JPH04276000A - Method for manufacturing silicon nitride whiskers - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for efficiently producing silicon nitride whiskers of good quality using a raw material system with a homogeneous composite composition.

0002

[Prior Art] Whiskers composed of acicular single crystals of silicon nitride have excellent performance characteristics in terms of strength, elastic modulus, heat resistance, chemical stability, etc., and are used in plastics, metals, alloys, etc. It is also useful as a composite reinforcing material for ceramics.

Conventionally, various methods have been known for producing silicon nitride whiskers, but they can be broadly classified into gas phase methods and solid phase methods. Among these methods, the gas phase method is, for example, as described in JP-A-56-100115, in which silicon monoxide gas generated from a silicon-containing raw material is led together with an inert gas into a separate chamber, where it is reacted with nitrogen gas. Although it consists of a process of converting it into silicon nitride, the production yield is low and it is not suitable for industrial production means. On the other hand, the solid phase method, in which silicon source raw material powder and carbonaceous material powder are mixed and reacted by heating in a nitrogen gas atmosphere, has a higher production yield than the gas phase method; Microscopic homogeneous dispersion and bulky mixing state of the powder are important factors for obtaining silicon nitride whiskers with good quality without shot, bending, curling, etc. However, in conventional technology, the silicon source raw material powder and the carbonaceous material powder are generally dry mixed by mechanical stirring, which requires strict stirring conditions and long mixing times to obtain a sufficiently uniform dispersion state. year,
Further, there is a problem that the formed homogeneous dispersion state causes segregation during the subsequent handling process and becomes inhomogeneous.

In order to solve the above problem, decomposable silicon compounds such as silicon tetrachloride and trichlorosilane and hydrocarbon compounds such as methanol, benzene, kerosene, and creosote oil are introduced into hot gas containing water vapor. A mixed aerosol containing silicon oxide and elemental carbon is generated, and this dispersoid is collected to produce a mixed raw material with a bulk specific gravity of 0.2 g/cc or less, high uniformity, and fine constituent particles. A technique for obtaining the system (Japanese Unexamined Patent Publication No. 121198/1982) has been proposed. This gas-phase pyrolysis method makes it possible to form a composite raw material system with good dispersibility. Increasing complexity and operational complexity are unavoidable.

[0005] The present inventors have discovered that by introducing a water glass aqueous solution and a hydrocarbon into a high-temperature combustion gas stream, it is possible to obtain a homogeneously dispersed composite composition raw material with good operability without the above-mentioned problems. Then, a water glass aqueous solution and hydrocarbons are sprayed from the same or different positions into a high-temperature combustion gas flow flowing in a closed cylindrical furnace, and the glass fine particle intermediates and hydrocarbons produced by dealkalization of water glass are thermally decomposed. The produced carbon black is retained in a furnace to prepare a spherical silica/carbon black composite composition raw material with a weight ratio of SiO2:C of 100:60 to 200, and the spherical silica/carbon black composite raw material is heated in a nitrogen gas atmosphere at a ratio of 1300 to 200. 15
We have developed a method for producing silicon nitride whiskers by carrying out a heating reaction at a temperature of 0.000C and have already proposed it in Japanese Patent Application No. 331335/1999.

[0006]

[Problems to be Solved by the Invention] According to the above-mentioned prior art, SiO2 and carbon black co-produced have a composite composition in which they are homogeneously dispersed, and the properties and mixing ratio of the raw material system are suitable for producing silicon nitride whiskers. It becomes possible to prepare the product in a suitable state. However, this method uses a process in which the metal catalyst components necessary for whisker growth are added and mixed into the composite raw material afterward, which makes the operating procedure complicated and also causes micro-homogeneous dispersion and bulkiness of the composite raw material during addition and mixing. There was a risk of damage to the condition.

An object of the present invention is to improve the prior art in order to solve these difficulties, and to introduce a metal catalyst into a high-temperature combustion gas stream together with a water glass solution and a hydrocarbon to form a three-component mixture containing metal catalyst fine particles. Prepare a composite composition raw material of the system,
Therefore, it is an object of the present invention to provide a method for producing silicon nitride whiskers of consistently high quality and stable quality without a secondary addition step of a metal catalyst.

[0008]

[Means for Solving the Problems] A method for producing silicon nitride whiskers according to the present invention to achieve the above object includes adding a water glass aqueous solution, a hydrocarbon, and a metal catalyst to a high-temperature combustion gas flow flowing in a closed cylindrical furnace. A solution or suspension of is sprayed from the same or a different location to collect fine glass particle intermediates produced by dealkalization of an aqueous water glass solution, carbon black produced by thermal decomposition of hydrocarbons, and thermally decomposed particles of metal catalysts. A three-component composite raw material consisting of spherical silica/carbon black/metal catalyst fine particles having a composition containing a metal catalyst at a weight ratio of SiO2:C of 100:60 to 200 is prepared by remaining in a furnace, and the composite raw material is The structural feature is that the reaction is carried out by heating in a temperature range of 1300 to 1500°C in a nitrogen gas atmosphere.

The high-temperature combustion gas flow flowing through the closed cylindrical furnace is formed by injecting fuel hydrocarbons together with an oxygen-containing air stream into the furnace head and completely combusting them. As the apparatus, a structural furnace having the same design as a carbon black generating furnace having a configuration in which a head combustion chamber and a cylindrical reaction chamber are connected can be effectively applied. As the fuel oil, oily hydrocarbons commonly used for producing carbon black, such as light oil, heavy oil, creosote oil, and ethylene bottom oil, can be used, but propane, Preferably, gaseous hydrocarbons such as methane, butane, etc. are used. The temperature inside the furnace needs to be maintained at a high temperature level of 1300° C. or higher at least at the position where the water glass aqueous solution is sprayed.

The water glass aqueous solution may be, for example, commercially available industrial water glass dissolved in water to an appropriate viscosity. Spray into the furnace using the spray nozzle. The concentration of water glass solution is 20-80%
It is preferable that the amount is within this range, and if it is out of this range, disadvantageous results such as a long time required for dealkalization and difficulty in spray introduction will occur. Hydrocarbons that serve as raw materials for producing carbon black include, for example, styrene monomer,
Benzene and the like are preferably used. Metal catalysts include compounds of transition metals such as iron, nickel, and cobalt;
Alkali metal compounds such as sodium, potassium, lithium, etc. or magnesium, calcium, strontium,
One or more alkaline earth metal compounds such as barium are used and are used as a solution or suspension dissolved or dispersed in water or other liquid medium. These hydrocarbon and metal-based catalyst solutions or suspensions are sprayed into the furnace from the same or different location as the water glass aqueous solution. When spraying from the same position, the three components are mixed or suspended and sprayed from the same spray nozzle, and when introduced from different positions, each component or two components are sprayed through separate spray nozzles. and inject into the furnace.

[0011] The water glass aqueous solution sprayed into the furnace is rapidly thermally decomposed to cause a dealkalization reaction, and is converted into a highly pure siliceous fine glass particle intermediate. At the same time, solutions or suspensions of hydrocarbons and metal-based catalysts also undergo thermal decomposition in the furnace and are converted into fine particles of carbon black and metal catalyst, respectively. When these components continue to remain in the high-temperature furnace for a certain period of time, the glass fine particle intermediate becomes spheroidal and further causes a foaming phenomenon to form micro hollow balloons with a particle size of 1 μm or less, and the resulting carbon black and metal catalyst fine particles and micro Spherical silica homogeneously dispersed in carbon black/
A composite raw material having a composition consisting of metal catalyst fine particles is prepared.

In the above process, the weight ratio of SiO2:C can be adjusted to a desired ratio by controlling the amount of hydrocarbon supplied into the furnace, and the SiO2:C weight ratio can be adjusted to a desired ratio by controlling the solution concentration or suspension concentration of the metal catalyst. The amount of catalyst for each component can be adjusted, the properties of spherical silica can be adjusted to a solid or hollow balloon structure by controlling the residence time in the furnace, and carbon black can be controlled by controlling conditions such as the amount of hydrocarbon supplied and the temperature inside the furnace. It becomes possible to adjust the characteristics.

[0013] The component ratio of the composite raw material must be adjusted so that the weight ratio of SiO2:C is in the range of 100:60 to 200, and the fine metal catalyst powder is included in this. S
If the ratio of C to 100 parts by weight of iO2 is less than 60 parts by weight, the formation of voids necessary for the growth of silicon nitride whiskers will be insufficient, and the conversion reaction to SiO will not proceed smoothly. If the amount exceeds parts by weight, the production yield of silicon nitride whiskers will decrease, and a large amount of unreacted carbon black will remain, making the removal process complicated.

[0014] Suitable raw material properties for producing silicon nitride whiskers include spherical silica constituting the composite raw material having a hollow balloon structure, carbon black particle properties having a nitrogen adsorption specific surface area (N2SA) of 90 m2/g or more, and DBP oil absorption. Amount: 100 ml/100 g or more, iodine adsorption amount: 10
It should be set at 0 mg/g or higher. In this property, since the spherical silica has a hollow balloon structure, the density difference with carbon black is reduced, and the ability to maintain a homogeneously dispersed structure is improved.Furthermore, based on the large specific surface area and high structure of carbon black, Bulky composite composition is advantageous for the formation of silicon nitride whiskers
Become an organization.

[0015] The composite raw material consisting of spherical silica/carbon black/metallic catalyst fine particles prepared in the above process is
The reaction is carried out by heating in a temperature range of 1300 to 1500°C in a nitrogen gas atmosphere. After the reaction, remaining unreacted carbon black components are removed by combustion treatment in the atmosphere.

The silicon nitride whiskers produced in this manner are α-type acicular single crystals without lattice defects, with a diameter of about 1.5 μm, an aspect ratio of 30 to 70, and a shot, bend, or curl shape. It has high quality properties.

[0017]

[Operation] The three-component composite composition constituting the raw material of the present invention achieves homogeneity with excellent operability through dealkalization of an aqueous water glass solution and thermal decomposition of a solution or suspension of hydrocarbons and metal catalysts. It can be prepared as a composite raw material with a desired dispersion state, desired composition ratio, and property structure. This eliminates the need for a secondary addition and mixing step of metal catalyst powder, and the dispersion form of the catalyst also becomes microscopic.

[0018] The raw material composition is the weight ratio of SiO2:C.
By adjusting the ratio of 100:60 to 200 so that the metal catalyst fine particles are uniformly dispersed, it becomes possible to produce high quality silicon nitride whiskers without shot contamination or deformation. A particularly suitable raw material composition is that the spherical silica has a hollow balloon structure and the carbon black has a nitrogen adsorption specific surface area (NSA).
)90m2/g or more, DBP oil absorption 100ml/10
0g, and an iodine adsorption amount of 100mg/g or more. In this case, the raw material structure is a bulky structure that is advantageous for the formation of silicon nitride whiskers, and has a form with no risk of segregation. Moreover, the progress of the reaction [SiO2(
S) →SiO(G)], the intervening position of the hollow balloon functions as a growth space for silicon nitride whiskers, so the occurrence of crystal bending, curling, etc. is effectively prevented.

[0019]

[Examples] Examples of the present invention will be explained below in comparison with comparative examples. Examples 1 to 2, Comparative Examples 1 to 3 (1) Preparation of ternary composite raw materials A combustion chamber equipped with a combustion burner at the head of the furnace (diameter 200 mm)
, length 500 mm), a narrow diameter reaction chamber (diameter 80 mm, length 200 mm) and a wide diameter reaction chamber (diameter 120 mm, length 1800 mm) coaxially connected to the combustion chamber.
In a horizontal closed cylindrical furnace having the same configuration as the carbon black generating furnace, there is a spray nozzle for water glass solution located 550 mm downstream from the furnace head, and a spray nozzle 650 mm downstream from the furnace head.
Spray nozzle for metal catalyst solution in downstream position, same 800
A spray nozzle for hydrocarbon for producing carbon black was set at a downstream position of mm, and a cooling water injection nozzle for stopping the reaction was installed at a rear position of the wide-diameter reaction chamber.

The raw material components are commercially available water glass No. 3, benzene as a hydrocarbon for producing carbon black, and a pulverized mixture of calcium oxide and ferric oxide as a metal catalyst liquid at a ratio of 4:1 (weight ratio). A suspension dispersed in water was used, and propane was used as the fuel hydrocarbon. Using the above-mentioned furnace and raw material components, a composite raw material with a composition of silica/carbon black/metallic catalyst was prepared under various production conditions shown in Table 1, and the characteristics of the obtained composite raw material were compared with the production conditions. It is shown in Table 1. In addition, "CB" in Table 1
refers to "carbon black" (the same applies hereinafter).

(2) Production of silicon nitride whiskers Each of the three-component composite materials prepared as described above was placed on a carbon porous plate (porosity 65%, average pore diameter 55 μm) and kept in a nitrogen gas atmosphere. The mixture was transferred to a heated electric resistance heating furnace and subjected to a heating reaction at a temperature of 1440° C. for 2 hours. After the heating reaction, the contents were collected and heat treated in the atmosphere at a temperature of 600°C to burn off remaining unreacted carbon black components. Table 2 shows the properties of each silicon nitride whisker thus obtained.

[0022]

[0023]

From the results shown in Table 2, high quality silicon nitride whiskers with no poor properties can be obtained in the examples that meet the compositional requirements of the composite raw material according to the present invention, but in comparison where the weight ratio of SiO2:C is less than 100:60. In Examples 1 and 2, many poor properties were observed. Further, in Comparative Example 3 in which the weight ratio of C exceeds 200, the amount of residual carbon black increases, reducing operability.

Comparative Examples 4 to 5 A composite raw material having a composition of silica/carbon black was prepared under the same conditions as in Example 2 except that the catalyst dispersion was not sprayed, and calcium oxide and carbon oxide were added to the composite raw material as catalyst components. S
It was added secondarily to the amount of 5% by weight based on iO2, and thoroughly stirred and mixed using a juicer mixer. Next, the mixed raw materials were heated and reacted in a nitrogen gas atmosphere in the same manner as in Example 2 to produce silicon nitride whiskers. Table 3 shows a comparison of the properties of the obtained composite raw material and the properties of the silicon nitride whiskers produced (Comparative Example 4).

As a conventional example, silica powder with a particle size of 44 μm or less was mixed with 160% carbon black (SEAST 5H, manufactured by Tokai Carbon Co., Ltd.) and the same catalyst components as in Comparative Example 4, and mixed with a V-type mixer. The properties of silicon nitride whiskers produced using the stirred and mixed solid-phase raw materials are also listed in Table 3 (Comparative Example 5).

[0027]

[0028] In Comparative Example 4, whiskers equivalent to those in Example were produced, but the addition of catalyst to the silica/carbon black composite raw material and the operating procedure were complicated. Further, in Comparative Example 5 based on the conventional technology, bending, curling, etc. occur frequently, and the whisker properties deteriorate.

[0029]

As described above, according to the present invention, a three-component system consisting of spherical silica/carbon black/metallic catalyst fine particles in a micro homogeneous dispersion state can be obtained in a well-operated process without a secondary catalyst mixing step. By using this composite raw material, it is possible to consistently produce high quality silicon nitride whiskers. Therefore, plastics,
It is useful as a means for manufacturing reinforcing materials that compositely strengthen materials such as metals, alloys, and ceramics.

Claims (2)

[Claims] Claim 1: Dealalization of the water glass solution by spraying a water glass solution, a solution or suspension of a hydrocarbon and a metal catalyst from the same or different positions into a high temperature combustion gas stream flowing in a closed cylindrical furnace. The glass fine particle intermediate produced by
A three-component composite raw material consisting of spherical silica/carbon black/metal catalyst fine particles having a composition containing a metal catalyst with an O2:C weight ratio of 100:60 to 200 is prepared,
The composite raw material is heated at 1300 to 1500°C in a nitrogen gas atmosphere.
A method for producing silicon nitride whiskers, characterized by carrying out a heating reaction in a temperature range of . Claim 2: The spherical silica constituting the composite raw material of spherical silica/carbon black/metal catalyst fine particles has a hollow balloon structure, and the carbon black has a nitrogen adsorption specific surface area (NSA) of 90 m2/g or more and a DBP oil absorption of 1.
00 ml/100g or more, iodine adsorption amount 100 m
2. The method for producing silicon nitride whiskers according to claim 1, wherein the particle size is greater than or equal to g/g.