Thermodynamic analysis of alumina refractory corrosion by sodium or potassium hydroxide in glass melting furnaces

• Published in: Journal of the Electrochemical Society 2002-01, Vol.149 (12), p.B551-B559
• Main Authors: SPEAR, Karl E, ALLENDORF, Mark D
• Format: Article
• Language: English
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Chemical industry and chemicals; Exact sciences and technology; Refractory products; Silica-alumina refractories
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.1516773

In this paper the high-temperature corrosion of Al sub 2 O sub 3 refractories by MOH(g) (M = Na, K) found in the combustion atmospheres of typical air- and oxygen-fired glass-melting furnaces is examined using thermodynamic equilibrium calculations. These hydroxide species are considered to be the primary reactive alkali species since their partial pressures are significantly larger than those of M(g), the next most abundant gas-phase alkali-containing species expected in typical furnace atmospheres. Thermochemical simulations show that corrosion of alpha -alumina by NaOH(g) at typical furnace p sub NaOH(g) of around 200 ppm under oxy/fuel-fired conditions is unlikely as long as the refractory temperature exceeds 1564 K. For KOH(g) at 200 ppm, the temperature of the refractory must exceed 1515 K to avoid corrosion. Under air-fired conditions, p sub NaOH(g) considerably lower (40-80 ppm); at 50 ppm, corrosion is thermodynamically unfavorable at temperatures above 1504 K. For KOH(g) at furnace levels of approx =50 ppm, temperatures must be above 1458 K. The paper also presents a re-evaluation of the thermodynamic and phase equilibrium properties of the Na sub 2 O-Al sub 2 O sub 3 and K sub 2 O-Al sub 2 O sub 3 binary systems to develop accurate and self-consistent thermodynamic data. The data for MAl sub 9 O sub 14 ( beta -alumina) and M sub 2 Al sub 12 O sub 19 ( beta ''-alumina) are particularly critical since these phases are likely products of the corrosion of alumina refractories by MOH vapors in glass melting furnaces.