JPH05339057A - Production of high purity beta silicon carbide sintered body - Google Patents

Abstract

PURPOSE:To provide a high-purity beta silicon carbide sintered body having high productivity without losing demensional stability by adding a binder to high- purity beta silicon carbide-carbon mixture powder, compacting, hardening by heating, heat treating, impregnating the compact with a silicating agent of carbon, and then effecting the reaction for sintering. CONSTITUTION:A liquid high-purity silicon compd. (e.g. ethyl silicate) and a liquid high-purity compd. (e.g. phenol resin) having functional groups which produces carbon by heating are used as the source material. To this material, a polymn. or crosslinking catalyst which uniformly dissolves in the source material is added to effect the reaction to obtain a precursor material. The precursor is then heated and carbonized at 700-1100 deg.C in a nonoxidative atmosphere. Further, the carbonized material is baked at 1600-2200 deg.C in the same atmosphere as above to obtain a high-purity beta silicon carbide-carbon mixture powder (with <=10wt.% carbon content). A binder (e.g. resol-type phenol resin) is added to this powder and compacted, heated, and hardened. The compact is heat treated and impregnated with a silicating agent (e.g. molten liquid of high purity silicon) of carbon, and then subjected to the reaction for sintering at 1450-1600 deg.C. The obtd. sintered body contains <=1ppm impurities.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a β-type silicon carbide sintered body having a high content of silicon carbide, a high purity and a high productivity without impairing the dimensional stability of a complicated shape. It relates to a manufacturing method. Therefore, it can be used as a heat-resistant component in the semiconductor industry or in the manufacture of optical elements, which requires high purity.

[0002]

2. Description of the Related Art Silicon carbide has been conventionally used for heat resistant materials, but is known as a non-sinterable material because it is a covalent bond substance. Hot pressing method, atmospheric pressure sintering method, and reactive sintering method (RSSC) are used for sintering silicon carbide.
It has been known. The general process of the RSSC method with which the present invention is concerned is as follows. That is, this method is 1. Raw material mixture (silicon carbide powder + carbon powder) 1. Molding 3. 3. Reaction sintering and 4. If necessary, it consists of post-processing steps. The characteristic of this RSSC method is that the carbon particles of the molded body are silicified in the above-mentioned 3 sintering step, the dimensional change of the molded body is small, and a sintering aid is not required.

According to this method, carbon powder is usually added to silicon carbide powder and mechanically mixed to obtain a mixed powder, and a binder is added to the mixed powder to shape and sinter to obtain a sintered body. , The commonly available carbon powder contains impurities, the mixing of impurities in the mixing process cannot be ignored, and the additives such as binders are also likely to contain impurities. However, there is a big problem in that it is not easy. Further, there is a problem that the mixing process requires a long time and the productivity is not good.

As a method for obtaining a sintered body containing a small amount of impurities, there has been proposed a method comprising the following 6 steps, which is obtained by adding two purification steps to the method used in the ordinary RSSC method (Japanese Patent Laid-Open No. 2000-242242). 64-72964). That is, this method is 1. Raw material mixture (silicon carbide powder + carbon powder + binder, etc.) 1. Molding 3. Calcination 4. Purification 5.
Reaction sintering and 6. It consists of each step of repurification. The purification described here means that the calcined porous compact is 100
This is a method in which hydrogen chloride gas is flowed at 0 to 1200 ° C., and the impurity metal is converted to chloride to be evaporated and removed. This method is performed again after the reaction sintering. The impurity metals referred to here are aluminum, iron, nickel, chromium and the like.

However, with this method, alkali metals, alkaline earth metals, copper, rare earth metals and the like cannot be removed because their chlorides have high boiling points. Further, the metal such as aluminum present in the raw material silicon carbide crystal lattice cannot be removed, but only the metal such as aluminum on the surface is removed. Thus, even with this method, the removal of impurities cannot be said to be sufficient, and this problem has not been solved. Furthermore, this method has problems in economic efficiency and productivity in terms of process steps and use of toxic gas.

[0006]

As described above, the method for producing a β-type silicon carbide sintered body has various problems, and there are many problems to be solved in order to obtain a high-purity sintered body.

The present invention aims to provide a method for producing a β-type silicon carbide sintered body which has a high purity and a high productivity without deteriorating the dimensional stability of the complicated shape which is a characteristic of the RSSC method. To aim.

[0008]

A high-purity β according to claim 1
The method for producing a silicon carbide sintered body is a high-purity polymerization in which a liquid high-purity silicon compound and a liquid high-purity organic compound that has a functional group and generates carbon when heated are used as raw materials Alternatively, a crosslinking catalyst is added, and the precursor substance obtained by the polymerization or crosslinking reaction is heated and carbonized in a non-oxidizing atmosphere, and the obtained intermediate product is calcined at a higher temperature in a non-oxidizing atmosphere. A β-type silicon carbide formed by adding a binder to a pure β-type silicon carbide-carbon mixed powder, molding the mixture, heat-treating the molded body, and then impregnating this with a silicifying agent for carbon and subjecting this to reaction sintering. In the method for producing a sintered body, the carbon / silicon molar ratio in the intermediate product is 2.2 to 3.5, and the amount of carbon in the high-purity β-type silicon carbide-carbon mixed powder is 10% by weight. % Or less, and the binder has a high purity level. Characterized in that it is a phenol type or novolac type phenol resin, the silicifying agent for the carbon is a high-purity silicon melt, and the content of each impurity element in the β-type silicon carbide sintered body is 1 ppm or less. And

That is, the present inventors have focused on impurities, composition of carbide (intermediate product), composition of β-type silicon carbide-carbon mixed powder, etc. in the method for producing β-type silicon carbide sintered body, As a result of extensive studies, substances that are substantially free of impurity elements, substances used in all steps, intermediate products with a specified carbon / silicon molar ratio, mixed powder with a specified amount of carbon, and this method By using a binder and a carbon silicifying agent suitable for the above, the object was achieved and the present invention was completed.

The present invention will be described in detail below. The liquid silicon compound used in the present invention includes methyl silicate, alkyl silicate such as ethyl silicate, silicic acid or silicic acid polymer aqueous solution obtained by dealkalizing alkali silicate, and organic compound having a hydroxyl group and silicic acid. Examples thereof include ester solutions. Among them, ethyl silicate monomer and oligomer are preferably used.

In the present invention, the liquid high-purity organic compound which has a functional group and produces carbon by heating has a particularly high residual carbon rate and is an organic compound which is polymerized or crosslinked by a catalyst or heating, such as a phenol resin, Examples include resins (polymers) such as nitrile resin, furan resin, polyimide resin, styrene resin, xylene resin, polyphenylene oxide, polyphenylene sulfide, and polyaniline, and prepolymers. Of these, resol type or novolak type liquid phenolic resins and furfuryl alcohol are preferable.

In the present invention, as the polymerization or crosslinking catalyst which is uniformly dissolved in the raw material, when phenol resin or furfuryl alcohol is used as the raw material, acids such as toluenesulfonic acid, hydrochloric acid, sulfuric acid and oxalic acid are preferable. When used as a monomer or oligomer of a nitrile resin, commonly used radical polymerization initiators such as ammonium persulfate, hydrogen peroxide, various hydroperoxides, alkyl peroxides, peroxide esters, azo compounds are suitable. Also, when other organic compound is used, a polymerization or crosslinking catalyst which is usually used can be used.

In the present invention, in the step of obtaining a molded product by adding a binder to the high-purity β-type silicon carbide-carbon mixed powder,
Examples of the binder include high-purity resol-type or novolac-type phenolic resins, furan resins, nitrile resins, and other resins having residual carbon properties. Resol-type or novolac-type phenolic resins are preferable. The reason why the binder having a residual carbon property is used is to improve the strength of the molded body (also referred to as a calcined body) after the heat treatment and reduce "breaks" and the like. Addition amount of binder is 10-40% by weight of mixed powder
Is used. In the present invention, an additive is used together with the binder. This is necessary in order to make the molded body porous (open pores) and to be able to impregnate the carbon silicifying agent, so the additives will decompose or evaporate at the heat treatment (degreasing, debinding) temperature of the molded body. It must be a volatile substance. This open pore is also used because it was obtained in the carbonization step. Examples of additives include alkyl phthalates, waxes, polyvinyl alcohol, methacrylic resins, chain hydrocarbons such as polyethylene and polybutylene, ethylene-vinyl acetate resins, and thermal decomposability of vinyl alcohol / ethylene / vinyl acetate copolymers. Resin etc. are mentioned. The amount of the additive is usually 10% by weight or less of the mixed powder.

As the carbon silicifying agent to be impregnated into the mixed powder compact of the present invention, a high-purity silicon melt or silicon vapor is usually used, but a silicon melt is preferred.

In the present invention, various molding methods are adopted in the step of adding a binder to the mixed powder to obtain a molded body, but any of injection molding, extrusion molding, compression molding and the like can be used, and the liquid phenol resin is used as the binder. By using, it is possible to perform cast molding.

In the present invention, the precursor substance obtained by polymerizing or crosslinking reaction of the raw materials is heated and carbonized in a non-oxidizing atmosphere, and the carbonization temperature in that case is 700 to 1100 ° C.
Is used, and preferably 800 to 1000 ° C. is adopted. Further, the intermediate product obtained by carbonizing the precursor substance is fired at a higher temperature in a non-oxidizing atmosphere, and the temperature in that case is 1600 to 2200 ° C. and 1700 to 2
000 ° C. is preferably used. A binder is added to the mixed powder, and the mixture is molded and heat-treated to heat-treat it, followed by reaction sintering to obtain a sintered body. The temperature of the heat-curing, the heat treatment (degreasing and debinding) temperature, and the reaction baking The binding temperatures are room temperature to 250 ° C, 500 to 900 ° C and 1450, respectively.
A temperature of ~ 1600 ° C is usually suitable. Especially during heat treatment, due to the decomposition and evaporation of additives existing inside the molded body,
The temperature rising rate is 1 ℃ / so that the molded product will not crack.
Must be less than a minute.

The matters related to impurities, which are important elements in the present invention, are described below. Although the β-type silicon carbide sintered body does not substantially contain the impurity element, the content of each impurity element needs to be 1 ppm or less even if it is contained. Further, the β-type silicon carbide-carbon mixed powder,
Although it does not substantially contain the impurity element, the content of each impurity element must be 1 ppm or less even if it is included. Further, the raw material used in the present invention is used that does not substantially contain the impurity element, even if it contains,
The content of each impurity element is 0.5 ppm or less, preferably 0.1 ppm or less, but the firing temperature (1600 to 2
This does not apply to elements or compounds of elements that evaporate at 200 ° C. Furthermore, the catalyst used in the present invention,
It is necessary to use a high-purity substance that does not substantially contain impurities as a substance used in all the steps such as a binder, an additive, a silicifying agent for carbon, and a solvent (including water). Further, it is preferable that raw materials and products are handled in a clean booth of class 1000 or less.

Here, the impurity elements are Ia to I in the periodic table.
IIa group element, Ib to VIIIb group element, IVa group atomic number 3
2 or more elements, elements of Va group atomic number 33 or more, and rare earth elements.

In the present invention, the carbon / silicon molar ratio in the intermediate product obtained by carbonizing the precursor substance is 2.2.
To 3.5, preferably 2.3 to 3.0. This range is set in consideration of the fact that a binder such as a phenol resin added in the subsequent molding step serves as a carbon source. At least when this molar ratio exceeds 3.5, the silicon carbide formed after firing becomes a mixture of β type and α type, and β type and α type are mixed in the sintered body obtained by reaction sintering. Therefore, the high temperature (1000 to 1300 ° C.) strength of the sintered body decreases. Therefore, it is not suitable for products requiring high temperature strength.

After all, in this molar ratio range of the present invention, the mixed powder after firing contains β-type silicon carbide having a high strength at high temperature and 10% by weight or less of carbon necessary for reaction sintering. Since it is considered that the binder serves as a carbon source as described above, this amount of carbon satisfies the necessary amount. Since the silicon carbide generated during the reaction sintering is also β-type, the components in the sintered body are all β-type silicon carbide single phase except unreacted silicon, so that the content thereof is extremely high.

In the present invention, since the raw materials of the liquid silicon compound as the silicon source and the liquid organic compound as the carbon source are polymerized or crosslinked, the obtained precursor substance is a molecular order of both silicon and carbon. Since it is homogeneously mixed and dispersed, it passes through the intermediate product after carbonization, and the mixed powder after firing has silicon carbide and carbon uniformly mixed and dispersed, and the sintered body after reaction sintering using this Has excellent physical properties. As described above, by mixing the liquid silicon source and the carbon source in a predetermined amount, a mixed powder having the necessary silicon carbide and carbon can be obtained, which is different from the method of mechanically mixing the silicon carbide powder and the carbon powder. In addition to being able to obtain mixed powder with good productivity, it is possible to prevent mixing of impurities during mixing, and in the end, without sacrificing the dimensional stability of the complicated shape that is a characteristic of the RSSC method, the desired high purity can be achieved with good productivity. A β-type silicon carbide sintered body can be obtained.

[0022]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

[Example 1] Si as a liquid silicon compound
High-purity ethyl silicate having an O ₂ content of 40%, a high-purity liquid resol-type phenol resin having a water content of 20%, and a 25% aqueous solution of high-purity p-toluenesulfonic acid as a catalyst were mixed at a ratio shown in Table 1 to obtain the effect. -Drying gave a homogeneous resinous solid. 1 at 900 ℃ under nitrogen atmosphere
Charred for hours. The carbon / silicon molar ratio of the obtained carbide was the value shown in Table 1 from elemental analysis. This carbide was heated to 1900 ° C. at a temperature rising rate of 40 ° C./min in an argon atmosphere, heated and held for 45 minutes to carry out a silicon carbide reaction. Residual carbon content in the obtained powder and impurity analysis of sodium, calcium, iron and aluminum (ICP
Table 1 shows the results of performing mass spectrometry and flameless atomic absorption spectrometry. The crystal form of silicon carbide as determined by X-ray diffraction was β type (cubic crystal). The β-type silicon carbide-carbon mixed powders thus obtained are designated as powder A and powder B as shown in Table 1. Examples of the sintered body using the powder A and the powder B are referred to as Examples-A and B, respectively.

High-purity novolac type phenolic resin and high-purity DBP were blended in powder A and powder B in the proportions shown in Table 2, 0.5% stearic acid and ethanol were added thereto, and a Teflon-coated mill was used. After mixing for 3 hours, it was granulated to 50 mesh or less using an extruder and dried. This was preheated to 100 ℃ with an injection molding machine 16
It was molded in a mold heated to 0 ° C. and heat-cured for 10 minutes. The dimensions of the obtained molded body were 50 mm × 20 mm and the thickness was 5 mm. This molded body is put into a furnace and heated to 900 ° C. at a heating rate of 25 ° C./hour in an argon atmosphere,
After holding for 45 minutes, the furnace was cooled. This carbonized compact was brought into contact with high-purity silicon melted at 1500 ° C. in an argon atmosphere and held for 1 hour for reaction sintering. The silicon adhering to the surface of this sintered body was removed, the surface was further washed with high-purity hydrochloric acid and high-purity nitric acid, and then the density, the amount of residual silicon and the impurity analysis were carried out. The crystal form of silicon carbide in this sintered body was β type.

[Comparative Example] Except that 5% by weight of carbon black was added to commercially available β-type silicon carbide having an average particle size of 6 μm.
A reaction sintered body sample was obtained in the same manner as in the example. Table 2 shows the results of the density, the amount of residual silicon, and the impurity content after the same treatment as in the example.

[0026]

[Table 1]

[0027]

[Table 2]

As can be seen from the results of Tables 1 and 2, in comparison with the comparative example, the sintered body obtained in this example with high productivity using the β-type silicon carbide-carbon mixed powder of high purity is as follows. It was revealed from the density and the amount of residual silicon that the content of silicon carbide was high, and from the content of impurities that the purity was high.

[0029]

EFFECTS OF THE INVENTION Since the method for producing a high-purity β-type silicon carbide sintered body of the present invention has the above-mentioned constitution, it has a high content of silicon carbide and a high purity without impairing the dimensional stability of a complicated shape. It has an excellent effect that a sintered body having high productivity can be manufactured.

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[Procedure amendment]

[Submission date] October 28, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0018

[Correction method] Change

[Correction content]

Here, the impurity elements are Ia to V in the periodic table.
IIa group elements, VIII group elements, Ib～ IIIb group element, refers to an atomic number 33 or more elemental atomic number 32 or more elements and Group Vb of group IVb.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] 0023

[Correction method] Change

[Correction content]

[Example 1] Si as a liquid silicon compound
High-purity ethyl silicate having an O ₂ content of 40%, a high-purity liquid resol-type phenol resin having a water content of 20% and a 25% aqueous solution of high-purity p-toluenesulfonic acid as a catalyst were mixed at a ratio shown in Table 1 and cured. -Drying gave a homogeneous resinous solid. 1 at 900 ℃ under nitrogen atmosphere
Charred for hours. The carbon / silicon molar ratio of the obtained carbide was the value shown in Table 1 from elemental analysis. This carbide was heated to 1900 ° C. at a temperature rising rate of 40 ° C./min in an argon atmosphere, heated and held for 45 minutes to carry out a silicon carbide reaction. Residual carbon content in the obtained powder and impurity analysis of sodium, calcium, iron and aluminum (ICP-
The results of mass spectrometry and flameless atomic absorption spectrometry are shown in Table 1. The crystalline form of silicon carbide by X-ray diffraction was β-type (standing orthorhombic). The β-type silicon carbide-carbon mixed powders thus obtained are designated as powder A and powder B as shown in Table 1. Examples of the sintered body using the powder A and the powder B are referred to as Examples-A and B, respectively.

Claims (1)

[Claims] 1. A liquid high-purity silicon compound and a liquid high-purity organic compound which has a functional group and produces carbon by heating are used as raw materials, and a high-purity polymerization or crosslinking catalyst which is uniformly solubilized is added thereto, The precursor substance that has been polymerized or cross-linked is heated and carbonized in a non-oxidizing atmosphere, and the obtained intermediate product is calcined at a higher temperature in a non-oxidizing atmosphere. A method for producing a β-type silicon carbide sintered body, which comprises adding a binder to carbon mixed powder, molding the mixture, heat-treating the molded body, and then impregnating this with a silicifying agent for carbon and subjecting this to reaction sintering. In the intermediate product, the carbon / silicon molar ratio is 2.2 to 3.5, and the carbon amount in the high-purity β-type silicon carbide-carbon mixed powder is 10% by weight or less, The binder is a high-purity resol type or novolac High-purity, which is a phenolic phenol resin, the carbon silicifying agent is a high-purity silicon melt, and the content of each impurity element in the β-type silicon carbide sintered body is 1 ppm or less. Manufacturing method of β-type silicon carbide sintered body.