Influences of Zirconia and Silicon Nucleating Agents on the Devitrification of Li2O · Al2O3· 6SiO2 Glasses

The effects of Si and ZrO₂ dopants on the crystallization and phase transformation process in Li₂O · Al₂O₃· 6SiO₂ glasses were investigated using differential thermal analysis, X-ray powder diffractometry (XRD), and high-resolution transmission electron microscopy (TEM) interactively. Phase separation was observed in the studied glasses prior to substantial crystallization. Elemental Si (1 mol%) significantly aided in glass devitrification. Dropletlike phase-separated regions in the as-quenched or heat-treated glass devitrified at ∼760°C, which in turn provided sites for the heterogeneous nucleation and growth of β-quartz(ss) (solid solution), which transformed to β-spodumene(ss) at higher temperature. Low-temperature surface crystallization in these glasses occurred as low as 760°C. ZrO₂ has limited solubility in this glass system. Small ZrO₂ crystallites (·5 nm) in the as-quenched glass acted as sites for the heterogeneous nucleation and subsequent growth of large (<5 μm) β-quartz(ss) crystals in glasses containing 1.0 mol% or more ZrO₂. The transformation from β-quartz(ss) to β-spodumene(ss) was increasingly inhibited with ZrO₂ additions. The nucleating efficiency of Si was significantly greater than that of ZrO₂ in this glass system.