JPH01188469A - Production of silicon carbide sintered compact - Google Patents

Abstract

PURPOSE:To obtain the subject sintered compact consisting of smalldiameter grains and having high density and mechanical strength by compacting a mixture of SiC powder, a B-contg. compd., and a C-contg. compd., impregnating the compact with a soln. of an org. Al compd., and sintering the impregnated compact in a nonoxidizing atmosphere. CONSTITUTION:From 99.92-97.5wt.% SiC powder consisting essentially of beta-SiC having 0.03-0.3mu grain diameter, 0.02-0.1wt.% B-contg. compd. (e.g., B) corresponding to B atom, and 0.03-0.15wt.% C-contg. compd. (e.g., carbon black) corresponding to C atom are mixed. The mixture is compacted into a specified shape, and the compact is impregnated with the soln. of an org. Al compd. (e.g., aluminum alkoxide) in a solvent (e.g., benzene) so that the total amt. of the Al, B, and C atoms is controlled to 0.08-0.35wt.%. The impregnated compact is then sintered in a nonoxidizing atmosphere.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for producing a sintered body of silicon carbide (hereinafter referred to as StC), and more specifically, the present invention relates to a method for producing a sintered body of silicon carbide (hereinafter referred to as StC), and more specifically, a sintered body having a small particle size, high density, and excellent mechanical strength. The present invention relates to a method for producing a SiC sintered body.

[Prior Art] SiC sintered bodies have excellent heat resistance and a low coefficient of thermal expansion, and high-density sintered bodies have high strength at high temperatures, so they are attracting attention as structural materials for high temperatures. However, since it is difficult to sinter the SiC powder itself, various sintering aids have been proposed to achieve higher density.

For example, aluminum (hereinafter referred to as A text) is used as a sintering aid in Japanese Patent Publication No. 57-41538, etc.
No. 1-148712 and Japanese Patent Publication No. 57-32035 disclose a combination of boron (hereinafter referred to as B) and carbon (hereinafter referred to as C). In addition, the special public corporation Showa 4
8-7486 and JP-A-55-116667M, etc., oxides of Ma group elements are disclosed in JP-A-57-1609.
Rare earth elements are disclosed in Publication No. 70@ and the like.

[Problem to be solved by the invention] In the above-mentioned conventional technology, the amount of sintering aid added is
Generally, it is in the range of 0.5 to 4% by weight based on the powder, and if the amount added is less than this, sintering is said to be difficult. However, as the amount of the sintering aid added increases, the SiC powder tends to undergo abnormal grain growth during sintering, resulting in a problem in that the strength of the sintered body decreases. The reduction in strength of the sintered body may be due to abnormal grain growth particles or to low density as a result of grain growth preceding densification.

In order to prevent such problems,
Publication No. 9785 discloses that Ag, B, and C are used simultaneously to reduce the amount of 8λ added due to the synergistic effect, thereby reducing the total amount of sintering aid added, thereby increasing the density of the sintered body. A manufacturing method is disclosed.

The present invention further improves the technique disclosed in Japanese Patent Publication No. 58-9785, and provides a manufacturing method capable of producing a high-density sintered body.

[Means for Solving the Problems] The method for producing a SiC sintered body of the present invention includes 5i-C powder 99
．． 92 to 97.5% by weight, a B-containing compound in an amount corresponding to 0.02-, -0°1% by weight of B atoms, and 0.03 to 97.5% by weight.
A molding process in which a C-containing compound corresponding to 0.15% by weight of C atoms is mixed to form a molded body of a predetermined shape, and a total group of A atoms, B atoms, and C atoms in the sintered body 0.
08- An impregnation step of impregnating the molded body with a solution of an organic Al compound to a concentration of 0.35% by weight; a sintering step of sintering the molded body impregnated with the organic Al compound in a non-oxidizing atmosphere; It is characterized by:

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

β-8iC is usually used as SiC powder, but
α-8iC can be used alone or in combination. The particle size is 0.03 to 0.0, which is the same as before.
A thickness of 3 μm is preferable.

B-containing compounds include B alone, 5ac1BN, AlB
2, etc., which are similar to conventional ones, can be used. This B-containing compound is mixed with the SiC powder and the C-containing compound in an amount of 0.02 to 0.1% by weight in terms of B atoms. When the amount added is less than 0.021% by weight, sintering becomes difficult, and when it is more than 0.1% by weight, grain growth of the sintered body is promoted.

Carbon black and graphite are typical examples of the C-containing compound, but other organic compounds that are thermally decomposed during sintering to supply C atoms can also be used. However, since organic compounds contain parts that decompose and disappear during sintering, in some cases, the disappeared parts become pores and remain, reducing the density. Therefore, it is preferable to use carbon black or the like, which has almost no disappearing portion. This C-containing compound is 0.03 to 0°1 in terms of C atoms.
It is mixed with SiC powder and a B-containing compound to a concentration of 5% by weight. C may be present in SiC or in silica (SiO) formed from oxygen adsorbed during heating.
2), and also fixes free silicon as carbide. Further, some of the material remaining during sintering suppresses movement of grain boundaries or grain growth. Therefore, if the amount added is less than 0.033 weight percent, the smooth progress of sintering will be hindered, and if it is more than 0.15% by weight, the oxidation resistance of the sintered body will deteriorate.

After the above three components are mixed sufficiently and uniformly, a molded article having a predetermined shape is formed by a known molding method such as compression molding or slip casting molding. Note that this molding step is preferably performed in a non-oxidizing atmosphere. This is to prevent oxygen from being adsorbed on the SiC powder surface and taking away C during sintering.

The impregnation step, which is the most characteristic feature of the present invention, is a step of impregnating the molded article with a solution of an organic Al compound. Yes 11Af
Fi compounds include Ai (OCH3)3, which becomes a solution when dissolved in benzene etc., Ai(OCx)-1s)3,
A, e(OC3H7)3, AJ! (OC@HsCHz)
Aluminum alkoxides such as No. 3 are suitable, but those that can be dissolved in thin ice, an organic solvent, etc. to form a solution can also be used.

In 6 of the 11Affi compounds impregnated in this impregnation step, the total amount of Aλ atoms, B atoms and C atoms in the sintered body is 0.
．． The loss is estimated to be 0.08 to 0.35% by weight.

This can be easily done by adjusting the concentration of the organic λ compound solution. The total amount of 3 atoms is 0
．． If it is less than 0.08% by weight, sintering becomes difficult;
When the amount exceeds 1%, grain growth occurs and density and strength decrease. Note that this impregnation step is also desirably performed in a non-oxidizing atmosphere.

This is to prevent oxygen from being adsorbed on the SiC powder surface and taking away C during sintering.

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

[Operations and Effects of the Invention] In the method for producing a SiC sintered body of the present invention, an organic Affi compound in a solution state is impregnated into the molded body formed in the molding step. Therefore, the molded body formed in the molding process has AJ2
Since no atoms exist, the content of SiC powder in the molded product can be reduced compared to the method of mixing all the sintering aids at the same time and molding, as in Japanese Patent Publication No. 58-9785. SiC particles are in close contact with each other. In addition, in the impregnation step, the organic Ai compound in a solution state is impregnated into the voids in the molded body, so the apparent volume of the molded body does not change, and the SiC particles are extremely close together as in the molding process.

Therefore, during sintering, SiC particles are easily sintered, and a sintered body with high density can be manufactured.

Furthermore, since Affi is impregnated in a solution state, it is distributed extremely uniformly in the molded body, and a synergistic effect with B atoms is reliably exerted. Therefore BlC, AJf! If the total amount of these three types of atoms is at least lower than that of the conventional method, the synergistic effect results in excellent sinterability and grain growth is suppressed.

Therefore, the SIC sintered body manufactured by the manufacturing method of the present invention has a small particle size, high density, and excellent mechanical strength.

[Example] Hereinafter, this will be explained in detail using examples.

<Example 1> (1) Molding process Carbon black with a particle size of approximately 200 mm was heated under reduced pressure to 1380 mm
℃ to react with silicon monoxide (SiO), unreacted SiO
was removed by evaporation to synthesize β-8iC powder with a particle size of 500 to 800 particles. This SiC powder and C powder as an eluent were heated to 750° C. in a fluidized bed in a hydrogen stream to remove surface oxygen and collected in benzene.

Amorphous BID powder was synthesized by a gas phase reaction of boron tribromide (BBr3) and hydrogen, and stored in benzene at a predetermined concentration. In addition, 90% of this B powder has a particle size of 0.07 to 0.1
There is a range of 0 μm.

Carbon black powder with a particle size of about 200 was thoroughly dispersed in an FFI mill coated with nylon 6.6, and then stored in benzene at a predetermined concentration.

SiC, B and C powders each stored in benzene are mixed so that the B powder is 0.03% by weight, the C powder is 0.05% by weight, and the balance is SiC powder in terms of solid content,
After mixing in a resin ball mill for 72 hours, the benzene was dried in nitrogen gas.

And 15? 150kg/Cl12 of the mixed powder
The molded product was first molded at a pressure of 2,000 kg/cm 2 , and then subjected to isostatic pressing at a pressure of 5,000 kg/cm 2 to form a molded product of a predetermined shape. Note that the molding was performed under a nitrogen gas atmosphere.

(2) Impregnation process A 5% by weight benzene solution of aluminum isopropoxide is prepared, the entire molded body is immersed in this benzene solution, the pressure is reduced, and then the molded body is coated with aluminum isopropoxide in a nitrogen gas atmosphere. Impregnated with de. In addition, the amount of impregnation is 0.02ffi amount% in the molded body in terms of λ atoms.
It is.

(3) Sintering process The molded body impregnated with aluminum isopropoxide is 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 to sinter. did.

(4) Measurement of characteristic values The total porosity, average grain size and three-point bending strength of the obtained sintered body were measured, and the results are shown in the table. The total porosity was measured by the Archimedes method using n-butanol, the average particle size was measured by a scanning electron microscope, and the bending strength was determined by JIS-R.
Measured according to 1601. The sintered body obtained in this example can be sintered with high density even if the total amount of sintering aid is small, and has a small particle size and excellent 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 AI were changed as shown in the table, and the characteristic values were measured in the same manner. The results are shown in the table. From the table, the porosity is at most 8.8% by volume, which is 9% of the theoretical density.
It shows a sinterability of up to 0%. Regarding the particle size, although there is a tendency for the particle size to be slightly smaller in the sintered bodies with higher porosity, they all have very fine particle sizes of 0.8 to 1.2 μm. Furthermore, the bending strength is 45 to 60 kgf/mm2 even for a sintered body with a large porosity, which shows excellent strength.

(Comparative Example) Using the same SiC powder, B powder, and C powder as in Example 1, ΔMoon powder with an average particle size of about 1 μm was mixed with benzene in the composition shown in the table, and a molded body was prepared in the same manner as in Example 1. was formed. Note that the Affi powder used had the anti-oxidation film on the surface removed with a solvent.

The molded body was then sintered in the same manner as in Example 1 without performing the impregnation step. The characteristic values of the obtained sintered body were measured on the same sphere, and the results are shown in the table.

From the table, the sintered bodies of the comparative examples have the same composition as the sintered bodies of the examples, but the total porosity is large and the bending strength is low.

That is, it is clear that the reason why the sintered body of this example has excellent properties is due to the effect of the impregnation process.

Patent applicant: Toyota Motor Corporation Agent: Patent attorney: Hiroshi Okawa

Claims (1)

[Claims] (1) 99.92 to 97.5% by weight of silicon carbide powder and 0
．． A molded article having a predetermined shape is prepared by mixing an amount of a boron-containing compound corresponding to 02 to 0.1% by weight of boron atoms and an amount of a carbon-containing compound corresponding to 0.03 to 0.15% by weight of carbon atoms. and an impregnation step of impregnating the sintered body with a solution of an organoaluminum compound so that the total amount of aluminum atoms, boron atoms, and carbon atoms in the sintered body is 0.08 to 0.35% by weight. and a sintering step of sintering the compact impregnated with the organic aluminum compound in a non-oxidizing atmosphere.