JPS62158164A - Manufacture of silicon carbide formed body - 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 manufacturing a silicon carbide molded body.

(Prior Art) Known methods for producing silicon carbide molded bodies include, for example, extrusion molding, mold molding, rubber pressing, hot pressing, and slip casting.

Further, a molded body of a mixture consisting of silicon carbide powder, carbon powder, and an organic binder is cut and heated to a high temperature to decompose and remove the organic binder.

A so-called reactive sintering method is also known in which a Si melt or vapor is brought into contact with the Si to react with the carbon in the compact.

This reaction sintering method allows a sintered body of any shape to be obtained, but
In the previous step, the step of heating and decomposing the organic binder used in shaping the molded body to remove it (referred to as the degreasing step),
There is a problem in that the binder temporarily softens and swells when the temperature rises, causing deformation or cracking of the molded product, making it virtually impossible to manufacture molded products such as large, long tubes in particular.

(Structure of the invention) This is the result of intensive study by the inventors on this point.

By employing the method described below, we succeeded in stably producing a silicon carbide molded body and completed the present invention.

That is, in the present invention, a molded body made of a mixture of silicon carbide powder, carbon powder, and an organic binder is embedded in an fIA heat container with heat-resistant powder being filled in the hollow and outer periphery of the molded body. , a method for producing a silicon carbide molded body, characterized in that heat treatment is performed from the outside of the heat-resistant container at a temperature higher than the softening temperature of the organic binder and lower than the decomposition temperature of silicon carbide (2700°C), whereby It has become possible to produce molded bodies that do not undergo any deformation or cracking during heat treatment.

The present invention will be explained in detail below.

The silicon carbide powder used as a raw material in the present invention has an average particle size of 5
0#Lm or less, preferably 10gm or less,
The crystal structure can be either α or β type.

Carbon powder can be used regardless of its type and its shape is arbitrary, but the average particle size is 50 #Lm or less, preferably 1
071m or less is good.

As the organic binder, various thermosetting resins, thermosetting resins, polyvinyl alcohol, cellulose ether, and water-soluble polymers such as starch can be used, but in the present invention, silicone resins are preferred. This is usually used as a solution dissolved in a suitable solvent.

The blending ratio of silicon carbide powder, carbon powder, and organic binder in the method of the present invention is 20 to 90%, respectively.

5 to 50%, 3 to 30% (the above weight %, the same below) is suitably blended depending on the purpose and specifications of the product.

These raw material mixtures are thoroughly kneaded in a mixer, and then formed into arbitrary shapes such as cylinders, cylinders, rectangular tubes, and pillars by means such as extrusion molding, mold molding, rubber pressing, hot pressing, and slip casting. Molded into a hollow or solid shaped body.

Next, this molded body is buried in a heat-resistant container with its hollow and outer circumference filled with heat-resistant powder, and heat-treated to remove the organic binder (degreasing treatment) from the outside of the container.

The heat-resistant powder referred to here refers to powder of inorganic refractories or metals, but if we take into account the advantages of not reacting with the material of the molded object or contaminating the molded object through oxidation or corrosion, it is possible to use inorganic powder. Refractory materials such as oxide-based refractories such as alumina and silica, carbon-based refractories such as graphite, carbon, and silicon carbide, silicon nitride, and boron nitride are preferred. Examples include nitride refractories such as nitride refractories and composites or mixtures thereof, but other refractories can also be used.

However, in the case of heat treatment of the 5iC-C molded body of the present invention, it is effective to use silicon carbide or carbon powder, which is a material of the same quality, in terms of aggravating the contamination of the molded body by foreign substances. be.

In addition, the heat-resistant container used here is a container made of metal or the above-mentioned refractory material, but it has a heat transfer effect during external heating,
Metal has an advantage in terms of material cost and when a large container is required.

The embodiment is generally as shown in FIG.
+61 In order to efficiently remove the gas generated by the decomposition of the organic binder during the heat treatment of the compact l embedded in the thermal powder 2, an exhaust port 4 should be provided on the top surface of the container 3, or It is desirable that a part of the molded body is open, and depending on the shape of the molded body and other conditions, it may be necessary to completely enclose a part of the molded body l with the heat-resistant powder 2, as shown in Fig. 2. Even with heat treatment, the same effects as in the case of FIG. 1 can be obtained.

When a molded body of any shape is heated for degreasing, the molded body becomes fluidized as it approaches the softening point of the organic binder. However, by using the method of the present invention, even if the molded product softens and swells, the shape fixation effect of the refractory powder is maintained. By alleviating the rapid gas generation caused by direct heat treatment of the molded body, it is possible to produce a molded body without any deformation or cracking.

Furthermore, the method of the present invention can be applied not only to silicon carbide-carbon based molded bodies, but also to the degreasing process of molded bodies using other inorganic or refractory material powders and organic binders.

Next, an example will be given.

Example 1 A mixture of 60% silicon carbide powder bundles and 30% carbon powder was mixed with 10% silicone resin as an organic binder and a solvent, and then kneaded well as a raw material, 56φX60φX50.
The inside of a 0L cylinder is filled with silicon carbide powder, which is the same as the raw material.

This is placed in a stainless steel container filled with the same silicon carbide powder bundle, and the silicon carbide powder bundle is poured over the container and the molded body is buried. This was heated to 800° C. at a rate of 40° C./hr under a nitrogen atmosphere, maintained at this temperature for 1 hour, and then slowly cooled. The circular distortion (difference between the maximum diameter and the minimum diameter) of the obtained tubular molded product was 0.
．． It was 4am.

For comparison, when the same molded body was placed in a furnace as it was and heat-treated without using the method of the present invention, the molded body was greatly deformed and cracked, so that it could not be made into a product.

Example 2 The same mixture as in Example 1 was heated 400X520X too.

The hollow part of the formed body is filled with carbon powder, and it is placed in a V-shaped stainless steel container with an angle of 90° with carbon powder lined at the bottom. Cover with powder and 800 at 1()0”C/hr under nitrogen atmosphere.
The temperature was raised to .degree. C., maintained for 1 hour, and then cooled, and the molded article was taken out from the mold.

The difference in the length of the diagonal lines in the square cross section of the obtained molded body was 0.2 mm.

For comparison, when the same molded body was put into a furnace as it was and heat-treated without using the method of the present invention, warpage occurred in the length direction and cracks appeared, and the product could not be obtained.

(Effects of the Invention) As described above, the method of degreasing a molded body according to the method of the present invention has the effect that a good molded body with few cracks and deformations can be obtained.

[Brief explanation of drawings]

FIGS. 1 and 2 are cross-sectional views illustrating embodiments of the present invention, in which FIG. 1 shows a case where the compact is embedded in heat-resistant powder, and FIG. 2 shows a case where a part is exposed. show. 1... φ molded body, 2... heat-resistant powder, 3... container. Patent applicant: Shin-Etsu Chemical Komata Co., Ltd., agent: Ryo Yamaki -, i'bu

Claims (1)

[Claims] 1. A molded body made of a mixture of silicon carbide powder, carbon powder, and an organic binder is buried in a heat-resistant container with heat-resistant powder filled in the hollow and outer periphery of the molded body, and the heat-resistant container 1. A method for producing a silicon carbide molded article, which comprises heating from the outside at a temperature that is higher than the softening temperature of the organic binder and lower than the decomposition temperature of silicon carbide.