Thermodynamic analysis of silica refractory corrosion in glass-melting furnaces

Corrosion of refractory silica brick used to line the roof or "crown" of ma ny glass-melting furnaces is a serious problem in furnaces using oxygen-fue l rather than air-fuel mixtures. In this work, we report equilibrium calcul ations that support a corrosion mechanism in which alkali hydroxide gas (Na OH 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 prod uce an alkali silicate liquid with a composition;hat depends on the tempera ture of the crown. Our reported calculations predict the variable-compositi on liquid-solution corrosion product phase as a function of key furnace var iables. Critical thermodynamic data needed for the liquid corrosion product were generated using a modified associate species solution model and criti cal 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 fo r 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 temperat ure," 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.