxidation with oxygen, air and / or NO _X H ₂ O, for example, at temperatures around 800 ° C. In this oxidation process, carbon or carbon-containing matrix can be oxidized and can be removed as process gas from the system, for example, as carbon monoxide. The purified silicon carbide then possibly still comprises one or more matrices of silicon oxide or possibly small amounts of silicon.

Silicon carbide itself is relatively resistant to oxidation by oxygen at temperatures above 800 ° C. In direct contact with oxygen, it forms a passivation layer of silicon dioxide (SiO ₂ , passive oxidation). At temperatures above approximately 1600 ° C and 25 with simultaneous oxygen deficiency (partial pressure below approximately 5 kPa (50mbar)) there is formation of gaseous SiO, not glass-like SiO ₂ ; there is no longer a protective effect, and SiC is quickly burned (active oxidation). This active oxidation occurs when the free oxygen in the system is exhausted.

^A C-based reaction product or a carbon matrix reaction product, in particular a pyrolysis product, obtained according to the invention contains carbon, in particular in the form of coke

51/114 and / or carbon black and silicic acid and possibly fractions of other forms of carbon, such as graphite, and is especially low in impurities, for example, the elements boron, phosphorus, arsenic, iron and aluminum and their compounds.

Pyrolysis and / or calcination products can preferably be used as a reducing agent in the production of silicon carbide from sugar, coke and silicic acid at high temperature. In particular, the calcination and / or pyrolysis product containing carbon or containing graphite according to the invention is used, because of its conductivity properties, for the production of the electrodes according to the invention and for the production of the electrodes of the reactor according to the invention, in particular as electrode material. For example, in an arc reactor, or as a catalyst and according to the invention as a raw material for the production of pure silicon, in particular for the production of solar grade silicon. Obtainable silicon carbide can also be used for the production of high-purity refractories for coating reactors, a reaction space or for coating other connections, supply lines or discharge lines.

High purity silicon carbide can also be used as an energy source and / or as an additive for the production of high purity steel.

The present invention, therefore, relates to a method for the production of pure to high purity silicon carbide by the reaction of silicon oxide, in particular purified silicon oxide according to the above definition, in particular silicon dioxide purified, and a carbon source comprising at least one carbohydrate, in particular a source of pure carbon, at elevated temperature, and in particular isolation of silicon carbide. The invention also relates to a silicon carbide or a composition containing silicon carbide obtainable by this method and the pyrolysis and / or calcination product obtainable by the method according to the invention, and in particular isolation thereof.

The invention relates to a commercial process,

52/114 preferably a large scale commercial for industrial reaction or pyrolysis and / or industrial calcination of a pure carbohydrate or mixture of carbohydrates at elevated temperature with addition of silicon oxide, in particular purified silicon dioxide, and its conversion. According to an especially preferred variant of the method, the commercial process for the production of high purity silicon carbide consists of the reaction of pure carbohydrates, optionally mixtures of carbohydrates, with silicon oxide, in particular purified silicon dioxide, and oxide of silicon formed in situ, at elevated temperature, in particular between 400 and 3000 ° C, preferably at 1400 to 1800 ° C, especially preferably between approximately 1450 and below approximately 1600 ° C.

According to the invention, a pure to high purity silicon carbide is optionally isolated with a carbon matrix and / or silicon oxide matrix or a matrix comprising carbon and / or silicon oxide, in particular it is isolated as a product, optionally containing silicon. The isolated silicon carbide can have any crystalline phase, for example, an α or β phase of silicon carbide or mixtures thereof or other silicon carbide phases. All together, more than 150 polytype phases of silicon carbide are generally known. Preferably, the pure to high purity silicon carbide obtained by the method contains little if any silicon or is only infiltrated with silicon to a small extent, in particular in the range of 0.001 and 60% by weight, preferably between 0.01 and 50% by weight, especially preferably between 0.1 and 20% by weight with respect to the silicon carbide containing said matrices and optionally silicon. According to the invention, as a rule no silicon is formed during calcination or reaction at high temperature, because there is no agglomeration of the particles and as a rule fusion is not formed. Silicon would not form unless a melt formed. The additional silicon content can be controlled by silicon infiltration.

Pure or high-purity silicon carbide means that a silicon carbide as defined at the start of the description under Definitions.

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Pure to very high purity silicon carbides or high-purity compositions can be obtained using the reagents, the source containing carbon carbohydrate and the used silicon oxide, as well as the reactors, reactor components, tubes, reagents storage tanks, the reactor coating, jacketing and optionally reaction gases or inert gases added with the necessary purity in the method according to the invention.

Pure to high purity silicon carbide or the high purity composition according to the above definition, in particular including a carbon content; for example, in the form of coke, carbon black, graphite; and / or silicon oxide, in particular in the form of SiO ₂ , or preferably in the form of purified silicon oxide reaction products, has a contamination profile with boron and / or phosphorus or with compounds containing boron and / or containing phosphorus , which for the boron element is preferably below 100 ppm, in particular between 10 ppm and 0.001 ppt, and for phosphorus below 200 ppm, in particular between 20 ppm and 0.001 ppt. Preferably the boron content in a silicon carbide is between 7 ppm and 1 ppt, preferably between 6 ppm and 1 ppt, especially preferably between 5 ppm and 1 ppt or less, or for example, between 0.001 ppm and 0.001 ppt, preferably at analytical detection limit region. The phosphorus content in a silicon carbide should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and 1 ppt, especially preferably between 10 ppm and 1 ppt or less. The phosphorus content is preferably in the region of the analytical detection limit. Figures in ppm, ppb and / or ppt should be understood in all parts as proportions by weight, in particular in mg / kg, pg / kg, ng / kg or in mg / g, pg / g or ng / g etc. .

According to the invention, carbohydrates or saccharides; or mixtures of carbohydrates or suitable carbohydrate derivatives, are used in the method according to the invention as the carbon source comprising at least one carbohydrate, in particular a pure carbon source. Naturally occurring carbohydrates, their anomers,

54/114 inverted sugar and synthetic carbohydrates can be used. It is also possible to use carbohydrates that have been obtained biotechnologically, for example, by fermentation. Preferably, the carbohydrate or derivative is selected from a monosaccharide, disaccharide, oligosaccharide 5 or polysaccharide or a mixture of at least two of the determined saccharides. Especially preferably, the following carbohydrates are used in the method: monosaccharides, that is, aldoses or ketoses, such as trioses, tetroses, pentoses, hexoses, heptoses, especially glucose and fructose, as well as oligo- and polysaccharides based on said 10 monomers, such like lactose, maltose, sucrose, raffinose, to name just a few, and it is also possible to use derivatives of the determined carbohydrates, as long as they meet the determined purity requirements - even including cellulose, cellulose derivatives, starch, including amylose and amylopectin, glycogen, glycosans and fructans, to mention only a few polysaccharides. However, a mixture of at least two of the aforementioned carbohydrates can also be used as a carbohydrate or carbohydrate component in the method according to the invention.

It is generally possible to use all carbohydrates, derived from the 20 carbohydrates and carbohydrate mixtures in the method according to the invention, which are preferably of sufficient purity, in particular with respect to the elements boron, phosphorus and / or aluminum. The sum total of the elements determined as impurities in the carbohydrate or mixture should be below 100 pg / g, in particular below 100 pg / g 0.001 pg / g, 25 preferably below 10 pg / g 0.001 pg / g, especially preferably below 5 pg / g to 0.01 pg / g. The carbohydrates to be used according to the invention consist of the elements carbon, hydrogen and oxygen and optionally have the impurity profile determined.

Carbohydrates consisting of the elements carbon, hydrogen, oxygen and nitrogen optionally with the aforementioned impurity profile can be advantageously used in the method, whether a doped silicon carbide or a silicon carbide containing nitride

55/114 silicon must be produced. For the production of silicon carbide containing silicon nitride, in which case silicon nitride is not considered an impurity, chitin can also be used advantageously in the method.

Other carbohydrates available on an industrial scale are lactose, hydroxypropylmethylcellulose (HPMC) and other usual tablet forming excipients, which can optionally be used for the formulation of silicon oxide with the usual crystalline sugars.

A crystalline sugar that is available in economical quantities, a sugar such that it can be obtained, for example, by crystallizing a solution or a broth from sugar cane or beet by well-known methods, that is, commercially crystalline sugar available, in particular food-grade crystalline sugar, is especially preferred in the method according to the invention. Sugar or carbohydrate can provide the impurity profile 15 that is suitable for the method, generally also to be used naturally in the method in liquid form, such as syrup, in solid phase, that is, also amorphous. Optionally, a formulation and / or drying step is then performed previously.

The sugar may also have been previously purified with liquid phase lumen exchangers, optionally in demineralized water or another suitable solvent or solvent mixture, optionally to remove particular impurities, which are less easily separated by crystallization. Ion exchangers can be strongly acidic, weakly acidic, amphoteric, neutral or basic ion exchangers. The selection of the appropriate lomco exchanger, according to the impurities to be removed, will be familiar as such to a person skilled in the art. Then, the sugar can be crystallized, centrifuged and / or dried or mixed with silicon oxide and dried. Crystallization can be carried out by cooling or adding an anti-solvent or by other techniques that are familiar to one skilled in the art. The crystalline components can be separated by filtration and / or centrifugation.

According to the invention, the carbon source containing at least

56/114 minus a carbohydrate, or mixture of carbohydrates, in particular a source of pure carbon, has the following impurity profile: boron less than 2 [pg / g], phosphorus less than 0.5 [pg / g] and aluminum less than 2 [pg / g], preferably less than or equal to 1 [pg / g], in particular iron less than 60 [pg / g], 5 preferably the iron content is below 10 [pg / g], especially preferably below 5 [pg / g]. Together, according to the invention it is desirable to use carbohydrates in which the content of impurities, such as boron, phosphorus, aluminum and / or arsenic etc., is below the respective technically possible limit of detection.

Preferably, the carbohydrate source comprising at least one carbohydrate, according to the invention the carbohydrate or the mixture of carbohydrates, has the following contamination profile with boron, phosphorus and aluminum and optionally with iron, sodium, potassium, nickel and / or chrome. Boron (B) contamination is in particular between 5 and 0.00001 pg / g, 15 preferably 3 to 0.00001 pg / g, especially preferably 2 to 0.00001 pg / g, according to the invention below 2 to 0.00001 pg / g. Contamination with phosphorus (P) is in particular between 5 and 0.00001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 1 to 0.00001 pg / g, according to the invention below 0 , 5 to 20 0.00001 pg / g. Contamination with iron (Fe) is between 100 and 0.00001 pg / g, in particular between 55 and 0.00001 pg / g, preferably 2 to 0.00001 pg / g, especially preferably below 1 to 0.00001 pg / g, according to the invention below 0.5 to 0.00001 pg / g. Contamination with sodium (Na) is in particular between 20 and 0.00001 pg / g, preferably 15 to 25 0.00001 pg / g, especially preferably below 12 to 0.00001 pg / g, according to the invention below 10 to 0.00001 pg / g. Contamination with potassium (K) is in particular between 30 and 0.00001 pg / g, preferably 25 to 0.00001 pg / g, especially preferably below 20 to 0.00001 pg / g, according to the invention below 16 at 30 0.00001 pg / g. Contamination with aluminum (Al) is in particular between 4 and

0.00001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention

57/114 below 1.5 to 0.00001 pg / g. Contamination with nickel (Ni) is in particular between 4 and 0.00001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1 , 5 to 0.00001 pg / g. Contamination with chromium 5 (Cr) is in particular between 4 and 0.00001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1 to 0.00001 pg / g.

According to the invention, a crystalline sugar, for example, refined sugar, is used or a crystalline sugar is mixed with a silicon dioxide containing water or a silicic acid sol, dried and used in particulate form in the method. Alternatively any carbohydrate, in particular sugar, inverted sugar or syrup is mixed with a dry silicon oxide, containing water or aqueous, silicon dioxide, a silicic acid containing water or a silicic acid sol or the determined silicon oxide components below, optionally dried and used in the method as particles, preferably with a particle size of 1 nm to 10 mm.

Usually sugar with an average particle size of 1 nm to 10 cm, in particular 10 pm to 1 cm, preferably 100 pm to 0.5 cm 20 is used. Alternatively, sugar with an average particle size in the micrometer to millimeter range can be used, in the range of 1 micrometer to 1 mm, preferably preferably 10 micrometers to 100 micrometers which are preferred. The particle size can be determined, for example, by sieve analysis, TEM (25 transmission electron microscopy), SEM (scanning electron microscopy) or optical microscopy. A dissolved carbohydrate can also be used as a liquid, syrup, or paste, evaporating the high-purity solvent before pyrolysis. Alternatively, a drying step may be included for solvent recovery.

³⁰ Preferred raw materials as a carbon source, in particular as a source of pure carbon, are, in addition, all organic compounds known to one skilled in the art that

58/114 comprise at least one carbohydrate and satisfy the purity requirements, for example, carbohydrate solutions. The carbohydrate solution used can also be an aqueous-alcoholic solution or a solution containing tetraethoxysilane (Dynasylan® TEOS) or a tetraalkoxysilane, the solution being evaporated and / or pyrolyzed before appropriate pyrolysis.

The silicon oxide or silicon oxide component used is preferably a SiO, especially preferably a SiO _x with x = 0.5 to 1.5, SiO, SiO ₂ , silicon oxide (hydrate), aqueous or water-containing SiO ₂ , a silicon oxide in the form of pyrogenic or precipitated, wet, dry or calcined silicic acid, for example, Aerosil® or Sipernat®, or a silicic acid sun or gel, porous or dense glassy silica, quartz sand, glass fibers quartz, for example, optical fibers, quartz glass beads, or mixtures of at least two of the aforementioned forms of silicon oxide. The particle sizes of the individual components are adjusted together in a manner known to one skilled in the art.

Within the scope of the present invention, sol means a colloidal solution, in which the solid or liquid substance is dispersed in extremely fine distribution in a solid, liquid or gaseous medium (see also Rõmpp Chemie Lexikon [Roompp’s Dictionary of Chemistry]).

The particle size of the carbon source comprising a carbohydrate and the particle size of the silicon oxide are in particular adjusted to each other, in order to provide good homogenization of the components and prevent demixing before or during the process.

Preferably, a porous silicic acid is used, in particular with an internal surface of 0.1 to 800 m7g, preferably from 10 to 500 m ² / g or from 100 to 200 m ² / g, and in particular with a particle size medium of 1 nm or greater or also from 10 nm to 10 mm, in particular silicic acid of high (99.9%) to ultra-high (of 99.9999%) purity, total content of impurities, such as B compounds , P, As and Al advantageously being less than 10 ppm by weight with respect to the total composition. Purity is determined by analyzing samples known for a

59/114 well versed in the technique, for example, by detection in ICP-MS (analysis for the determination of trace impurities). Electronic spin spectrometry can provide particularly sensitive detection. The internal surface, for example, can be determined using the BET method (DIN ISO 9277, 1995).

A preferred average particle size of silicon oxide is in the range 10 nm to 1 mm, in particular from 1 to 500 pm. The particle size can be determined, for example, by TEM (transmission electron microscopy), SEM (scanning electron microscopy) or optical microscopy.

As suitable silicon oxides, consideration can generally be given to all compounds and / or minerals containing a silicon oxide, as long as they are of a purity suitable for the method and therefore for the method product and do not introduce unwanted elements and / or compounds in the process or do not burn without residues. As stated above, compounds or materials containing pure or high purity silicon oxide are used in the method.

According to the invention, a purified silicon oxide, corresponding to the above-mentioned definition and / or produced according to the partial method described above, is especially preferably used in the method for the production of silicon carbide.

Using the various silicon oxides, in particular the various silicas, silicic acids etc., agglomeration during pyrolysis can vary depending on the pH value of the particle surface. Generally, with silicon oxide, which is slightly acidic, we observe intensified particle agglomeration as a result of pyrolysis. Therefore, for the production of pyrolysates and / or calcination products with little agglomeration, it may be preferable to use silicon oxides with neutral to basic surfaces in the method, for example, with pH values between 7 and 14.

According to the invention, silicon oxide comprises a silicon dioxide, in particular a pyrogenic or precipitated silicic acid, preferably a high purity pyrogenic or precipitated silicic acid

60/114 or higher, according to the invention a purified silicon oxide. Higher purity means a silicon oxide, in particular a silicon dioxide in which the contamination of silicon oxide with boron and / or phosphorus or for compounds containing boron and / or containing phosphorus for boron must be less than 10 ppm, in particular between 10 ppm and 0.0001 ppt, and for phosphorus it should be less than 20 ppm, in particular between 10 ppm and 0.0001 ppt. The boron content is preferably between 7 ppm and 1 ppt, preferably between 6 ppm and 1 ppt, especially preferably between 5 ppm and 1 ppt or less, or for example, between 0.001 ppm and 0.001 ppt, preferably in the region of the analytical detection limit . The phosphorus content of silicon oxide should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and 1 ppt, especially preferably between 10 ppm and 1 ppt or less. The phosphorus content is preferably in the region of the analytical detection limit.

Silicon oxides, such as quartz, quartzite and / or silicon dioxides produced in the usual manner, are also advantageous. These can be silicon dioxides that occur in crystalline modifications, such as morganite (chalcedony), α-quartz (low temperature quartz), β-quartz (high temperature quartz), tridymite, cristobalite, cohesite, stishovite or also SiO ₂ amorphous, especially if they meet the requirements of determined purity. In addition, silicic acids, in particular precipitated silicic acids or silica gels, pyrogenic SiO _2, pyrogenic silicic acid or silica can preferably be used in the method and / or composition. Usual pyrogenic silicic acids are amorphous SiO ₂ powders with an average of 5 to 50 nm in diameter and with a specific surface of 50 to 600 m ² / g. The above list should not be construed as final, it is obvious to one skilled in the art that other sources of silicon oxide that are suitable for the method can also be used in the method, if the source of silicon oxide is of appropriate purity or is after it has been purified.

The silicon oxide, in particular SiO ₂ supplied and / or used, can be powdery, granular, porous, foamed, as extruded, as a mold and / or as porous glass optionally in conjunction with other additives,

61/114 in particular in conjunction with the carbon source comprising at least one carbohydrate and optionally a binder and / or mold aid.

A powdery, porous silicon dioxide is preferably used as a formed material, in particular as an extrudate or mold, especially preferably in conjunction with the carbon source comprising a carbohydrate in an extrudate or mold, for example, in a pellet or briquette. In general, all solid reagents, such as silicon dioxide, and optionally the carbon source comprising at least one carbohydrate must be used in the method or must be in a composition, in a form that offers the largest possible surface for the reaction to occur . In addition, increased porosity is desirable for the rapid removal of gases from the process. Therefore, a particulate mixture of silicon dioxide particles coated with carbohydrate can be used according to the invention. This particulate mixture is in particular packaged, in an especially preferred embodiment, as a composition or kit.

The quantities of materials used as well as the respective proportions of silicon oxide, in particular silicon dioxide and the carbon source comprising at least one carbohydrate are based on circumstances or requirements known to one skilled in the art, for example, in a subsequent process for silicon production, sintering process, process for producing electrode material or electrodes.

In the method according to the invention, the carbohydrate can be used in a weight ratio of carbohydrate to silicon oxide, in particular silicon dioxide, in a weight ratio of 1000: 0.1 to 1: 1000 with respect to total weight. Preferably the carbohydrate or mixture of carbohydrates is used in a weight to silicon oxide ratio, in particular silicon dioxide, from 100: 1 to 1: 100, especially preferably from 50: 1 to 1: 5, very especially from preferably from 20: 1 to 1: 2, with the preferred range from 2: 1 to 1: 1. According to a

62/114 preferred mode, the carbon is used in the method, through the carbohydrate, in excess in relation to the silicon to be reacted in the silicon oxide. If silicon oxide is used in excess in an advantageous manner, when selecting the ratio it is necessary to ensure that the formation of silicon carbide is not suppressed.

Also according to the invention, the carbon content of the carbon source comprising a carbohydrate for silicon content of silicon oxide, in particular silicon dioxide, is in a molar ratio of 1000: 0.1 to 0.1: 1000 in relation to the total composition. Using usual crystalline sugars, the preferred range of carbon moieties, introduced through the carbon source comprising a carbohydrate, for silicon moieties, introduced through the silicon oxide compound, is in the range of 100 mol: 1 mol to 1 mol: 100 mol (C for Si in the educts), especially preferably C for Si is in a ratio of 50: 1 to 1:50, most especially, preferably from 20: 1 to 1:20, according to the invention in the range 3: 1 to 2: 1 or even 1: 1. Molar proportions are preferred in which carbon is added through the carbon source in approximately equimolar proportions or in excess of silicon in silicon oxide.

The method component is usually designed as a multistage process. A first step comprises pyrolysis of the carbon source comprising at least one carbohydrate in the presence of silicon oxide with graphitization, in particular there is formation on and / or within the silicon oxide component, such as SiOx with x = 0.5 to 1, 5, SiO, SiO ₂ , silicon oxide (hydrate), pyrolysis products containing carbon, for example, coatings containing fractions of graphite and / or carbon black. Pyrolysis is followed by calcination. Pyrolysis and / or calcination can be carried out successively in one reactor or separately from each other in different reactors. For example, pyrolysis takes place in a first reactor, and subsequent calcination, for example, in a fluid bed microwave oven. One skilled in the art is aware that the settings of the reactor, vessels, supply and / or discharge lines, and the oven settings themselves

63/114 should not contribute to contamination of method products.

The method component is generally designed so that silicon oxide and the carbon source comprising at least one carbohydrate, intimately mixed, dispersed, homogenized or in a formulation, are fed into a first pyrolysis reactor. This can be done continuously or discontinuously. Optionally, the substances used are dried before being fed into the appropriate reactor, preferably adherent water or residual moisture can remain in the system. The component of the complete technical and industrial method is divided into a first phase, in which pyrolysis takes place, and another phase, in which the calcination takes place. The reaction can be carried out at temperatures starting at 150 ° C, preferably starting at 400 to 3000 ° C, with, in a first pyrolysis step (low temperature mode), a reaction that takes place at lower temperatures, in in particular at 400 to 1400 ° C and subsequent calcination at higher temperatures (high and temperature mode), in particular from 1400 to 3000 ° C, preferably from 1400 to 1800 ° C. Pyrolysis and calcination can be carried out immediately after one another in one process, or in two separate steps. For example, the pyrolysis method product can be packaged as a composition and then used by an additional processor for the production of silicon carbide or silicon.

Alternatively, the reaction of silicon oxide, in particular purified silicon oxide and the carbon source comprising a carbohydrate, in particular the pure carbon source, can start with a low temperature range, which, for example, starts at 150 ° C, preferably at 400 ° C and be increased continuously or gradually, for example, up to 1800 ° C or higher, in particular around 1900 ° C. This procedure can be favorable to remove the process gases that are formed.

According to another alternative process mode, the reaction can be carried out directly at high temperatures, in particular at temperatures above 1400 ° C to 3000 ° C, preferably between 140CTC and

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1800 ° C, especially preferably between 1450 and below approximately 1600 ° C. In order to stop the decomposition of the silicon carbide that has formed, in the case of a low oxygen atmosphere, the reaction is preferably carried out at temperatures below the decomposition temperature, in particular below 1800 ° C, preferably below 1600 ° C. The isolated method product according to the invention is high purity silicon carbide as defined below.

Appropriate pyrolysis (low temperature stage) is usually carried out at temperatures below approximately 800 ° C. Depending on the desired product, pyrolysis can be carried out under normal pressure, under vacuum or at increased pressure. Whether working under vacuum or at low pressure, process gases can be removed easily and highly porous, particulate structures are obtained after pyrolysis. Under conditions in the region of normal pressure there is normally increased agglomeration of the porous, particulate structures. If pyrolysis is carried out at increased pressures, the volatile reaction products may condense on the silicon oxide particles and possibly react with each other or with reactive silicon dioxide groups. For example, decomposition products of the carbohydrates that form, such as ketones, aldehydes or alcohols, can react with free hydroxyl groups of the silicon dioxide particles. This considerably reduces pollution of the environment with process gases. The porous pyrolysis products obtained are in this case slightly more agglomerated.

As well as pressure and temperature, which can be selected freely over a wide range depending on the desired pyrolysis product, and for which the exact fit between them is well known to one skilled in the art, the pyrolysis of the carbon source containing at least a carbohydrate can also be carried out in the presence of moisture, in particular residual moisture from the educts, or by adding moisture, in the form of condensed water, steam or components containing hydrate, such as SiO ₂ nH ₂ O, or other familiar hydrates for one versed in the technique. The presence of moisture in particular has the effect that the carbohydrate undergoes

65/114 pyrolysis more readily, and that expensive pre-drying of the educts can be omitted. Especially preferably, the method for producing silicon carbide is carried out by the reaction of silicon oxide, in particular purified silicon oxide, and a carbon source comprising at least one carbohydrate, in particular a pure carbon source, at an elevated temperature especially at the beginning of pyrolysis in the presence of moisture, optionally moisture is also added or fed during pyrolysis.

As a rule, pyrolysis takes place, in particular in at least one first reactor, in the low temperature mode around 700 ° C, normally between 200 ° C and 1600 ° C, especially preferably between 300 ° C and 1500 ° C, in particular from 400 to 1400 ° C, preferably a pyrolysis product containing graphite being obtained. Preferably the internal temperature of the reagents is considered to be the pyrolysis temperature. The pyrolysis product is preferably obtained at temperatures from 1300 to 1500 ° C.

The method is usually carried out in the low pressure range and / or under an inert gas atmosphere. Argon or helium are preferred as an inert gas. Nitrogen can also be advantageous, or if optionally silicon nitride were to be formed in addition to silicon carbide or n-doped silicon carbide in the calcination step, which may be desirable depending on how the process is conducted. In order to produce ndoped silicon carbide in the calcination step, nitrogen can be added to the process in the pyrolysis and / or calcination step, optionally also through carbohydrates, such as chitin. The production of specially p-doped silicon carbide can also be advantageous, and in this special exception, the aluminum content, for example, may be higher. Doping can be done using substances containing aluminum, for example, using trimethyl aluminum gas.

Depending on the pressure in the reactor, pyrolysis products or compositions with varying degrees of agglomeration and varying porosity can be produced at this stage. As a rule, pyrolysis products obtained under

66/114 vacuum are less agglomerated and have higher porosity than under normal pressure or increased pressure.

The pyrolysis time can be between 1 minute and usually 48 hours, in particular between 15 minutes and 18 hours, preferably between 30 minutes and approximately 12 hours at the determined pyrolysis temperatures. The phase of heating to the pyrolysis temperature is usually included here.

The pressure range is normally 0.1 kPa to 5000 kPa (1 mbar at 50 bar), in particular 0.1 kPa to 1000 kPa (1mbar at 10 bar), preferably 0.1 kPa to 500 kPa (1 mbar at 5 Pub). Depending on the desired pyrolysis product, and in order to minimize the formation of carbon from the process containing carbon, in the method the pyrolysis step can also be carried out in a pressure range of 100 to 5000 kPa (1 to 50 bar), preferably 200 to 5000 kPa (2 to 50 bar), especially preferably 500 to 5000 kPa (5 to 50 bar). One skilled in the art knows that the pressure to be selected is a compromise between gas removal, agglomeration and reduction of process gases containing carbon.

Pyrolysis of the reagents, such as silicon oxide and carbohydrate, is followed by the calcination step. Calcination (high temperature region) means a section of the process in which the reagents are substantially converted to high purity silicon carbide, optionally containing a carbon matrix and / or a matrix of silicon oxide and / or mixtures thereof. In this step, there is optionally evaporation of water of crystallization and sintering of the products of the method. As a rule, the calcination step (high temperature step) follows pyrolysis directly, although it can also be performed at a later time, for example, when the pyrolysis product is sold. The temperature ranges of the pyrolysis and calcination steps can optionally overlap slightly. Calcination is normally carried out at 1400 to 2000 ° C, preferably between 1400 to 1800 ° C. If pyrolysis is carried out at temperatures below 800 ° C, the calcination step can also extend over a temperature range of 800 ° C to approximately 1800 ° C. Oxide spheres

67/114 high purity silicon, in particular quartz glass spheres and / or silicon carbide spheres or generally quartz glass and / or silicon carbide particles can be used in the method, for improved heat transfer. Preferably, these heat exchangers are used with rotary ovens or also in microwave ovens. In microwave ovens, microwaves cause excitation in the quartz glass particles and / or silicon carbide particles, so that the particles are heated. Preferably the spheres and / or particles are well distributed in the reaction system, to allow uniform heat transfer.

The calcination or the high temperature region of the process normally takes place in the pressure range of 0.1 kPa to 5000 kPa (1 mbar to 50 bar), in particular between 0.1 kPa and 100 kPa (1 mbar and 1 bar ) (ambient pressure), in particular 0.1 to 25 kPa (1 to 250 mbar), preferably 0.1 to 1 kPa (1 to 10 mbar). The possible inert gas atmospheres are those already mentioned. The calcination time depends on the temperature and the reagents used. As a rule it is between 1 minute and can normally be 48 hours, in particular between 15 minutes and 18 hours, preferably between 30 minutes and approximately 12 hours at the determined calcination temperatures. The heating phase at the calcination temperature should normally be included here.

The reaction of silicon oxide and the carbon source containing a carbohydrate can also be carried out directly in the high temperature region, and it must be possible for the resulting gaseous reagents or process gases to be properly removed from the reaction zone. This can be ensured by a loose charge or a charge comprising parts formed of silicon oxide and / or the carbon source or preferably with parts formed comprising silicon dioxide and the carbon (carbohydrate) source. The gaseous reaction products or process gases that form can be, in particular, steam, carbon monoxide and subsequent products. At high temperatures, particularly in the high temperature region, there is mainly the formation of

68/114 carbon.

The reaction for silicon carbide at elevated temperature, particularly in the calcination step, preferably takes place at a temperature of 400 to 3000 ° C, preferably the calcination takes place in the high temperature range between 1400 and 3000 ° C, preferably from 1400 ° C to 1800 ° C, especially preferably between 1450 and 1500 and 1700 ° C. The temperature ranges should not be limited to those revealed, as the temperatures reached are also directly dependent on the reactors used. The determined temperatures are based on measurements with high temperature and standard temperature sensors, for example, encapsulated (PtRhPt element) or alternatively from the color temperature by visual comparison with a spiral filament.

All reactors known to one skilled in the pyrolysis and / or calcination technique can be considered as reactors for use in the method according to the invention. So, all reactors known to one skilled in the art? laboratory reactors, pilot plant reactors or preferably large scale industrial reactors, for example, rotary tube reactor or also microwave reactor, as used for ceramic sintering, can be used for pyrolysis and subsequent calcination for formation Sic and optionally graffiti.

Microwave reactors can be operated in the high frequency range (HF range), high frequency range being understood within the scope of the present invention as 100 MHz to 100 GHz, in particular between 100 MHz and 50 GHz or also 100 MHz to 40 GHz. The preferred frequency bands are approximately between 1 MHz and 100 GHz, with 10 MHz to 50 GHz being especially preferred. The reactors can be operated in parallel. Especially preferably, 2.4 MHz magnetrons are used for the method.

The high temperature reaction can also be carried out in melting furnaces customary for the production of steel or silicon, such as metallurgical silicon, or other suitable melting furnaces, for example, induction furnaces. The design of the said melting furnaces, especially

69/114 preferably electric ovens, which use an electric arc as the energy source, are sufficiently familiar to one skilled in the art and are not part of this patent application. In the case of direct current furnaces, they have a melting electrode and a bottom electrode or as an alternating current furnace they usually have three melting electrodes. Arc length is controlled by an electrode controller. Arc furnaces are usually based on a reaction space made of refractory material. The raw materials, in particular the pyrolyzed carbohydrate in silicic acid / SiO _2] are fed at the top, where the graphite electrodes for arc generation are also arranged. These forams are generally operated at temperatures in the region of 1800 ° C. One skilled in the art is also aware that the oven settings themselves should not contribute to the contamination of the produced silicon carbide. Preferably, the high temperature reaction for silicon carbide is carried out in a reactor according to the invention and / or with electrodes according to the invention and / or in a device according to the invention.

The invention also relates to a composition comprising silicon carbide optionally with a carbon matrix and / or silicon oxide matrix or a matrix comprising silicon carbide, carbon and / or silicon oxide and optionally silicon, which is obtainable by component of the method according to the invention, in particular by the calcination step, and in particular is isolated. Isolation means that after carrying out the method, the composition and / or the high purity silicon carbide is obtained and isolated, in particular as a product. The silicon carbide can also be supplied with a passivation layer, for example, containing SiO ₂ .

This product can then serve as a reagent, catalyst, material for the production of articles, for example filters, formed articles or green articles and can be used in other applications familiar to one skilled in the art. Another important application is the use of the composition comprising silicon carbide as a reaction initiator and / or reagent and / or in the production of the electrode material or in the production of the carbide of

70/114 silicon with sugar coke and silicic acid.

The invention also relates to the pyrolysis product and optionally product calcination, in particular a composition obtainable by the method component according to the invention and in particular the pyrolysis and / or calcination product isolated from the method, with a carbon content for silicon oxide, in particular silicon dioxide, from 400: 0.1 to 0.4: 1000.

Preferably, the conductivity of the component products of the method, in particular the component products of the powder, high density tablets, measured between two pointed electrodes, is in the range κ [m / Dm ² ] = 1 · 10 ' ¹ to 1 · 10 ' ⁶ . A low conductivity, which is directly correlated with the purity of the method product, is desirable for the respective component product of the silicon carbide method.

Preferably the composition or product of pyrolysis and / or calcination has a graphite content of 0 to 50% by weight, preferably 25 to 50% by weight in relation to the total composition. According to the invention, the composition or the product of pyrolysis and / or calcination has a proportion of silicon carbide of 25 to 100% by weight, in particular from 30 to 50% by weight, in relation to the total composition.

The invention also relates to a silicon carbide with a carbon matrix comprising coke and / or carbon black and / or graphite or mixtures thereof and / or with a silicon oxide matrix comprising silicon dioxide, silicic acid and / or mixtures thereof or with a mixture of the above mentioned components, obtainable by the method according to the invention, in particular according to one of Claims 1 to 10. In particular SiC is isolated and further used, as described below. The total content of the elements boron, phosphorus, arsenic and / or aluminum is preferably below 10 ppm by weight in silicon carbide as defined by the invention.

The invention also relates to a silicon carbide optionally with fractions of carbon and / or fractions of silicon oxide or

71/114 mixtures, comprising silicon carbide, carbon and / or silicon oxide, in particular silicon dioxide, with an impurity content as defined above.

According to one embodiment, the invention relates to the use of silicon carbide or a pyrolysis and / or calcination composition or product of the method in the production of pure silicon, in particular in the production of solar grade silicon. The invention relates in particular to the use in the production of solar-grade silicon by reducing silicon dioxide, in particular purified silicon oxide, at high temperatures or in the production of silicon carbide by reaction coke, in particular coke of sugar, and silicon dioxide, in particular a silicic acid, preferably a silicic acid or SiO ₂ - pyrogenic, precipitated or purified by ion exchange - at high temperatures, such as material crushing, insulating, as refractory, such as resistant tile heat, or in the production of articles or in the production of electrodes.

The invention also relates to the use of silicon carbide or a pyrolysis and / or calcination composition or product obtainable by the method according to the invention as a catalyst, in particular in the production of silicon, preferably in the production of purified silicon, in particular in the production of solar grade silicon, in particular in the production of solar grade silicon by reducing silicon dioxide at high temperatures. And optionally in the production of silicon carbide for semiconductor uses or for use as a catalyst in the production of ultrapure silicon carbide, for example, by purification, or as a reactant in the production of silicon or in the production of silicon carbide, in particular coke , preferably sugar coke, and silicon dioxide, preferably with silicic acid, at high temperatures, or for use as material for articles or as electrode material, in particular for arc furnace electrodes. The use as the material of articles, in particular electrodes, comprises the use of the material as material for the articles or also the use of the material still processed for the production of the articles, for example, sintered material or crushing materials.

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Another object of the invention is the use of at least one carbohydrate, in particular a pure carbohydrate, in the production of pure to ultrapure silicon carbide, in particular silicon carbide that can be isolated as a product, or composition containing silicon carbide or a product pyrolysis and / or calcination containing silicon carbide, in particular in the presence of silicon oxide, preferably in the presence of silicon oxide and / or silicon dioxide.

Preferably a selection of at least one carbohydrate and one silicon oxide, in particular a purified silicon dioxide, in particular without additional components, is used for the production of silicon carbide, and silicon carbide, a composition containing silicon carbide. or a pyrolysis and / or calcination product is isolated as a reaction product.

The invention also relates to the use of a composition, in particular formulation, or a kit comprising at least one carbohydrate and silicon oxide, in particular purified silicon oxide, in the method according to the invention. Therefore, the invention also relates to a kit, containing separate formulations, in particular in separate containers, such as vases, bags and / or cans, in particular in the form of an extrudate and / or silicon oxide powder, in particular of purified silicon oxide, preferably purified silicon dioxide, optionally in conjunction with S1O2 carbohydrate pyrolysis products and / or the carbon source comprising at least one carbohydrate, in particular for use as described above. It may be preferable if the silicon oxide directly with the carbon source comprising a carbohydrate, in particular a source of pure carbon, for example, impregnated with it or carbohydrate supported on SiO ₂ etc. in the form of tablets, as granules, extruded, briquette, in particular as pellet or briquette, is in a container in the kit and optionally an additional carbohydrate and / or silicon oxide as a powder in a second container.

The invention also relates to the use of an article, in particular of a green product, formed material, sintered part, of an electrode, of

73/114 a heat resistant component, comprising a silicon carbide according to the invention or a composition according to the invention containing silicon carbide, and optionally additional usual additives, processing aids, pigments or binders in the complete method according to with the invention. The invention, therefore, relates to an article containing a silicon carbide according to the invention, or which is produced using the silicon carbide according to the invention and its use in the complete method according to the invention.

Use of SiC as an activator in reducing silicon dioxide with the carbon source

As explained at the beginning, silicon carbide can also be added in the complete method according to the invention for the production of pure silicon.

According to the invention, the economic efficiency of the method for the production of pure silicon is increased considerably by the addition of an activator, which performs the function of a reaction initiator, reaction accelerator and / or as a carbon source.

At the same time, the activator, ie, reaction initiator and / or reaction accelerator, must be as pure and economical as possible. Especially preferred reaction initiators and / or reaction accelerators should not by themselves introduce unwanted impurities or preferably only impurities in the minimum amounts in the silicon melt, for the reasons stated at the beginning.

The method according to the invention can be carried out in several ways, and according to an especially preferred embodiment, a silicon oxide, in particular silicon dioxide, preferably a silicon dioxide purified by acid precipitation, is reacted at elevated temperature, by addition of silicon carbide to the process as a source of pure carbon or as an activator for silicon oxide, according to the invention for precipitation-purified silicon oxide, or silicon carbide (SiC) in a composition containing silicon oxide , being especially preferable if silicon oxide, in particular

74/114 silicon, and silicon carbide are added in approximately stoichiometric proportions, that is, approximately 1 mol of SiO ₂ to 2 mol of SiC for silicon production, in particular the reaction mixture for silicon production consists of silicon oxide and silicon carbide.

Another advantage of this way of carrying out the method is that by adding SiC correspondingly less CO is released by Si formed. Gaseous pollution, which decisively limits the process, is thus advantageously reduced. Thus, process intensification is advantageously possible by adding SiC.

According to another especially preferred embodiment, precipitation-purified silicon oxide, in particular silicon dioxide, is reacted at an elevated temperature, where silicon carbide and another source of pure carbon are added to silicon oxide or silicon carbide and a source of pure carbon, in particular a second source of pure carbon, in a composition containing silicon oxide, or are reacted. In this variant, the concentration of silicon carbide can be reduced to such an extent that it functions more as a reaction initiator and / or reaction accelerator and less as a reagent. Preferably, approximately 1 mol of silicon dioxide can also be reacted with approximately 1 mol of silicon carbide and approximately 1 mol of a second carbon source in the method.

According to the invention, in the method for the production of silicon by the reaction of purified silicon oxide at high temperature, the silicon carbide is added to the silicon oxide or optionally added in a composition containing purified silicon oxide, in particular a electric arc is used as a power source. The target is for a silicon carbide to be added as an activator, that is, as a reaction initiator and / or reaction accelerator and / or as a carbon source, that is, as a reagent, in the method and / or that is added in a composition in the method.

Silicon carbide is thus fed in the method

75/114 separately. Preferably, silicon carbide is added as a reaction initiator and / or reaction accelerator in the method or composition. As the silicon carbide itself does not decompose until temperatures of approximately 2700 to 3070 ° C are reached, it was surprising 5 that it can be added to the method for the production of silicon as a reaction initiator and / or reaction accelerator or as a reagent or also as a means of thermal exchange. Entirely surprising, it was observed in an experiment that after firing an electric arc, the reaction between silicon dioxide and carbon, in particular graphite, which starts and continues very slowly, in small amounts added of the powdered silicon carbide conducted inside a short time for a very sharp increase in reaction. Luminous effects were observed, and surprisingly the entire subsequent reaction was carried out with an intensive, bright incandescence, in particular until the end of the reaction.

An additional or second source of pure carbon, in particular additional to silicon carbide, has been defined, in the context of the method for the production of silicon, as compounds or materials that do not consist of silicon carbide, do not have silicon carbide or do not contain silicon carbide. Therefore, the second carbon source does not consist of silicon carbide, has no silicon carbide, or does not contain silicon carbide. The function of the second carbon source is somewhat that of a pure reagent, whereas silicon carbide is also a reaction initiator and / or reaction accelerator. As the second source of carbon, consideration can be given in particular to sugars, graphite, coal, charcoal, carbon black, coke, anthracite, lignite, activated carbon, petroleum coke, wood like flakes or wood pellets, barks or stalks of rice, carbon fiber, fullerenes and / or hydrocarbons, in particular gaseous or liquid, and mixtures of at least two of the declared compounds, as long as they are of adequate purity and do not contaminate the method of undesirable compounds or elements. The second carbon source is preferably selected from the determined compounds. Contamination of the additional or second carbon source

76/114 pure with boron and / or phosphorus or compounds containing boron and / or containing phosphorus must be for boron below 10 ppm, in particular between 10 ppm and 0.001 ppt, and for phosphorus below 20 ppm, in particular between 20 ppm and 0.001 ppt, in weight proportions. The amounts given in ppm, ppb and / or ppt must be understood everywhere as proportions by weight in mg / kg, pg / kg etc.

The boron content is preferably between 7 ppm and 1 ppt, preferably between 6 ppm and 1 ppt, especially preferably between 5 ppm and 1 ppt or less, for example, between 0.001 ppm and 0.001 ppt, preferably in the region of the analytical detection limit . The phosphorus content should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and 1 ppt, especially preferably between 10 ppm and 1 ppt or less. The phosphorus content is preferably in the region of the analytical detection limit. Generally these limit values are desirable for all reagents or additives in the method, to be suitable for the production of semiconductor and / or solar grade silicon.

The purified or high purity silicon oxide defined above, in particular a purified or high purity silicon dioxide, is preferably used as silicon oxide.

In addition to precipitation-purified silicon oxide, other pure silicon oxides similarly can be used in the method for producing pure silicon.

The addition of another suitable silicon oxide in addition to the purified silicon oxide can also be advantageous, that is, quartz, quartzite and / or silicon dioxides produced in the usual manner. These can be silicon dioxides that occur in crystalline modifications, such as morganite (chalcedony), α-quartz (low temperature quartz), β-quartz (high temperature quartz), tridymite, cristobalite, cohesite, stishovite or also SiO ₂ amorphous. In addition, silicic acids, pyrogenic SiO _2, pyrogenic silicic acid or silica can preferably be used in the method and / or in the composition. Usual pyrogenic silicic acids are SiO ₂ powders

77/114 amorphous with an average of 5 to 50 nm in diameter and with a specific surface of 50 to 600 m ² / g. The above list should not be taken as final, it is obvious to a person skilled in the art that other sources of silicon oxide suitable for the method can be used in the method and / or in the composition.

Purified silicon oxide, in particular purified silicon dioxide, and silicon carbide and optionally a second carbon source, in particular, a second pure carbon source, is preferably used in the method in the following determined molar ratios and / or% by weight , where the figures can relate to the educts and in particular to the reaction mixture in the method:

For 1 mol of a silicon oxide, for example, silicon monoxide, such as Patinai®, approximately 1 mol of a second source of pure carbon and silicon carbide in small amounts can be added as reaction initiators or reaction accelerators. Usual amounts of silicon carbide as a reaction initiator and / or reaction accelerator are approximately 0.0001% by weight to 25% by weight, preferably 0.0001 to 20% by weight, especially preferably 0.0001 to 15% by weight , in particular 1 to 10% by weight relative to the total weight of the reaction mixture, in particular comprising silicon oxide, silicon carbide and a second carbon source and optionally additional additives.

It may also be especially preferable to add to the method, per 1 mol of a purified silicon oxide, in particular silicon dioxide, approximately 1 mol of pure silicon carbide and approximately 1 mol of a second carbon source, in particular pure carbon. If a silicon carbide containing carbon fibers or similar compounds containing additional carbon is used, the amount of a second mol source of carbon can be reduced analogously. Per 1 mole of silicon dioxide, approximately 2 moles of a second source of carbon and silicon carbide in small amounts can be added as a reaction initiator or reaction accelerator. Usual amounts of silicon carbide as a reaction initiator and / or

78/114 reaction accelerator is approximately 0.0001% by weight to 25% by weight, preferably 0.0001 to 20% by weight, especially preferably 0.0001 to 15% by weight, in particular 1 to 10% by weight in in relation to the total weight of the reaction mixture, in particular comprising silicon oxide, silicon carbide and a second carbon source and optionally additional additives.

According to a preferred alternative, per 1 mol of silicon dioxide, approximately 2 mol of silicon carbide can be used as a reagent in the method and optionally a second carbon source can be present in small amounts. Usual amounts of the second carbon source are approximately 0.0001% by weight to 29% by weight, preferably 0.001 to 25% by weight, especially preferably 0.01 to 20% by weight, most especially, preferably between 0.1 to 15% by weight, in particular 1 to 10% by weight relative to the total weight of the reaction mixture, in particular comprising silicon dioxide, silicon carbide and a second carbon source and optionally additional additives.

Stoichiometrically, in particular silicon dioxide can be reacted with silicon carbide and / or a second carbon source according to the following reaction equations:

SiO ₂ + 2 C -> Si + 2 CO

SiO ₂ + 2 SiC -> 3 Si + 2 CO or

SiO ₂ + SiC + C -> 2 Si + 2 CO or

SiO ₂ + 0.5 SiC + 1.5 C -> 1.5 Si + 2 CO or SiO ₂ + 1.5 SiC + 0.5 C -> 2.5 Si + 2 CO etc.

As the purified silicon dioxide can react in a molar ratio of 1 mol with 2 mol of silicon carbide and / or the second carbon source, it is possible to control the method by means of the molar proportion of silicon carbide and the additional or second source of pure carbon. Preferably, silicon carbide and the second carbon source together should be used in the method or be present in the method

79/114 approximately in the proportion of 2 mois to 1 mol of silicon dioxide. Thus, the 2 milliles of silicon carbide and optionally the second carbon source can be composed of 2 mol of SiC at 0 mol of the second carbon source up to 0.00001 mol of SiC at 1.99999 of the second carbon source ( Ç). The proportion of silicon carbide to the second carbon source preferably varies within the stoichiometry of approximately 2 mois for reaction with approximately 1 mol of silicon dioxide according to Table 1:

Table 1

Reaction: Dioxide Silicon carbide (SiC) Second source of mol silicon in mol carbon (C) in mol No. 1 1 2 0 No. 2 1 1.99999 0.00001 The The No. ⁰⁰ 1 0.00001 1.9999 where SiC + C always together reach approximately 2 mois.

For example, the 2 moles of SiC and optionally C together are composed of 2 to 0.00001 moles of SiC and 0 to 1.99999 moles of C, in particular from 0.0001 to 0.5 moles of SiC and 1, 9999 to 1.5 to 2 mol of C, preferably 0.001 to 1 mol of SiC and 1.999 to 1 to 2 mol of C, especially preferably 0.01 to 1.5 mol of SiC and 1.99 to 0.5 to 2 moles of C, in particular it is preferred in the method according to the invention to use 0.1 to 1.9 moles of SiC and 1.9 to 0.1 to 2 moles of C for approximately 1 mole of silicon dioxide.

As silicon carbides for use in the method according to the invention or the composition according to the invention, consideration can be given preferably to pure to ultrapure silicon carbides as defined above, and generally all polytype phases, and optionally the carbide of silicon can be covered with a passivation layer of SiO2. Individual polytyp phases with varying stability can preferably be used in the method, because, for example, the course of the reaction or the start of the reaction in the method can be

80/114 controlled with them. High purity silicon carbide is colorless and is preferably used in the method. In addition, as a silicon carbide in the method or composition, it is possible to use commercial SiC (carborundum), metallurgical SiC, SiC bonding matrices, open or dense pore silicon carbide ceramics, such as silicate carbide bonded, Recrystallized SiC (RSiC), reaction-bound silicon carbide, silicon infiltrate (SiSiC), sintered silicon carbide, hot compressed (isostatically) silicon carbide (HpSiC, HiPSiC) and / or liquid-phase sintered silicon carbide ( LPSSiC), carbon fiber reinforced silicon carbide compounds (CMC, ceramic matrix compounds) and / or mixtures of these compounds, with the proviso that the contamination is so small that the silicon produced is suitable for the production of grade silicon semiconductor grade solar and / or silicon. The aforementioned silicon carbides can also be added to the method in small amounts as long as the total contamination of the pure silicon corresponds to that according to the invention. Therefore, silicon carbides can also be recycled in certain amounts in the method according to the invention as long as the total contamination of the pure silicon produced is achieved. One skilled in the art is aware that the total contamination of the pure silicon obtained can be controlled by the addition of different charges and with different impurity profiles.

Contamination of silicon carbide suitable for the method with boron and / or phosphorus or with compounds containing boron and / or containing phosphorus is preferably for boron below 10 ppm, in particular between 10 ppm and 0.001 ppt, and for the phosphor below 20 ppm, in particular between 20 ppm and 0.001 ppt. Preferably the boron content in a silicon carbide is between 7 ppm and 1 ppt, preferably between 6 ppm and 1 ppt, especially preferably between 5 ppm and 1 ppt or less, or for example, between 0.001 ppm and 0.001 ppt, preferably at analytical detection limit region. The phosphorus content of a silicon carbide should preferably be between 18 ppm and 1 ppt, preferably between 15 ppm and 1 ppt, especially preferably between 10 ppm and 1 ppt

81/114 or less. The phosphorus content is preferably in the region of the analytical detection limit.

As silicon carbides are increasingly being used as composites, for example, for the production of semiconductors, brake disc material or heat shields and other products, the method according to the invention and the composition or formulation offer a possibility of elegant recycling of these products after use or of the residues or scrap that arise in their production. The only requirement to be satisfied for the silicon carbides that must be recycled is sufficient purity for the method, and preferably silicon carbides that satisfy the above specification with respect to boron and / or phosphorus are recycled. Silicon carbide can be added to method a) as a powdery or granular material and / or as lumps and / or b) contained in a porous glass, in particular quartz glass, in an extrudate and / or mold, such as pellet or briquette, in particular in a formulation described above, optionally in conjunction with other additives.

All reagents, i.e., purified silicon oxide, silicon carbide and optionally additional sources of pure carbon, each separately or in compositions or formulations, can be added to the method continuously or discontinuously. Preferably, silicon carbide is added in quantities and over the course of the method to an extent such that an especially economical implementation of the method is achieved. Therefore, it can be advantageous if the silicon carbide is added gradually continuously, in order to maintain a continuous reaction acceleration of the reaction. The reaction can be carried out in usual melting furnaces for the production of silicon, carried out as described in the beginning. The method is preferably carried out in a device according to the invention, reactor and with electrodes according to the invention.

As mentioned above, depending on the impurity profile of other reagents, silicon carbide can be used as silicon carbide, as pure silicon carbide or as ultrapure silicon carbide

82/114 or as a mixture of these. In mixtures, silicon carbides are preferably formulated earlier, in particular briquetted. The general rule is: the more contaminated the silicon carbide, the less its quantity in the method.

The method can be carried out in a way that

a) the silicon carbide and purified silicon oxide, in particular silicon dioxide, and optionally another source of pure carbon is each fed separately in the method, in particular the reaction space, and optionally then is mixed together and / or

b) silicon carbide together with purified silicon oxide, in particular silicon dioxide, and optionally another source of pure carbon in a formulation and / or

c) the purified silicon oxide, in particular silicon dioxide, together with a source of pure carbon in a formulation, in particular in the form of an extrudate or mold, preferably as a pellet or briquette, and / or

d) silicon carbide in a composition with the additional source of pure carbon is added or fed in the method. This formulation can comprise a physical mixture, an extrudate or mold or also a carbon fiber reinforced silicon carbide.

As already mentioned for silicon carbide, silicon carbide and / or silicon oxide and optionally at least one additional source of pure carbon can be fed into the method as a material to be recycled. The only requirement imposed on all compounds to be recycled is that they are of sufficient purity to form a silicon in the method, from which solar grade silicon and / or semiconductor grade silicon can be produced.

Similarly, in the method according to the invention, in addition to the purified silicon oxide it is also possible to use silicon oxides of sufficient purity that must be recycled. Quartz glasses are suitable, for example, broken glass. To take only a few, these can be Suprasil, SQ 1, Herasil, Spektrosil A. The purity of these quartz glasses can

83/114 can be determined, for example, from absorption rates at specified wavelengths, such as 157 nm or 193 nm. For example, nearly consumed electrodes, which have been reduced to a desired shape, for example, as dust, can be used as the second carbon source.

The pure silicon produced or obtained with the method according to the invention is, according to the invention, optionally after zone melting / directional solidification, suitable as solar grade silicon. It is preferably suitable a) for further processing in processes for the production of solar grade silicon or semiconductor grade silicon.

The contamination of silicon produced with compounds containing boron and / or containing phosphorus must correspond to the spectrum defined at the beginning of this description, but it can also be, for boron in the range below 10 ppm to 0.0001 ppt, in particular in the range of 5 ppm at 0.0001 ppt, preferably in the range of 3 ppm to 0.0001 ppt or especially preferably in the range of 10 ppb to 0.0001 ppt, even more preferably in the range of 1 ppb to 0.0001 ppt and for phosphorus in the range below from 10 ppm to 0.0001 ppt, in particular in the range of 5 ppm to 0.0001 ppt, preferably in the range of 3 ppm to 0.0001 ppt or especially preferably in the range of 10 ppb to 0.0001 ppt, even more preferably in the range of 1 ppb to 0.0001 ppt, determined in weight proportions. The range of impurities generally has no lower limit, but is determined only by the current limits of detection of analytical techniques. According to the invention, pure silicon has the profile of contamination with boron, aluminum, calcium, iron, nickel, phosphorus, titanium and / or zinc stated at the beginning.

Advantageously, molten silicon can be treated with rare earth metals in order to remove carbon, oxygen, nitrogen, boron or any other impurity that is present from the molten silicon.

The invention also relates to a composition that is especially suitable for use in the aforementioned method for the production of silicon and whose quality is preferably suitable as

84/114 solar grade silicon or for the production of solar grade silicon and / or semiconductor grade silicon, with the composition containing silicon oxide and silicon carbide and optionally a second carbon source, in particular a pure carbon source . Those determined above can be considered as purified silicon oxide, in particular silicon dioxide, silicon carbide and optionally the second carbon source, and preferably also satisfy the determined purity requirements.

Silicon carbide can also be present, optionally together with other additives, in the formulation, as described above a) as a powder, as granules and / or as lumps and / or b) contained in a porous glass, in particular quartz glass , in an extrudate and / or pellet. In additional embodiments, the formulation may contain silicon carbide infiltrated with silicon and / or silicon carbide containing carbon fibers. These formulations should be preferred if the corresponding silicon carbides are recycled, as they can no longer be used in any other way, for example, production scrap or used products. As long as the purity is sufficient for the method according to the invention, it is thus possible for silicon carbides, silicon carbide ceramics, such as hot plates, brake disc material, to be recycled again. As a rule, because of the production process, these products are already sufficiently pure. The invention, therefore, can also relate to the recycling of silicon carbides in a method for the production of silicon. The binders defined above, in particular heat resistant or refractory binders, can be used as binders for producing the formulation.

The invention also relates to the use of silicon produced by the method according to the invention as a material based on solar cells and / or semiconductors or in particular as a starting material for the production of solar grade silicon.

85/114

Reactors suitable for use in the complete method according to the invention

The invention also relates to a reactor, a device and electrodes, suitable in particular for the production of solar grade silicon or semiconductor grade silicon.

In order to be able to produce high purity silicon, it is necessary to develop reduction furnaces, with which contamination with impurities can be avoided to the greatest extent possible. As a rule, reactors are currently coated with refractories, such as graphite and / or silicon carbide. The electrodes of the reduction furnaces are also made of graphite. Graphite has the necessary conductivity and heat resistance. An important disadvantage of the materials is the insufficient purity present. Refractories are usually contaminated with boron, phosphorus, aluminum and iron.

According to one embodiment, the invention therefore relates to a reactor which is particularly suitable for use with induction furnaces, direct current and / or alternating current, preferably suitable for the production of silicon, in accordance with with the invention of pure silicon production, where the reactor can correspond to reactor 1 and / or 2 described below. The reactor according to the invention is characterized in that it has silicon carbide electrodes or silicon carbide electrodes infiltrated with silicon. The silicon carbide infiltrated with silicon from the electrodes has the advantage that ... in particular by the reaction of SiO ₂ , preferably of purified silicon dioxide, and the pyrolysis and / or calcination of at least one carbon source containing carbohydrate, preferably a source of pure carbon, in particular of the following purity:

The content of boron, phosphorus, arsenic, aluminum, iron, sodium, potassium, nickel, and chromium is, for pure silicon carbide, for each element preferably below 5 ppm at 0.01 ppt (by weight), and for high purity silicon carbide in particular below 2.5 ppm to 0.1 ppt. Especially preferably, the silicon carbide obtained after reaction

86/114 of a silicon oxide and a source of pure carbohydrate, in particular purified sugar, optionally with carbon and / or Si _y O _z matrices, has a purification profile for SiC as defined at the beginning of the description.

Especially preferred pure to high purity silicon carbide or a high purity composition contains or consists of silicon carbide, carbon, silicon oxide and optionally small amounts of silicon, and the high purity silicon carbide or the high purity composition in particular have a profile of contamination with boron, phosphorus, arsenic, aluminum, iron, sodium, potassium, nickel, chromium, sulfur, barium, zirconium, zinc, titanium, calcium, magnesium, copper, chromium, cobalt, zinc, vanadium, manganese and / or lead below 100 ppm for pure silicon carbide, preferably below 20 ppm to 0.001 ppt for high purity silicon carbide, especially preferably between 10 ppm and 0.001 ppt for the complete high purity composition or carbide of high purity silicon.

Especially preferably, silicon carbide is obtained from the reaction of a purified silicon oxide and a pure carbohydrate source, in particular purified sugar as described above. During the reaction, the silicon content can be controlled by the reaction conditions or by addition of the separated silicon. Preferably, silicon carbide is produced by the method presented above for the production of silicon carbide.

The attainable purity of silicon carbide or silicon carbide infiltrated with silicon as electrode material corresponds to the purity shown above. Preferably, silicon carbide is pure to ultrapure. To improve mechanical stability, silicon carbide electrodes infiltrated with silicon or silicon carbide electrodes can be reinforced with carbon fibers. According to the invention, the reactor for carrying out the method according to the invention is used for the production of pure silicon.

A pure to high purity silicon carbide or silicon carbide infiltrated with silicon, optionally containing carbon, in particular

87/114 as electrode material or for coating a reactor or device, it is characterized in that the impurity content corresponds to the SiC ranges defined at the beginning of this description, in particular the total of the impurities mentioned above is less than 5 ppm, preferably less than 4 ppm, especially preferably less than 3 ppm, most especially, preferably between 0.5 and 3 ppm and especially preferably between 1 ppm and 0.001 ppt. A silicon carbide with preferred ranges in the limit values is considered to be of high purity.

The corresponding limit values for aluminum, boron, calcium, iron, nickel, phosphorus, titanium and zinc apply to high-purity graphite. These are in particular:

- Boron below 5.5 [pg / g], in particular between 5 and 0.000001 pg / g, preferably 3 and 0.00001 pg / g, especially preferably 2 and 0.00001 pg / g, according to invention below 2 to 0.00001 pg / g,

- Phosphorus below 5.5 [pg / g], 5 to 0.000001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 1 to 0.00001 pg / g, according to the invention below 0.5 to 0.00001 pg / g.

- Aluminum between 4 and 0.000001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 2.5 to 0.00001 pg / g, according to the invention below 2 to 0.00001 pg / g.

- Iron between 100 and 0.000001 pg / g, preferably between 60 and 0.00001 pg / g, in particular between 10 and 0.000001 pg / g, preferably 5 to 0.00001 pg / g, especially preferably 2 to 0 .001001 pg / g, most especially, preferably below 1 to 0.00001 pg / g, according to the invention below 0.5 to 0.00001 pg / g.

- Sodium (Na) between 20 and 0.000001 pg / g, preferably 15 to 0.00001 pg / g, especially preferably below 12 to 0.00001 pg / g, according to the invention below 10 to 0.00001 pg / g,

- Potassium (K) between 30 and 0.000001 pg / g, preferably 25 to 0.00001 pg / g, especially preferably below 20 to 0.00001 pg / g, according to the invention below 16 to 0.00001 pg / g,

88/114

- Nickel (Ni) between 4 and 0.000001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1.5 to 0 , 00001 pg / g,

- Chromium (Cr) between 4 and 0.000001 pg / g, preferably 3 to 0.00001 pg / g, especially preferably below 2 to 0.00001 pg / g, according to the invention below 1 to 0.00001 pg / g.

Minimal contamination with the respective elements is preferred, especially preferably below 100 ppm, most especially, preferably below 10 ppb or below 1 ppb.

Another disadvantage of the reactors currently in use is multiple coating with ordinary refractory bricks, of which impurities can be introduced into the hot silicon melt. Even if the refractory bricks are not in direct contact with the melt.

The invention also relates to a 0 reactor, in particular for use with industrial ovens, for example, microwave ovens, induction, direct current and / or alternating current, preferably for the production of silicon or pure metals and / or alloys, in particular pure silicon, where said reactor 0 can also correspond to a reactor 1 and / or 2 defined below, with at least reaction space 1 of reactor 0 or reactors 0 for fusion and optionally for reduction, in particular silicon oxide with at least one or more carbon sources, having a hole for metal and optionally a hole for slag

- has a sandwich construction with at least two layers, in particular, the sandwich construction consists of a first inner layer 7, another outer layer 6 and optionally the outermost layer 8,

- reaction space 1 or reactor 0 internally coated with a first layer 6 of high-purity refractory material, in particular with pure to high-purity silicon carbide or high-purity graphite,

- it has an outer layer 7, which acts as an insulation and / or diffusion barrier against impurities, particularly at high temperatures, and

89/114 pure to high purity metals, metalloids or alloys or mixtures thereof.

A first layer (7) of the high-purity refractory material should be understood as any material that is suitable for use at 5 high temperatures and has a defined impurity profile. This first layer comes into direct contact with molten silicon or hot reagents. A high purity graphite or high purity silicon carbide preferably has an impurity profile as defined above. All ancillary components and connection points or connection parts of the reactor 10 for the complete installation (device) can have this first layer (7) of high purity refractory material. The first layer is preferably segmented, to allow partial substitutability of burnt or worn segments, for example, of high-purity graphite coverage. Without segmentation, the entire first layer would have to be replaced if a local area was damaged or consumed by the process. The segmentation can be connected by the groove / spring principle.

The sandwich construction has the advantage according to the invention that at high temperatures, mobile contaminants, for example, boron, from more remote parts of the installation may no longer diffuse up to 20 degrees as at the moment through hot graphite or internal carbide coating silicon at high temperatures in the reaction space and thereby introduce the melt.

In sandwich construction, the outer layer (6) acts as an insulation and / or diffusion barrier against impurities, in particular it prevents diffusion of boron at the high temperatures of the reactor from the outside in the high-purity refractory that the first layer, for example, graphite, and thus molten silicon. The optional stable mechanical outer layer (8) can be made of usual heat-resistant materials, which due to the diffusion barrier according to the invention are not subject to increased requirements with respect to purity.

90/114 boron diffusion at the reactor's high temperatures from the outside in the high-purity refractory than the first layer, for example, graphite, and thus in the silicon melt. The optional stable mechanical outer layer 8 can be made of usual heat-resistant materials, which due to the diffusion barrier according to the invention are not subject to increased requirements with respect to purity.

The outermost layer 6 with the function of an insulation and / or diffusion barrier can be a vacuum or a vacuum hollow part, for example, a hollow part made of high purity glass, in particular quartz glass, which is preferably silver and has a vacuum inside. According to the invention, the hollow part has a vacuum and is provided with an infrared mirror on the side towards the reactor space, preferably covered with it. The vacuum can also be produced chemically, in particular so-called super-insulation, whereas the hollow part, which corresponds to the outer layer 6, is silvered on the side towards the reaction space, preferably with an infrared reflection material.

Alternatively, the first layer and the outer layer can also be joined tightly, to stop gas inlet or exhaust, in particular to be able to produce a vacuum in a cavity formed between them. As an alternative to a vacuum, it is also possible to use a heat-resistant porous, optionally foam-like material as the outer insulation layer. For this reason, for example, the first layer is preferably supplied, in particular covered with high-purity glass or high-purity ceramic, possibly followed by, as an outer layer, a porous foam of glass, glass spheres or simply spacers. high purity fines, preferably expanded spheres. In an especially preferred embodiment, this layer is followed by an outer layer, which is joined to the first layer in such a way that the middle layer (outermost layer, for example, with expanded glass) can additionally have a vacuum applied. The sandwich construction according to the invention can minimize

91/114 the thermally induced diffusion of impurities from the external parts of the installation in the reaction space.

Due to the consumption of the reactor's refractory lining or reaction space, it is preferable to adapt the reactor size so that it can be operated in power between 600 kW and below 1 MW. According to the invention, industrial reactors, in particular in a production line of a device according to the invention, preferably industrial reactors for arc furnaces, in each case have 100 kW to 1 MW, preferably between 600 kW and below 1 MW, especially preferably between 700 kW and 950 kW, especially preferably between 800 and 900 kW, in particular these ovens are closed. To ensure high yields as desired for silicon, in particular solar grade silicon, several reactors can be operated in parallel.

Generally, reactors can also be operated in parallel if, for example, they are arranged in a process line and are supplied with reagents continuously or discontinuously through a preceding reactor for the production of silicon carbide or for pyrolysis of carbohydrates. Similarly, purified silicon oxide feed can be carried out in the process line directly or indirectly through silicon carbide or pyrolysis products.

The invention also relates to electrodes, for example 10, in particular for use with induction, direct current and / or alternating current furnaces, in particular for the production of silicon, preferably pure silicon, said electrodes containing carbide silicon infiltrated with silicon or silicon carbide. In order to improve the mechanical properties, silicon carbide is preferably reinforced with carbon fibers. In addition, silicon carbide may have graphite components. The exact adjustment of the composition of silicon carbide to silicon and / or graphite and / or carbon fibers depends in the individual case on the respective desired process conditions, the desired conductivity and heat resistance. Silicon carbide electrodes infiltrated with silicon optionally reinforced with graphite fibers or

92/114 carbon fibers are used according to the invention.

In their design, the electrodes can correspond to the usual designs, to allow continuous impulse of the electrodes, which are consumed during the reduction. Therefore, as a rule, the electrodes are made up of individual segments, in particular disks, normally constructed as round disks, which come together but can be separated. Generally, segments can be of any reasonable shape and preferably can be joined. Normally, the electrodes, for example, in the shape of a disc, have, on one flat side, one or more projections, which can project at corresponding negative intervals on the opposite flat side of the discs. Preferably projections and intervals can be positively linked.

Discs or other formats can be produced by producing the usual green compacts and sintering them. The production of green compacts and sintering additives is well known to one skilled in the art. It is decisive that in this case, the purity of the electrodes is not reduced by sintering additives. It is therefore necessary to ensure that sintering additives only contain unwanted elements within the specified limits or allow the limit values to be observed on the produced electrodes.

For use, segmented electrodes, in particular disk-shaped electrodes, can be inserted into a hollow part, with which they are joined in such a way that the electrodes comprising the superimposed discs have permanent conductivity and stability. For example, a large number of discs in the hollow part may be in direct contact with each other and firmly joined to the hollow part by tempering, to form an electrode. As an alternative to gaps, the electrode segments can be screwed together or can be joined with plug-and-socket or soldering connections. The connectivity of said segmented electrodes is familiar as such to a person skilled in the art, and attention should be paid to the purity of the connections used.

According to an alternative modality, the segmented electrodes are pushed into the hollow parts made of silicon, for example,

93/114 pure silicon tubes, and in particular positively joined, for example, by means of a plug-and-socket connector or by spot welding. This construction allows easy impulse or repositioning of spent electrodes in the arc furnace, in which segments of the electrode made of silicon carbide or silicon carbide infiltrated with silicon, in particular with graphite and / or carbon fibers or with C matrices, can be propelled continuously from above or outside the oven into the hollow part made of silicon. The hollow part can generally be of any suitable material, with the use of silicon being preferred for the production of silicon, in particular pure or high purity silicon. In processes for the production of steel, the hollow part can also be made of other suitable metals or alloys of said metals, for example, an iron tube can receive high-purity graphite electrodes or silicon carbide electrodes.

The purity requirements correspond essentially to those mentioned above. In particular, an electrode comprising silicon carbide must comprise high purity silicon carbide and / or high purity graphite and / or mixtures thereof, in particular it is also possible to use silicon carbide infiltrated with high purity silicon, preferably the electrodes they consist of one or more of the high-purity materials or a corresponding mixture, and the connectors can be made of other materials.

The invention also relates to a device, in particular an installation, preferably for the production of silicon, especially preferably for the production of pure silicon, in particular by the method according to the invention, said device having at least one reactor 1 for melting and optionally for reduction, in particular silicon oxide with at least one or more carbon sources, with a metal orifice and optionally a slag orifice, in particular a sandwich construction reactor according to Claim 14 and in particularly with silicon carbide or silicon carbide-infiltrated silicon electrodes according to Claim 15, and optionally has at least one reactor 2 upstream of reactor 1, said reactor 2 serving for calcination

94/114 and / or reduction, in particular silicon oxide with at least one or more carbon sources. The reactor 2 can in particular be a microwave reactor optionally with a rotary tube reactor space or a fluidized bed.

The device is generally suitable as an industrial oven, in particular it is also suitable for the reduction and / or melting of metallic compounds or mixtures of said metal compounds, in particular it is suitable for the production of pure to high purity metals, alloys and / or mixtures thereof.

According to the invention, each reactor 1 for the production of silicon has a power of 600 kW to 1 MW, preferably the reactor has a power of 670 kW to 990 kW, better still a power of 700 kW to 950 kW, according to with the invention from 700 kW to 950 kW.

Reactor 2 may, in contrast, be of greater design. A microwave reactor can preferably be used, as explained at the beginning, in particular, it works in the high frequency range between 100 MHz and 100 GHz. Especially preferably, 2.4 MHz magnetrons are used for reactor 2.

It has been proven advantageous to design reactors 1 with the lowest power estimates determined, in order to simplify the regularly required reconditioning of the reactors or the coating. Usually the goal is to supply even bigger reactors with even greater efficiency. The inventors have found, however, that the design of reactors with a power estimate as mentioned above is more suitable for the production of high purity compounds obtained by melting, for example, silicon, because the reactors, and in particular, the coating reactor must be replaced regularly, as it is consumed during continuous operation. In addition, the reactors must be operated under substantially oxygen-free conditions, to minimize the burning of graphite from the electrodes and the internal coating, in particular a segmented internal coating.

According to the invention, a device is therefore operated

95/114 with at least one, in particular, with a large number of reactors, for example, with 1 to 200, in particular, reactors 1. A reactor coating, therefore, can be renewed regularly, without having to shut down the entire device when some reactors are coated with refractory material.

In addition, it is easier to remove process gases in smaller reactors. For rapid reduction, the carbon monoxide that forms must be removed continuously and promptly from the reaction space. The amount of process gas can be controlled in the reduction reactor for silicon production using the amount of silicon carbide as an activator or as a carbon source. Increasing the amount of silicon carbide reduces the amount of carbon monoxide in the step of reducing silicon production. In addition, the removal of gases from the process can be optimized, which is made possible by the addition of porous briquettes and / or a smaller design of the reactors.

According to the invention, the reactors, in particular reactors 1 and / or 2, have the sandwich construction described above, in order to stop the thermally induced diffusion of impurities, in particular boron, in the reaction space. Consequently, it is still preferred that all parts of the device or installation that are operated at high temperatures or are heated indirectly to high temperatures have this sandwich construction. For example, in silicon production by reduction in the arc furnace, temperatures above 1800 ° C are achieved.

Preferably all parts of the device, in particular all parts of the device that come into contact with reagents and / or reaction products, preferably reactor 1, reactor 2, electrodes, ancillary components, connectors and / or tubes of the device , in particular, which are operated at high temperatures or are heated indirectly, also by contact with hot gases, are coated with high-purity refractory material, in particular with high-purity silicon carbide or high-purity graphite.

According to the invention, all parts of the device that come into contact with reagents and / or reaction products, in particular

96/114 with silicon oxide, a carbon source, process gases or reaction products, such as reactor 1 for melting and optionally for reducing silicon oxide comprising a metal orifice and optionally a slag orifice, in particular electrodes, and optionally at least one reactor 2 upstream of reactor 1, said reactor 2 serving for calcination and / or reduction of silicon oxide with at least one or more carbon sources, are coated with high purity refractory material, in particular with high purity silicon carbide or high purity graphite. Preferably, coating with silicon carbide infiltrated with silicon and / or with carbon fibers containing graphite and / or containing silicon carbide is also possible. Alternatively, it may be preferable for the silicon carbide to be of high purity and substantially free of carbon that is not bound to the silicon carbide.

A sandwich construction with at least two layers is also preferred for all parts of the device that are operated at high temperatures, or are heated indirectly, for example, by hot process gases, with the sandwich construction, for example, of a line feed, discharge line or a connector being internally coated with a first layer 7 of the high purity refractory material, in particular, with high purity silicon carbide or high purity graphite, and having another external layer 6, which acts as insulation and / or the diffusion barrier against impurities, and optionally outside the aforementioned layer has a mechanically stable outer layer 8.

According to the invention, the high-purity refractory material is silicon carbide, silicon carbide infiltrated with silicon, graphite, each optionally reinforced with graphite fibers and / or carbon fibers. The total content of impurities, such as boron, phosphorus, aluminum, iron is in particular below 100 ppm by weight, preferably below 10 ppm by weight. The high-purity refractory material according to the invention has the impurity profile defined at the beginning or the purity defined above for

97/114 pure to high purity silicon carbide or high purity graphite. Impurity can be determined by ICP-MS, spectral analysis or resistance measurement.

If reactor 1 is operated without reactor 2, a separate gas outlet is required to remove gases from the process.

The reactor 2 can be designed as a reduction shaft, for example, it can be electrically heated, in particular, by electrodes, which according to the invention contain silicon carbide infiltrated with silicon or silicon carbide, projecting through the shaft walls , according to an alternative, the reduction axis can be heated by a microwave oven, for example, in this modality it can be designed as a kind of fluidized bed, and in this alternative, the process gases left at the bottom of the reactor 1 can be conducted through the fluidized bed and thus contribute to the heating of silicon oxide and carbon sources.

Preferred complete method of silicon production

According to a general embodiment of the present invention, the method of reducing the purified silicon dioxide can be carried out as follows in a general process line.

Starting, for example, from the soluble glass of purchased silicate solutions, if the silicate solutions are no longer of sufficient purity, purification of the silicate solution can be carried out. This, for example, can be accomplished, in a first step, by diluting the silicate solution with deionized water or distilled water, separating solid constituents by usual filtration techniques, which are known to one skilled in the art.

The diluted and filtered silicate solution can, in a special variant of the present method of phosphorus separation, be conducted over an ion exchange column with molybdenum salts. Alternatively, an appropriately diluted silicate solution can also be purified by a method of EP 0 5004 467 B1 to a stable aqueous silica sol. The silica sol thus obtained must be completely dissolved again

98/114 before additional acid precipitation and then undergo precipitation according to the invention in an acidifying agent.

Since each additional process step means additional expense, the method according to the invention will preferably start from the usual silicate solutions acquired and the additional steps described above can preferably be carried out when a sufficiently clean silicate solution is not available or is prepared by dissolving contaminated silicon dioxides.

Any solid constituents present can be removed from the silicate solutions by filtration.

Purified silicon oxide is produced from the silicate solution by precipitation as described above.

Preferably, however, crystalline sugar (source of pure carbon) is added to at least a portion of this silicon oxide, at least partially in a wet state, and optionally a thermal black and siloxanes are added as binders. The pasty mixture obtained is formed, for example, in an extruder and undergoes at least partial drying.

The briquettes obtained can then be pyrolysed to obtain a source of pure carbon with active carbon. Pyrolysed carbon (active carbon) is added to the subsequent process for the production of silicon to improve thermal and / or electrical conductivity.

Another portion of the briquettes can be pyrolyzed and calcined to produce briquettes containing silicon carbide. These briquettes containing silicon carbide are added to the processes according to the invention afterwards to reduce the proportion of carbon monoxide in the current reduction step to pure silicon. Other functions of silicon carbide are as an activator, a reaction accelerator and to improve conductivity.

To reduce purified silicon dioxide, preferably briquettes containing purified silicon dioxide, thermal black and / or sugar and briquettes from the aforementioned pyrolysis and / or briquettes that

99/114 underwent pyrolysis and calcination are reduced to pure silicon in an arc furnace at approximately 1800 ° C. The process gas loading with carbon monoxide can be controlled directly by adding the silicon carbide content. According to the invention, the reaction is preferably carried out in an arc furnace with a reactor of the determined sandwich construction, the inner lining of which is of high purity silicon carbide. The electrodes used are preferably segmented silicon carbide electrodes infiltrated with silicon containing carbon fiber. Molten silicon can be discharged into the metal orifice, and directional solidification may be necessary.

The silicon obtained was necessary for solar grade silicon. The device according to the invention and the reactor according to the invention are explained below, without limiting the invention to these modalities.

Thus, figure 7 shows a preferred mode of the reactor according to the invention.

List of reference symbols:

reactor reaction space orifice for slag orifice for metal residual gas / gas outlet electrode sleeve diffusion barrier, in particular with super-insulation (outermost layer) coating of the reactor space (first layer) vehicle of the reactor body (mechanically stable layer outermost) cover of the electrode slope electrode

A reactor according to invention 0, in particular as a

100/114 arc furnace, has a reaction space 1, in which the electrodes 10 project through the electrode bushing 5 in the reactor cover 9. Preferably the reactor has several electrodes, in particular three electrodes 10. These electrodes 10 can be segmented, to allow continuous feed from outside 5 of reactor 0. To allow process gases that form, such as carbon monoxide, to escape, the reactor has a gas outlet 4. Preferably below the reactor, a hydraulic tilt system Separate 11 is provided, which allows reactor 0 to be tilted so that the slag that is formed is discharged through the orifice for slag 2. The molten silicon produced is discharged continuously or discontinuously from the reaction space 1 through the metal orifice 3. The diffusion and / or insulation barrier 6 preferably comprises a glass body, which is silvered towards the reaction space. The glass body 6 is especially preferably made of high purity quartz glass and / or is provided with an infrared reflective layer towards the interior of the reactor. Preferably, the glass body has a vacuum inside, in particular, a super-insulation, which, for example, is produced chemically. Towards the interior of the reactor, the diffusion barrier (6, outermost layer) is supplied with high purity silicon carbide or high purity graphite, or also appropriately pure silicon carbide and / or pure graphite, as a coating reactor space coating 7. The reactor space coating forms the first layer 7. To improve the economy of the reactor operation and therefore increase the life of the reactor space coating, the latter is segmented. The individual segments 25 of the first layer 7 can be detachably joined by a groove / spring principle. Reactor 0 can be filled continuously or discontinuously. For batch filling, the cover of the reactor 9 can be opened. For continuous operation, the reactor can be supplied with an additional supply line.

The following examples explain the method according to the invention in more detail, without limiting the invention to these examples.

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Measurement methods:

Determination of the pH value of the precipitation suspension

The method, based on DIN EN ISO 787-9, is used to determine the pH value of an aqueous silicon dioxide suspension or the pH value of a washing liquid substantially free of SiOj.

Before carrying out the pH measurement, the pH meter (from Knick, type: 766 pH-Meter Calimatic with temperature sensor) and the pH electrode (Schott's single-stem measurement cascade, type N7680) must be calibrated using solutions buffered at 20 ° C. The calibration function must be selected such that two buffered solutions used include the expected pH value of the sample (buffered solutions with pH 4.00 and 7.00, pH 7.00 and pH 9.00 and if necessary pH 7.00 and 12.00).

In steps a) and d) of the precipitation process for the production of purified silicon dioxide, the pH value is determined at 20 ° C. In step c of this method, the measurement is carried out at the respective temperature of the reaction solution. To measure the pH value, the electrode is first rinsed with deionized water, then with a little of the suspension, and then it is immersed in the suspension. When the pH meter indicates a constant value, the pH value is read on the monitor.

D ₅ Determination of the average particle size of the high purity silicon dioxide to particle sizes smaller than 70 with the laser diffraction instrument Coulter LS 230

Description:

The application of laser diffraction according to the Fraunhofer model for determining particle sizes is based on the phenomenon that particles disperse monochromatic light with a pattern of different intensity in all directions. This dispersion depends on the particle size. The smaller the particles, the greater the dispersion angles.

Procedure:

After switching on, the Coulter LS 230 laser diffraction instrument requires a warm-up time of 1.5 to 2.0 hours in order to obtain values

102/114 measured constant. The sample must be shaken thoroughly before measurement. First, the Coulter LS 230 program is started with double click. Verify that Use Optical Bench is enabled and that the monitor on the Coulter instrument displays Speed off. Press the Drain button and keep it down until the water in the measurement cell drains, then press the On button on the fluid transfer pump and again keep it down, until the water flows in the instrument overflow. Perform this operation twice. Then press Fill. The program starts on its own and removes any air bubbles from the system. The speed is automatically increased and reduced again. Establish the power of the pump selected for the measurement.

Before the measure, it is necessary to establish whether the measure will be with or without PIDS. To start the measurement, select Measurement Measuring cycle.

a) Measure without PIDS

Measurement time is 60 seconds, waiting time 0 seconds. Then the calculation model forming the basis of laser diffraction is selected. Basically, a reference measurement is performed automatically before each measurement. After reference measurement, place the sample in the measurement cell, until a concentration of 8 to 12% is reached. This is reported by the program, with OK appearing above. Finally, click Ready. The program now performs all the necessary steps by itself and, after a measurement cycle, generates a particle size distribution of the test sample.

b) Measure with PIDS

PIDS measurements are performed when the expected particle size distribution is in the submicron range.

Measurement time is 90 seconds, waiting time 0. Then the calculation model forming the basis of laser diffraction is selected. Basically, a reference measurement is performed automatically before each measurement. After reference measurement, place the sample in the measurement cell, until a concentration of at least 45% is reached. This

103/114 is reported by the program, with OK appearing above. Finally, click Ready. The program now performs all the necessary steps by itself and, after a measurement cycle, generates a particle size distribution of the test sample.

Determination of d ₅₀ of the average particle size of the products in a screw-shaped or mushroom-hat shape

100 representative particles are selected and the diameter of each particle [is measured] under an optical microscope. As the particles can be irregularly shaped, the diameter is determined at the point with the largest diameter. The average value of all determined particle diameters corresponds to the value of d ₅₀ .

Determination of the dynamic viscosity of silicate solutions with the ball guideway viscometer

The dynamic viscosity of the soluble glass is determined with the ball drop viscometer (Viscometer Hõppler, by Thermo Haake). Procedure

The soluble glass (approximately 45 cm ³ ) is poured without bubbles into the tube of the drop-down viscometer (Thermo Haake, Drop-down Viscometer C) below the end of the tube and then the sphere (Thermo Haake, set of spheres type 800-0182, Sphere 3, density δκ = 8.116 g / cm ³ , diameter dK = 15.599 mm, specific constant K for sphere = 0.09010 mPa * s * cm ³ / g) is inserted. The viscometer temperature is adjusted accurately, using a circulating thermostat (Jalubo 4) at 20 + 0.03 ° C. Before the measurement, the sphere is passed once through the tube to completely mix the soluble glass. After a 15-minute break, the first measurement begins.

The measuring element locks in the 10 ° position defined on the base of the instrument. By rotating the measurement element by 180 °, the sphere is brought to the initial measurement position. The time t for falling through the measurement section A-B is determined with a stopwatch. The start of the measurement time begins when the bottom edge of the sphere touches the upper ring sight mark A, which should appear as a line at the

104/114 observer. The measurement time ends when the bottom edge of the sphere reaches the lower annular mark B, which must also appear as a line. By rotating the measuring element 180 ° again, the ball falls back to its starting position. After a 15-minute break, a second measurement as described is performed. Repeatability is checked if the measured values do not differ by more than 0.5%.

The dynamic viscosity of the soluble glass (r | wGi_) in mPa * s is calculated from the numerical value equation qWGL ⁼ K * (Õ K-ÕwGL) * t

Sphere constant: K = 0.09010 mPa * s * cm ³ / g Sphere density: õK = 8.116g / cm ³ Soluble glass density: õWgl in g / cm ³ t = travel time of the sphere, s with a accuracy to one decimal place.

100 mPa * s correspond to 1 poise.

Determination of the conductivity of the washing medium

To determine the electrical conductivity of an aqueous suspension of silicon dioxide - or the electrical conductivity of washing liquid substantially free of SiO ₂ - the aqueous suspension / washing liquid is carried out at room temperature based on DIN EN ISO 787-

14.

Flow speed determination

The flow rate is determined using the PCE-Group's P-670-M volume flow meter with the water flow probe. The probe is positioned in a region of the reactor that is defined transversely by the reactor semi-ray ± 5 cm and longitudinally by the surface of the feed / precipitation suspension 10 cm below the surface of the feed / precipitation suspension. Read the instrument's instructions.

Determination of impurity content:

Description of the method for determining trace elements in silica by high-coupled induction plasma-mass spectrometry

105/114 resolution (HR-ICPMS) (similar to test report A080007580)

Weigh 1 to 5 g of the sample material to an accuracy of + 1 mg in a PFA beaker. Add 1 g of mannitol solution (approximately 1%) and 25 to 30 g of hydrofluoric acid (approximately 50%). After briefly turning, heat the PFA beaker in a heating block to 110 ° C, so that the silicon contained in the sample as hexafluorosilicic acid and the excess hydrofluoric acid slowly evaporate. Dissolve the residue with 0.5 ml of nitric acid (approximately 65%) and a few drops of hydrogen peroxide solution (approximately 30%) for approximately 1 hour and adjust to 10 g with ultrapure water.

To determine trace elements, take 0.05 ml or 0.1 ml of the decomposition solutions, transfer each one to a polypropylene test tube, add 0.1 ml of indium solution (c = 0.1 mg / l) as an internal standard and adjust up to 10 ml with diluted nitric acid (approximately 3%). The preparation of these two sample solutions in various dilutions serves to ensure internal quality, that is, checking whether errors were made during the measurement or in the sample preparation. In principle, it is also possible to work with only one sample solution.

From multi-element stock solutions (c = 10 mg / l), containing all elements to be analyzed except indium, four calibration solutions are prepared (c = 0.1; 0.5; 1.0; 5.0 pg / l), again with the addition of 0.1 ml of indium solution (c = 0.1 mg / l) to 10 ml of final volume. In addition, blank solutions are prepared with 0.1 ml of indium solution (c = 0.1 mg / l) for a final volume of 10 ml.

The content of elements in the blank, calibration and sample solutions are quantified by high resolution coupled induction mass spectrometry (HR-ICPMS) and by external calibration. The measurement is carried out with a mass resolution (m / Am) of min. 4000 or 10000 for the elements potassium, arsenic and selenium.

The following examples will explain the present invention in more detail but do not limit it in any way.

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Comparative Example 1

Based on example 1 in WO 2007/106860 A1, 397.6 g of soluble glass (27.2 wt% SiO ₂ and 8.0 wt% Na ₂ O) were mixed with 2542.4 g deionized water. The diluted soluble glass was then passed through a column with an internal diameter of 41 mm and a length of 540 mm, filled with 700 ml (500 g dry weight) of Amperlite IRA 743 in water. After 13.5 min, a pH value of more than 10 was measured at the column outlet, so that by this point in time the first soluble glass passed through the column. A sample of a total of 981 g of purified soluble glass, taken between 50 ° and 74 ° minute, was used for subsequent tests.

The analytical data for the soluble glass before and after purification are shown in Table 1 below:

Table 1:

Poisoning Content in Glass of water before ion exchange Glass of water after ion exchange Aluminum PPm 31 31 Boron PPm <1 <1 Calcium PPm 3 3 Iron PPm 8 7 Nickel PPm <0.3 <0.3 Phosphor PPm <10 <10 Titanium PPm 8 2 Zinc PPm <1 <1 Total for all measured elements PPm 66 57.5

The data in Table 1 show that the step described in WO 2007/106860 A1 as important in the purification of the soluble glass in Amperlite IRA 743 with the commercially available soluble glass does not show any marked purification effect and only causes a slight improvement in the case of the content of titanium.

The purified soluble glass was further processed, as in Example 5 in WO 2007/106860 A1, to SiO ₂ . For this, 700g of soluble glass

107/114 were acidified with 10% sulfuric acid in a 2000 ml round bottom flask, with stirring. The initial pH value was 11.26. After adding 110g of sulfuric acid, the gel point was reached at pH 7.62, and 100g of deionized water was added to restore the agitability of the suspension. After adding a total of 113g of sulfuric acid, a pH value of 6.9 was reached, and it was stirred for 10 minutes at this pH value. Then it was filtered with a 150 mm diameter Buchner funnel. The product obtained had very poor filterability. After washing five times, with 500 ml of deionized water each time, the conductivity was 140 pS / cm. The filter cake obtained was dried for 2.5 days at 105 ° C in a circulating air drying oven, obtaining 25.4 g of the dry product. The analytical results are given in Table 2.

Example 1 (according to the invention)

1808g of soluble glass (27.2% by weight of SiO ₂ and 7.97% by weight of Na ₂ O) and 20.1 g of 50% sodium hydroxide solution were placed in a round glass bottom flask 4000 ml quartz with two-necked adapter, ball condenser, Liebig condenser (each made of borosilicate glass) and 500 ml graduated cylinder to collect the distillate. The sodium hydroxide solution was added to provide an increased Na ₂ O content in the concentrated soluble glass. The solution was covered with nitrogen to prevent the reaction with carbon dioxide from the air and was then heated to a boil using a heating blanket. After 256 ml of water had been distilled, the Liebig condenser was replaced with a stopper and the boiling was continued under reflux for an additional 100 min. Then the concentrated soluble glass was cooled under an atmosphere of nitrogen to room temperature and left to stand overnight. 1569 g of concentrated soluble glass with a viscosity of 537 mPa * s (ie 5.37 poises) were obtained.

2513 g of sulfuric acid 16.3% and 16.1 g of hydrogen peroxide 35% were placed at room temperature in a 4000 ml double-necked quartz glass flask with precision glass shaker and drip funnel (each made borosilicate glass). Within 3

108/114 min, 1000 ml of the previously prepared concentrated soluble glass (9.8% by weight of Na ₂ O, 30.9% by weight of SiO ₂ , density 1.429 g / ml) were added dropwise so that the pH value remained below 1. The temperature of the reaction mixture increased to 50 ° C and turned a deep orange. The suspension was stirred for an additional 20 min and then the solid obtained was allowed to settle.

It was processed by decanting the supernatant solution and adding a mixture of 500 ml of deionized water and 50 ml of 96% sulfuric acid to the residue. Upon mixing, the suspension was heated to a boil, allowed the solid to settle and the supernatant was decanted again. This washing process was repeated until the supernatant only had an extremely light yellow color. Then it was washed repeatedly with 500 ml of deionized water each time, until a pH value of the wash suspension of 5.5 was reached. The conductivity of the wash suspension was now 3 pS / cm. The supernatant was decanted and the product obtained was dried overnight at 105 ° C in a circulating air drying oven. The analytical data of the product obtained are shown in Table 2 below:

Table 2

Poisoning Content in SiO ₂ after Comparative Example 1 SiO ₂ according to the invention after Example 1 Aluminum PPm 720 0.5 Boron PPm 1 <0.1 Calcium PPm 42 0.1 Iron PPm 170 0.2 Nickel PPm <0.3 0.3 Phosphor PPm <10 <0.1 Titanium PPm 57 0.4 Zinc PPm <3 0.1 Sodium PPm 6800 0.5 Potassium PPm 34 0.3 Total for all measured elements PPm <7837.3 <2.6

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The silicon dioxide produced by the method according to the invention has a total impurity content - for all measured elements - of only 2.6 ppm. The levels of contamination with the elements critical for the production of solar grade silicon are, as shown in Table 2, within an acceptable range. It can be seen from this formula that with the method according to the invention - against the teaching of the prior art ~ it is possible to produce, without chelating agent or the use of ion exchange columns, commercially available concentrated soluble glass and commercially available sulfuric acid, a silicon dioxide which, based on its impurity profile, is eminently suitable as a starting material for solar grade silicon.

Examples - Pyrolysis

Comparative Example 2

Commercially available refined sugar was melted in a quartz glass under protective gas and then heated to approximately 1600 ° C ^: There was considerable foaming of the reaction mixture, partially escaping - caramel formation was also observed, and the pyrolysis product adhered to the reaction vessel wall (see Fig. 3a).

Example 2

Commercially available refined sugar was mixed with SiO;> (Sipemat® 100) in a 20: 1 weight ratio, melted and heated to approximately 800 ° C. No caramel formation was observed, and no foaming occurred. A particulate pyrolysis product containing 25 graphite was obtained, which advantageously did not substantially adhere to the wall of the reaction vessel.

Examples: Pyrolysis and Calcination

Comparative Example 3:

Commonly available refined sugar was melted in a quartz glass and then heated to approximately WOO'C. There is considerable foaming of the reaction mixture during heating and a little escapes from the quartz glass. At the same time, caramel training

110/114 is observed. The formed pyrolysis product adheres to the reaction vessel wall (Fig. 3a).

Example 3a:

Commercially available refined sugar was mixed with

SíO _a (Sípernat® 100) in a weight ratio of 1.25 to 1 _s melted and then heated to approximately 80CFC. Caramel formation is observed, but no foam. A particulate pyrolysis product containing graphite is obtained, which in particular does not adhere to the reaction vessel wall (Fig, 3b). Fig, 4 is a micrograph of the pyrolysis product of Example 3a.

The pyrolysis product is distributed over and presumably also in the pores of the SiO? Particle. The particulate structure is conserved.

Example 3b:

Commercially available refined sugar was mixed with

SiOà (Sipemat® WO) in a 5 to 1 weight ratio, melted and then heated first to approximately 800 * 0 and then to approximately 1800 ° C. Formation of cáramélb is observed, but there is no foam. A silicon carbide with graphite components is obtained. Figs. 5 and 6 are the micrographs of the two samples of the calcined product. The formation of silicon carbide was detected from XPS spectra and determination of the binding energies. In addition, Si ~ O structures were also detected. It was concluded from the metallic luster under an optical microscope that graphite was formed.

Example 4:

A fine particulate formulation of sugar coated particles of SiOg is reacted at elevated temperature in a rotary furnace with _SiO2 balls for heat distribution. For example, produced by dissolving sugar in an aqueous silicic acid solution with subsequent drying and if necessary homogenization. There was still residual moisture in the system. Approximately 1 kg of formulation was used.

111/114 SiO ₂ particles, is reacted at elevated temperature in a rotary kiln with SiO ₂ spheres for heat distribution. For example, produced by dissolving sugar in an aqueous silicic acid solution with subsequent drying and if necessary homogenization. There was still residual moisture in the system. Approximately 1 kg of formulation was used.

The residence time in the rotary kiln depends on the water content of the fine and particulate formulation. The rotary kiln was equipped with a preheating zone for drying the formulation, so the formulation passed through a pyrolysis and calcination zone with temperatures from 400 ° C to 1800 ° C. The residence time including the drying step, pyrolysis step and calcination was approximately 17 hours. Throughout the process, the process gases that have formed, such as steam and CO, can be removed by simple means from the rotary kiln.

The SiO ₂ used had a boron content of less than 0.1 ppm, phosphorus of less than 0.1 ppm and an iron content of less than approximately 0.2 ppm. The iron content of sugar was determined before formulation at less than 0.5 ppm.

After pyrolysis and calcination, the contents were determined again, with the content of boron and phosphorus being determined below 0.1 ppm, and the iron content had increased to 1 ppm. The increased iron content can only be explained by the product coming into contact with parts of the oven that are contaminated with iron.

Example 5:

Example 4 was repeated, with a laboratory rotary tube oven previously covered with high purity silicon carbide. This was reacted at an elevated temperature with SiO ₂ spheres for heat distribution and a fine-particulate formulation containing sugar, covered in SiO ₂ particles. For example, prepared by dissolving in sugar in an aqueous silicic acid solution with subsequent drying and if necessary homogenization. There was still residual moisture in the system. Approximately 10 g of the formulation was used.

111/114

The residence time in the rotary kiln depends on the water content of the fine and particulate formulation. The rotary kiln was equipped with a pre-heating zone for drying the formulation, so the formulation passed through a pyrolysis and caicination zone with 5 temperatures of 40 ° C to fSMTC. The residence time including the drying stage, pyrolysis stage and caicination was approximately 17 hours. Throughout the process, the process gases that have formed, such as steam and CO, can be removed by simple means from the rotary kiln.

The SiO ₂ used had a boron content of less than 0.1 ppm, phosphorus of less than 0.1 ppm and an iron content of less than approximately 0.2 ppm. The iron content of sugar was determined before formulation at less than 0.5 ppm.

After pyrolysis and caicination, the contents were determined again, with the boron and phosphorus content being determined below 15 0.1 ppm, and the iron content had increased to 1 ppm. The increased iron content can only be explained by the product by contacting parts of the oven that are contaminated with; iron.

Example 5:

Example 4 was repeated, with a laboratory rotary tube oven previously covered with high purity silicon carbide. This was reacted at elevated temperature with SiO? for heat distribution and a fine-particulate formulation containing sugar, covered in SiQ ₂ particles. For example, prepared by dissolving in sugar in an aqueous silicic acid solution with subsequent drying 25 and if necessary homogenization. There was still residual moisture in the system. Approximately 10 g of the formulation was used.

The residence time in the rotary kiln depends on the water content of the fine-particulate formulation. The rotary kiln was equipped with a pre-heating zone for drying the formulation, so the formulation passed through a pyrolysis and caicination zone with temperatures from 400 ° C to 1800 ° C. The residence time including the stage

113/114 approximately 0.2 ppm. The iron content of sugar was determined before formulation at less than 0.7 ppm.

After pyrolysis and calcination, the silicon carbide content was determined again and the boron and phosphorus content was still less than 0.17 ppm or less than 0.15 ppm respectively, and in addition, the iron content was determined in less than 0.7 ppm.

Example 7:

The corresponding reaction of a pyrolyzed formulation according to Example 3 was carried out in a microwave reactor. For this, approximately 0.1 kg of a dry, fine-particulate formulation of pyrolysed sugar in SiO ₂ particles were reacted at frequencies above 1 gigawatt for silicon carbide in a carbon matrix. The reaction time is directly dependent on the power input and the reagents.

If the reaction is carried out starting from carbohydrates and SiO ₂ particles, the reaction times are correspondingly longer.

Example 8

SiO ₂ (Aerosil® OX 50) and C (graphite) were reacted in a weight ratio of approximately 75:25 in the presence of SiC.

Procedure: an electric arc, which serves as an energy source, is fired in a known manner. The reaction starts insidiously with the evolution of gaseous compounds between SiO ₂ and C. Then 1% by weight of powdery SiC is added. After a very short time, a very sharp increase in the reaction can be observed from the occurrence of light phenomena. After this, the reaction continued after adding SiC with an intense, bright orange glow (approximately 1000 ° C). The solid obtained during the reaction was identified as silicon based on its typically dark brown color (MJ Mulligan et al. Trans. Soc. Can. [3] 21 III [1927] 263/4; Gmelin 15, Part B p 1 [1959]) and scanning electron microscopy (SEM).

Example 9

SiO ₂ (Aerosil® OX 50) and C were reacted in a proportion

114/114 weight of approximately 65:35 in the presence of SiC.

Procedure: an electric arc, which serves as a source of energy, is fired in a known manner. Reaction between SiO ₂ and C starts insidiously. Gases evolve to be recognized. 1% by weight of powdery SiC is added after a short time which leads to a marked increase in the reaction, discernible from the occurrence of light effects. After adding SiC, the reaction continued for some time, with an intense, flickering glow. The solid obtained during the reaction was identified as silicon by SEM and EDX 10 analysis (energy-dispersive x-ray spectroscopy).

Comparative Example 4

SiO ₂ (Aerosil® OX 50) and C were reacted in a tube as a 65:35 mixture at high temperature (> 1700 ° C). The reaction has barely begun, and there has been no noticeable progress. No bright glowing was observed.

Claims (16)

1. Method for the production of pure silicon, characterized by the fact that it comprises the reduction of purified silicon oxide by precipitation of an aqueous solution, preferably by precipitation of a silicon oxide dissolved in an aqueous phase in an acidifying agent, preferably a dioxide of purified silicon, with one or more sources of pure carbon. Method according to claim 1, characterized in that the pH value during precipitation in the precipitation suspension is less than 2, preferably less than 1.5, especially preferably less than 1, very especially preferably less than 0 , 5. Method according to any one of claims 1 or 2, characterized by the fact that the source of pure carbon or one of the carbon sources comprises an organic compound of natural origin, a carbohydrate, graphite, coke, coal, carbon black, thermal black, non-pyrolysed carbohydrate, in particular sugar pyrolysate, preferably due to the fact that a high purity carbohydrate or high purity pyrolyzed carbohydrate is used as the carbon source or as one of the carbon sources is used in at least one step of the full method method. Method according to any one of claims 1 to 3, characterized by the fact that carbon is obtained by pyrolysis of carbohydrates in a component step of the method, using SiO ₂ , especially a silicon dioxide purified by acidic precipitation, as an antifoaming agent in pyrolysis. Method according to any one of claims 1 to 4, characterized by the fact that high purity silicon carbide is prepared from silicon dioxide and carbohydrates in a component step of the method, and this silicon carbide is preferably used for one or more of the following purposes: a) for coating reactor components 2/5 b) for production of blast furnace process electrodes c) as a carbon source for the reaction with silicon dioxide purified by acidic precipitation d) as a reaction accelerator for the reaction of another carbon source with silicon dioxide purified by acidic precipitation. A method according to any one of claims 1 to 5, characterized by the fact that silicon oxide, preferably silicon dioxide, purified by precipitation is present together with at least one source of pure carbon and optionally a silicon carbide, preferably high purity silicon carbide and optionally silicon, a) in a formulation comprising purified silicon oxide and at least one source of pure carbon and optionally silicon carbide and optionally silicon and / or b) in a formulation comprising purified silicon oxide and optionally silicon carbide and optionally silicon and / or c) in a formulation comprising at least one source of pure carbon and optionally silicon carbide and optionally silicon, and the respective formulations optionally contain binders. Method according to any one of claims 1 to 6, characterized by the fact that the reduction of purified silicon oxide with one or more sources of pure carbon takes place in an arc furnace, a thermal reactor, an induction furnace, a rotary furnace and / or an oven microwave. Method according to any one of claims 1 to 7, characterized by the fact that the reduction of purified silicon oxide with one or more sources of pure carbon takes place in a reaction space coated with high-purity refractories and optionally the electrodes used consist of high-purity material. Method according to any one of claims 1 to 8, characterized by the fact that pure molten silicon is obtained, which 3/5 is optionally further purified by zone fusion. 10. Formulation, in particular for the method as defined in any one of claims 1 to 9, characterized by the fact that it is a formulation according to alternatives a), b) and / or c), and comprises a) a pure silicon oxide together with at least one source of pure carbon and optionally a silicon carbide and optionally silicon, b) a pure silicon oxide and optionally silicon carbide and optionally silicon, c) at least one source of pure carbon and optionally silicon carbide and optionally silicon and the respective formulation optionally contains a binder. 11. Reactor and / or electrodes, in particular for use with industrial furnaces, such as induction, direct current and / or alternating current furnaces, characterized by the fact that the reactor has silicon carbide or silicon carbide electrodes inside in silicon and / or the fact that the electrodes contain silicon carbide or silicon carbide infiltrated in silicon, the silicon carbide or silicon carbide infiltrated in silicon preferably being obtained by the method as defined in claim 5. 12. Reactor (0), preferably according to claim 11, characterized by the fact that at least the reaction space (1) of the reactor or reactors (0) for fusion and optionally for reduction, in particular silicon oxide with at least one or more carbon sources, it has a hole for metal (3) and optionally a hole for slag (2) - has a sandwich construction with at least two layers, - and the reaction space (1) or the reactor is internally coated with a first layer (7) of high-purity refractory material, in particular with high-purity silicon carbide or high-purity graphite, 4/5 - an outermost layer (6), which acts as an insulation and / or diffusion barrier against impurities, particularly at high temperatures, and - optionally has a mechanically stable outer layer on the outside (8). 13. Device, in particular for the production of silicon, characterized by the fact that it comprises at least one reactor (1) for fusion and optionally for reduction, in particular silicon oxide with at least one or more carbon sources, with a orifice for metal and optionally a orifice for slag, in particular as defined in claim 10 or 11 and in particular with electrodes as defined in claim 10, and optionally has at least one reactor (2) upstream of the reactor (1), the reactor (2) it serves for calcination and / or reduction, in particular of silicon oxide with at least one or more carbon sources. 14. Device according to claim 13, characterized by the fact that the reactor (1), the reactor (2), the electrodes, ancillary components of the device, connectors and / or tubes that are operated at high temperatures or are heated indirectly , are coated with high-purity refractory material, in particular with high-purity silicon carbide or high-purity graphite. 15. Use of at least one silicon oxide containing impurities characterized by the fact that it is for the production of silicon, comprising the following steps, I) conversion of the silicon oxide containing impurities to a silicate dissolved in an aqueous phase, II) addition of the silicate dissolved in aqueous phase, to an aqueous, acidic solution, with impurities remaining in solution, and a precipitate of purified silicon dioxide is obtained, III) the silicon oxide thus obtained is reacted in the presence of at least one or more carbon sources, and optionally by the addition of an activator, to the silicon. 16. Invention, characterized by any of its 5/5 embodiments or categories of claim encompassed by the material initially disclosed in the patent application or in its examples presented here.