JPH0733285B2 - Method for manufacturing silicon carbide sintered body - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a silicon carbide (hereinafter referred to as SiC) sintered body, and more specifically, to a sintered body having a small particle size, high density, and excellent mechanical strength. TECHNICAL FIELD The present invention relates to a method for manufacturing a SiC sintered body capable of obtaining a body.

[Prior Art] A SiC sintered body is excellent in heat resistance, has a small coefficient of thermal expansion, and a high-density sintered body has high strength at high temperatures. However, since it is difficult to sinter the SiC powder itself, various sintering aids have been proposed so far to increase the density.

For example, as a sintering aid, aluminum (hereinafter referred to as Al) is disclosed in Japanese Patent Publication No. Sho 57-41538 and the like.
Japanese Patent Publication No. 57-32035 and the like disclose a combination of boron (hereinafter referred to as B) and carbon (hereinafter referred to as C). Also, Japanese Patent Publication No. 48-7486 and Japanese Patent Laid-Open No. 55-55
-116667 discloses oxides of group IIIa elements, which are disclosed in
57-160970 and the like disclose rare earth elements.

[Problems to be Solved by the Invention] In the above-mentioned conventional techniques, the amount of the sintering aid added is generally in the range of 0.5 to 4% by weight with respect to the SiC powder. It is considered difficult. However, there has been a problem that as the amount of the sintering aid added increases, the SiC powder tends to grow abnormally during sintering and the strength of the sintered body decreases. The decrease in strength of the sintered body may be due to abnormal grain growth grains or to low density as a result of grain growth preceding densification.

As a means to prevent such problems, Japanese Patent Publication No. 58-97
In Japanese Patent Publication No. 85, the density of the sintered body is increased by simultaneously using Al and B and C, and reducing the additive amount of Al by a synergistic effect to reduce the total additive amount of the sintering aid. A manufacturing method is disclosed.

The present invention is to further improve the technique disclosed in JP-B-58-9785, and provides a manufacturing method capable of obtaining a sintered body having a higher density.

[Means for Solving the Problems] A method for manufacturing a SiC sintered body according to the present invention includes a SiC powder 99.92 to 97.5.
Wt% and an amount of B equivalent to 0.02 to 0.1 wt% B atom
Forming step of forming a shaped body of a predetermined shape by mixing the containing compound with an amount of C-containing compound corresponding to 0.03 to 0.15% by weight of C atom, and Al atom, B atom and C atom in the sintered body Is 0.08 ~
It consists of an impregnation step of impregnating the molded body with a solution of the organic Al compound to 0.35% by weight and a sintering step of sintering the molded body impregnated with the organic Al compound in a non-oxidizing atmosphere. Characterize.

The molding step is a step of mixing SiC powder, a B-containing compound and a C-containing compound to mold a molded body having a predetermined shape.

Β-SiC is usually used as SiC powder, but α-SiC is used.
C may be mixed or used alone. The particle diameter is preferably 0.03 to 0.3 μm as in the conventional case.

As the B-containing compound, B alone, B ₄ C, BN, AlB ₂ and the like can be used. This B-containing compound is B
It is mixed with the SiC powder and the C-containing compound so as to be 0.02 to 0.1% by weight in terms of atoms. If the addition amount is less than 0.02% by weight, sintering becomes difficult, and if it is more than 0.1% by weight, grain growth of the sintered body is promoted.

Typical examples of the C-containing compound are carbon black and graphite, but it is also possible to use other organic compounds that are thermally decomposed during sintering and supply C atoms. However, since the organic compound contains a portion that decomposes and disappears during sintering, the disappeared portion may become a pore and the density may decrease in some cases. Therefore, it is preferable to use carbon black or the like that has almost no disappeared portion. This C-containing compound is 0.03 to 0.15% by weight in terms of C atoms.
To be mixed with SiC powder and a B-containing compound. C exists in SiC, or acts to reduce silica (SiO ₂ ) formed from oxygen adsorbed during heating, and fixes free silicon as a carbide. In addition, a part of what remains during sintering suppresses grain boundary movement or grain growth. Therefore, the amount added is 0.03% by weight.
If it is less, smooth progress of sintering is excluded, and if it is more than 0.15% by weight, the oxidation resistance of the sintered body is deteriorated.

After the three components are mixed sufficiently uniformly, a molded product having a predetermined shape is formed by a known molding method such as compression molding or slip casting molding. It should be noted that it is desirable that this molding step be performed in a non-oxidizing atmosphere. This is to prevent oxygen from being adsorbed on the surface of the SiC powder or the like and deprived of C during sintering.

The impregnating step, which is the greatest feature of the present invention, is a step of impregnating the molded body with a solution of an organic Al compound. As an organic Al compound, Al (OCH ₃ ) which becomes a solution by dissolving in benzene etc.
_{3, Al (OC 2 H 5} ) 3, Al (OC 3 H 7) 3, but Al aluminum alkoxides such as _{(OC 6 H 5 CH 2)} 3 are suitable, other water, dissolved, etc. in an organic solvent What becomes a solution can be used. The amount of the organic Al compound impregnated in this impregnation step is 0.08 to 0 when the total amount of Al atoms, B atoms and C atoms in the sintered body.
The amount is 35% by weight. To do this, organic Al
It can be easily performed by adjusting the concentration of the compound solution. If the total amount of 3 atoms is less than 0.08% by weight, sintering becomes difficult, and if it exceeds 0.35% by weight, grain growth occurs and the density and strength are reduced. It is desirable that this impregnation step is also performed in a non-oxidizing atmosphere. This is to prevent oxygen from being adsorbed on the surface of the SiC powder or the like and deprived of C during sintering.

The sintering step is a step of heating and sintering the molded body impregnated with the organic Al compound in a non-oxidizing atmosphere, and can be performed in the same manner as the conventional one.

[Operation and Effect of the Invention] In the method for manufacturing a SiC sintered body of the present invention, the molded body molded in the molding step is impregnated with the organic Al compound in a solution state. Therefore, Al atoms do not exist in the molded body molded in the molding process, and compared with the method in which all the sintering aids such as those found in Japanese Patent Publication No. 58-9785 are mixed and molded at the same time. , The content of SiC powder in the compact can be increased, and the SiC particles are close to each other. Further, in the impregnation step, since the organic Al compound in the solution state is impregnated into the voids in the molded body, the apparent volume of the molded body does not change, and the SiC particles are extremely close to each other as in the molding. Therefore, at the time of sintering, the SiC particles are easily sintered and a sintered body having a high density can be manufactured.

Further, since it is impregnated in an Al solution state, it is distributed extremely uniformly in the molded body, and the synergistic effect with B atoms is surely exhibited. Therefore, the total amount of the three types of atoms of B, C, and Al is at least as high as that of the conventional one, the sinterability is excellent due to the synergistic effect, and grain growth is suppressed.

Therefore, the SiC sintered body produced by the production method of the present invention has a small particle size and a high density, and has excellent mechanical strength.

[Examples] Hereinafter, specific examples will be described.

(Example 1) (1) Forming process Carbon black having a particle size of about 200Å is reacted with silicon monoxide (SiO) at 1380 ° C under reduced pressure, and unreacted SiO is removed by evaporation to obtain β having a particle size of 500 to 800Å. -SiC powder was synthesized. This SiC powder and the powder as detached material were used in a fluidized bed in a hydrogen gas stream.
The mixture was heated to 0 ° C. to remove surface oxygen and collected in benzene.

Boron tribromide (BBr ₃ ) was reacted with hydrogen in a gas phase to synthesize an amorphous B powder, which was stored in benzene at a predetermined concentration. 90% of the B powder has a particle size of 0.07 to 0.10 μm.

Carbon black powder having a particle size of about 200Å was sufficiently dispersed by a vibrating mill coated with 6.6 nylon and then stored in benzene at a predetermined concentration.

The SiC, B and C powders respectively stored in benzene were mixed so that the B powder was 0.03% by weight, the C powder was 0.05% by weight and the balance was SiC powder by solid fractionation, and they were mixed with a resin ball mill. After mixing for an hour, benzene was dried in nitrogen gas. Then, the obtained mixed powder was subjected to primary molding at a pressure of 150 kg / cm ² , and then hydrostatic molding at 5000 kg / cm ² to form a molded product having a predetermined shape. The molding was performed in a nitrogen gas atmosphere.

(2) Impregnation Step A 5% by weight benzene solution of aluminum isopropoxide was prepared, the entire molded body was immersed in this benzene solution to reduce the pressure, and then the molded body was impregnated with aluminum isoproxide under a nitrogen gas atmosphere. Let The impregnated amount is 0.02% by weight in the molded body in terms of Al atoms.

(3) Sintering Step A molded body impregnated with aluminum isopropoxide was heated in a helium gas atmosphere supplied from a pipe cooled with liquid nitrogen, and held at a maximum temperature of 2040 ° C. for 1.5 hours for sintering.

(4) Measurement of characteristic values Total porosity, average particle size and 3 of the obtained sintered body The point bending strength was measured and the results are shown in the table. The total porosity is measured by the Archimedes method using n-butanol,
The average grain size is measured by a scanning electron microscope, and the bending strength is JI.
It was measured according to S-R1601. The sintered body obtained in this example is sintered at a high density even if the total amount of the sintering aid is small, has a small grain size, and is excellent in bending strength.

(Other Examples) Each sintered body was formed in the same manner as in Example 1 except that the amounts of B, C and Al were changed as shown in the table, and the characteristic values were similarly measured. The results are shown in the table. From the table, the porosity is at most 8.8% by volume, which is 90% of the theoretical density.
It shows sinterability up to%. Regarding the particle size,
Sintered bodies with high porosity tend to have a slightly smaller grain size, but all have a very fine grain size of 0.8 to 1.2 μm. Furthermore, the bending strength is 45 to 60 even for sintered bodies with large porosity.
It shows excellent strength with kgf / mm ² .

Comparative Example Using the same SiC powder, B powder and C powder as in Example 1, Al powder having an average particle size of about 1 μm was mixed with benzene in the composition shown in the table, and a molded body was obtained in the same manner as in Example 1. Formed. The Al powder used was the one in which the antioxidant film on the surface was removed with a solvent.

Then, the impregnation step was not performed, and the molded body was sintered in the same manner as in Example 1. The characteristic values of the obtained sintered body were measured in the same manner, and the results are shown in the table.

From the table, the sintered body of the comparative example has the same composition as the sintered body of the example, but has a large total porosity and a small bending strength.
That is, it is clear that the sintered body of this example has excellent characteristics due to the effect of the impregnation step.

Claims (1)

[Claims] 1. Silicon carbide powder 99.92-97.5% by weight, 0.02
~ 0.1 wt% boron-containing compound in an amount corresponding to a boron atom, 0.03 ~ 0.15 wt% by mixing a carbon-containing compound in an amount corresponding to a carbon atom, a molding step of molding a molded body of a predetermined shape, An impregnation step of impregnating the compact with a solution of an organoaluminum compound so that the total amount of aluminum atoms, boron atoms and carbon atoms in the sintered body becomes 0.08 to 0.35% by weight, and the impregnation with the organoaluminum compound A method of manufacturing a silicon carbide sintered body, comprising: a sintering step of sintering a compact in a non-oxidizing atmosphere.