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 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 , all members being in powdered form, the mol ratio of said first group member or members to said second group member or members ranging from 1:9 to 9:1, heating said combined members to a temperature sufficient to form a spinel or spinel-like compound therefrom, cooling and grinding said compound to a fine powder, mixing said powdered compound with powdered Si 3 N 4 in a mol ratio between 8:92 and 40:60, 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, and all powders being finer than 300 mesh prior to heating.