JPH0142886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing silicon carbide (hereinafter referred to as SiC). For more details, see 3C (β) in fine detail.
This invention relates to a method for producing single-phase easily sinterable β-type SiC powder.

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.
Conventionally, methods for producing SiC powder include (1) SiO ₂ and C
reaction, (2) reaction of Si and C, and (3) gas phase synthesis from Si compounds and hydrocarbons, but industrially it is produced by the method described in (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) above is a non-uniform solid-gas reaction, it is difficult to obtain a homogeneous powder with uniform particle size, and
A small amount of 2H α-SiC coexists. This α-SiC
promotes grain growth during sintering and is harmful to densification. 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, and various mixing methods have been proposed in the past. ing.

For example, a method of using a silicic acid solution instead of the solid silica powder conventionally used as a raw material and processing it together with a carbonaceous powder or a carbon precursor material, that is, by mixing in the liquid phase, a homogeneous mixture can be obtained. The mixture is heated in a non-oxidizing atmosphere to
Method for manufacturing SiC (Japanese Unexamined Patent Publication No. 1988-88019)
It has been known.

However, although this method yields a physically homogeneous product, silica sol is generated and molecularly non-uniform, and when SiC is manufactured, β-type SiC
There was a problem in that the powder contained several percent or more of the 2H α-SiC phase, making it impossible to obtain single-phase β-type SiC.

The present invention was made to solve this problem, and its purpose is to provide a method for producing single-phase β-type SiC by obtaining raw materials that are molecularly uniformly mixed.

As a result of research to achieve the above object, the present inventors have found that 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 at least the organic compound is uniformly mixed with the organic compound. A polymerization or crosslinking reaction is caused by uniformly mixing them using a polymerization or crosslinking catalyst that dissolves, to obtain a solid containing Si, O and C, which is then used as a precursor material for obtaining SiC, i.e. discovered that single-phase β-type SiC can be obtained when used as a raw material,
The present invention was completed based on this knowledge.

In addition, if the viscosity of the silicon compound or organic compound that is liquid at room temperature is high and uniform mixing is not easy, the viscosity may be lowered using an appropriate solvent.

That is, the gist of the present invention is to provide a method for obtaining a single-phase β-type silicon carbide powder by heating a raw material containing silicon and carbon in a non-oxidizing atmosphere, wherein the raw material is a silicon compound that is liquid at room temperature. A liquid containing an organic compound that is liquid at room temperature and that has a functional group and generates carbon when heated, and a polymerization or crosslinking catalyst that uniformly dissolves at least the organic compound is dissolved in a molecular form by a chemical reaction of polymerization or crosslinking reaction. The present invention provides a method for producing single-phase β-type silicon carbide powder, characterized by using a precursor material containing silicon, oxygen, and carbon obtained by uniformly mixing the powder with silicon carbide.

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 hydrolyzable 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 organic compound having a functional group and a polymerization or crosslinking catalyst is dissolved in the liquid silicon compound, and a polymerization or crosslinking reaction is caused by heating to obtain a solid.

The polymerization or crosslinking reaction is carried out between (1) the functional group of the organic compound having a functional group and the liquid silicon compound, and (2) the functional group of the liquid organic compound having the functional group.

For example, polymerization reaction of phenolic resin (1) (2) Reaction between silanol groups in silicic acid polymers and methylol groups of organic compounds A solid is formed by the reaction, etc.

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.

The mixing ratio of the liquid silicon compound and the liquid organic compound having a functional group 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.

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, a homogeneous amorphous material containing Si, O, and C is obtained. It will be done.

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 around 1,600°C; if it is lower than 1,400°C, the reaction is slow, and since a temperature exceeding 200°C is not required, such a temperature is economically disadvantageous.

The obtained SiC powder was fine and had a uniform particle size distribution, and as a result of X-ray analysis, it was found to be β-SiC powder containing no α phase such as 2H.

Furthermore, when the molar ratio of C/Si is set to 3 in the raw material, pure β-type SiC powder with no residual carbon can be obtained, and no decarburization purification treatment is required.

Example 1 Ethyl silicate containing 41% by weight of SiO ₂ was used as a liquid silicon compound, and a resol type phenolic resin with a residual carbon content of 40% was used as a liquid organic compound having a functional group.

A mixed solution of 62% by weight of ethyl silicate and 38% by weight of the phenolic resin was cured under an acid catalyst to obtain a transparent resinous solid. This was heated to 1000°C at a temperature increase rate of 10°C/min in a room atmosphere. The obtained solid was a homogeneous and dense solid, and the content of C and Si was considered to be C/Si=3 based on the residual carbon ratio. The powder X-ray diffraction diagram of this solid was as shown in FIG. powder
In line diffraction analysis, only a line with a width characteristic of amorphous carbon-based materials appeared, and no other diffraction lines were detected. This shows that the solid is an amorphous solid containing Si, O, and C. Furthermore, this was heated to 1600℃ at a temperature increase rate of 30℃/min in an argon atmosphere.
After holding for 4 hours, β-SiC powder was obtained. 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 0.15μm Impurities Al0.03% by weight Fe0.03 〃 C0.5 〃 Color Yellow Also, the powder X-ray diffraction chart of the powder is Figure 2,
The shape of the powder was as shown in FIG. From Figure 2
Be a β-type SiC that does not contain α-phase SiC such as 2H,
Further, from FIG. 3, it can be seen that the powder is a fine powder with a uniform particle size.

Comparative Example 1 (Example 4 of JP-A-57-88019) A water glass No. 3 diluted aqueous solution (concentration: SiO ₂ :8% by weight) was mixed with cation exchange resin Amberlite 200C.
(H ⁺ form) was used to remove sodium in a column filled with silicic acid solution (concentration: SiO ₂ min, 5% by weight) and 20 g of dextran aqueous solution (containing 4 g of dextran).
was added, mixed and spray dried. The obtained white powder was heated at 1440℃ for 4 hours in a helium atmosphere.
SiC powder was obtained.

The obtained SiC powder has a particle size of 0.1~0.2μ and a crystalline phase.
It was 90% 3C and 10% SiC.

As is clear from the examples and comparative examples, according to the method of the present invention, a high-purity single-phase β-type SiC powder is obtained, whereas in the method of the comparative example, 2H α-phase SiC is added to the crystal phase. It will be a mixture of. this
2H α-phase SiC is easily transformed at high temperatures, promotes grain growth during sintering, and inhibits densification.

The reason why 2H α-phase SiC is not mixed in the method of the present invention is considered to be because molecularly homogeneous mixing is achieved through polymerization or crosslinking reaction.

Example 2 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. This, a resol type phenolic resin, and an acid catalyst were dissolved in the presence of alcohol, and heated to solidify. The mixing ratio of liquid silicic acid compound and phenolic resin was 47/53 by weight. The obtained resinous solid was treated in the same manner as in Example 1.
It was heated to 1000°C and further heat treated at 1600°C.
The solid obtained after treatment at 1000°C was homogeneous amorphous consisting of Si, C and O, and was C/Si3. The β-SiC powder obtained after the 1600°C treatment is a fine powder, and the powder X-ray diffraction and powder shape are the same as in Example 1. The properties of the powder were as follows.

True specific gravity 3.19-3.21g/cm ^3Crystal form Cubic (3C) single-phase grain Diameter 0.15-0.20μm Impurities Al0.04% by weight Fe0.02 〃 Na0.12 〃 C0.6 〃 Color Yellow Example 3 Water glass ( Silicic acid No. 4) was extracted with hydrochloric acid and tetrahydrofuran, and trimethylsilylated by a known method to obtain a liquid silicic acid compound. This, a resol type phenolic resin, and an acid catalyst were dissolved and cured to form a homogeneous solid. The mixing weight ratio of liquid silicic acid compound and phenolic resin is 54/46. Thereafter, the same heat treatment as in Examples 1 and 2 was performed.
The obtained powder was a single-phase β-SiC fine powder. In this example, since the phenolic resin serving as the carbon source was added in excess, the resulting β-SiC powder contained about 3% free carbon. Since it is necessary to add carbon to sinter SiC powder, the inclusion of free carbon in the powder is effective for sintering. The properties of the powder were as follows.

True specific gravity 3.19 to 3.20 g/cm ³ Crystal form Cubic (3C) single phase grain Size 0.15 to 0.20 μm Impurities Al 0.03% by weight Fe 0.02 〃 Na 0.10% by weight Free carbon 3.0% by weight As described above, the method of the present invention According to the method, a uniform fine powder of β-type SiC without 2H α-phase SiC can be easily obtained. Therefore, this crystal body has the effect of becoming dense without grain growth during sintering.

[Brief explanation of drawings]

Figure 1 shows the powder X-ray diffraction pattern (amorphous) of the SiC precursor material treated at 1000°C used in the method of the present invention, and Figure 2 shows the β type produced by the method of the present invention.
Powder X-ray diffraction pattern of SiC powder (β-type SiC single phase),
FIG. 3 is a SEM photograph of the particle structure of β-type SiC powder produced by the method of the present invention.

Claims (1)

[Claims] 1. A method for obtaining a single-phase β-type silicon carbide powder by heating a raw material containing silicon and carbon in a non-oxidizing atmosphere, wherein the raw material is a silicon compound that is liquid at room temperature; , a liquid containing an organic compound that is liquid at room temperature and that has a functional group and generates carbon when heated, and a polymerization or crosslinking catalyst that uniformly dissolves at least the organic compound is molecularly dissolved by a chemical reaction of polymerization or crosslinking reaction. A method for producing single-phase β-type silicon carbide powder, characterized by using a precursor material containing silicon, oxygen, and carbon obtained by uniformly mixing the same. 2. The method for producing a single-phase β-type 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 a single-phase β-type silicon carbide powder as described in 1. 4. The method for producing a single-phase β-type 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. The single-phase β type 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 producing silicon carbide powder. 6. The unit 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 with the silicon compound and is liquid at room temperature and generates carbon when heated. A method for producing phase β-type silicon carbide powder.