JPH06183837A - Production of silicon carbide sintered compact - Google Patents

Abstract

PURPOSE:To provide a method for producing a high-density and high-strength sintered compact having excellent characteristics by readily preparing a slurry in which a densifying sintering assistant is uniformly dispersed on silicon carbide powder particles. CONSTITUTION:Boric acid and/or a boric acid ester and a phenolic resin soluble in a dispersing medium as a boron source and a carbon source compound are respectively added into a slurry of the nonalcoholic and nonaqueous dispersing medium containing silicon carbide raw material powder in the densification sintering of silicon carbide to provide a slurry. A powdery or a granular substance obtained from the resultant slurry is then used to produce a silicon carbide sintered compact.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a silicon carbide sintered body, and more particularly, to a method for simplifying the operation of densifying and sintering silicon carbide, which has excellent characteristics of high density and high strength. The present invention relates to a method for producing a silicon carbide sintered body, which is capable of obtaining a silicon sintered body with good reproducibility.

[0002]

2. Description of the Related Art A so-called engineering ceramics silicon carbide (hereinafter simply referred to as SiC) sintered body is excellent in heat resistance, corrosion resistance and wear resistance, has high high temperature strength, and is remarkably developed as a mechanical material. . A SiC sintered body obtained by densification and sintering is mainly used as a material for the machine parts. Densification sintering is different from reaction sintering in that it is sintered by an additive, and it is effective to add boron and carbon as an additive (sintering aid) for densification sintering of SiC. well known. Conventionally, in the case of producing a silicon carbide sintered body, it is general that the above-mentioned sintering aid is uniformly added in a step generally called a granulation step. In such a granulation process, a dispersion medium is added to SiC powder and mixed, and a sintering aid or the like is added to the obtained slurry to disperse and mix. However, since the dispersion medium for preparing the SiC raw material powder slurry is often different from the solvent capable of dissolving each boron compound which is the boron source, the boron compound used can be directly mixed with the above slurry. Instead, it is used by once dissolving it in the solvent, for example, preparing an alcoholic or aqueous solution of boric acid, and then adding it to the non-aqueous dispersion medium slurry of the SiC raw material powder.

[0003]

However, in the conventional method as described above, a solvent different from the dispersion medium of the SiC raw material powder slurry must be used in the addition of the boron source of the sintering aid, so that the slurry must be used. The operation of preparation becomes complicated. Further, when the slurry dispersion medium is collected and reused, the boron source is lost due to volatilization at the time of collection, and the composition of the SiC material after the dispersion medium is removed is changed, so that the characteristics of the SiC sintered body can be easily improved. However, there is a problem that it is difficult to obtain a SiC sintered body having high strength and high density. Therefore, there is a demand for a slurry preparation that can easily disperse the sintering aid uniformly and can obtain a SiC sintered body having excellent characteristics by a simple operation. In view of the above problems of the conventional method, the present invention provides a slurry which is easy to prepare and which has a densification sintering aid uniformly dispersed on SiC powder particles, and has excellent properties.
An object of the present invention is to provide a method for manufacturing a silicon carbide sintered body which is a C sintered body. In order to achieve the above object, the inventors of the present invention firstly studied the dispersion medium constituting the SiC raw material powder slurry and the boron source of the sintering aid that can be dissolved therein, and arrived at the present invention.

[0004]

According to the present invention, in the densification sintering of silicon carbide, a densification sintering aid is added to a non-alcoholic and non-aqueous dispersion medium slurry containing silicon carbide raw material powder. The boric acid and / or boric acid ester soluble in the dispersion medium and the phenol resin are added as the boron source and the carbon source compound, respectively, and a powder or granular material obtained from the slurry is used. A method for manufacturing a silicon carbide sintered body is provided.

[0005]

The present invention is configured as described above, and uses the densification sintering aid soluble in the same dispersion medium as the non-alcoholic and non-aqueous dispersion medium of the silicon carbide raw material powder slurry.
The sintering aid can be mixed and dissolved in the solvent together with the raw material powder, and the slurry preparation operation is simple and easy.
The SiC raw material powder, the boric acid and / or boric acid ester of the boron source of the sintering aid, and the phenolic resin of the carbon source are uniformly dispersed and contained in the slurry. Therefore,
A powder or granular material obtained from such a slurry has a densification sintering aid uniformly dispersed on a SiC raw material powder, and a SiC sintered body obtained by performing a sintering process using the powder or granular material. Is sufficiently sintered to have high density and high strength.

The present invention will be described in detail below. The SiC raw material powder of the present invention may be either α-type or β-type SiC. Further, the average particle size of the SiC raw material powder is not particularly limited, and the same powder as that conventionally used according to various molding methods can be used. Usually, a SiC raw material powder having an average particle size of 0.05 to 5 μm, preferably 1 μm or less is used.

In the present invention, a non-alcohol-based to non-aqueous dispersion medium is used as the dispersion medium forming the slurry containing the SiC raw material powder. Alcohols cannot be used because they produce boric acid and an ester, and boric acid or boric acid ester is entrained and removed during recovery distillation of the dispersion medium after the SiC slurry is prepared. The dispersion medium of the present invention is not accompanied by boric acid or borate ester at the time of recovery, and
It can be uniformly dispersed and fixed on the iC raw material powder.
As the dispersion medium as described above, generally, ketones and esters having a low boiling point are used, for example, acetone,
Examples include methyl ethyl ketone and ethyl acetate. Of these, acetone is particularly preferable because it is inexpensive and easy to handle.

Boric acid and / or boric acid ester (R ₃ BO _{3 as} a boron source of the densification and sintering aid of the present invention, provided that
R is an alkyl group) is soluble in the above dispersion medium, and the boric acid ester is a low molecular weight alkyl boric acid ester such as boric acid methyl ester or boric acid ethyl ester. These boric acid esters generally have a low boiling point and are close to the boiling point of the dispersion medium of the above-mentioned SiC molding slurry, but as mentioned above, they are distilled off together during the distillation for recovering the dispersion medium of the present invention. Never. Conventionally, these low-boiling borate esters are boron compounds that have not been used because they are removed from the slurry at the same time when the dispersion medium of the slurry is distilled off. However, unlike traditional predictions,
When used in combination with the above-mentioned non-alcoholic and non-aqueous dispersion medium of the present invention, it is not distilled off even in the operation of removing the slurry dispersion medium. Moreover, the present inventors have for the first time found that even after distilling the dispersion medium, the SiC powder is uniformly dispersed in the obtained SiC powder and functions as a densification sintering aid. Further, boric acid produces alcohol and boric acid ester as described above, but no ester is produced in the slurry dispersion medium of the present invention and is dispersed and held in a SiC powder or granular state even after the dispersion medium is distilled off. . Further, since the solubility of boric acid in the dispersion medium is low, it cannot be used with the conventional boron source addition amount as described below, but the boron addition amount of the present invention may be a trace amount within the range of the soluble amount. There can be used.

In the present invention, the boric acid and / or borate ester added to the non-alcoholic and non-aqueous dispersion medium slurry containing the SiC raw material powder is the SiC contained in the slurry on the basis of boron element. It is preferably about 0.05 to 0.8% by weight of the raw material powder. If the addition amount is less than 0.05% by weight, sintering does not proceed sufficiently,
It is not possible to obtain a high density SiC sintered body. on the other hand,
If it exceeds 0.8% by weight, boron is segregated at the grain boundaries, so that the oxidation resistance and the corrosion resistance decrease, which is not preferable. The boron source for the densification and sintering of the conventional method was required to be added in an amount of 0.5 to 1.5 wt% of the raw SiC powder based on boron when preparing the slurry, whereas the boron source of the present invention was added. As described above, boric acid and / or boric acid ester is not lost when the slurry dispersion medium is distilled off, so that the necessary minimum amount of boric acid and / or boric acid ester can be added.

The phenolic resin as the carbon source of the sintering aid for the densification and sintering of the present invention is added to the above-mentioned non-alcoholic and non-aqueous dispersion medium in the same manner as the boric acid and / or borate ester as the boron source. It is not particularly limited as long as it is soluble. Usually, a commercially available phenol resin can be appropriately selected and used. The addition amount of the phenol resin is preferably about 1 to 5% by weight of the SiC raw material powder contained in the slurry on the basis of carbon element. If the addition amount is less than 1% by weight, the sintering does not proceed sufficiently and a high density SiC sintered body cannot be obtained. On the other hand, 5% by weight
If it exceeds, excess carbon remains in the SiC sintered body as residual carbon, which is unfavorable because it causes a reduction in oxidation resistance.

In the present invention, the non-alcoholic and non-aqueous dispersion medium slurry containing the SiC raw material powder contains the above-mentioned SiC raw material powder, the boron source of the densification aid and the carbon source of each of the above, in the dispersion medium. The compounds can be prepared by mixing or separately supplying them to a non-alcoholic and non-aqueous dispersion medium to disperse and dissolve them. The concentration of the SiC raw material powder in the slurry is not particularly limited and can be appropriately selected depending on the particle size distribution of the SiC raw material powder to be used, the desired properties of the granular material, and the like. Usually 12
It is 0 to 140% by weight. Further, the powdery or granular material of the present invention is obtained by distilling off an excess dispersion medium by a usual method from the non-alcoholic and non-aqueous dispersion medium slurry prepared as described above. The particle size, shape, etc. are arbitrary, and the particle size can be adjusted using a sieve or the like, if necessary.

In the dispersion medium slurry of the SiC raw material powder of the present invention, various additives such as a binder and a molding aid, which are added as necessary, can be added to an ordinary slurry. These various additives are not particularly limited as long as they do not impair the functions of the boric acid ester and the phenol resin of the sintering aid added in the present invention, and can be appropriately selected and used. Furthermore, the SiC of the present invention
As described above, the sintered body uniformly disperses the SiC raw material powder, boric acid and / or boric acid ester, and phenol resin in a non-alcoholic and non-aqueous dispersion medium,
A SiC powder or granule obtained by dissolving and preparing a slurry and distilling off the dispersion medium from the prepared slurry is used, and the subsequent steps can be carried out by processing in the same manner as in the prior art. That is, the produced SiC powder is formed into a compact by an appropriately selected molding method using the granulated powder obtained by adjusting the particle size by sieving and the like as described above. A silicon carbide sintered body can be obtained by forming the molded body and drying, degreasing, and sintering the molded body. The processing conditions in each step in this case can be appropriately selected,
Usually, it can be performed in the same manner as the conventional method.

[0013]

EXAMPLES The present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples. Example 1 100 g of α-type SiC powder having an average particle diameter of 0.5 μm, 7 g of phenol resin (carbonization degree 50%) and methyl borate 1.4.
300 ml of acetone was added to 4 g of the mixture, and the mixture was dispersed, dissolved and mixed in a plastic ball mill for 24 hours to prepare a mixed slurry. The obtained mixed slurry was heat-treated to distill off acetone to obtain SiC powder particles. The obtained powder and granules are sieved with a 60-mesh sieve to adjust the particle size, and the powder that has passed through the sieve is used to obtain 500 kgf / cm ²
Uniaxially press at 1.5T / cm ³ CIP
(Hydrostatic pressure molding) treatment was performed to obtain a 50 × 50 × 6 (mm) plate-shaped molded body.

The molded body molded as described above is heat-treated in a nitrogen atmosphere at 600 ° C. for 1 hour to be degreased, and then fired in an argon atmosphere at 2100 ° C. for 2 hours to obtain S.
An iC sintered body was obtained. A sample was cut out from the obtained SiC sintered body, and its density and bending strength were respectively evaluated by the Archimedes method and room temperature three-point bending strength (JIS R1601).
Was measured using. The results are shown in Table 1. In Table 1, the amount of boron source added is the amount of Si in the mixed slurry.
The weight% based on the boron element based on the C raw material powder is shown.

Example 2 A SiC sintered body was prepared in the same manner as in Example 1 except that the added methyl borate was 2.89 g, and the density and bending strength of the sintered body were measured in the same manner as in Example 1. It was measured. The results are shown in Table 1.

Example 3 A SiC sintered body was obtained in exactly the same manner as in Example 1 except that 2.03 g of ethyl borate was used instead of methyl borate. The density and bending strength of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Table 1.

Example 4 An SiC sintered body was obtained in the same manner as in Example 1 except that 0.86 g of boric acid was used instead of methyl borate. The density and bending strength of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 1 SiC was mixed in the same manner as in Example 2 except that 300 ml of ethanol was added to the same mixture of SiC raw material powder, phenol resin and methyl borate as a mixed slurry to obtain SiC.
A sintered body was obtained. The density and bending strength of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Table 1.

[0019]

[Table 1] ¹⁾ Water-soluble phenolic resin

Comparative Example 2 An SiC sintered body was obtained in the same manner as in Example 4 except that a mixture of SiC raw material powder, phenol resin and boric acid was added to 300 ml of ethanol to prepare a mixed slurry. The density and bending strength of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Table 1.

Comparative Example 3 A SiC sintered body was obtained in the same manner as in Comparative Example 2 except that a water-soluble phenol resin was used as the phenol resin and water was used instead of ethanol. The density and bending strength of the obtained sintered body were measured in the same manner as in Example 1. The results are shown in Table 1.
It was shown to.

Comparative Example 4 A SiC sintered body was prepared in the same manner as in Example 1 except that the added phenol resin was 1.0 g, and the sintered body density and bending strength were measured. The results are shown in Table 1.

Comparative Example 5 An SiC sintered body was prepared in the same manner as in Example 1 except that the added phenol resin was 16.0 g, and the sintered body density and bending strength were measured. The results are shown in Table 1.

As is clear from the above Examples and Comparative Examples, the SiC sintered body prepared by using the mixed slurry prepared by dissolving the boron source compound in the solvent acetone together with the SiC raw material powder has high density and high It turns out that it is strength. It is also clear that even if the amount of the boron source added is as small as 0.15% by weight of the SiC powder, a sintered body of high density and high strength can be obtained. On the other hand, a SiC sintered body using a mixed slurry using ethanol or water as a dispersion medium is
Compared to using acetone as the dispersion medium with the same addition amount,
It can be seen that the density is low and the strength is low.

[0025]

INDUSTRIAL APPLICABILITY The present invention uses a densification sintering aid of a boron source and a carbon source compound, which is soluble in a non-alcoholic and non-aqueous dispersion medium that forms a SiC raw material powder slurry. A mixed slurry using a non-alcohol and non-aqueous dispersion medium of SiC can be prepared, and the obtained SiC sintered body has sufficient high density and high strength, and is industrially extremely useful.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masatoshi Onishi 30 Soya, Hadano, Kanagawa Prefecture Toshiba Ceramics Co., Ltd.

Claims (3)

[Claims] 1. In the densification sintering of silicon carbide, a boron-containing compound and a carbon-source compound of a densification sintering aid are added to a non-alcoholic and non-aqueous dispersion medium slurry containing silicon carbide raw material powder. A method for producing a silicon carbide sintered body, comprising using a powdery or granular material obtained by adding boric acid and / or boric acid ester soluble in a dispersion medium and a phenol resin, respectively, and using the powdery or granular material. 2. The total amount of the boric acid and / or borate ester is 0.05 to 0.8% by weight based on the boron element, and the phenol resin is 1 to 5 based on the carbon element based on the silicon carbide raw material powder. The method for producing a silicon carbide sintered body according to claim 1, wherein the weight percent is added. 3. The method for producing a silicon carbide sintered body according to claim 1, wherein the dispersion medium is acetone.