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Title: Phase equilibria and crystallisation in some lithium oxide systems
Author: West, Anthony Roy
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1971
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Phase equilibria in the orthosilicate systems Li4SiO4 - Zn2SiO4, Li4SiO4 - Mg2Sio4 and Li4SiO4 - Zn2SiO4 - Mg2siO4 have been studied. wide ranges of thermally active solid solutions based on (a) Li4SiO4 and (b) Li2(Zn, Mg) SiO4 form; metastable phases are frequently encountered. Subsolidus compatibility relations in the system Li4SiO4 - Zn2SiO4 - Mg2SiO4 - SiO2 have been established; the crystallisation of some quaternary glasses has been studied. Metastable phases commonly crystallise at lower temperatures; possible reasons for this are given. A hexagonal phase with wurtzite (ZnS) structure occurs particularly often. The Li2O - SiO2 system has been shovm previously to crystallise a range of metastable, silica-rich lithium disilicate solid solutions from glasses and melts at lower temperatures. In this study, a range of Lithia-rich disilicate solid solutions was also found. In addition, several structural variants of the silica-rich solid solutions form at lower temperatures. The occurrence of a metastable, silica-rich lithium metasilicate solid solution is suggested. 75 mol % SiO2 melts crystallise, at ca 900c, a new metastable phase, lithium trisilicate, Li2Si3O7 Applications of this work to glass-ceramics are discussed. The polymorphs of Li2ZnSiO4 and Li2MgSiO4, and also those of Li2CosiO4 and the corresponding germanates, are structural derivatives of the high-and low-forms of Li3PO4. New intermediate polymorphs of Li3VO4 and Li3AsO4 have been found, in addition to those forms know to be isostructural with high-and low-Li3PO4. Altogether, approximately 40 new ortho-silicate, grmanate, etc. phases have been found; powder X-ray data are presented for their characterisation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available