JPH0137324B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing silicon carbide (hereinafter referred to as SiC). For more details, please refer to B and/or
Alternatively, the present invention relates to a method for producing easily sinterable SiC powder containing Al.

SiC sintered bodies have high hardness and strength, excellent heat resistance, and are chemically stable, so they are widely used in wear-resistant mechanical parts, structural materials, heat-resistant materials, etc.

SiC powder has two crystal forms: α and β.

Conventional technology Conventionally known methods for producing SiC powder include (1) reaction of SiO ₂ and C, (2) reaction of Si and C, and (3) gas phase synthesis from Si compounds and hydrocarbons. However, it is industrially produced by the method (1) above. This is due to one of the following reactions at high temperatures.

SiO ₂ +3C→SiC+2CO(g) (1) SiO ₂ +C→SiO(g)+CO(g) SiO(g)+2C→SiC+CO(g) (2) However, (g) represents a gaseous substance.

Since the reaction (2) is a non-uniform solid-gas reaction, it is difficult to obtain a homogeneous powder with uniform particle size. Therefore, the reaction (1) above is used, but in order to promote the reaction (1), it is necessary to uniformly mix SiO ₂ and C.

High-purity SiC powder cannot be sintered, and additives are required for sintering. In particular, C, B, and Al are effective sintering aids. It is desirable that the additives be uniformly mixed or dissolved in the powder. For this purpose, a method of containing B and Al when synthesizing SiC powder was proposed in JP-A-55-20268.
This is a method in which solid silicon raw materials, carbon raw materials, B raw materials, and Al raw materials are mixed and heat treated to obtain SiC powder containing B and Al. However, this method only physically mixes the raw material powder for SiC powder synthesis, and it is not possible to obtain a molecularly homogeneous state.
During SiC synthesis, the reaction (2) above occurs to a considerable extent, and Al
However, it has the disadvantage that it is difficult to obtain fine SiC powder with uniform particle size, and pulverization is required during sintering.

Purpose of the Invention The present invention was made to solve this problem, and its purpose is to create a material containing B and Al, which has a uniform and minute particle size, and which can be used for sintering without pulverization or refining treatment. The present invention provides a method for synthesizing easily sinterable SiC powder.

Structure of the Invention First, the present inventors have developed a method for producing silicon carbide powder by heating a raw material containing silicon and carbon in a non-oxidizing atmosphere, as a method for solving the drawbacks of the conventional method. Si, O and We have invented a method for producing β-type silicon carbide, which is characterized by using a precursor material containing C.

As a result, an easily sinterable β-type silicon carbide powder was obtained which had an extremely uniform and fine particle size and could be subjected to sintering without pulverization or refining treatment.

However, the products obtained by this method require the addition of a sintering aid to further improve the sinterability.

As a result of further research, the present inventors found that a liquid silicon compound and an organic compound that has a functional group and is liquid at room temperature and that generates carbon when heated, and a boron compound that is liquid or a liquid at room temperature and/or A solution or an aluminum compound that is liquid at room temperature is used to uniformly solubilize the mixture and at least a catalyst for polymerizing or crosslinking the above organic compound, thereby producing a molecularly uniform polymerization or crosslinking reaction. If a substance containing mixed Si, O, C and B and/or Al is used as a SiC precursor material, and this is used as a raw material, B will mainly be produced through the reaction (1).
It has been found that uniform fine SiC powder containing Al and/or Al can be obtained. This powder is B and Al
Even a very small amount could be subjected to sintering without pulverization and refining treatment. It was also found that sintered bodies of α and β SiC can be produced. The present invention was completed based on this knowledge.

That is, the gist of the present invention is that B and/or
In producing SiC powder containing Al, the raw materials are a silicon compound that is liquid at room temperature, an organic compound that is liquid at room temperature and has a functional group and generates carbon when heated, and a boron compound that is liquid at room temperature or in solution form. and/or Si, O, C obtained by mixing an aluminum compound that is in solution form or liquid at room temperature and a polymerization or crosslinking catalyst that uniformly dissolves at least the organic compound, and then polymerizing or crosslinking the mixed liquid. The present invention provides a method for producing easily sinterable SiC powder, characterized by using a precursor material containing B and/or Al.

Examples of the liquid silicon compound used in the present invention include (1) a silicic acid polymer obtained by acid decomposition or dealkalization of an aqueous alkali silicate solution, for example, a silicic acid polymer obtained by dealkalization of water glass;
Esters of organic compounds with OH groups and silicic acid, such as the following group of polymers obtained by trimethylsilylation of silicic acid polymers, (3) Esters of hydrolyzed silicic acid compounds and organic compounds or organometallic compounds, such as ethyl silicate Examples include.

Examples of liquid organic compounds used as carbon sources include organic compounds that have a particularly high residual carbon content and can be polymerized or crosslinked by catalysts or heating, such as phenolic resins, furan resins, polyimides, polyurethanes, polyacrylonitrile, polyvinyl alcohol, and polyvinyl acetate. Resin monomers and prepolymers are preferred, and cellulose, sucrose, pitch, tar, and the like may also be used.

The liquid boron compound may be a solution of a boron compound such as H ₃ BO ₃ , BP, or a liquid organic boron compound such as borate ester B(OC ₂ H ₅ ) ₃ ,
etc.

Examples of the liquid aluminum compound include solutions of aluminum compounds, such as solutions of AlCl ₃ and Al(OH) ₃ , and liquid organic aluminum compounds, such as aluminum isopropoxide [(CH ₃ ) ₂ CH ₂ O] ₃ Al. can give.

The mixing ratio of the liquid silicon compound and the liquid organic compound as a carbon source is such that the atomic ratio of C and Si is 1<C/
It is preferable that Si<10, preferably C/Si3. When C remains in the synthesized precursor material, C/Si>3.

The mixing amount of B and/or Al is the SiC to be synthesized.
It can be selected arbitrarily depending on the amount to be contained in the powder, but as a powder for sintering, the atomic weight ratio is 0.002 < (Al+
B)/Si<0.05 is preferable.

The above mixture and a polymerization or crosslinking catalyst are dissolved, and a polymerization or crosslinking reaction is performed to obtain a solid. If the viscosity of a liquid silicon compound or a liquid organic compound as a carbon source is so high that uniform mixing is difficult, the viscosity may be lowered by using an appropriate solvent.

Polymerization or crosslinking reaction occurs between (1) the functional groups of an organic compound having a functional group and a liquid silicon compound, a liquid boron compound, or a liquid aluminum compound, and (2) between the functional groups of a liquid organic compound having a functional group. It will be done.

For example, polymerization reaction of phenolic resin (1) (2) Reaction between silanol groups in silicic acid polymers and methylol groups of organic compounds (3) Reaction between hydroxyl groups in aluminum or boron compounds and methylol groups in organic compounds A solid is formed by any or all of the reactions.

The catalyst may be selected from catalysts used in polymerization or crosslinking reactions, and includes, for example, mineral acids such as hydrochloric acid, sulfuric acid, and boric acid, alkalis such as sodium ethylate, organic peroxides, and organic sulfonic acids.

When a polymerization or crosslinking catalyst is mixed with the mixture in the above ratio and the cured mixture is treated at 600 to 1000°C in an inert gas atmosphere, Si, O, C and B
and/or a homogeneous amorphous material containing Al is obtained.

This amorphous material is heated in a non-oxidizing atmosphere such as vacuum, nitrogen, helium, or argon at a temperature of 1400 to 2000
SiC is obtained by heat treatment at ℃. The heat treatment temperature is preferably about 1,600 to 1,800°C; if it is lower than 1,400°C, the reaction is slow, and since a temperature exceeding 2,000°C is not required, such a temperature is economically disadvantageous.

The synthesized SiC powder has a fine and uniform particle size distribution, and is an easily sinterable SiC powder that can be subjected to sintering without pulverization or refining treatment. In addition, the crystal form of the powder is β (3C) type for SiC powder containing B,
Powders containing a large amount of Al tend to be in the 4H α form. All or part of the added B or Al is dissolved in SiC. The amount of solid solution depends on the synthesis temperature.

Effects of the Invention According to the method of the present invention, SiC powder containing a sintering aid having a uniform and fine particle size can be obtained, and sintering as it is without the need for pulverization or refining treatment as in conventional methods. It can be served at the end. Furthermore, α and β-SiC sintered bodies can also be manufactured, with excellent effects.

Example 1 Ethyl silicate containing 41% by weight of SiO ₂ as a liquid silicon compound, resol type phenolic resin with a residual carbon content of 40% as a liquid organic compound with a functional group, and boric acid ester B as a liquid boron compound
(OC ₂ H ₅ ) ₃ was used.

Ethyl silicate 61.6% by weight, phenolic resin
A mixed solution of 37.6% by weight and 0.7% by weight of boric acid ester was cured under an acid catalyst to obtain a transparent resinous solid. This was heated at a heating rate of 10℃/min under a nitrogen atmosphere.
Heated to 1000℃. The obtained solid was a homogeneous and dense solid, and the content ratio of C and Si was determined from the residual carbon ratio as C/Si=
It is considered to be 3. The powder X-ray diagram of this solid was as shown in FIG. In the powder X-ray diffraction results, only the broad diffraction characteristic of amorphous carbon-based materials appeared, and no other diffraction lines were detected. From this, the solid is Si,
It can be seen that it is an amorphous solid containing O, C and B. Furthermore, this was heated at a heating rate of 30% under an argon atmosphere.
The mixture was heated to 1800°C at a rate of °C/min and held for 30 minutes to obtain β-SiC powder containing B. The properties of the powder were as follows.

True specific gravity 3.19-3.21g/cm ³ crystal form Cubic (3C) single phase average particle size 0.08μm Specific surface area 15m ² /g B content 0.28% by weight Impurities Al 0.03% by weight Fe 0.03 〃 C 0.5 〃 Color Pale yellow The powder X-ray diffraction pattern was as shown in Figure 2, and the shape of the powder was as shown in Figure 3. It can be seen from Figure 2 that it is β-SiC containing no α phase, and from Figure 3 that it is a fine powder with a uniform particle size. 2% by weight of carbon was added to this powder and molded in argon gas.
Normal pressure sintering was performed at 2100℃ and pressure sintering was performed at 20MPa.
Pressure sintering has a density of 3.10g/cm ³ , and pressure sintering has a density of 3.10g/cm 3 .
It was densified to 3.15g/cm ³ .

Example 2 The same ethyl silicate, phenolic resin, and aluminum hydroxide as in Example 1 were used. 61.4% by weight of ethyl silicate, 37.6% by weight of phenol resin, and 1.0% by weight of aluminum hydroxide were uniformly dissolved under an acid catalyst and then cured to obtain a homogeneous resinous solid. This was treated in the same manner as in Example 1 to obtain α-SiC powder containing Al. The properties of the powder were as shown below.

True specific gravity 3.19-3.21g/cm ³ Crystal form α (4H) single phase average particle size 0.20μm Specific surface area 8.3m ² /g Al content 2.0% by weight Impurities Fe 0.03% by weight C 0.04 〃 Color Blue-green X-ray of powder The diffraction pattern is shown in FIG. from now
It can be seen that it is 4H type α-SiC. The particle shape was the same as in Example 1. To the obtained powder, 2% by weight of carbon was added and pressure sintered at 20 MPa and 2100°C, resulting in a powder of 3.11 g/cm ³ .

Example 3 Water glass (silicic acid No. 4) was dealkalized and extracted using hydrochloric acid and tetrahydrofuran by a known method to obtain a liquid silicic acid compound. 50g of this liquid silicic acid compound converted to silica, 90g of phenol resin
g, 1.3 g of boric acid ester and 1.2 g of aluminum isopropoxide Al(OCH ₂ CH ₂ CH ₃ ) ₃ were cured under an acid catalyst to obtain a resinous solid. This was heat treated at 1000°C and 1800°C in the same manner as in Example 1,
SiC powder containing Al and B was obtained. The properties of the powder were as shown below.

True specific gravity 3.19-3.21 g/cm ³ crystal form Mixed phase of β (3C) and α (4H) Average particle size 0.15 μm Specific surface area 9.6 m ² /g Al content 0.38 wt% B content 0.20 wt% C content 2.1% by weight Color: Gray The obtained powder was sintered under pressure at 20MPa and 2150°C, and was densified to a density of 3.07g/cm ³ .

Comparative example: To high-purity amorphous silica fine powder and carbon black (molar ratio 1:3.5), 0.5% by weight of boric acid and 1% by weight of γ-alumina fine powder were added to the total amount of both. Mixed and placed in a graphite container.
This was heated at 1800°C for 30 minutes under an argon gas stream to synthesize SiC. The obtained powder was as follows.

True specific gravity 3.20-3.21g/cm ^2Crystal form 3C and 4H Average particle size 2.6μm Specific surface area 4.1m ² /g B content 0.13% by weight Al content 0.16% by weight Color black This powder is sintered due to its large particle size. I couldn't tie it. Therefore, it was pulverized in an iron ball mill, decarburized, and purified. As a result, the particle size was 1.0 μm or less, and pressure sintering was performed in the same manner as in Example 1 to obtain a sintered body with a density of 3.12 g/cm ³ .

As is clear from the examples and comparative examples, according to the method of the present invention, easily sinterable fine powder containing Al and/or B can be obtained, whereas in the method of the comparative example, the particle size of the SiC powder is Because of the large size, pulverization is necessary for sintering. In the present invention, we used SiC raw materials that were molecularly uniformly mixed, so fine powder
SiC is synthesized.

[Brief explanation of drawings]

Figure 1 shows the powder X-ray diffraction pattern of the SiC precursor material treated at 1000°C used in Example 1 of the present invention;
The figure shows an X-ray diffraction pattern of the SiC powder containing B obtained in Example 1, Fig. 3 shows an SEM photograph of the same powder, and Fig. 4 shows an X-ray diffraction pattern of the SiC powder obtained in Example 2. .

Claims (1)

[Claims] 1. In producing silicon carbide powder containing boron and/or aluminum by heating raw materials containing silicon and carbon and boron and/or aluminum in a non-oxidizing atmosphere, As raw materials, a silicon compound that is liquid at room temperature, an organic compound that is liquid at room temperature that has a functional group and generates carbon when heated, and a boron compound that is in solution or liquid at room temperature and/or a solution or liquid at room temperature. An aluminum compound is mixed with a polymerization or crosslinking catalyst that uniformly dissolves at least the organic compound, and the mixture contains silicon, oxygen, carbon, boron, and/or aluminum obtained by a polymerization or crosslinking reaction. A method for producing easily sinterable silicon carbide powder, characterized by using a precursor substance. 2. The method for producing easily sinterable silicon carbide powder according to claim 1, wherein the silicon compound is obtained by acid decomposition or dealkalization of an aqueous alkali silicate solution. 3. Claim 1, wherein the silicon compound is an ester of an organic compound having a hydroxyl group and silicic acid.
A method for producing easily sinterable silicon carbide powder as described in . 4. The method for producing easily sinterable silicon carbide powder according to claim 1, wherein the silicon compound is an ester obtained by reacting a hydrolyzable silicon compound with an organic compound or an organometallic compound. 5. Easily sinterable carbonization according to claim 1, wherein the polymerization or crosslinking reaction is a polymerization reaction or crosslinking reaction using the catalyst of an organic compound that has a functional group and is liquid at room temperature and generates carbon when heated. Method for manufacturing silicon powder. 6. A patent claim in which the polymerization or crosslinking reaction is a polymerization reaction or crosslinking reaction using the catalyst of an organic compound that has a functional group with the silicon compound, boron compound, or aluminum compound and is liquid at room temperature and generates carbon when heated. A method for producing easily sinterable silicon carbide powder according to item 1.