Patent ID: 7049256

Claim:
A ceramic body made from a starting powder mixture that includes silicon nitride powder, and one or more powders that contribute aluminum, oxygen and nitrogen to a beta prime SiAlON phase and aluminum, oxygen, nitrogen and ytterbium to an alpha prime SiAlON phase, the ceramic body comprising: a two phase composite comprising the alpha prime SiAlON phase and the beta prime SiAlON phase wherein the alpha prime SiAlON phase containing ytterbium therein, and wherein the starting silicon nitride powder comprising less than or equal to about 1.6 weight percent beta-silicon nitride; the alpha prime SiAlON phase being present in an amount greater than or equal to about 20 weight percent of the two phase composite; an intergranular phase that includes an intergranular crystalline phase comprising at least one of YbAG and J-phase; and wherein the overall composition of the ceramic body is: Yb a Si b Al c O d N e , and wherein a in the overall composition can be either less than 0.5 or greater than or equal to 0.5, and when a is less than 0.05, the relative intensity of the peak associated with either one or both intergranular crystalline phases of YbAG and J-phase is greater than about 2.5 of major peak of the two-phase composite.