Patent ID: 8652981

Claim:
A silicon nitride body having at least 99% of theoretical maximum density, being substantially free of pores, produced in a single high temperature heat treatment step and comprising: about 85% to about 95% by weight of β-Si 3 N 4 ; and the remainder of material being contained primarily in grain boundary phase; and being about 4% to 12% by weight of at least one rare earth metal oxide and up to about 3% by weight of at least one alkaline earth oxide; wherein said rare earth oxide consists of at least 0.5% by weight of said body selected from the group consisting of La, Gd, Ce, Sm, Nd, Pr, Yb and Eu and the remaining rare earth oxide material is selected from the group consisting of La, Gd, Ce, Sm, Nd, Pr, Yb, Eu, Lu, Y and Er; wherein said alkaline earth oxide consists of at least one selected from the group of oxides consisting of Mg, Ca, and Ba and mixtures thereof; and wherein the β-Si 3 N 4 constitutes predominantly elongated grains, the longest of which are greater than 10 micrometers and up to 40 micrometers in length; wherein a microstructure section of 2419 micrometers squared contains a plurality of elongated grains that are longer than 10 μm.