Abstract: In a heat history initializing step, a heat treatment in performed in an atmosphere including at least one of hydrogen, helium, and argon while the temperature is increased in a range of 700.degree. C. to 1,000.degree. C. at a rate of 15.degree.-1,000.degree. C./min. In a controlled nuclei growing step, a heat treatment is performed in the above atmosphere while the temperature is kept constant in a range of 850.degree. C. to 980.degree. C. for 0.5-60 minutes.

Abstract: A method of producing a high density and high strength silicon carbide member for a heat treatment furnace to be used in the manufacture of a semiconductor device. In this method, SiC powder, carbon powder, deflocculating agent and water are mixed to form a slip. Then the slip is formed into a desired shape, cured under a nonoxidizing atmosphere, and removed of any impurity contained in the shaped body. Finally, the shaped body is immersed in a molten silicon to convert the carbon in the shaped body into silicon carbide.

Abstract: A method of manufacturing heating furnace parts having high purity which comprises the steps of molding a raw powder mainly consisting of silicon carbide powder into a prescribed form, and subjecting the molded product to a purification treatment at a temperature ranging between 1,500.degree. and 2,100.degree. C. in an atmosphere containing a gas selected from the group consisting of halogen gas and hydrogen halide gas, and an inert gas applied as a carrier gas.

Abstract: A method of manufacturing extremely high purity parts for use to the heating furnace comprising adding a sintering assistant of 0.5-2.0 weight % and a binder, to SiC powder which has an average particle diameter of 2 .mu.m or less, and molding it to a predetermined form; applying the purification treatment to this molded body by placing it in the 800.degree.-1,300.degree. C. atmosphere of a gas which is selected from a group consisting of halogen gas and hydrogen halide; degassing the purified molded body in vacuum under a temperature higher than that employed at the purification treatment; sintering the degassed molded body, and coating an SiC film on at least part of the sintered body according to the chemical vapor deposition.