PURPOSE: To obtain the silicon nitride sintered compact giving an extremely smooth surface, when subjected to a mirror-abrading treatment, by embedding a sintered compact produced at the atmospheric pressure in the powder of silicon nitride, etc., and subsequently subjecting the embedded sintered compact to a hot hydrostatic pressing treatment with an inactive gas excluding nitrogen gas.
CONSTITUTION: The method for producing the silicon nitride sintered compact comprises adding a Y2O3, Al2O3, MgO, etc., as a sintering auxiliary to the powder of silicon nitride, molding the mixture, sintering the molded product in nitrogen gas at the atmospheric pressure, embedding the sintered compact in silicon nitride powder, silicon oxide powder, the mixture powder of silicon nitride with silicon oxide, or the mixture of the powder with carbon powder, and subsequently subjecting the embedded sintered compact to a hot hydrostatic pressing treatment using an inactive gas excluding the nitrogen gas, such as argon gas, as a pressing medium gas. The method for producing the sintered compact gives the material capable of being used for molds useful for molding metal rolls, industrial mirrors, etc.
NISHI YOSHIJI
SHIOGAI TATSUYA
