The mechanism of nucleated crystallisation of glasses in lithia-alumina-silica and cordierite systems

Abstract

Two principal lines of investigation are discussed. In the first of these, in which glasses were crystallised under high pressure, it was shown that the low temperature α-forms of spodumene and eucryptite could be obtained. In further experiments the effects of substituting GeO₂ for SiO₂, Ga₂O₃ for Al₂O₃, MgO for Li₂O and TiO₂ for Al₂O₃ in Li₂O-Al₂O₃-SiO₂ glasses were studied. It was found possible to crystallise both α and β-forms of germanium and gallium containing spodumene and eucryptite. Infra-red absorption spectra, X-ray diffraction data and thermal expansion data are presented for the various crystal types. Based on the results of the investigation, it is suggested that nucleated crystallisation in the glasses may be due to the initial precipitation of a crystal phase which is isomorphous with the predominant crystal phase that is to be developed in the glass-ceramic, and that during the heat-treatment the crystals of the latter phase grow on the crystals of the primary phase.