Thermal properties and crystallization kinetics of a sodium aluminophosphate based glass

A ternary sodium aluminophosphate glass, NaAlP, has been used as an encapsulating phase for a calcium phosphate ceramic employed as a host for halide-containing radioactive waste, the final wasteform being prepared by a pressureless consolidation route or alternatively by cold pressing and sintering of ceramic/glass mixtures. During processing, the glass partially crystallizes to yield a mixture of crystalline products. In an attempt to improve the thermal stability and resistance of this glass to devitrification small additions of various additives were made to the glass, including Fe2O3, B2O3 and ZnO in amounts of less than 10 mol%. The thermal properties and crystallization kinetics of the resultant glasses were measured using non-isothermal differential scanning calorimetry, DSC, and differential thermal analysis, DTA. The glass transition and crystallization temperatures, and the activation energy for crystallization, increased with increasing Fe2O3 content, whilst the reduced glass temperature decreased. The other additives, and in particular the mixed Fe2O3/B2O3 addition, also led to minor improvements in some of these parameters, but overall it was concluded that the additives offered no great advantages over use of the unmodified NaAlP ternary glass as an encapsulating phase”.