Vitrification in the BaO-B2O3-Al2O3-TiO2 system containing small admixtures of PbO

The fields of vitrification in different diagrams were identified for the system BaO-Al2O3-B2O3-TiO2 containing 2.4-3.4 mol% admixtures of PbO and varied contents of other components. The glasses obtained were stable from spontaneous crystallization and had relatively low (1450 °C) melting temperature. Liquid phase immiscibility took place in all compositions investigated: TiO2-rich and B2O3-rich glassy phases were formed. The contents of B2O3 and Al2O3 determined the structure of glasses synthesized, glasses with [B2O3] in the range of 7-20 mol% and [Al2O3] < 22 mol% showed metastable liquid phase separation. Higher contents of Al2O3 and/or B2O3 (i.e. [R2O3] > 37 mol%) promoted spinodal decomposition. The structure of the main vitreous phase in the glasses with metastable liquid formation is formed by polyanions containing TiO6/2 and AlO6/2 octahedra altogether with (B3O6)3− rings, whereas the second vitreous phase includes BO3/2, BO4/2, TiO4/2 and AlO4/2 structural units.