Physicochemical processes occurring in nitride and oxide-nitride composites with phosphate binders during heating

The hardening of compositions based on aluminum and silicon nitrides is a result of the chemical reaction of their phosphate binder with the nitrides, while additions of, e.g.,α-corundum act as inert fillers up to a temperature of 570‡K. The reaction products are amorphous acid mono- and disubstituted aluminum and silicon phosphates, which on heating at first condense, forming poly- and metaphosphates, and then, at temperatures above 870‡K, decompose, forming (depending on their composition) aluminum orthophosphate or silicon pyrophosphate.