The formation of the melilite solid solution phase (M), Sm2Si3-xAlxO3xN4-x, in an alpha-sialon sample of overall composition Sm0.6Si9.28Al2.69O1.36N14.76, was studied as a function of time in the temperature interval 13751525C. The alpha-sialon ceramic contained only minor amounts of the 21R sialon polytype and some residual grain-boundary glass before heat treatment. In situ studies by high-temperature X-ray diffraction were combined with postsintering heat treatment followed by quenching. The M-phase was found to be formed by two different mechanisms: either crystallization of the residual grain-boundary liquid or a direct decomposition of the alpha-sialon phase. The liquid crystallized during the first 1015 min of heat treatment, yielding a rapid M-phase formation, and further formation of M-phase continued at a much slower rate, related to the decomposition of alpha-sialon
Godkänd; 1997; 20070508 (cira)