Silicon nitride sintered bodies and a method of manufacturing the same

Claim 1

A silicon nitride sintered body consisting essentially of Si 3 N 4 as a main ingredient, at least one oxide of a rare earth element present in an amount between 3-10% by weight and ZrO 2 present in an amount less than 1.0% by weight, wherein said sintered body has an intergranular phase which consists mainly of a J-phase solid solution, said J-phase solid solution being a crystal phase having a caspidiene structure of a monoclinic system represented by the formula: M 3 I (M 2 II M 7 III )M I M 2 IV , wherein M I is an element selected from the group consisting of Y, Mg, Fe and Ni; M II is an element selected from the group consisting of Si and Al; M III is an element selected from the group consisting of O and N; and M IV is an element selected from the group consisting of F, O and N.

Claim 6

A method of manufacturing a silicon nitride sintered body, comprising: preparing a powder consisting essentially of powdery raw materials of silicon nitride, at least one oxide of a rare earth element present in an amount between 3-10% by weight and ZrO 2 present in an amount less than 1.0% by weight as a sintering aid; molding the thus prepared powder; firing the resulting molding at a temperature between 1,650° and 2,000° C. in a nitrogen or inert gas; and precipitating an intergranular phase consisting mainly of a J-phase solid solution by controlling a temperature-descending step or reheating the sintered body, said J-phase solid solution being a crystal phase having a caspidiene structure of a monoclinic system represented by the following formula: M 3 I (M 2 II M 7 III )M I M 2 IV , wherein M I is an element selected from the group consisting of Y, Mg, Fe and Ni; M II is an element selected from the group consisting of Si and Al; M III is an element selected from the group consisting of O and N; and M IV is an element selected from the group consisting of F, O and N.

Claim 7

A method of manufacturing a silicon nitride sintered body, comprising: preparing a powder consisting essentially of powdery raw materials of silicon nitride, at least one oxide of a rare earth element present in an amount between 3-10% by weight and ZrO 2 present in an amount less than 1.0% by weight as a sintering aid; molding the thus prepared powder; firing the resulting molding at a temperature between 1,650° and 2,000° C. in a nitrogen or inert gas; and precipitating an intergranular phase consisting mainly of a J-phase solid solution by controlling a temperature-descending step or reheating the sintered body, said J-phase solid solution being a crystal phase having a caspidiene structure of a monoclinic system represented by the following formula: M 3 I (M 2 II M 7 III )M I M 2 IV , wherein M I is an element selected from the group consisting of Y, Mg, Fe and Ni; M II is an element selected from the group consisting of Si and Al; M III is an element selected from the group consisting of O and N; and M IV is an element selected from the group consisting of F, O and N.