Scoping studies for low-temperature melting ZnO–Bi2O3–(B2O3, SiO2) binder glass

Low melting point glass systems were explored as candidates for binders of solid oxide nuclear wastes which include volatile elements such as radioactive iodine. The base glass systems considered were ZnO–Bi2O3–B2O3 and ZnO–Bi2O3–SiO2, with specific compositions selected for synthesis trials based on available phase diagrams and a desire to explore the whole glass-forming region. Ten compositions were synthesized by melt quenching. Promising candidate glass binders were selected based on the absence of crystallization and favorable thermal properties, including low glass transition temperature (Tg) combined with a high crystallization onset temperature. These thermal properties indicate stable glass forming which would lead to sintering behavior needed for glass binding. Compositional effects include: higher Bi2O3 content led to lower Tg values, high ZnO content generally led to crystallization on quench, and high SiO2 content resulted in requirements for excessively high melting temperature. 25ZnO–15Bi2O3–60B2O3 was down-selected for some detailed crystallization versus time and temperature studies.