JPH0435435B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for producing a high-density silicon carbide sintered body. (Conventional technology) High-density silicon carbide sintered bodies have heat resistance, chemical resistance,
Because of its excellent wear resistance, it has attracted attention as a structural material under high temperatures, and it has been desired to establish a manufacturing method for it.One manufacturing method is disclosed in Japanese Patent Publication No. 308/1983. The manufacturing method disclosed in the publication was developed by focusing on the firing conditions of a press-molded body mainly made of silicon carbide, and the press-molded body was heated to a temperature of 5 torr or less from room temperature to 1,600 to 1,800 degrees Celsius. It is characterized by firing under a vacuum of 1,600 to 1,800°C to 2,000 to 2,500°C in an inert gas atmosphere that does not flow. According to this manufacturing method, the formation of a carbon film on the surface of the sintered body is extremely small compared to the case where everything is fired under vacuum, and the sintered body has the same high density as under the above firing conditions. is assumed to be obtained. (Problems to be Solved by the Invention) By the way, the present inventor has studied in more detail the firing conditions for the above-mentioned press-formed body, and has found that it is necessary to promptly remove CO, which is an inhibitory substance generated during firing. Of course, the densification of silicon carbide begins at 1800 to 2000°C, and we have found that removing inhibiting substances in this temperature range is extremely effective for densification of silicon carbide. Ta. Therefore, an object of the present invention is to obtain a high-density silicon carbide sintered body based on this knowledge. (Means for Solving the Problems) The present invention relates to a method for producing a high-density silicon carbide sintered body. Characterized by firing under vacuum, then firing under vacuum of less than 0.05 Torr at temperatures from 1800℃ to 2000℃, and finally firing under an inert gas atmosphere at temperatures from 2000℃ to 2100-2400℃ That is. The press-molded article in the present invention is made of silicon carbide or is made mainly of silicon carbide, and its raw materials, additives such as sintering aids, molding means, etc. may be any known appropriate materials or methods. There are no restrictions whatsoever. In the firing of the above-mentioned press-molded body, the temperature increase rate in each firing step may be set at an appropriate rate, for example, 5 to 10
A heating rate of °C/min is preferably employed. Also,
The final firing at a temperature from 2,000°C to 2,100 to 2,400°C is performed under an inert gas atmosphere such as argon or helium, but the inert gas may be in either a flowing or non-flowing state, preferably flowing in and out. I will do it. (Operations and Effects of the Invention) According to the manufacturing method of the present invention, baking is possible under vacuum at temperatures from room temperature to 2000°C, and from 2000°C to 2100°C.
Since the firing is performed under an inert gas atmosphere at temperatures up to 2400°C, a high-density sintered body is obtained with very little formation of carbon film on the surface of the sintered body, but the densification of silicon carbide begins. Firing at 1800-2000℃
Since the firing is carried out under a high vacuum of 0.05 torr or less, there are no or almost no substances that inhibit the densification of silicon carbide in the firing atmosphere, and a silicon carbide sintered body with a higher density can be obtained. (Example) 100 parts by weight of β-Sic powder with an average particle size of 0.4 μm, 0.7 parts by weight of B ₄ C powder with an average particle size of 2.0 μm, and 1.0 parts by weight of carbon black were mixed with water, and polyvinyl alcohol was added. A large number of press-molded products with an outer diameter of 50 mm and a thickness of 7 mm were formed by processing the powder under a pressure of 2.0 tons. Thereafter, the press-molded body was baked at 600° C. for 10 hours in a nitrogen atmosphere to remove polyvinyl alcohol as a binder from the press-molded body. Each of the obtained press-molded bodies was housed in a carbon pod having a porosity of 18% and a through-hole opening degree (%) of each value, and fired under various conditions in a firing furnace. The relative density (%) of each obtained sintered body is shown in the attached table. The heating rate of the firing furnace is 10°C/min from room temperature to 1800°C, and 5°C/min at temperatures above 1800°C.
min, and from 2000℃ argon is
The temperature was maintained at the maximum firing temperature for 30 min.
In Comparative Examples 5 and 6, the argon flow start temperature was 1800°C, in Comparative Example 7 it was 1900°C, and in Comparative Example 8 it was 1700°C. In addition, in the attached table, pod porosity and relative density mean the following items. Saya porosity *1: Percentage of through holes communicating inside and outside of the pod relative to the total surface area of the pod Relative density: *2: Ratio to the theoretical density of 3.21 g/cm ³

【table】

[Table] Referring to the above table, it is clear that a high-density sintered body can be obtained according to the production method of the present invention (Examples 1 to 6), and when the production method of the present invention is not used (Comparative Example 1, 2, 5 to 8), the density of the sintered body becomes low. In particular, referring to Comparative Examples 1, 2, and 5, it can be seen that the degree of vacuum during sintering at a temperature of 1,800 to 2,000°C has a large effect on the densification of the sintered body. Although Comparative Examples 3 and 4 apparently correspond to the manufacturing method of the present invention, the degree of pores in the pod is completely absent or small, making it difficult to quickly bring the atmosphere inside the pod to a predetermined degree of vacuum. It is understood that this is due to the fact that the firing conditions (particularly the degree of vacuum) of the molded body deviate from the conditions of the present invention.

Claims (1)

[Claims] 1Silicon carbide or a press-molded product mainly composed of silicon carbide is fired under a vacuum of 1 torr or less at temperatures from room temperature to 1800°C, and then fired under a vacuum of 0.05 torr or less at temperatures from 1800°C to 2000°C. and finally firing in an inert gas atmosphere at a temperature from 2000°C to 2100-2400°C.