CRYSTALLIZATION OF SILICATE AND PHOSPHATE-GLASSES

An overview is given of recent studies of crystal nucleation and growt h in silicate and phosphate based glasses, emphasising microstructural characterisation. The following topics are discussed: nucleation kine tics in silicate systems, comparisons with classical theory, and new e vidence in the early stages of crystallisation of Li2O . 2SiO(2) glass for the appearance of previously unreported metastable precursor phas es, probably crystalline polymorphs of lithium disilicate; the role of P2O5 as a nucleating agent in lithia-silica glasses; volume nucleatio n and glass ceramic formation in CaO-P2O5 based glasses, particularly the roles of additions of Al2O3, TiO2, SiO2 and B2O3; crystallisation of aluminosilicate glasses including celsian and barium osumilite comp ositions, and marked differences in crystallisation between melt-deriv ed and sol-gel derived compositions. (C) 1997 Elsevier Science B.V.