Ceramics-Silikáty 54 (3) 193-211 (2010)

EFFECT OF GLASS-BATCH MAKEUP ON THE MELTING PROCESS

 P. Hrma, M. J. Schweiger, C. J. Humrickhouse, J. A. Moody, R. M. Tate, T. T. Rainsdon, N. E. Tegrotenhuis, B. M. Arrigoni, J. Marcial, C. P. Rodriguez, B. H. Tincher

The response of a glass batch to heating is determined by the batch makeup and in turn determines the rate of melting. Batches formulated for a high-alumina nuclear waste to be vitrified in an all-electric melter were heated at a constant temperature-increase rate to determine changes in melting behavior in response to the selection of batch chemicals and silica grain-size as well as the addition of heat-generating reactants. The type of batch materials and the size of silica grains determine how much, if any, primary foam occurs during melting. Small quartz grains, 5 μm in size, caused extensive foaming because their major portion dissolved at temperatures <800°C, contributing to the formation of viscous glassforming melt that trapped evolving batch gases. Primary foam did not occur in batches with larger quartz grains, ±75 μm in size, because their major portion dissolved at temperatures >800°C when batch gases no longer evolved. The exothermal reaction of nitrates with sucrose was ignited at a temperature as low as 160°C and caused a temporary jump in temperature of several hundred degrees. Secondary foam, the source of which is oxygen from redox reactions, occurred in all batches of a limited composition variation involving five oxides, B₂O₃, CaO, Li₂O, MgO, and Na₂O. The foam volume at the maximum volume-increase rate was a weak function of temperature and melt basicity. Neither the batch makeup nor the change in glass composition had a significant impact on the dissolution of silica grains. The impacts of primary foam generation on glass homogeneity and the rate of melting in large-scale continuous furnaces have yet to be established via mathematical modeling and melter experiments.

Keywords: Glass batch makeup, Glass batch melting, Nuclear waste glass, Glass foaming