JPS6328871B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly electrically conductive silicon carbide ceramic material.

High-density silicon carbide ceramics are known as materials with high hardness and high high-temperature strength, and are being developed for various uses as useful engineering ceramics, including applications in high-temperature structural materials.

As is well known, silicon carbide is a compound with strong covalent bonds and is very difficult to sinter by itself. Therefore, in order to obtain a high-density sintered body, some kind of sintering aid is required. Known sintering aids for hot breath sintering or pressureless sintering include boron, boron carbide, aluminum,
Aluminum oxide, etc. By using these sintering aids, silicon carbide ceramics with high density and high strength can be produced. but,
Sintered bodies using these sintering aids still have problems in terms of characteristics for practical use. One of the problems is the difficulty in processing sintered bodies. High-density silicon carbide ceramics are often used to replace conventional metal parts, so high dimensional accuracy is usually required. It is rare that the sintered material is turned into a product. For this reason, machining of the sintered body is necessary, but in the case of complex shapes such as turbine blades, general machining becomes difficult. In this case, if the electrical conductivity of the silicon carbide sintered body is high, electrical machining methods such as electrical discharge machining or electrolytic polishing become possible. However, the electrical conductivity of the sintered body using the above-mentioned sintering aid is not high enough to enable these processes.

The present inventors arrived at the present invention in the process of studying the creation of high-density silicon carbide ceramics that can truly withstand practical use. The gist of this invention is to provide a highly electrically conductive silicon carbide ceramic material for electrical processing, which has a high density and is obtained by sintering a mixture of the following.

The silicon carbide ceramic highly electrically conductive material obtained according to the present invention can be subjected to electrical discharge machining and electrolytic polishing, and is suitable for various uses requiring low electrical resistance.

In the present invention, aluminum phosphate acts as a sintering aid not only in hot press sintering but also in pressureless sintering to densify silicon carbide and at the same time impart electrical conductivity to the sintered body. I understood.

The reason why this effect of adding aluminum phosphate occurs has not yet been fully elucidated.

However, at the sintering temperature of 1,900 to 2,300°C used in this case, aluminum phosphate reacts with silicon carbide and decomposes, resulting in phosphorus and aluminum or their compounds being solidly dissolved in silicon carbide and existing at grain boundaries. It is thought that sintering progresses and becomes denser. Further, the reason why the electrical resistance becomes smaller is thought to be that phosphorus forms a solid solution by substitution with carbon in silicon carbide and acts as an electron donor.

According to the inventor's experiments, when initially blended into silicon carbide powder, it does not necessarily have to be in the form of aluminum phosphate (AlPO ₄ ), but in a form that easily changes to aluminum phosphate by heating acidic aluminum phosphate, etc. It has been confirmed that it can also be used. In short, it is sufficient that aluminum phosphate is generated during heating, regardless of the form in which it is blended as a raw material.

It is necessary for the formed product of silicon carbide ceramics in the present invention to contain aluminum phosphate in order to achieve the above-mentioned desired effect, but if this amount is too large, the aluminum phosphate in the bonding portion If the amount is too large, it is undesirable because it will impair high temperature strength and reduce the characteristic of silicon carbide, which is low thermal expansion.If it is too small, it will not be sufficiently densified and the electrical conductivity Even the points become unfavorable. For the above reasons, the amount of aluminum phosphate that should be added is 0.5
-30% by weight, preferably 1.5-15% by weight.

Example 1 Commercially available silicon carbide powder with purity of 99% and particle size of 1
A material of micron or smaller was used. Add 3% by weight of aluminum phosphate powder (particle size 1μ) to this silicon carbide powder.
2000 min in an argon atmosphere.
Hot press at ℃, 1 hour, 200Kg/ ^cm2 ,
A sintered body with a diameter of 30 mm and a thickness of about 10 mm was obtained. The relative density of this sintered body to the theoretical density was 98.2%.
Furthermore, when the electrical resistance between both surfaces of this sintered body was measured, it was 2.1Ω.

Comparative Example 1 A sintered body was obtained in the same manner as in Example 1 except that 2% by weight of alumina (particle size of 1 micron or less) was used instead of 3% by weight of aluminum phosphate in Example 1. The relative density of the obtained sintered body was 99.0%, and the electrical resistance was
It was 2.5×10 ⁵ Ω.

Example 2 The same silicon carbide powder and aluminum phosphate powder as described in Example 1 were used. A mixture of this silicon carbide powder and 5% by weight of aluminum phosphate powder was pressed into a mold at a pressure of 300 kg/cm ² .
A molded body with a diameter of 30 mm and a thickness of about 10 mm was obtained. This molded body was heated at 2000°C for 1 hour in an argon atmosphere. The relative density of the obtained sintered body was 94.4%, and the electrical resistance was 7.0.
It was Ω.

Example 3 A mixed powder similar to that described in Example 2 was first heated at 1700° C. for 1 hour in an argon atmosphere. This powder was crushed, molded and fired in the same manner as described in Example 2. The relative density of the obtained sintered body is 97.4
%, and the electrical resistance was 2.8Ω.

Claims (1)

[Claims] 1. A highly electrically conductive silicon carbide ceramic material for electrical processing, obtained by sintering a mixture consisting of 0.5 to 30% by weight of aluminum phosphate and the remainder silicon carbide.