JPS60251175A - Manufacture of formed body made from silicon carbide and carbon - 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 (a) Industrial Application Field The present invention relates to a method for manufacturing a molded article made of silicon carbide and carbon that can be used in various industrial fields as a heat-resistant material, wear-resistant material, chemical-resistant material, etc. It is something.

(b) Background technology Silicon carbide has high hardness and is difficult to mold.

Therefore, when producing a silicon carbide molded body of a desired shape, a sintering method using silicon carbide powder as a starting material is generally employed. However, in the production of silicon carbide molded bodies using the sintering method, if pressure sintering is used, the silicon carbide powder must be heated to a high temperature in a mold and compressed with great force, which requires extremely large-scale equipment. There is a problem with becoming. In addition, when using this method, it is difficult to sinter with silicon carbide powder, so B and A are used as sintering aids.
It is necessary to modify I, C, etc. or their compounds, but adding such a sintering aid causes strength deterioration at high temperatures, making it difficult to maintain the original heat resistance of silicon carbide. .

There is also a method in which a carbonized molded body is used as a base material and its surface is coated with silicon carbide; It relates to silicon carbide formation on the surface, or coating of silicon carbide produced by a gas phase reaction between a silicon compound and a carbon compound onto a carbon group. However, with such a method, only a portion of the surface of the carbon substrate having a thickness of about 11 or less can be converted into silicon carbide.

Therefore, the present inventor has recently developed and proposed a new manufacturing method for obtaining molded bodies of silicon carbide (and carbon), differing from these conventional techniques (Japanese patent application No. 5
No. 8-25291). That is, in this method, a carbon molded body previously formed into a desired shape is placed together with a silicon-containing material in an inert atmosphere that is not affected by oxygen at a high temperature higher than the melting point of the silicon-containing material. is permeated into the carbon molded body to obtain a molded body made of silicon carbide and carbon having substantially the same shape as the carbon molded body, and silicon carbide and carbon with few impurities can be obtained using relatively simple equipment. The present invention has the characteristic that a composite molded article consisting of the following can be easily produced, and can provide a suitable manufacturing method that can replace conventional methods.

By the way, according to the research of the present inventor, one of the problems with this new manufacturing method is that the proportion of silicon carbide in the composite molded article obtained after the infiltration reaction of the silicon-containing material is saturated at a relatively low level. has been done. In other words,
According to this method, the silicon-containing material melted at high temperature penetrates into the voids of the carbon material (molded body), where it reacts with carbon to produce silicon carbide. This causes volumetric expansion (approximately 2.4 times) to close the voids in the molded body, and as a result, further infiltration reaction is suppressed, putting a limit on the increase in the silicon carbide conversion rate. This silicon carbide conversion rate depends on the proportion of continuous voids in the original carbon material (carbon compact), but according to the conventional manufacturing method of this type, the proportion of silicon carbide is The actual situation is that only about 0.3 or less can be obtained.

(c) Purpose The present invention has been made in view of these problems, and its purpose is to develop a method for manufacturing a molded body made of silicon carbide and carbon based on the previous proposal of the present inventors. While improving and incorporating the characteristics inherent to this type of manufacturing method,
In particular, the object is to be able to arbitrarily control the proportion of silicon carbide in a molded body obtained by reaction over a wide range.

(d) Structure In order to achieve this object, the present invention makes a carbon molded body molded into a desired shape mildly oxidized at a temperature of 400 to 800°C to make it lightweight and porous, and this lightweight and porous carbon The molded body is placed together with a silicon-containing material in an inert atmosphere that is not affected by oxygen at a high temperature above the melting point of the silicon-containing material, and the silicon-containing material is allowed to penetrate and react with the carbon molded body to restore the original carbon molding. The present invention is characterized by obtaining a molded body made of silicon carbide and carbon that has substantially the same shape as the body.

The first step of the present invention is to caulk and mold a carbon material (carbon molded body) into a desired shape.
It is oxidized slowly at a temperature of 600°C to make it lightweight and porous while retaining its original shape, and to obtain a molded body having an arbitrary bulk density (porosity). In other words, if oxidation is performed slowly within this temperature range, the carbon molded body will become lightweight and porous as a function of time, and by controlling the oxidation temperature and oxidation time, it can be finished with any desired bulk density. It is something that can be done. The reason why the oxidation temperature was set at 600°C is that when this temperature is exceeded, the oxidation type changes from internal diffusion oxidation to surface oxidation, making it possible to adjust the porosity while maintaining the initial shape of the carbon molded body. This is because it becomes impossible to do so. Furthermore, the lower limit of the oxidation temperature was set at 400° C. mainly to ensure the oxidation rate.

Next, as a second step, the carbon molded body that has been made light and heavy and porous in the first step and whose bulk density (porosity) has been arbitrarily adjusted is converted into silicon carbide by a process similar to the conventional manufacturing method of this type. . That is, a carbon molded body together with a silicon-containing material,
The silicon-containing material is placed in an inert atmosphere unaffected by oxygen at a high temperature above the melting point of the silicon-containing material, and the silicon-containing material is allowed to permeate and react with the carbon molded body, so that the shape is approximately the same as the original carbon molded body. In other words, molded bodies made of silicon carbide and carbon having approximately the same shape and approximately the same dimensional accuracy are obtained.

In this way, when the silicon-containing material is allowed to permeate and react with the carbon molded body whose bulk density has been adjusted in advance in the first step,
As mentioned above, the silicon carbide conversion rate depends on the porosity of the original carbon molded body, so on the condition that at least the necessary amount of the silicon-containing material is allowed to undergo an infiltration reaction,
It becomes possible to control the proportion of silicon carbide in the composite molded body obtained by the infiltration reaction to an arbitrary value corresponding to its porosity.

In the present invention, any general carbon material can be used as the carbon material for molding. Further, as the silicon-containing material, powdered or small-sized metallic silicon, an alloy containing silicon (eg, ferrosilicon, titanium silicon, etc.), or a mixture of silicon and other metals is used. In order to infiltrate and react this silicon-containing material into the carbon molded body, for example, a powdered silicon-containing material dispersed in a suitable binder or solvent is attached to the surface of the carbon molded body, Alternatively, if the carbon molded body is relatively small, it is sufficient to simply place a small lump of silicon-containing material on the carbon molded body. The manner of initial contact with the carbon material is appropriately selected depending on the shape and size of the carbon molded product.

Furthermore, the oxidizing device used in the first stage has an oxidation rate of at least 400 ml in order to gently oxidize the carbon compact.
Various types of furnaces can be used as long as they can maintain temperatures between 600°C and 600°C. On the other hand, as the heating device used to create an atmosphere for the osmosis reaction in the second stage, a normal high temperature heating device may be used. That is, such a heating device maintains the atmosphere in the furnace in an inert state (for example, argon, helium, etc.) that is not affected by oxygen, and uniformly heats the carbon molded body to remove the silicon-containing material. as long as it can be maintained in a molten state.

Again, the type of furnace does not matter.

(e) Examples Hereinafter, the present invention will be specifically explained with reference to Examples.

Bulk density p = 1.47 g / cta' cr)
It was confirmed that when a carbon molded body (IOX 40X 5 mm) was oxidized in air at a temperature of 550°C, it became lighter and more porous over time while maintaining its initial shape. The table below shows the relationship between the number of processing days and the bulk density of the molded body.

Thus, it was found that at a constant temperature, the bulk density of the molded material becomes a function of temperature. In addition, for a certain period of time, it is a function of bulk density, but if the temperature exceeds 600°C at this time, the oxidation rate becomes excessive and surface oxidation increases, so it was found that the molded product did not maintain its initial shape. Ta. Therefore, by controlling the oxidation time and temperature, it was possible to obtain a carbon molded body having an arbitrary bulk density and retaining its initial shape.

Then, metallic silicon was attached to the surface of the carbon molded body thus obtained, and heated to a temperature of 1800° C. in an argon stream using a high-temperature heating device. However, under such conditions, silicon was observed to melt and penetrate into the voids of the carbon molded body. Bulk density p = 0.8
, 1.0 and 1.3 g/cm], the molar ratios of silicon carbide in the molded bodies after the reaction were 0.85, 0.75 and 0, respectively.
．． It was 45. In addition, powder X of each of these reaction compacts
Linear diffraction measurements revealed that the composition was mainly silicon carbide and carbon.

(f) Effects As described above, in the manufacturing method of the present invention, when silicon carbide is produced by penetrating the carbon molded body with a silicon-containing material, the carbon molded body is subjected to a predetermined oxidation treatment in advance to reduce the weight. Since it is made porous and its bulk density (porosity) can be arbitrarily controlled, it accurately solves the problems of the manufacturing method previously proposed by the wood inventor, and carbonization obtained by osmosis reaction. The proportion of silicon carbide in the molded body made of silicon and carbon is varied over a wide range, specifically in a molar ratio of 0.3
It is possible to arbitrarily control the temperature within the range of ~1.0. Even if the acid immersion treatment step is added, as long as the specific processing conditions described above are followed, the final molded product will be lower than the starting molded product. This means that it retains the advantage of maintaining approximately the same shape,
The present invention directly realizes the features of the manufacturing method previously proposed by the present inventor, except for the above-mentioned improvement that the proportion of silicon carbide can be controlled.

Agent: Patent Attorney Hiroshi Akazawa

Claims (1)

[Claims] The carbon molded body molded into the desired shape is heated at 400 to 600°.
Gently oxidize at a temperature of C to make it lightweight and porous, and place this lightweight and porous carbon molded body together with a silicon-containing material in an inert atmosphere that is not affected by oxygen at a high temperature above the melting point of the silicon-containing material. A molded body made of silicon carbide and carbon, characterized in that the silicon-containing material is permeated into the carbon molded body and reacted to obtain a molded body made of silicon carbide and carbon having approximately the same shape as the original carbon molded body. Production method.