Thermodynamic analysis of silica refractory corrosion in glass-melting furnaces

Corrosion of refractory silica brick used to line the roof or "crown" of many glass-melting furnaces is a serious problem in furnaces using oxygen-fuel rather than air-fuel mixtures. In this work, we report equilibrium calculations that support a corrosion mechanism in which alkali hydroxide gas (NaOH or KOH), produced by reaction of water vapor in the combustion eas with the molten glass, reacts with the silica brick in the furnace crown to produce an alkali silicate liquid with a composition;hat depends on the temperature of the crown. Our reported calculations predict the variable-composition liquid-solution corrosion product phase as a function of key furnace variables. Critical thermodynamic data needed for the liquid corrosion product were generated using a modified associate species solution model and critical analysis of thermochemical information found in the literature for the Na2O-SiO2 and K2O-SiO2 systems. Excellent agreement with reported Na2O-SiO2 and K2O-SiO2 phase diagrams and with experimentally measured activities for Na2O and K2O is achieved. The results of our current calculations are for temperatures between 1273 and 1973 K (1000-1700 degreesC) under either air-fired or oxy-fired conditions, and are used to define a "critical temperature," above which corrosion is not expected to occur for a given NaOH(g) or KOH(g) partial pressure. (C) 2001 The Electrochemical Society. All rights reserved.