Microstructure of Powellite‐Rich Glass‐Ceramics: A Model System for High Level Waste Immobilization

Abstract

In this study, we synthesized glass‐ceramics from glasses in the system SiO 2 –B 2 O 3 –Na 2 O–CaO–Al 2 O 3 –MoO 3 –Gd 2 O 3 by various heat treatments. Glass‐ceramics contain only one crystalline phase in the bulk: powellite ( CaMoO 4 ). The influence of molybdenum and rare earth contents on powellite crystallization was studied using SEM and XRD . Heat treatments were optimized to lead to a wide range in size and concentration of powellite. Moreover, the molybdenum content left in residual glasses, calculated using XRD quantitation, showed that the residual glasses have a similar composition for a given Gd 2 O 3 content after heat treatments. This work had led to the synthesis of two phase glass‐ceramics with constant borosilicate glass matrices and powellite crystals with controlled sizes and concentrations.