JPH092811A - Low oxygen porous silicon granule and method for producing the same - Google Patents

Abstract

(57) [Summary] [Structure] An average particle diameter of 0.2 to 10 mm obtained by granulating metal silicon powder having an average particle diameter of 4 μm to 10 μm.
Of the metal silicon granules having a specific surface area of 0.5 m ² / g or more and an oxygen content of 0.4 wt% or less,
The carbon content is less than 1% by weight and the mode of pore size is 1 μm
A low-oxygen porous silicon granule characterized by having a particle size of 2 μm or less. [Effects] The low-oxygen porous silicon granules of the present invention, when subjected to a nitriding reaction in a rotary furnace or a fluidized bed reaction furnace, do not cause deposition of metallic silicon powder in the reaction tube at the time of nitriding and the reaction rate is improved, High quality α-type silicon nitride can be produced at a high rate.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention is particularly used for producing silicon nitride powder by a direct nitriding method of metallic silicon,
The present invention relates to a low-oxygen porous silicon granule having good reactivity capable of efficiently producing a silicon nitride powder having a high α-type ratio, and a method for producing the same.

[0002]

2. Description of the Related Art In recent years,
Silicon nitride has attracted attention for its excellent properties such as heat resistance, impact resistance, and mechanical strength, but when it is commercialized, it can be sintered without sacrificing the above-mentioned excellent properties of silicon nitride to obtain various shapes. Need to be molded into. Here, there are α-type and β-type crystal types of silicon nitride, and among these, β-type is said to be inferior in sinterability to α-type, and it can be sintered without impairing the characteristics of silicon nitride. It is desirable that the ratio of α-type is as high as possible.

Conventionally, as a method for producing silicon nitride powder, a direct nitriding method of metallic silicon, a silica reduction method, and a thermal decomposition method of imide are known. Among them, the silica reduction method and the imide thermal decomposition method are easy for obtaining silicon nitride having a high α-type ratio, but both methods are not suitable for mass production.

On the other hand, although the direct nitriding method of metallic silicon is suitable for mass production, this method requires a large reaction heat of 176 kcal per 1 mol of silicon nitride, resulting in an extremely high temperature. It has a drawback that the proportion of β-type silicon nitride that is easily generated increases.

In general, the direct nitriding method of metallic silicon is
The metal silicon powder, which is the raw material, is charged in a tray, and nitriding is performed while it is left standing, or nitriding is performed while it is left in a block shape, so that heat is easily stored and the proportion of β-type silicon nitride tends to increase. In addition, there is a problem in that the α-conversion rate of the obtained silicon nitride varies due to the temperature rise in the reaction furnace and the temperature variation in the reaction furnace.

Therefore, in order to solve the above problems, a method for producing silicon nitride using a tunnel type continuous furnace as a reaction furnace has been proposed (Japanese Patent Laid-Open No. 58-88107).
However, even with this method, it is difficult to sufficiently control the temperature distribution in the furnace, and the problem regarding the variation in the content of the α-type silicon nitride has not been sufficiently improved.

On the other hand, as a result of the study by the present inventors, a method of efficiently producing silicon nitride having a high α-type ratio by using a rotary kiln such as a rotary kiln and a fluidized bed reaction furnace with less variation was attempted. ing. However,
When metal silicon powder having an average particle size of 10 μm or less is used as a raw material in consideration of reactivity, adhesion of metal silicon powder grows on the discharge pipe, the discharge pipe is blocked, and metal silicon powder on the inner surface of the reaction pipe is used. The fluidity becomes unstable due to the adherence of
In some cases, the internal temperature fluctuates greatly, the reaction rate and the α-conversion rate of the obtained silicon nitride powder vary, and the quality fluctuates.

In this case, granulation of metallic silicon powder has also been studied, but the organic binder remains in the granulated product by simply granulating with an organic binder,
Since the granulated product is easily broken, it has been attempted in advance to make it into a granulated product having good fluidity by calcination. However, when the oxygen content in the granulated product increases due to the calcination, the metal silicon powder adheres to the inner surface of the reaction tube as described above, which causes clogging of the discharge tube.

Moreover, the melting of finely powdered metal silicon, which is also the purpose of calcination, reduces the specific surface area, resulting in good fluidity, but poorly reactive granules. It has been difficult to obtain a metal silicon granule as a nitriding raw material that can efficiently produce silicon nitride having a high α-type ratio with little variation.

The present invention has been made in view of the above circumstances, and silicon nitride having a high α-type ratio has a small variation,
Moreover, it is an object of the present invention to provide a low-oxygen porous silicon granule having good reactivity, which can be efficiently produced, and a method for producing the same.

[0011]

Means for Solving the Problems In order to achieve the above object, the present inventor has conducted extensive studies on a granulated product of metallic silicon powder, which is a raw material for manufacturing silicon nitride, and a manufacturing method thereof. As a result, when a certain amount of carbon powder was added to metallic silicon powder, mixed and granulated with an organic binder, and heat-treated under specific conditions, surprisingly, the average particle diameter was 0.2 to 10 mm and the specific surface area was 0. 5m ² / g or more,
A low-oxygen porous silicon granule having a mode of pore distribution of 1 to 2 μm is obtained, and when this granule is used as a raw material to carry out a nitriding reaction in a rotary furnace or a fluidized bed reactor, an α-type ratio of It has been found that high silicon nitride can be efficiently produced with little variation.

That is, carbon powder was added to metallic silicon powder having an average particle diameter of 4 to 10 μm in an amount of less than 5% by weight based on the total weight of the metallic silicon powder, mixed and granulated with an organic binder, and then at 0250 to 1400 ° C. By performing heat treatment for 5 to 5 hours in an inert atmosphere excluding nitrogen, oxygen existing on the surface of the metal silicon powder particles can be removed by the reducing action of the carbon powder, that is, the reaction of SiO ₂ + C → SiO + CO. It becomes possible to reduce the oxygen content in the obtained granulated product to 0.4% by weight or less. When this granulated product is used as a raw material for nitriding in a rotary furnace or a fluidized bed reactor, It is possible to suppress fluctuations in the internal temperature that result from the instability of the flow due to the adherence of granules to the surface, maintain good fluidity, and also to ensure that granules adhere to the discharge pipe. The occurrence of clogging of the discharge pipe due to can be prevented. Moreover, the added carbon powder is
Since the pores are formed after the reaction, the average particle diameter of the granulated product is 30
It is possible to obtain a low-oxygen porous silicon granulated product having a fine and large number of pores with a mode of pore diameter of 0 μm or less and 1 to 2 μm, and using the granulated product as a raw material, a nitriding reaction in a rotary furnace or a fluidized bed reactor. When it is carried out, it has been found that the reactivity is improved due to the increase in the specific surface area, silicon nitride having a high ratio of a good α-type can be efficiently produced with little variation, and the present invention has been achieved. is there.

Therefore, the present invention is a metal silicon granule having an average particle diameter of 0.2 to 10 mm obtained by granulating metal silicon powder having an average particle diameter of 4 μm or more and 10 μm or less. Low oxygen characterized by having a specific surface area of 0.5 m ² / g or more, an oxygen content of 0.4% by weight or less, a carbon content of less than 1% by weight, and a mode of pore diameter of 1 μm or more and 2 μm or less. Porous silicon granules and average particle size is 4
To the metallic silicon powder having a particle size of 10 μm or more, 0.3% by weight or more and less than 5% by weight of carbon powder is added to the total amount of the metallic silicon powder, an organic binder is added, and the mixture is mixed and granulated. Low oxygen porous silicon granulation, characterized in that the obtained granules are heat-treated in a temperature range of 1250 ° C. or more and 1400 ° C. or less for 0.5 hours or more and 5 hours or less in an inert atmosphere excluding nitrogen. A method of manufacturing a product is provided.

The present invention will be described in more detail below. In the low oxygen porous silicon granule of the present invention, carbon powder is added to the raw material metal silicon powder, mixed and granulated with an organic binder, and then heated. It can be obtained by processing. In this case, the metal silicon powder as a raw material has an average particle size of 4 to 10 μm,
It is particularly preferably 5 to 7 μm, and the average particle size is 4
If it is smaller than μm, the crushing cost for making fine powder becomes high and it is not practical. On the other hand, when the average particle diameter is larger than 10 μm, not only does it become difficult to react, but it becomes difficult to granulate. Further, the metal silicon powder has a specific surface area of 1 to 6 m.
² / g, especially 2-5 m ² / g, oxygen content 0.2-1.
It is preferably 5% by weight, particularly preferably 0.2 to 1% by weight.

The carbon powder to be added is not particularly limited, but has a specific surface area of 20 to 500 m ² / g, especially 50
It is preferably ˜300 m ² / g. The amount of carbon powder added is 0.3 with respect to the total amount of metallic silicon powder.
It is preferable to add it in a proportion of not less than 5% by weight and not more than 5% by weight, particularly 0.3 to 3% by weight. Addition amount of carbon powder is 5
If the content is more than weight%, the residual carbon content in the granulated product is 1
The reactivity becomes worse because the content is more than 1% by weight. On the other hand, if it is too small, pore formation does not occur, and adding 0.3% by weight or more increases the specific surface area and improves the reactivity. Is preferred.

The organic binder to be used is not particularly limited, and known binders such as polyvinyl alcohol (hereinafter referred to as PVA), polybutyl alcohol, and other alcohol-based and acrylic-based binders can be used. The amount of the organic binder added is preferably 1 to 5% by weight, more preferably 2 to 3% by weight, based on the total amount of the metal silicon powder.

Next, the method for producing the low-oxygen porous silicon granules will be described in detail. The carbon powder and the metal silicon powder are usually mixed in a mixer such as a Henschel mixer in a dry manner for about 2 minutes. Then, a method of adding an aqueous solution of an organic binder of 1 to 5% by weight (concentration: 10%) to the total amount of metallic silicon powder and further mixing for several minutes may be adopted. Moreover, the obtained mixture can be granulated by an extrusion type, agitation type, or other type of granulator and dried. The drying method is not particularly limited and may be 100 to 150 under ventilation such as nitrogen.
It is sufficient to carry out at a temperature of ° C for 10 to 20 hours. The average particle diameter of the granulated product is preferably 0.2 to 10 mm.

The dried product thus obtained is heated in a heating furnace under an inert atmosphere except for nitrogen in the temperature range of 1250 to 1400 ° C., more preferably 1330 to 1350 ° C., at 0.5 to 5 ° C.
The heat treatment is performed for an hour, more preferably 1 to 2 hours. In this case, the oxygen content in the granulated product exceeds 0.4% by weight in the temperature range lower than 1250 ° C., and the adhesion of the metal silicon powder on the inner surface of the reaction tube adversely affects the fluidity, resulting in fluctuation of the internal temperature. growing. On the other hand, in the temperature range over 1400 ° C., the specific surface area is less than 0.5 m ² / g, which adversely affects the reactivity. If the heating time is less than 0.5 hours, deoxidization and fine powder generation rate are adversely affected, and if it exceeds 5 hours, the specific surface area is adversely affected.

The heating furnace is not particularly limited, and a box furnace type, a tunnel furnace type, a rotary furnace type, etc. are preferably used. Further, the atmosphere is an inert atmosphere and may be an atmosphere such as helium or argon, but nitrogen is excluded because a nitriding reaction occurs.

The metallic silicon granules of the present invention which can be obtained by the above production method have an average particle diameter of 0.2 to 10 m.
m, especially 0.5 to 5 mm is preferable. The average particle size is 0.
If it is smaller than 2 mm, it tends to scatter out of the fluidized bed, while if it is larger than 10 mm, the fluidized state deteriorates.

In this case, it is particularly necessary for the granulated product to have a large number of fine pores in order to increase the specific surface area and improve the reactivity. Specifically, the average particle size of the granulated product is When it is 300 μm or less, the mode of the pore diameter is 1 μm or more and 2 μm or less. Mode is 1 μm
If it is out of the range of 2 μm or less, the reactivity cannot be improved and the granulated product becomes unstable and easily broken.

The specific surface area of the granulated product of the present invention is 0.5.
It is preferably m ² / g or more, particularly preferably 1 to ² m ² / g. If the specific surface area is less than 0.5 m ² / g, sufficient reactivity cannot be obtained. Further, the oxygen content is preferably 0.4% by weight or less, particularly preferably 0 to 0.3% by weight,
If the oxygen content is more than 0.4% by weight, metallic silicon as a raw material may adhere to the reaction furnace and cause clogging of the exhaust pipe. Further, the carbon content is preferably less than 1% by weight, particularly preferably 0 to 0.8% by weight. If the carbon content exceeds 1% by weight, the reactivity deteriorates.

The low oxygen porous silicon granules of the present invention can be suitably used as a raw material (nitriding raw material) in the production of silicon nitride by the direct nitriding method. In this case, as a method for producing silicon nitride using this granulated product,
There is no particular limitation except that this granulated material is used as the nitriding raw material, and a known method can be adopted. For example, a nitriding reaction is carried out in a rotary furnace or a fluidized bed reactor in a nitrogen atmosphere containing a certain amount of hydrogen at a temperature of 1150 to 1400 ° C. for 3 to 10 hours. Adheres to the inside of the reaction tube and does not cause fluctuations in the internal temperature due to blockage of the discharge tube or instability of the flow, and the obtained silicon nitride has a high reaction rate and a high ratio of α-type silicon nitride. Is to have.

The low oxygen porous silicon granule of the present invention is useful as a raw material for nitriding reaction, but its use is not limited to this.

[0025]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 and 2] 5 kg of metal silicon powder having an average particle diameter of 5 μm and an oxygen content of 0.6% by weight and carbon powder having a specific surface area of 50 m ² / g were dry mixed in a 10 L Henschel mixer. Then, there is a P concentration of 10% by weight.
1 kg of a VA aqueous solution was added, and the mixture was further mixed for 3 minutes, and granulated to an average particle diameter of 0.3 mm. The obtained granulated product was dried at 150 ° C. for 20 hours under nitrogen ventilation. The dried product was heat-treated at 1350 ° C. for 2 hours in an argon stream using a box furnace. The amount of oxygen, the amount of carbon, the specific surface area, the pore size mode, and the average particle size of the obtained granulated product were measured. The results are shown in Table 1.

[Comparative Examples 1 and 2] According to Examples 1 and 2, only the carbon addition rate was 0% by weight (Comparative Example 1), 5% by weight.
The physical properties of the obtained granulated product were measured in the same manner as (Comparative Example 2). The results are shown in Table 1.

[Comparative Example 3] In accordance with Examples 1 and 2, the heating temperature of the nitriding reaction was set to 1240 ° C., and the physical properties of the obtained granulated product were measured in the same manner. The results are shown in Table 1.

[Comparative Example 4] In accordance with Examples 1 and 2, only the heating time of the nitriding reaction was set to 20 minutes, and the physical properties of the obtained granulated product were measured in the same manner. The results are shown in Table 1.

[Comparative Example 5] In accordance with Examples 1 and 2, the average particle diameter of the metal silicon powder was 15 μm and the oxygen content was 0.1.
The physical properties of the obtained granulated product were measured in the same manner by using 5% by weight. The results are shown in Table 1.

[0031]

[Table 1]

For Examples 1 and 2 and Comparative Examples 1 and 2, a mercury pore meter (POROUS MATERIALS) was used.
INC. (Manufactured by the company). Figure 1 shows the results
~ 4.

Next, 10 g of the obtained granulated product was charged into an alumina boat, and a nitriding reaction was carried out by maintaining the temperature of 1250 ° C. for 5 hours in a tubular furnace in an atmosphere of nitrogen containing 15% by weight of hydrogen. It was With respect to the obtained silicon nitride, the nitriding reaction rate, the adhesion state in the furnace at the time of nitriding, and the ratio of α-type silicon nitride were examined. Table 2 shows the results.

[0034]

[Table 2]

[0035]

The low oxygen porous silicon granules of the present invention are
When the nitriding reaction is carried out in a rotary furnace or a fluidized bed reactor, metal silicon powder does not adhere to the reaction tube during nitriding, the reaction rate is improved, and high-quality α-type silicon nitride can be produced at a high rate. Further, according to the production method of the present invention, such a low-oxygen porous silicon granule can be produced easily and reliably.

[Brief description of drawings]

FIG. 1 is a graph showing a pore distribution by a mercury porosimeter of Example 1 of the present invention.

FIG. 2 is a graph showing pore distribution by a mercury porosimeter of Example 2 of the present invention.

FIG. 3 is a graph showing the pore size distribution of the mercury porosimeter of Comparative Example 1 of the present invention.

FIG. 4 is a graph showing the pore size distribution of the mercury porosimeter of Comparative Example 2 of the present invention.

Claims (2)

[Claims] 1. An average particle diameter of 0.2 to 10 obtained by granulating metal silicon powder having an average particle diameter of 4 μm or more and 10 μm or less.
mm metal silicon granules having a specific surface area of 0.5 m ² / g or more, an oxygen content of 0.4 wt% or less, a carbon content of less than 1 wt%, and a pore diameter of Mode is 1
A low-oxygen porous silicon granule characterized by having a diameter of from 1 μm to 2 μm. 2. To a metal silicon powder having an average particle size of 4 μm or more and 10 μm or less, 0.3% by weight or more and less than 5% by weight of carbon powder with respect to the total amount of the metal silicon powder, and an organic binder are added. , The granulated product obtained by mixing and granulating it under an inert atmosphere excluding nitrogen,
A method for producing a low-oxygen porous silicon granulated product, which comprises performing heat treatment in a temperature range of 1250 ° C. or more and 1400 ° C. or less for 0.5 hours or more and 5 hours or less.