Metastable phase formation in the early stage crystallisation of lithium disilicate glass

Abstract

Early stage crystallisation behaviour of binary lithium disilicate [LS 2] glass containing 33.91 mol% Li 2O has been investigated. Two metastable crystalline phases, α′- and β′-LS 2 precipitated prior to crystallisation of stable lithium disilicate in samples heat treated at 454±1°C for 120–480 h. Metastable α′- and β′-LS 2 phases transformed to stable LS 2 after extended holds (∼551 h) at 454°C. The broader 29 Si MAS-NMR crystalline peaks in samples nucleated for >228 h at 454°C, than those of samples crystallised at 600°C, indicate the presence of multiple polymorphs or a disordered structure in the former samples. The streaking of some of the spots observed in electron diffraction patterns from β′-LS 2 crystals is consistent with this observation.