Silicon nitride with improved high temperature strength

Abstract From the Canadian patent

The flexural strength of isostatically hot pressed silicon nitride containing between 1 and 12 weight per cent of rare earth oxide and not more than 0.5 weight per cent alumina is substantially increased by treating green bodies in flowing nitrogen at a temperature between 1000 and 1500C before degassing for the isostatic hot pressing. The iron content of the bodies is also reduced by this heat treatment, and this is believed to eliminate sources of fracture failure. Silicon nitride bodies with a flexural strength in excess of 525 MPa at 1370°C can be prepared in this way.