BiO1.5-BO1.5-GeO2 GLASS SYSTEM AND CRYSTALLIZATION OF Bi4Ge3O12 PHASE

BiO1.5-BO1.5-GeO2 glass samples were prepared by fusion in a Pt crucible and cast in a brass mould. For each nominal composition a sample's physical properties, such as Tg, crystallization (Tx) temperatures and densities, were measured. The 45BiO1.5-40BO1.5-15GeO2 (mol%) glass sample with Tg=385plus/minus 2 C, Tx=517plus/minus 2 C presented a density of 6.94plus/minus 0.02 g cm-3. A nonisothermal crystallization study of this glass by DSC showed that the directionality of crystal growth was equal to 1.1 and that the activation energy was approx 54 kcal mol-1. The presence of two crystalline phases, Bi6B10O24 (surface) and Bi4Ge3O12 (BGO) (bulk), was detected by powder XRD and composition analysis. Experiments of isothermal crystallization showed that the crystal growth rate was 1.5 mm/min at 520 C. 9 refs.