Lithium metasilicate produced under high pressure and high temperature and their thermal stability at atmospheric pressure

Reference	Presenter	Authors (Institution)	Abstract
10-046	Silvio Buchner	Buchner, S.(Universidade Federal do Rio Grande do Sul); Kulbieda, F.R.(Universidade Federal do Rio Grande do Sul); Fokin, V.M.(Vavilov State Optical Institute); Soares Jr., P.C.(Pontifícia Universidade Católica); Machado, �.D.(Universidade Federal do Rio Grande do Sul); Balzaretti, N.M.(Universidade Federal do Rio Grande do Sul);	The stable orthorhombic phase of lithium disilicate, Li2Si2O5, is usually produced by thermal treatment of lithium disilicate (LS2) glass at ambient pressure. In this work it was observed the nucleation of small grains of lithium metasilicate Li2SiO3 (MS) crystalline phase embedded in the glass host after thermal treatment of LS2 under high pressure (7.7 GPa). After that it was investigated the thermal stability of these grains of MS phase during subsequent thermal treatments at ambient pressure. The samples were analyzed by X-ray diffraction, Raman spectroscopy and optical microscopy as a function of the heating time. The small nuclei of the MS phase produced under high pressure remained stable up to 1h of thermal treatment at 610 oC. For longer heating times, the LS2 glass transform to quartz and Li2Si2O5 while the large (~100 µm) MS grains remained practically stable up to 9.5 h of thermal treatment probably due to stoichiometric constraints.
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