The Role of TiO₂ and Composition in the Devitrification of Near-stoichiometric Cordierite
Devitrification behavior and thermal expansion of glasses and glass-ceramics, doped with TiO2, near the stoichiometric cordierite composition were investigated. The activation energy for growth of surface nucleated crystals was shown to be approximately 433 kJ/mol. And was independent of TiO2 content in the glass. Volume nucleation was achieved by the addition of approximately 8 wt% TiO2, but the mechanism of volume nucleation was different depending upon cordierite composition. Regions in the MgO-Al2O3-SiO2 phase diagram near the stochiometric cordierite compound were investigated using thermal analysis, X-ray powder diffraction and dilatometry. Glass in glass phase separation was postulated for MgO-lean glasses, whereas precipitation of mullite and Al2TiO5 preceded devitrification in other compositions. In each case, the formation of a silica-rich glass is believed to initiate the devitrification. Coefficients of thermal expansion for the glass-ceramics increased with increasing TiO2 content resulting from increasing levels of uncrystallized glass and the formation of mullite and rutile during crystallization.
D. T. Weaver et al., "The Role of TiO₂ and Composition in the Devitrification of Near-stoichiometric Cordierite," Journal of Material Science, Springer Verlag, Jan 2004.
Materials Science and Engineering
Keywords and Phrases
Activation Energy; Composition; Precipitation (Chemical); Thermal Expansion; Vitrification; Crystal growth; Glass-ceramics; Glass; Nucleation; Phase diagrams; Titanium dioxide
Article - Journal
© 2004 Springer Verlag, All rights reserved.