Kinetic model for quartz and spinel dissolution during melting of high-level-waste glass batch
The dissolution of quartz particles and the growth and dissolution of crystalline phases during the conversion of batch to glass potentially affects both the glass melting process and product quality. Crystals of spinel exiting the cold cap to molten glass below can be troublesome during the vitrification of iron-containing high-level wastes. To estimate the distribution of quartz and spinel fractions within the cold cap, we used kinetic models that relate fractions of these phases to temperature and heating rate. Fitting the model equations to data showed that the heating rate, apart from affecting quartz and spinel behavior directly, also affects them indirectly via concurrent processes, such as the formation and motion of bubbles. Because of these indirect effects, it was necessary to allow one kinetic parameter (the pre-exponential factor) to vary with the heating rate. The resulting kinetic equations are sufficiently simple for the detailed modeling of batch-to-glass conversion as it occurs in glass melters. The estimated fractions and sizes of quartz and spinel particles as they leave the cold cap, determined in this study, will provide the source terms needed for modeling the behavior of these solid particles within the flow of molten glass in the melter.
Effects of Al2O3, B2O3, Na2O, and SiO2 on nepheline formation in borosilicate glasses: chemical and physical correlations
Raman spectroscopy was applied to complex sodium alumino-borosilicate glasses that precipitate nepheline as their primary phase. The main focus was on the Raman band at 850 cm−1 (wavenumber) observed in quenched glasses. Based on the literature, the 850 cm−1 band was assigned to AlIV–O–Si units in which tetrahedral AlIV are substituted for Si in the network, creating [AlO4/2]− anions that are charge-balanced by Na+ cations. The same glasses with various temperature histories were examined with optical microscopy, scanning electron microcopy and transmission electronic microscopy. The results indicated that the 850 cm−1 Raman band was associated with nanocrystals that formed in the melts and were preserved in the quenched samples. The chemistry of these nanocrystals resembled nepheline. Models relating the intensity of the Raman band at 850 cm−1 and the liquidus temperature (TL) to glass composition revealed that a relationship exists between these two properties. An increase in B2O3 and SiO2 decreased the Raman band intensity and the TL, whereas an increase in Al2O3 and Na2O increased both properties. These effects were attributed to the influence of various oxides on the Na+–[AlO4/2]− activity in the melt.
Thermal Analysis of Reactions in Soda–Lime Silicate Glass Batches Containing Melting Accelerants: I, One‐ and Two‐Component Systems
To identify each glass melting reaction in a multicomponent system, one-component and two-component reaction processes were studied using DTA, TGA, and XRD. Two-component mixtures were prepared by choosing pairs in the same ratio as in a commercial container glass batch composition (sand-soda ash-calcite-dolomite-feldspar). The presence of silica in the silicia-calcite system decreased the termination temperature of the decomposition of calcite, but did not alter the onset of decomposition. Similar behavior was found in the dolomite-silica system. A double carbonate (Na[sub 2]Ca(CO[sub 3])[sub 2]) formed via solid-state reaction in the calcite-soda ash system, and metasilicate/disilicate phases were detected during the fusion process in the soda ash-silica system. The effects of reaction accelerant additions in the soda ash-silica system were investigated using 1 wt% additions of sodium sulfate, sodium nitrate, and sodium chloride. Sodium chloride was the most effective melting accelerant, lowering the termination temperature of CO[sub 2] release by [approximately]80C compared with the soda ash-silica system with no additives. NaCl additions caused complete reaction and/or fusion of Na[sub 2]CO[sub 3] prior to its melting temperature. Sodium sulfate additions acted to suppress metasilicate/disilicate formation by coating quartz grains and shifted consequent CO[sub 2] release to higher temperature.