DEGRADATION OF CROWN SILICA REFRACTORIES IN GLASS TANK MELTERS

摘要

A reproducible oxyfuel simulation test has been developed for evaluating superstructure refractories under conditions close to those in the commercial melting of Na-Ca-silicate glasses. The simulation tests have permitted the evaluation of commercial crown silica compositions and to make inferences about the mechanisms of degradation. There is a direct correlation between open porosity of the silica compositions and Na-penetration. The results of the corrosion tests (1450-1550 degrees C, 10 to 500 ppm NaOH, 80h) indicated only cristobalite at the hot face. Beyond this zone, both, cristobalite and tridymite are observed. The measurements performed include characterization of phases by optical microscopy (reflected light and cathodoluminescence) and SEM, XRD, chemical analysis along the thermal gradient of the refractories, as well as porosity, permeability and density, and chemical composition of mortars. The cristobalite to tridymite ratio can be explained qualitatively from the thermal gradient imposed on the crown during furnace operation.