Crystallization of some spodumene-lithium zinc orthosilicate glasses

By using thermal analysis, X-ray diffraction, polarizing and electron microscopy the effect of compositional variation, thermal treatment and nucleation catalysts TiO₂ and ZrO₂ on the nature, type and stability fields of the crystallizing phases, as well as the resulting microstructures, is described for some stoichiometric glass compositions within the system LiAlSi₂O₆-Li₂ZnSiO₄. Intense uniform volume crystallization was achieved. Transparent glass-ceramics with ultrafine microstructures could also be obtained at temperatures near 700 °C. Crystallization begins with the formation of a proto - and/or _II-Li₂ZnSiO₄ followed by, or concomitant with, -eucryptite ss. The proto -phase was formed over a narrow temperature range and rapidly transformed into its _II-modification which, although showing a wider stability range, ultimately transformed into the stable _o-modification. The metastable -eucryptite ss starts its transformation into -spodumene around 800 °C. By prolonged heating at temperatures as high as 1000–1040 °C, -spodumene and _o-Li₂ZnSiO₄ were the main stable end products. TiO₂ and ZrO₂ have contrasting effects on the stability of the LiZn orthosilicates and -eucryptite ss -spodumene transformations. The former exhibits a catalytic effect and the latter showed a retarding effect on these processes.