Low-Temperature Transient Glass-Phase Processing of Monoclinic SrAl2Si2O8

The use of transient glass-phase processing to lower the glass-melting temperature and subsequent heat-treatment temperature of stoichiometric SrAl₂Si₂O₈ to produce the stable monoclinic form has been described. Two nonstoichiometric, low-melting, alumina-deficient, strontium aluminosilicate compositions were melted, quenched, and milled into glass powders. B₂O₃ was dissolved into one of the glass compositions to control the crystallization behavior. The glass powders were then wet-mixed with enough alpha-Al₂O₃ powder so that the overall composition was that of stoichiometric SrAl₂Si₂O₈ (B₂O₃ neglected). The four compositions were dry-pressed into pellets and sintered in three processes. Glass-alumina pellets with dissolved B₂O₃ were densified via viscous-phase sintering at 1100°C, followed by complete dissolution of the alumina and crystallization to ~100% monoclinic SrAl₂Si₂O₈. Pellets without dissolved B₂O₃ required considerably higher temperatures to form ~100% monoclinic SrAl₂Si₂O₈ in a modified process.