Corrosion of Mullite in Contaminated Water Rich Gas Mixtures at High Temperatures: The Effect of Impurity Diffusion

Two series of mullite single crystal plates of thicknesses between 0.9 and 1.9 mm were exposed up to 12 h to a slowly flowing water rich gas mixture (O2/H2O = 80/20; 100 ml/min) at temperatures of 1670°C. The heat treated samples show up to about 50 μm into the mullite a partial surface decomposition. Decomposition products are sodium containing silicon-rich aluminosilicate glass and α-alumina within melt cavities. Concentration profiles through the plate cross sections show the effect of inward and outward diffusion of OH forming species and Na and Mg impurity enrichment on ppm level in the bulk.