The crystallisation of the yttrium-sialon glass: Y(15.2)Si(14.7)A(18.7)O(54.1) N-7.4

The development of microstructure during crystallisation of a glass with co mposition Y15.2Si14.7Al8.7O54.1N7.4 has been studied by analytical and high resolution transmission electron microscopy. Crystal nucleation at tempera tures in the range 965-1050 degrees C occurs by the heterogeneous nucleatio n of lenticular-shaped yttrium, silicon and aluminium containing crystals o n silicon-rich clusters that formed during glass preparation. The lenticula r crystals have a wide range of composition after heat treatment at 1050 de grees C; the yttrium cation percentage varies around that of the expected B -phase composition Y2SiAlO5N but the aluminium content is lower and the sil icon content generally significantly higher than that. The crystals display the hexagonal crystal structure of B-phase, although the results from EDX analysis imply that the atomic arrangement of the lattice is not the previo usly proposed B-phase structure. Crystal growth during prolonged heat treat ment at 1050 degrees C occurs to a significant extent by coalescence. (C) 2 000 Elsevier Science B.V. All rights reserved.