Method for producing a sintered silicon nitride base ceramic and said ceramic

Claim 1

A process of preparation of a silicon nitride based ceramic comprising the steps of combining 60 to 92 mol percent of finely powdered Si 3 N 4 with at least one member of a first group consisting of MgO, ZnO and NiO and at least one member of a second group consisting of Al 2 O 3 , Cr 2 O 3 , Y 2 O 3 , TiO 2 and SnO 2 , said Si 3 N 4 powder and said members being in powdered form finer than 300 mesh, the mol ratio of said first group member or members to said second group member or members ranging from 1:9 to 9:1 and the combined total quantity of said members lying between 8 and 40 mol percent of the combination including said Si 3 N 4 , mixing said powdered materials, forming said mixed powders into a green compact and sintering said green compact at a temperature between 1600°C and 1800°C in an inert gas in the absence of applied pressure, the resultant composition consisting essentially of Si 3 N 4 and members of said first and second groups.