Abstract: Disclosed is a method of producing a sintered body of ceramics, wherein a powder mixture consisting, essentially of at most 10%, exclusive of 0%, by weight of yttrium oxide, at most 10%, exclusive of 0%, by weight of aluminum oxide, at most 10%, exclusive of 0%, by weight of aluminum nitride, at most 5%, exclusive of 0%, by weight of at least one material selected from the group consisting of titanium oxide, magnesium oxide and zirconium oxide, and the balance essentially of silicon nitride is sintered under a non-oxidizing atmosphere.

Abstract: There are disclosed a sintered body of ceramics, comprising 0.1 to 10% by weight of Y.sub.2 O.sub.3 ; 0.1 to 10% by weight of Al.sub.2 O.sub.3 ; 0.1 to 10% by weight of AlN; 0.1 to 5% by weight of at least one oxide selected from the group consisting of Li.sub.2 O, BeO, CaO, V.sub.2 O.sub.5, MnO.sub.2, MoO.sub.3 and WO.sub.3 or a combination of at least one of these oxides with at least one oxide selected from the group consisting of B.sub.2 O.sub.3 MgO, TiO.sub.2, Cr.sub.2 O.sub.3, CoO, NiO, ZrO.sub.2, Nb.sub.2 O.sub.5, HfO.sub.2 and Ta.sub.2 O.sub.5 ; and the balance of Si.sub.3 N.sub.4, and a process for producing a sintered body of ceramics, which comprises molding a powder mixture of the same composition, and sintering the resultant molded compact in a non-oxidative atmosphere.The process of the present invention requires no hot press and therefore very suitable for bulk production.

Abstract: There are disclosed a sintered body of ceramics, comprising 0.1 to 10% by weight of yttrium oxide; 0.1 to 10% by weight of aluminum oxide; 0.1 to 10% by weight of aluminum nitride; 0.1 to 5% by weight of at least one silicide selected from the group consisting of magnesium silicide, calcium silicide, titanium silicide, vanadium silicide, chromium silicide, manganese silicide, zirconium silicide, niobium silicide, molybdenum silicide, tantalum silicide and tungsten silicide; and the balance being silicon nitride, and a process for producing a sintered body of ceramics, which comprises molding a powder mixture of the same composition, and sintering the resultant molded compact in a non-oxidative atmosphere.According to the present invention, it is possible to manufacture sintered body having high density and excellent impact resistance.

Abstract: A method for producing powder of a .alpha.-silicon nitride which comprises the steps of adding 0.1 to 2 parts by weight of carbon and 0.005 to 1 part by weight of at least one silicon compound selected from the group consisting of Si.sub.3 N.sub.4, SiC and Si.sub.2 ON.sub.2 to one part by weight, when converted to SiO.sub.2, of a liquid alkylchlorosilane that forms a precipitate and HCl by hydrolysis which precipitate is convertible to SiO.sub.2 at a baking temperature of 1300.degree. to 1550.degree. C., hydrolyzing the resultant mixture, washing the mixture to separate a solid component, and baking the solid component at a temperature of 1300.degree. to 1550.degree. C. in an atmosphere mainly consisting of a nitrogen gas or a gas of a nitrogen compound to effect formation of .alpha.-silicon nitride.

Abstract: Disclosed is a method of producing a sintered body of ceramics, wherein a powder mixture consisting, essentially of at most 10%, exclusive of 0%, by weight of yttrium oxide, at most 10%, exclusive of 0%, by weight of aluminum oxide, at most 10%, exclusive of 0%, by weight of aluminum nitride, at most 5%, exclusive of 0%, by weight of at least one material selected from the group consisting of titanium oxide, magnesium oxide and zirconium oxide, and the balance essentially of silicon nitride is sintered under a non-oxidizing atmosphere.

Abstract: A method of producing ceramic articles having a density substantially equal to the theoretical density comprises heating a highly porous preliminary molding made of a ceramic powder to obtain a preliminarily sintered molding of a porosity below 30%, followed by sintering the preliminarily sintered molding under a uniform pressure by the use of a powder acting as a pressure transmitting medium. This method permits producing a ceramic article having a desired shape, and no deformation in it.

Abstract: A method for producing powder of .alpha.-silicon nitride which comprises the steps of:adding 0.3 to 2 parts by weight of powder of carbon and 0.005 to 1 paret by weight of at least one silicon compound selected from the group consisting of Si.sub.3 N.sub.4, SiC and silicon oxide nitride series compounds to one part by weight (as converted to SiO.sub.2) to a liquid silane derivative which produces a precipitate and HCl by hydrolysis and further causes SiO.sub.2 to be grown by the baking of said precipitate, or the precipitate produced by hydrolysis of the liquid silane derivatives;hydrolyzing the resultant mixture, if necessary;washing the mixture to separate a solid component, if necessary; andbaking the solid component for reduction and nitrogenization at a temperature of 1300.degree. to 1500.degree. C. in an atmosphere mainly consisting of a nitrogen gas or a gas of a nitrogen compound.

Abstract: Disclosed is a silicon nitride-based sintered material having high heat resistance and containing crystal compounds prepared from the silicon nitride and at least one oxide of a rare earth element.

Abstract: Disclosed is a silicon nitride-based sintered material having high heat resistance and containing crystal compounds prepared from the silicon nitride and at least one of oxides of the elements belonging to the III A group in the periodic table.

Abstract: We had previously disclosed a heat resistive and reinforced composite material which was prepared by sintering a finely powdered mixture of trisilicon tetranitride and an oxide of yttrium group elements.More improved similar composite material having excellent bending strength can be obtained by sintering a finely powdered mixture of trisilicon tetranitride, yttrium oxide and aluminum oxide. Cerium oxide, lanthanum oxide or scandium oxide can also be used instead of yttrium oxide.