Hot corrosion of alumina

The hot corrosion of single crystal and polycrystalline aluminas has been investigated in SO₂–SO₃–O₂ environments and in the presence of molten Na₂SO₄-based deposits at temperatures of 700 and 1000 °C. The effect of microstructure and impurities on the corrosion has been emphasized. Weight changes and wetting angles were determined, and the evolution of the morphology of the exposed substrates and the reaction products was investigated in detail. The corrosion was small under the conditions of this study and generally increased with the impurity content of the polycrystalline aluminas. Based on the experimental results, particularly those obtained by electron microscopy and microanalysis using the SEM/EPMA (scanning electron microscope–electron probe microanalyzer), mechanisms are proposed for the corrosion of polycrystalline aluminas which emphasize the role of the silicate impurities and the synergy of their corrosion with that of the alumina grains. As a result, the alumina grains were dissolved by acidic fluxing under the acidic and the basic experimental conditions.