Liquidus temperature in the spinel primary phase field: A comparison between optical and crystal fraction methods

Abstract Liquidus temperature (TL) was measured for 38 simulated high-level waste borosilicate glasses covering a Hanford composition region, using optical microscopy and crystal-fraction extrapolation methods to analyze isothermally heat-treated specimens. The glasses encompassed a one-component-at-a-time variation of 16 components from a representative Hanford HLW simulant baseline composition. The TL values ranged from 1006 °C to 1603 °C. First-order models were fit to data to obtain component effects on TL (per 1 mass% additions) and then the components were grouped into three categories: TL-increasing components [i.e., Cr2O3 (264 °C), “Others” (minor components, 163 °C), oxides of noble metals (137 °C), NiO (91 °C), as well as Al2O3 and Fe2O3 (~ 19–21 °C)]; TL-decreasing components [i.e., K2O (−26 °C), Na2O (−41 °C), and Li2O (−68 °C)]; and those of little effect [i.e., MnO, P2O5, ZrO2, F, Bi2O3, SiO2, B2O3, and CaO (9 to −12 °C)]. Also presented are temperatures at which 1 vol% of spinel is at equilibrium with the melt (T1%) as these values are considered relevant to the Hanford Tank Waste Treatment and Immobilization Plant. The measured and estimated values are compared and contrasted and the effect of TL and T1% on glass formulation is discussed. The different methods for measuring TL are compared and contrasted.