SiAlON ceramic and method of making the same

A SiAlON ceramic body made from a starting powder mixture that includes silicon nitride powder and one or more powders that provide aluminum, oxygen, nitrogen, at least one of La and Ce and at least one selected rare earth element to the SiAlON ceramic body wherein the selected rare earth element is selected from at least one group of the following two groups of rare earth elements wherein Group II comprises Gd, Tb, Dy and Ho, and Group III comprises Er, Tm, Yb and Lu, and the SiAlON ceramic body comprising:

• a two phase composite comprising an alpha prime SiAlON phase and a beta prime SiAlON phase, and the alpha prime SiAlON phase containing one or more of the selected rare earth elements wherein there being no detectable amount of either La or Ce in the alpha prime SiAlON phase;
• and
• the silicon nitride powder comprises at least about 70 weight percent of the starting powder mixture.

A SiAlON ceramic body made from a starting powder mixture that includes silicon nitride powder and one or more powders that provide aluminum, oxygen, nitrogen, ytterbium and cerium, and the SiAlON ceramic body comprising:

• a two phase composite comprising an alpha prime SiAlON phase and a beta prime SiAlON phase, and the alpha prime SiAlON phase contains ytterbium wherein there is no detectable amount of cerium in the alpha prime SiAlON phase;
• and
• the silicon nitride powder comprises at least about 70 weight percent of the starting powder mixture.