JPS61295272A - Manufacture of silicon carbide formed body with high pore rate - 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 <Industrial Application Field> The present invention relates to a method for producing a silicon carbide molded body having a high porosity and which can be used as a carrier for supporting a catalyst or the like.

<Prior art and its problems] As a conventional high porosity silicon carbide, for example,
As shown in Japanese Patent No. 7-53241, a silicon polymer compound such as polycarbosilane is applied to the pores existing between a large number of sintered silicon carbide particles.

polydimethylsiloxane, polydiphenylsiloxane,
There is silicon carbide obtained by impregnating it with a benzene solution such as polycarbosiloxane, drying it, and then firing it at 1250 to 1500°C in a non-oxidizing atmosphere, but the manufacturing method is complicated and the raw materials are expensive. Furthermore, a porous silicon carbide body was required as a base material.

Another method, as shown in JP-A-60-5072, is to impregnate rice husks with Fe, etc., dry them, carbonize them at 400 to 1000°C in a nitrogen atmosphere, and make the powder. There are hot pressing methods, but the silicon carbide obtained by these methods has a low porosity of 34 to 47%, which is insufficient.

Means for Solving the Problems The present invention starts from inexpensive materials and is easy to operate.
.

The purpose of the present invention is to provide a method for obtaining a silicon carbide molded body having a higher porosity, the gist of which is to carbonize rice husks and/or rice stalks at 400 to 1000°C in a non-oxidizing atmosphere, and then crush them. Oxidize directly or in air, then at 1700°C under a pressure of 100 to 400 kg/cd.
The resulting sintered body was sintered in an oxidizing atmosphere for 400 min.
This is a method for producing a silicon carbide molded body having a high porosity, characterized by heating the sintered body to a temperature above .degree. C. to burn out the carbon in the sintered body.

<Function> Charcoal of rice husks and rice stalks is composed of silica and carbon.
Approximately 60% by weight silica and the remainder carbon.

The reaction in which silicon carbide is produced from carbon (C) and silica (Si02) is thought to involve the following two consecutive reactions. That is, C+5i02→SiO+CO(1) 2C0S i O−=S i C0CO(2) Here, the reaction (1) starts to occur around 1400°C, and (2)
reaction occurs at higher temperatures. Furthermore, SiO is in a gas state, and if a catalyst is not present, the reaction (2) will be slow, so some SiO will volatilize.

The composition of the carbonized rice husks and rice stalks is as described above, so
Even if all of the 5iO2 in the carbide becomes SiC, there will be an excess of C in calculations, but because some of the 5iOz evaporates as SiO, the resulting sintered body will have an even greater excess of C. ing. A sintered body with an excess of carbon is heated to 400°C or higher in an oxidizing atmosphere in the air to burn off the carbon and create pores where the carbon was, resulting in a high porosity. A silicon carbide sintered body having the following properties is obtained.

<Example> The method of the present invention will be described in detail below with reference to Examples.

The 11-membered upper rice husk was carbonized at 500° C. in a nitrogen gas stream, and the carbide was pulverized using a Raikai machine for 16 hours. This carbonized rice husk powder was put into a hot press mold and 200 kg/ci
The temperature was raised to 1700℃ at a pressure of
Holds time.

During the temperature increase process, the micrometer attached to the hot press device rotated rapidly at around 1200° C., causing a phenomenon that appeared to be causing volumetric contraction within the mold. After that, a gradual volume contraction was observed, and a reaction to generate SiC from around 1600°C and a
There was a volumetric contraction that appeared to be accompanied by the volatilization of O gas.

When the mold was taken out of the furnace, the carbon fibers surrounding the mold were found to be white, indicating that SiO was attached.The obtained sintered body was black, indicating that carbon was mixed in. It turns out that there is.

This sintered body was heated to 700° C. in air and held for 3 hours to obtain a pale silicon carbide molded body.

In this case, the amount of carbon burnt off was 53.1% by weight, the amount of silica in the obtained silicon carbide molded body was 4.4% by weight, and the porosity was 79.4%. The X-ray diffraction diagram of the silicon carbide molded body obtained in this Example 1 is shown in the drawing.
It can be seen from the angle of the diffraction lines that the silicon carbide obtained is α-type silicon carbide.

The hot press temperature in Example 1 was changed from 1700°C to 1850°C.
, and everything else was the same as in Example 1.

In this case, the amount of carbon burned out was 41.8% by weight, and the shrinkage of the obtained silicon carbide molded body was 19.5%.
If even a part of 2 is not burnt out as SiO, then 2
Since it must be 6.9%, this indicates that a part of 5i02 is volatilized as SiO. The amount of silica in the obtained silicon carbide molded body was 4.4% by weight, and the porosity was 79.6%. The X-ray diffraction diagram of the silicon carbide molded article obtained in Example 2 is shown in the drawing, and it can be seen from the angle of the diffraction lines that the obtained silicon carbide is α-type silicon carbide.

As shown in the X-ray diffraction diagrams of silicon carbide obtained in Examples 1 and 2 above, the diffraction intensity increases with the hot pressing temperature at 185
Although it is larger in Example 2 at 0°C, the amount of silica contained as an impurity is approximately the same, so the increase in diffraction intensity is due to an increase in the crystallinity of the silicon carbide produced. I think that the.

In addition, in the method of the present invention, when heating a sintered body containing carbon in an oxidizing atmosphere, if the heating temperature is low, it will take a long time to burn off the carbon, so the temperature should be at least 400°C or higher. desirable.

<Effects of the Invention> As described above, according to the method of the present invention, a silicon carbide molded body having a porosity of about 80% can be obtained by using inexpensive materials as raw materials and by simple operations.

The silicon carbide molded product obtained by the method of the present invention has excellent heat resistance and corrosion resistance because it contains little silica as an impurity, and together with the feature of silicon carbide that it is inert itself, it is suitable as a carrier. It has excellent effects.

[Brief explanation of drawings]

The drawings are X-ray diffraction diagrams of silicon carbide molded bodies obtained by the methods shown in Examples 1 and 2 of the present invention.

Claims (1)

[Claims] 1. Rice husks and/or rice stalks are heated in a non-oxidizing atmosphere to
After carbonizing at 1000℃, pulverizing it, oxidizing it as it is or once in the air, and then oxidizing it at 100-400kg/cm^2
Carbonization with high porosity characterized by sintering at 1700°C or higher under a pressure of A method for producing a silicon molded body. 2. The manufacturing method according to claim 1, wherein the silicon carbide molded body obtained has a porosity of 50% or more.