Ceramics-Silikáty 49, (3) 153 - 161 (2005)

The contribution of BaO to the crystallization characteristics and crystalline phase assemblages developed from thermally treated glasses based on Li₂O-B₂O₃-SiO₂ system were investigated by differential thermal analysis (DTA), X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). Different barium-containing phases including barium silicates and lithium barium borate together with lithium diborate, lithium meta-, di-silicates and, in some cases, minor of α-quartz were detected. SEM micrographs showed that BaO promoted volume crystallization of the studied glasses. The addition of TiO₂ and MgF2 as nucleation catalysts to glass with high content of BaO led to the formation of fresnoite, and magnesium fluoride phases. The thermal expansion characteristics of the glasses and their crystalline solids were investigated. The data of the glasses were correlated to the local structure changes induced by BaO, TiO₂ or MgF₂ and their contributions to the thermal expansion property of the glasses. The results of the crystalline solids were explained in relation to the nature, composition and concentration of all phases formed including a residual glass matrix.