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Thermal stability of lithium metasilicate produced under high pressure from lithium disilicate glass
Author(s) -
Buchner Silvio,
Kulbieda Felipe R.,
Fokin Vladimir M.,
Soares Paulo,
Machado Álvaro D’.,
Schmelzer Jürn W. P.,
Balzaretti Naira M.
Publication year - 2019
Publication title -
international journal of applied glass science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.383
H-Index - 34
eISSN - 2041-1294
pISSN - 2041-1286
DOI - 10.1111/ijag.13416
Subject(s) - materials science , crystallization , lithium (medication) , thermal stability , atmospheric pressure , phase (matter) , raman spectroscopy , analytical chemistry (journal) , orthorhombic crystal system , stoichiometry , mineralogy , chemical engineering , crystallography , crystal structure , chemistry , optics , chromatography , medicine , oceanography , physics , organic chemistry , geology , engineering , endocrinology
Crystalline lithium disilicate, Li 2 Si 2 O 5 (LS 2c ) is usually produced at atmospheric pressure by suitable heat treatment of the glass with the same stoichiometric composition (LS 2g ). At this pressure, the orthorhombic phase of lithium disilicate is thermodynamically stable. The heat treatment of LS 2g under high pressure (7.7 GPa) induces the crystallization of lithium metasilicate Li 2 SiO 3 (LS m ) phase, which remains metastable after pressure release. In this work, distinct heat treatments under high pressure were chosen to produce lithium metasilicate crystals with different grain sizes embedded in the glass matrix: smaller than 10 µm, about 100 µm and larger than 100 µm. Thermal stability of this set of samples was investigated during subsequent heat treatments at atmospheric pressure. All samples were analyzed by X‐ray diffraction, Raman spectroscopy and optical microscopy. Small LS m crystals produced under high pressure remained detectable only up to 1 hour of heat treatment at 610°C at atmospheric pressure while for longer heating times, the formation of quartz and crystalline LS 2c was observed. On the other hand, for the samples containing larger LS m crystals produced under high pressure, the metasilicate phase remained detectable up to 9.5 hours of subsequent heat treatment, forming spherulitic configurations.