Alteration of Microstructure of West Valley Glass by Heat Treatment

Abstract

Samples of West Valley reference glass WVCM-59 were subjected to isothermal heat treatment according to a systematic schedule of time-temperature combinations. Phases crystallizing during heat treatment were analyzed and quantified using an SEM equipped with an energy dispersive x-ray detector and image processing and analyzing capabilities. Only small amounts of noble metals (e.g. Rh, Pd) and RuO2 were present in the as-melted glass, but these frequently serve as nucleation sites during heat treatment. Iron-group spinels containing Fe, Ni, Cr, and Mn in variable proportions were the most common phases observed, appearing in quantities up to 3.5 vol% in heat treated glass. The formation of a thoria-ceria phase occurred at temperatures of 900°C and below. Acmites formed at temperatures of 800°C and below. A lithium phosphate phase with a particularly interesting morphology developed after prolonged heat treatment at temperatures between 600–750°C. The same phase appeared in a range of glass compositions. However, canister cooling curves preclude such a phase in production glass. Furthermore, no such phase was found in actual canister-cooled glass.