JPS61168515A - Production of silicon carbide - Google Patents

Abstract

PURPOSE:To obtain silicon carbide powder, by hardening a mixture of a specific silicon polymer, a solid carbonaceous material and optionally silica fine powder in the presence of a hardening catalyst and calcining the obtained solid precursor in a non-oxidizing atmosphere. CONSTITUTION:The silicon polymer of formula (R<1>-R<4> are C1-6 hydrocarbon residue; n is 1-10) is mixed homogeneously with a solid carbonaceous material (preferably e.g. finely pulverized various carbon black, petroleum coke, etc. which may be liquefied with a solvent such as ethyl alcohol), and the mixture is hardened with a hardening catalyst to obtain a precursor. The objective silicon carbide is produced by calcining the precursor in a non-oxidizing atmosphere. A part of the silicon polymer used as the first component may be replaced by fine silica powder in the synthesis of the precursor. The amount of the silica powder is selected to give the objective product having a C/Si ratio of 1<C/Si<10.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing silicon carbide (hereinafter referred to as SiC), and more particularly, to a method for producing fine and easily sinterable SiC powder. .

[Conventional technology] SiC sintered bodies have high hardness and strength.

Because it has excellent heat resistance and is chemically stable, it is widely used in wear-resistant mechanical parts, structural materials, heat-resistant materials, etc. There are two crystal forms of SiC powder, α and β, and the manufacturing method is conventional.

■　S　　method by reaction between O2 and C.

The following methods are known: (1) a method based on a reaction between Si and C, and (2) a method based on gas phase synthesis from a Si compound and a hydrocarbon. Among these methods, SiC powder is manufactured industrially by method (2), which has advantages such as inexpensive raw materials and easy reaction operations.

As the method (2) above, the synthesis method using an Acheson furnace is famous, but the SiC product obtained by this method is in the form of lumps, and it has the disadvantage that it requires long pulverization for pulverization. are doing. Therefore, in recent years, many improvements have been made to the method (1), and a method for synthesizing β-3iC fine powder by continuous production has also been proposed. This method is as follows at high temperature.
Or, it is due to the reaction of formula 11 (however, in ■, formula II, (g) represents a gaseous substance).

S io2+3C+S ic+2co (g)...■
In order to continuously produce β-3iC fine powder, research has been carried out on methods of mixing and solidifying solid siliceous raw materials and carbonaceous raw materials.
Publication No. 325 discloses that by making a solid material using a binder that can be carbonized in a high temperature range, such as pitch, and performing heat treatment at 400°C or higher, a mixed solid material of a silicon material and a carbonaceous material is produced. It is disclosed that continuous production is possible without any adhesion.

In addition, as a further improvement of the method of Japanese Patent Publication No. 58-18325, Japanese Patent Publication No. 58-34405 discloses that carbonaceous raw materials are used in large excess for the purpose of efficient utilization of SiO produced in the reaction of formula II. A method has been proposed for use in

Further, JP-A-55-20268 discloses that easily sinterable SiC can be obtained by adding a boron-based or aluminum-based sintering accelerator during SiC synthesis.

On the other hand, Japanese Patent Application Laid-Open No. 58-91026 discloses silicon carbide which is prepared by mixing carbonaceous substances such as silicon flukoxide and carbon black with an acid or alkaline aqueous solution, gelling the mixture, drying it, and then calcining it in a non-oxidizing atmosphere. A manufacturing method is disclosed.

[Problems to be Solved by the Invention] However, in all of the above conventional methods, the resulting products contain residual carbon and silica, and a great deal of effort is required to remove them.

Therefore, as a result of various studies in order to obtain high purity SiC, the inventors have found that in order to obtain high purity SiC, it is possible to cause the SiC conversion reaction in a state where the silicon material and the carbonaceous material are uniformly and in close contact with each other. It was found that this is an essential requirement.

However, none of the above conventional methods satisfy this requirement.

In addition, the method described in Japanese Patent Application Laid-open No. 58-91026 is as follows:
Although the reaction appears to be carried out in a homogeneous system, according to the examples of this publication, the resulting product contains residual carbon, which must be removed by oxidation treatment. Furthermore,
The gelation of ethyl silicate and carbon with hydrochloric acid and the drying process in the examples require a long time, and the yield is not necessarily good, so it is not efficient as a manufacturing process.

The present invention has been made to solve the above-mentioned conventional problems, and its purpose is to produce silicon carbide that can produce high-purity easily sinterable SiC fine powder at a high yield. The purpose is to provide a method.

[Means for Solving the Problem] In order to achieve this object, the method for producing silicon carbide of the present invention has the following characteristics: A silicon polymer represented by a hydrogen residue (n represents an arbitrary integer from 1 to 10) and (1) a solid carbonaceous material are uniformly mixed and (1) cured with a curing catalyst to obtain a precursor. A method for producing silicon carbide, characterized by heating and firing a silicon carbide body in a non-oxidizing atmosphere.

That is, as a result of detailed study on the synthesis of SiC by the reaction of formula II, the present inventors found that SiC
We found that in order to react efficiently, it is necessary for the siliconaceous raw material and the carbonaceous N material to be in a uniform and intimate state until just before the formation of SiC. Based on this knowledge, we conducted further studies and found that The present invention was achieved by discovering that when a specific silicon polymer as a component and a solid carbonaceous material as a component are cured in the presence of a curing catalyst as a component, the reaction proceeds efficiently under ideal conditions. This is what I did.

In addition, the present inventors have found that in addition to the above components (1) and (2), fine silica powder is further mixed uniformly as the (2) component, and the reaction is progressed more effectively by curing with the curing catalyst of the @component. I found out what I can do.

The present invention will be explained in detail below.

Component (1) used as a raw material in the present invention is represented by the general formula (wherein, RI, , lli 4 is a hydrocarbon residue having 1 to 6 carbon atoms, and n represents any integer from 1 to 10). It is a silicon polymer. In the above formula, R1-R4 include, for example, any residue selected from methyl, ethyl, propyl, butyl, amyl, phenyl, cyclohexyl, and the like. Also.

Although n is an integer from 1 to 10, it is not necessarily a single integer, and the silicon polymer of the present invention may be a mixture of polymers having different values of n.

Examples of the solid carbonaceous material of the @ component include various carbon blacks, natural graphite, petroleum coke, coal powder, and the like. All of these are preferably finely pulverized or liquefied with a solvent such as ethyl alcohol. As component (2), carbon black in a non-granulated state is particularly preferred.

In the present invention, the above-mentioned components (1) and (2) are mixed, blended, and brought into a sufficiently uniform state for curing. During curing, a curing catalyst, which is component (2), is used. The curing catalyst for component (1) plays an important role in keeping component (2) and component (2) in uniform adhesion.

■As a component, an acid catalyst or an alkali catalyst is used, and among them, 4I-free catalysts such as hydrochloric acid and sulfuric acid are used! Preferred are acids, organic acids such as toluenesulfonic acid, and particularly preferred are organic acids.

Note that the (2) component and the [phase] component can also be cured by heating in the absence of a catalyst, but in the present invention, the curing reaction is carried out with high efficiency by using the above-mentioned curing catalyst.

In the present invention, when a precursor is synthesized from component (1), component (2), and component (2), fine silica powder as component (2) can be used in place of a portion of the silicon polymer of component (2). In this case as well, as mentioned above, it is important to maintain a homogeneous mixture of both the components (■) and (2) and the @component, and it is also important that the catalyst of the (■) component allows for efficient curing. is important. Therefore, when using component (■) together, it is preferable that the ratio of component (■)/component (■) be 2/8 or more by weight. Among them, soft silica and amorphous silica are preferred, and the particle size of the powder is preferably as fine as possible.

The composition ratio of the raw materials for synthesizing SiC is 800 to 14
It is determined based on the atomic ratio of Si to C of the processed material obtained by processing at a temperature of 00°C. ■ingredient and ■ingredient, or when using this together with ■ingredient, ■ingredient, ■
The components and @components are such that the atomic ratio of C and Si in the treated product obtained by such treatment is 1 < C/ Si < 1
It is preferable to determine the respective mixing ratios so that C/5t=3. In addition, when C remains in the product after synthesis, C/S i >
Determine the amount so that it becomes 3.

■Ingredients, ■Ingredients and @Ingredients, or even more @Ingredients,
To obtain a precursor for calcination, these are mixed, preferably stirred very thoroughly, and the resulting mixture is uniformly solidified by the action of a curing catalyst, which is an ingredient, or by heating as necessary. Let it solidify.

The precursor solid thus obtained, either as it is or after being prepared to a suitable particle size, is first heated in a non-oxidizing atmosphere, such as vacuum, nitrogen, helium or argon, to about 80%
By treating at a temperature of 0-1400°C and then heat-treating the obtained carbide to about 1600-2000°C,
SiC can be obtained. Note that the above-mentioned treatment at a temperature of 800 to 1400° C. in a non-oxidizing atmosphere is performed for determining the atomic ratio, and is not necessarily necessary for SiC synthesis.

In the present invention, a boron compound and/or an aluminum compound may be added at the time of homogeneous mixing and curing of the (■component, There are no particular limitations, and examples of boron compounds include boric acid, boric anhydride, borax, borosilicate glass, silicon boride, and other organic boron compounds, and examples of aluminum compounds include:
Examples include aluminum boride, aluminum oxide, aluminum hydroxide, aluminum carbide, and aluminum chloride.

The amount of boron compound and/or aluminum compound added is determined depending on the purpose of synthesis, but is preferably 10% by weight or less of the resulting synthesis product.

[Function] In the method for producing silicon carbide of the present invention, a mixture of components (1), (2), and (2), a mixture of components (1), (2), (2), and (2), or a mixture of these with a boron compound and/or an aluminum compound added thereto. is solidified, and this solidified product is heated and fired in a non-oxidizing atmosphere. Therefore, in the present invention, the siliceous raw material and the carbonaceous raw material are uniformly and in close contact with each other until immediately before the formation of SiC, so that the reaction between them proceeds extremely well.
Easily sinterable SiC powder can be obtained efficiently.

Therefore, if each component is mixed so that the C/Si (atomic ratio) in the processed material at a temperature of 800 to 1400°C in a non-oxidizing atmosphere is 3 or a value close to 3, pure carbon with no residual carbon can be produced. β-5iC powder is obtained.

In addition, when no boron compound and/or aluminum compound is added, the obtained SiC has a β phase that does not contain an α phase.
-5iC powder, while aluminum compound is S
When added in an amount of 2% by weight or more of the iC product, α-5iC powder is obtained.

[Examples] Next, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

The average value of CH of the liquid silicon compound (■component) represented by Example 1 is 4
and contains 41% by weight of S i 02min, ) 53% by weight
, carbon black (@component) 13% by weight of acid, 28% by weight of ethyl alcohol, and 6% by weight of water were uniformly mixed.Next, about 4% by weight of an acid catalyst (@component) was added to this mixture and vigorously stirred. After stirring, the mixture was allowed to stand for about 10 minutes and solidified.

The obtained solid material was heated to 10'07 m1 under a non-oxidizing atmosphere.
The temperature was raised to 1600° C. at n, maintained for 4 hours, and then cooled.

When the obtained treated product was examined by powder X-ray diffraction method, it was found that
The diffraction lines were as shown in FIG. 1, indicating that β-5iC fine powder was obtained. The properties of the obtained β-3iC fine powder are as shown in Table 1 below.

This powder was subjected to sintering without being decarburized. That is, 2% by weight of carbon and 0.2% by weight of boron were added to this powder, which was then molded and subjected to normal pressure sintering or pressure sintering at 20 MPa at 2100°C in argon gas. . As a result, the density was increased to 3.10 g/Cm' by pressureless sintering, and 3.15 g/Cm' by pressure sintering.

Example 2 19% by weight of the liquid silicon compound used in Example 1, 9% by weight of carbon black, 8% by weight of silica fine powder (component ■),
62% by weight of ethyl alcohol and 2% by weight of water were uniformly mixed.Next, approximately 2% by weight of an acid catalyst was added to this mixture and the mixture was vigorously stirred. After stirring, the mixture was allowed to stand for about 10 minutes and solidified. The obtained solid material was heat treated in the same manner as in Example 1.

When the obtained treated product was examined by powder X-ray diffraction method, it was found that
The diffraction lines were as shown in FIG. 2, and it was revealed that β-5iC fine powder was obtained. The properties of the obtained β-5iC fine powder are as shown in Table 1.

This powder was sintered in the same manner as in Example 1.

The density was increased to 3.10 g/cm'' by pressureless sintering, and 3.15 g/cm'' by pressure sintering.

Example 3 Example except that 12% by weight of the liquid silicon compound used in Example 1, 9% by weight of carbon black, 12% by weight of fine silica powder, 65% by weight of ethyl alcohol, and 2% by weight of water were uniformly mixed. The same operation as in 2 was performed.

When the obtained treated product was examined by powder X-ray diffraction method, it was found that
The diffraction lines were as shown in FIG. 3, indicating that β-3iC fine powder was obtained. The properties of the obtained β-3iC fine powder are as shown in Table 1.

When this powder was sintered in the same manner as in Example 1, it was found that the density was 3.5 mm after pressureless sintering. lOg/cm'', 3.15 for pressure sintering
It was densified to g/crn'.

Comparative example l CH3S i (OCH:l) 372 m, novolac type phenol resin 40 g, methyl alcohol 200
mJ1, Hz B O3 aqueous solution (0.64 g H3B
03 dissolved in 100 mM of water) were mixed, and then 72 rnfL of 28% ammonia water was added at room temperature to gel. The gelled product was dried in an oven at 60°C for 18 hours and then pyrolyzed at 1200°C for 3 hours in an argon atmosphere.

This material was further heated under a 101 Pa argon atmosphere.

The reaction was carried out at 1600°C for 2 hours.

When the obtained product was examined by powder X-ray diffraction method, β-
It turned out to be 5iC. The properties of this powder are shown in Table 1.As shown in Table 1, β-3 obtained in Comparative Example 1
iC had 7.5% residual carbon and required decarburization treatment before it could be used for sintering. Furthermore, when the crystallite size was measured from the (420) plane of the X-ray diffraction diagram of this β-3iC powder, it was 115 or less than the particle size determined by an electron microscope, indicating that the powder was polycrystalline. was confirmed.

Further, after decarburizing this powder, it was sintered under the same conditions as in Example 1, and the density of the obtained sintered body was 2.9 g/crn' in normal pressure sintering, and 2.9 g/crn' in pressure sintering. It was 3.0 g/Cm3 in sintering, and was not densified by pressureless sintering.

As is clear from the Examples and Comparative Examples in Table 1, even when raw materials containing stoichiometric amounts of Si and C are used, the residual carbon in the products in the Examples is as low as 1.0 to 1.5%. On the other hand, in the comparative example, the amount is as high as 7.5%.

Each ρ − (+ 1”)
The powder in the example of 10 width Dan Ayu Frog 1 + I + pot requires decarburization treatment,
Therefore, while pressureless sintering does not result in densification, in the examples, densification can be achieved by pressureless sintering, and it is clear that the products obtained in the examples are significantly superior.

From these results, it is clear that according to the present invention, β-5iC fine powder with extremely good sinterability can be efficiently produced.

[Effects of the Invention] As detailed above, the method for producing silicon carbide of the present invention has the following features:
If desired, fine silica powder (@component) is added to a specific silicon polymer (component) and solid carbonaceous material (component (1)), and this is solidified using a curing catalyst. S by heating and baking in a non-oxidizing atmosphere
This is a new synthesis method for obtaining iC powder, and it is capable of efficiently reacting a siliceous raw material and a carbonaceous raw material, and therefore, it is possible to obtain extremely high purity SiC powder with a high yield.

The powder thus obtained can be directly subjected to sintering, and an extremely dense sintered body can be obtained by sintering.

Further, in the present invention, it is also possible to mix the boron compound and/or the aluminum compound extremely uniformly, and it is also possible to obtain easily sinterable SiC. Moreover, by appropriately selecting conditions, it is possible to synthesize β-3iC or α-5iC with high selectivity as desired.

Further, SiC fine powder can be obtained simultaneously with the firing.

[Brief explanation of the drawing]

1 to 3 are powder X-ray diffraction diagrams of β-type SiC obtained in Examples 1 to 3, respectively.

Claims (1)

[Claims] (1) [a] General formula ▲ Numerical formulas, chemical formulas, tables, etc. ) and [b] a solid carbonaceous material are uniformly mixed, [c] is cured with a curing catalyst to obtain a precursor, and this precursor is heated in a non-oxidizing atmosphere. A method for producing silicon carbide, which comprises firing.