The selection of raw materials affects the rate of batch-to-glass conversion. In all-electric melters, foam under the batch blanket limits the heat flux from the molten glass, thus slowing the rate of melting. In this study, the authors compare the melting behaviours of three batches formulated to vitrify high-alumina high-level waste, and show that a slowly dissolving refractory component can cause excessive foaming. Faster melting batches with gibbsite or boehmite as an alumina source produced substantially less foaming than at atch with corundum. Although gibbsite and boehmite dissolved below 500 deg C, corundum was still present in the batch up to 900 deg C; hence, the glass-forming melt lacked alumina in the batch with corundum. The low viscosity of that batch caused the open pores to close prematurely at 660 deg C, trapping gases and expanding to foam. This would explain the literature-reported slow melting rate of a batch with corundum, as compared to batches with gibbsite and boehmite.
