Corrosion of Ni in Molten Alkali Sulphates

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Abstract
The corrosion of Ni base alloys under molten ash deposits containing considerable quantities of alkali sulphates can take place as a sulphidation or oxidation. The former is very dangerous with respect to gas turbine operation since it gives rise to a decrease in strength of the materials; this type of corrosion is also predominant under thick layers of molten deposits at higher oxygen pressures, the effect being then increased by the poorer transport properties of the melt respect to oxygen diffusion. When cobalt sulphate is found in the ash the accelerated oxidation of Ni base alloys is due to the stable redox system Co+2/Co+2 in the melt Increasing the acidity of the flue gases (increasing SO3 content) enhances the corrosion rate and the solubility of corrosion products in the melt.