HOT CORROSION OF ALUMINA

The hot corrosion of single crystal and polycrystalline aluminas has b een investigated in SO2-SO3-02 environments and in the presence of mol ten Na2SO4-based deposits at temperatures of 700 and 1000-degrees-C. T he effect of microstructure and impurities on the corrosion has been e mphasized. 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 th e conditions of this study and generally increased with the impurity c ontent of the polycrystalline aluminas. Based on the experimental resu lts, particularly those obtained by electron microscopy and microanaly sis using the SEM/EPMA (scanning electron microscope-electron probe mi croanalyzer), mechanisms are proposed for the corrosion of polycrystal line aluminas which emphasize the role of the silicate impurities and the synergy of their corrosion with that of the alumina grains. As a r esult, the alumina grains were dissolved by acidic fluxing under the a cidic and the basic experimental conditions.