PNNL

Abstract

The melting behaviors of three glass batches formulated to vitrify high-level waste were compared. These batches, otherwise identical, differed in the alumina source: one was prepared with corundum (Al2O3), another with gibbsite [Al(OH)3], and the other with boehmite [AlO(OH)]. Batch samples, in the form of loose batches or pressed pellets, were heated at 5°C/min up to 1200°C. The expansion of pellets was monitored photographically. Quenched samples of batches, heated in crucibles, were thin-sectioned, investigated with optical microscopy, and analyzed with X-ray diffraction to quantify crystalline phases. Finally, batch-to-glass conversion was investigated with thermal analysis. Corundum was still present in one batch up to 900°C whereas gibbsite and boehmite dissolved below 500°C. In the batch with corundum, quartz, the source of silica, dissolved marginally earlier than in the batches with gibbsite and boehmite. Unlike the batch with corundum that exhibited considerable foaming, the batches with gibbsite and boehmite did not produce primary foam and made a more homogeneous glass. The occurrence of primary foam in the batch with corundum is a likely cause of a low rate of melting within the cold cap of a large-scale electric melter.