Corrosion of silica by Na2CO3 - CaCO3 melts

Abstract

Vertical vitreous silica rods were immersed in Na2CO3 - CaCO3 melts for varying times at 950 °C and their corrosion measured afterwards. Addition of calcium carbonate caused a considerable increase in rate of corrosion of the silica and more than about 15 mol% CaCO3 caused a reversal of the taper of the corroded part of the rod. The extent of corrosion was linear with time and the dependence of rate on depth of immersion much less than expected for control by free convection and diffusion in the melt. The rods also had a pitted surface texture suggesting drilling by gas bubbles to be the main corrosion mechanism. Rate of corrosion increased approximately exponentially with calcium content of the melt. Although not conclusive, the evidence suggests that this was caused by vigorous gas evolution accompanying the formation of particles of a solid phase, probably β-2 CaO · SiO2.