Effect of bubbles and silica dissolution on melter feed rheology during conversion to glass

Nuclear-waste melter feeds are slurry mixtures of wastes with glass-forming and glass-modifying additives (unless prefabricated frits are used), which are converted to molten glass in a continuous electrical glass-melting furnace. The feeds gradually become continuous glass-forming melts. Initially, the melts contain dissolving refractory feed constituents that are suspended together with numerous gas bubbles. Eventually, the bubbles escape, and the melts homogenize and equilibrate. Knowledge of various physicochemical properties of the reacting melter feed is crucial for understanding the feed-to-glass conversion that occurs during melting. We studied the melter feed viscosity during heating and correlated it with the volume fractions of dissolving quartz (SiO2) particles and the gas phase. The measurements were performed with a rotating spindle rheometer on the melter feed heated at 5 K/min, starting at several different temperatures. The effects of undissolved quartz particles, gas bubbles, and compositional inhomogeneity on the melter feed viscosity were determined by fitting a linear relationship between the logarithm of viscosity and the volume fractions of suspended phases.