JPH0431364A - Production of silicon carbide sintered compact - Google Patents

Abstract

PURPOSE:To sufficiently remove an impurity oxygen in SiC and improve sinterability by arranging deoxygenated members around a formed compact of SiC, temporarily sintering the compact in a vacuum, adsorbing the oxygen in the SiC on the deoxygenated members and carrying out normal sintering. CONSTITUTION:For example, a formed compact 1 of SiC and formed compacts 2 of aluminum nitride as deoxygenated members surrounding the formed compact 1 so as not to mutually contact are arranged in a sheath 3 made of carbon to carry out temporary sintering at 1650 deg.C in a vacuum. The formed compacts 2 are then removed from the interior of the sheath 3 to perform normal sintering at 2050-2150 deg.C. Thereby, silicon oxide in the SiC is released to the atmosphere by heating in the vacuum, adsorbed on the aluminum nitride and converted into aluminum oxide. Since the SiC raw material is purified to a high purity by releasing of the oxygen, sinterability is improved to enable reduction in the amount of a sintering assistant and sintering temperature. As a result, growth of grains following phase transition at high temperatures is reduced to provide the objective dense and high-strength sintered compact.

Description

[Detailed description of the invention] [Purpose of the invention] (Industrial application field) The present invention relates to a method for manufacturing a silicon carbide sintered body.

(Prior Art) Silicon carbide, along with silicon nitride, is one of the materials that are difficult to sinter.

This is thought to be because silicon carbide and silicon nitride have high covalent bonding properties, and the driving force for sintering, which is calculated by subtracting the total grain boundary energy associated with grain boundary formation from the total surface energy of the powder system, is small.

Various methods have been developed to improve sinterability, and three methods are commonly used: hot press method, pressureless sintering method, and reaction sintering method.

The hot press method is a pressure sintering method that applies external mechanical pressure, usually 0.01 to 0.05 GPa (approximately 1
Sintering is performed using a high frequency induction type or resistance type heating method at a pressure of about 0.02 to 510 kg/c ().

The pressureless sintering method does not apply mechanical pressure, and a molded body to which various sintering aids have been added is sintered under atmospheric pressure. Sintering may also be performed in vacuum or inert gas.

The reaction sintering method is a method in which SiC or 5i3N4 is reaction-synthesized using Sl, N2, C, etc. as starting materials during heating, and self-sintering is performed at the same time.

(Problems to be Solved by the Invention) With such materials that are difficult to sinter, it is necessary to add a sintering aid in order to provide driving force for sintering.

However, silicon carbide raw material powder inevitably contains oxygen, and in order to remove this impurity oxygen, it is necessary to use some of the carbon added as a sintering aid as a deoxidizing agent. Ta.

Adding a large amount of such additives may cause a decrease in the mechanical strength of the sintered body, so it is preferable to use as little additive as possible, but depending on the purity of the raw material powder, a considerable amount of depletion may occur. Although this method requires an acid agent and improves sinterability by removing oxygen from silicon carbide, there is a problem in that the strength of the obtained sintered body is insufficient.

In addition, when °τβ type silicon carbide is used as the starting material, a considerably high temperature is required for sintering, so surface diffusion occurs in the silicon carbide compact before the sintering temperature is reached, causing coarsening of the particles. Therefore, there is a problem that the progress of densification is hindered.

Such problems with the sinterability of silicon carbide hinder the improvement of manufacturing efficiency, and how to efficiently obtain high-quality silicon carbide sintered bodies has become an important issue.

The present invention was made to solve these problems, and aims to sufficiently remove impurity oxygen from silicon carbide, reduce the amount of sintering aid added, and reduce the sintering temperature, thereby improving sinterability. It is an object of the present invention to provide a method for manufacturing a silicon carbide sintered body that can improve strength and provide high strength.

[Structure of the Invention] (Means for Solving the Problems) The method for manufacturing a silicon carbide sintered body of the present invention includes arranging an oxygen removing member around a silicon carbide molded body, performing temporary sintering in a vacuum, The method is characterized in that oxygen contained in the silicon carbide is adsorbed by the oxygen removing member, and then main sintering is performed at a temperature at which the silicon carbide is densified.

In the present invention, the deoxidizing member preferably has aluminum nitride as its main component, and can be used in various forms such as a compact or powder.

However, this aluminum nitride is placed in a heating furnace so as not to come into contact with silicon carbide, and the oxygen contained in silicon carbide is adsorbed.

This is because if silicon carbide and aluminum nitride come into contact, there is a risk that aluminum oxide will move to the silicon carbide side and become mixed therein.

In addition to aluminum nitride, metal non-oxides such as carbides, nitrides, and borides can also be used as the oxygen-removing member. For example, aluminum carbide, aluminum boride, etc.

Further, the preliminary sintering in the present invention is performed in a vacuum at a temperature of 1350 to 1
It is carried out at a temperature in the range of 950°C. If this temperature is too low, oxygen adsorption to aluminum nitride occurs, and if it is too high, aluminum nitride decomposes and the partial pressure of AI and N in the atmosphere increases, which is not preferable. A more effective pre-sintering temperature is around 1500''C.

Furthermore, if the oxygen partial pressure in the atmosphere is high, it becomes difficult for oxygen to escape from silicon carbide, so it is preferable to perform the treatment in a vacuum.

Thereafter, the aluminum nitride oxygen scavenger is removed from the heating furnace, and main sintering is performed at a temperature in the range of 1950 to 2300°C, thereby producing a silicon carbide sintered body having high strength.

(Function) Silicon carbide contains oxygen in the form of silicon oxide.

By heating this silicon oxide in a vacuum, it is released into the atmosphere, and is adsorbed by the aluminum nitride of the oxygen removing member to become aluminum oxide.

That is, since the oxygen partial pressure in the atmosphere is always low, the oxygen in silicon carbide is easily and quickly released.

Since the silicon carbide raw material is highly purified by the release of oxygen, sinterability is improved and it becomes possible to lower the sintering temperature.

This reduces the growth of particles due to phase transition at high temperatures, producing a dense and strong sintered body.

(Example) Next, examples of the present invention will be described.

Examples 1 to 6 First, a predetermined amount of boron and carbon were added and mixed to α-8iC raw material powder with an average particle size of 0.5 μm, and 50a+m
A molded body with dimensions of 50ss and 4mm was produced.

On the other hand, aluminum nitride powder was used at 250 kgf/ca+
Press molded at a pressure of 30nn+ as an oxygen absorbing member.
An aluminum nitride molded body with dimensions of 30 mm and 10 mm was produced.

Thereafter, the silicon carbide molded body and the aluminum nitride molded body are combined, for example, as shown in FIG. They were placed in a vacuum chamber so as not to come into contact with each other, and pre-sintering was performed at 1650° C. in a vacuum.

Thereafter, the aluminum nitride molded body 2 was removed from the inside of the sheath 3, and main sintering was performed at a temperature in the range of 2050°C to 2150°C.

The density and mechanical strength of the obtained silicon carbide sintered body were measured. Measurement of mechanical strength is carried out by JIS
A three-point bending test was conducted according to R-1601. These results are shown in Table 1.

Examples 7 to 12 As in Example 1, predetermined amounts of boron and carbon were added and mixed to α-8IC raw material powder, and 5 (1wm×50m5×4
A molded body of +m was produced.

On the other hand, aluminum nitride powder was placed around silicon carbide as an oxygen absorbing member, and pre-sintered under the same conditions as in Example].
Next, the aluminum nitride powder was removed and main sintering was performed. In addition, measurements of density and strength were performed in the same manner. These results are shown in Table 1.

Comparative Examples 1 to 6 Same as Example 1, predetermined amounts of boron and carbon were added and mixed to α-8IC raw material powder, and 50+*aX 50sa+X
A molded body of 4ata was produced.

Then, without using an oxygen absorbing member, in a vacuum at 2050°C ~
Sintering was performed at a temperature of 2150°C.

The density and mechanical strength of the silicon carbide sintered body thus obtained were also measured.

These results are shown in Table 1 together with the results of Examples.

As is clear from the results shown in Table 1, in the example using the oxygen scavenging member made of aluminum nitride, a dense and high-strength silicon carbide sintered body was obtained.

In addition, when comparing the sintering temperature of 2050°C and 2150°C, the sintered body of the comparative example does not reach the required strength unless the temperature is raised to 2150°C, whereas the sintered body of the example The sintering of the compact proceeded satisfactorily even at 2050°C, making it possible to lower the sintering temperature than before.

Examples 13 to 18 First, a predetermined amount of boron and carbon was added and mixed to β-3iC raw material powder with an average particle size of 0.15μ, and 50m+
A molded body measuring a x 50 mm x 4 mm was produced.

On the other hand, aluminum nitride powder was used at 250 kgf/cm 2
Press molded at a pressure of 30ml as an oxygen absorbing member.
An aluminum nitride molded body having a size of 30 mw and 10 cm was prepared.

Thereafter, the silicon carbide molded body and the aluminum nitride molded body were placed in a carbon pod so as not to contact each other, and pre-sintered at 1650° C. in a vacuum.

After that, the aluminum nitride molded body was removed from inside the pod,
Main sintering was performed in the range of 2050°C to 2150°C.

The density and mechanical strength of the obtained silicon carbide sintered body were determined. These results are shown in Table 2.

Examples 19 to 24 As in Example 13, predetermined amounts of boron and carbon were added and mixed to the β-8iC raw material powder to produce molded bodies of 50 cm x 50 cm x 4 cm.

On the other hand, as an oxygen absorbing member, aluminum nitride powder was used as a packing powder, preliminary sintering was performed under the same conditions as in Example 13, and then main sintering was performed after removing the aluminum nitride packing powder.

In addition, measurements of density and strength were performed in the same manner. These results are shown in Table 2.

Comparative Examples 7 to 12 Same as Example 13, a predetermined amount of boron and carbon was added and mixed to β-5iC raw material powder, and 5Dtsta×50+*sX
A 4 tpm molded body was produced.

Then, without using an oxygen absorbing member, in a vacuum at 2050°C ~
Sintering was performed at a temperature of 2150°C.

The density and mechanical strength of the silicon carbide sintered body thus obtained were also measured.

These results are shown in Table 2 together with the results of Examples.

(The following is a blank space) As is clear from the results in Table 2, in the example using the oxygen scavenging member made of aluminum nitride, a dense and high-strength silicon carbide sintered body was obtained.

In addition, when comparing the sintering temperature of 2050°C and 2150°C, the sintered body of the comparative example does not reach the required strength unless the temperature is raised to 2150°C, whereas the sintered body of the example The sintering of the compact proceeded satisfactorily even at 2050°C, making it possible to lower the sintering temperature than before.

[Effects of the Invention] As explained above, in the method for producing silicon carbide of the present invention, a metal non-oxide is placed together with silicon carbide as an oxygen scavenging member and pre-sintered, and the oxygen in the silicon carbide is removed from the metal. Since the sintering agent is adsorbed on the non-oxide, unnecessary oxygen can be removed without increasing the amount of sintering aid added, and denseness and strength can be improved.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the arrangement during preliminary sintering in the method for manufacturing a silicon carbide sintered body of the present invention. 1...Silicon carbide molded body 2...Aluminum nitride molded body 3...
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Claims (2)

[Claims] (1) Arrange a deoxidizing member around the silicon carbide molded body, perform temporary sintering in a vacuum, allow the oxygen contained in the silicon carbide to be adsorbed to the deoxidizing member, and then the silicon carbide becomes densified. A method for producing a silicon carbide sintered body, characterized by performing main sintering at a high temperature. (2) The method for manufacturing a silicon carbide sintered body according to claim 1, wherein the oxygen removing member uses aluminum nitride.