JPS6065765A - Process for sintering cubic silicon carbide powder - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for sintering cubic silicon carbide (hereinafter referred to as β-3i (hereinafter referred to as E)) powder.

Sintered silicon carbide threads are widely used as wear-resistant and heat-resistant materials because of their high hardness and high-temperature strength. Silicon carbide can be roughly classified into two crystal forms, α and β, and the present invention relates to a method for sintering β-8iO powder. Conventionally, as a method for sintering β-3iO powder, a method is known in which this powder is mixed with a certain amount of boron and carbon, and the mixture is fired in a vacuum, a CO gas atmosphere, or an inert gas atmosphere.

In the sintering of β-3iO powder, the difficulty in making it compact is that grain growth occurs at the final stage of sintering, and for example, the grain size is 100 μm.
The problem is that a large amount of the above particles are generated and it is difficult to increase the density. Boron effectively acts to densify the sintered body, but at the same time has the effect of promoting grain growth at the final stage of sintering. In addition, carbon is an impurity contained in β-8iG powder, 5in2 (
However, it was considered harmful if the amount exceeded the amount required for deoxidation.

Therefore, the amounts of boron and carbon mixed into the β-8iO powder were used within a certain range. For example, boron 0.5
~5.0% by weight, carbon 1.5~5.0% by weight (Tokuko Sho 5
No. 8-17146), boron 0.3 to 3% by weight, carbon 0.
It is used in an amount of 1 to 1.0% by weight (Japanese Patent Publication No. 57-32035).

In this way, boron should be used in an amount of 0.3% by weight or more, and carbon should not be added in an amount more than necessary.

However, these methods still have the drawback that a sintered body with a satisfactory high density cannot be obtained.

Conventionally, a method has been proposed in which carbon and boron are mixed in amounts of 11 to 5% by weight of each of β-3ift powder produced by a specific method and fired (Japanese Patent Publication No. 46996/1983). In this method, it is possible to use boron in an amount of up to 0.1% by weight, but in all of the examples, the amount of boron used is 1.0%. High-density β-8 can be obtained even with β-8iO powder regardless of the manufacturing method.
The object of the present invention is to provide a sintering method capable of producing a sintered body of three powders.

As a result of detailed study on the reaction mechanism and conditions for sintering β-8iO powder, the present inventors found that (1)
The grain boundary energy of iO particles is reduced by interposing a carbon material (or other inorganic material) between the particles, and this interposition promotes sintering and suppresses grain growth.

[g) 5102 accompanying β-8iO generates CO gas through a reaction with carbon mixed at 1000° C. or higher: 5in2+ O = SiO+ 00 (1) SiO+ 30 = SiO+ 200 (2). This CO reacts with the mixed B and jQ+13=BO+G (3) This reaction produces BO gas and consumes B. Therefore, the amount of B used can be reduced by removing 5 in2 without wasting B before sintering. It requires 10% before sintering.
-1100~1500℃ under low vacuum of -1~10-8 atmospheres
It is necessary to heat it to That is, 10-10
Reactions (1) and (2) occur at an atmospheric pressure of 1,100 to 1,500°C, and the generated CO gas does not react with boron and is released outside the prefecture, and reaction (3) does not occur, so there is no consumption of boron.

(5) The amount of boron mixed is as shown in Figure 2.
0.4% by weight to increase density without removal of 2.
However, the density of the sintered body is still only 3.
Only Off/am2 or less can be obtained.

On the other hand, when preprocessing is performed to remove 5102, 0.1
~0.3% by weight is sufficient, and the density of the obtained sintered body is 3.1
It is possible to reach K up to 82/crIL3.

It should be noted that if the amount of boron is increased more than this, grain growth will be promoted in the final stage of sintering and the density will be reduced.

(4) As shown in Figure 1, the amount of carbon added varies somewhat depending on the type of carbon source, but it is more than 1% by weight and 3% by weight.
It is preferable that the carbon content be less than 1% by weight (1 part of carbon is consumed by removing 5 in 2), and if it is less than 1% by weight, the thickness of the phase interposed between the particles will be insufficient and densification will be difficult, and if it exceeds 3% by weight. and to prevent excessive urbanization.

The present invention has been completed based on the above findings.

The gist of the present invention is to mold a mixture of cubic silicon carbide powder containing more than 1% by weight of carbon and less than 3% by weight of carbon and 0.10 to 0.3% by weight of boron. 10""
~10-51:) Te 1100-15o under pressure.

After heating to ℃ and performing pretreatment to exhaust and remove the generated CO gas, it was heated for 1 hour in a vacuum or in a chemically inert atmosphere.
A method for sintering cubic silicon carbide powder characterized by firing at a temperature of 900 to 2200°C.

Conventionally, it is known that it is good to remove 5i02 accompanying the β-8iO powder before sintering the powder. (JP-A-57-166369, JP-A-57-16
(No. 6372) In both of these methods, in order to activate the water production surface for one whole winter, it is treated in a reduced pressure atmosphere of reducing gas (H2,00).
0 = p5in2 is removed by the reaction of SiO+Co2. 10-4 to 10- when no reducing gas is used
It promotes a reaction that requires a high vacuum of 7 atmospheres.

The above method uses a reducing gas, which is not only dangerous and troublesome to operate, but also requires a reducing gas. Further, in the case of a high vacuum atmosphere, maintaining the vacuum at 10 -4 to 10 -7 atmospheres in a normal sintering furnace generally requires a high-grade exhaust system.

In contrast, the method of the present invention does not require 10 to 10 ml of gas and can be performed with a simple exhaust system. Since the generated GO is immediately exhausted under the atmosphere at a temperature fτ of 1500° C. or lower, it does not react with boron and is not consumed.

If the heating temperature is lower than 1,100°C, decomposition of SiO□ will be difficult to occur, and if it is raised to 1,500°C, SiO will decompose and inhibit sintering, so the heating temperature needs to be in the range of 1,100 to 1,500°C. be. Also, if the degree of vacuum is greater than ^0-1, the decomposition and exhaust into CO gas will be slow, or 10-1.
If the temperature is lower than 5, heating will cause decomposition of 5i (3), so it is necessary to have a degree of vacuum of 10 to 10-3.

In the method of the present invention, carbon is added to the β-8iG powder by adding a polyprepolymerized product such as pitch tar, furan resin, phenol resin, or polyimide or polyacrylonitrile resin raw material to acetone, benzene, alcohol, etc. It is incorporated by forming carbon on the surface of the solvent powder.

As mentioned above, the relationship between the amount of carbon added and the density of the obtained sintered body is preferably more than 1% by weight and less than 3% by weight (consumed for removal of 5in2), as shown in Figure 1. That's right.

As shown in Figure 2, the amount of boron added is as large as 0.4% by mass in order to increase the density, since boron is consumed when vacuum pretreatment is not performed in the present invention (curve 1). However, when vacuum pretreatment is performed (curve 2), the amount of boron added is 0.10-0.3% by weight, although high density cannot be obtained.
It is preferable that

Furthermore, regarding the relationship between boron addition amount and grain growth, Figure 3 shows the relationship between boron addition amount and density 9 grain growth (firing temperature 2050
C) was shown. The black circles in the figure represent grain growth.

White circles are those without grain growth, and numbers are density.

Figure: The optimum amount of i-ion ion added is 0.1 i-member% or more.
It can be seen that the amount is less than 3% by weight. That is, if the boron content is 0.3% or more, grain growth occurs, and if it is less than 0.10%, densification is insufficient.

The β-8iC powder containing the above amounts of carbon and boron is molded, and the molded product is heated to 11
Heat treatment at 00-1500°C.

The obtained molded product is fired at 1900 to 22 oo<0>C in a chemically inert atmosphere such as argon gas. 19
Temperatures lower than 00° C. result in insufficient sintering and a high density product cannot be obtained, whereas temperatures higher than 2200° C. are not necessary for sintering and are economically disadvantageous.

Examples are given below to clarify the features of the present invention.

Example 1 β-8iO powder shown in Table 1 below was used. β used
8iO powder is made by reacting 5i02 with carbon.

Table 1 β-8iO powder used True specific gravity 3.19-3.22 Ta/α3 Crystal shape Cubic crystal (3G) Average particle size 0.25-0.28 μm Particles of 1 μm or less 95-98% Specific surface area 15.1-18.7 m2/r impurity amount A
tO,03~0.06%FeO,03~0.07
#5in2 0.22-0.33// C0834-0.47// Phenol resin was used as a carbon source. Phenol resin was dissolved in acetone, and with this solution, an amount of 2% by weight of residual carbon was attached to β-3iO powder, kept in a vacuum dryer at about 100°C for 24 hours, dried thoroughly, and dried in an argon gas atmosphere. 3℃ per minute until it reaches 400-550℃ in the furnace
The temperature was raised to uniformly form carbon on the surface of the β-8iO powder. 0.2% by weight of boron was added to this, thoroughly mixed, and molded to about 60% of the theoretical density using a rubber press.

This molded product was heated to 1400°C and heated to 10°C.
It was baked at 32,100°C for 15 minutes.

The obtained sintered body consisted of particles of about 3 to 10 μm, no abnormal grain growth was observed, and the density was 3.08 f/儂' (
The density reached 96% of the theoretical density, and a highly dense sintered body was obtained.

The characteristics of the sintered body are shown in Table 2, and an 83M photograph of the structure is shown in FIG. Figure (a) shows a broken surface and (b) shows an etched surface.

Table 2 Characteristics of β-8iO sintered body C Added amount 2% by weight f3〃0.2// Density 3.15 f/F3 Particle size 3 to 10 μm Strength Room temperature 600 MPa 1500°C 650 MPa Female comparative example 1 Example The molded product was sintered in the same manner as in Method 1 except for the pretreatment of vacuum heating. The obtained sintered body was as follows.

Density: 240 f/♂ Strength: Room temperature: 370 MPa 1500°C: 410 MPa As described above, according to the method of the present invention, the amount of boron used in the conventional method is small and is not influenced by the manufacturing method of silicon carbide. , the excellent effect of easily obtaining a high-density sintered body can be achieved.

[Brief explanation of drawings]

Figure 1 shows the relationship between the amount of carbon added and the density of the sintered body obtained. Figure 2 shows the relationship between the amount of boron added and the density of the sintered body obtained. One curve; If done, 2 curves:
This shows the case where no pretreatment of vacuum heating was performed. Figure 3 shows the relationship between boron addition amount and grain growth. Figure 4 is an 83M photograph of the sintered body of the present invention, and (a) is a fractured surface.

Claims (1)

[Claims] A mixture of cubic silicon carbide powder containing more than 1% by weight and less than 3% by weight of carbon and 0.10 to 0.3% by weight of boron is molded, and this molded product is Sintering method of raw powder.