Hot Corrosion of Iron in Molten Sulfate

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Abstract
The corrosion of iron in an alkali-sulfate melt containing Fe2(SO4)3 was studied using an electrochemical polarization technique. The corrosion rate of iron increased with increasing ferric ion concentrations below 12 mol%. The corrosion rate estimated from the polarization resistance was consistent with that obtained from mass loss measurements. The iron polarization curves represented the anodic dissolution of iron and the cathodic reduction of ferric ion in the potential region from 0.3 to − 0.5 V. The polarization study shows that the corrosion reaction is controlled by the diffusion-limited cathodic reduction of ferric ion, the rate of which was proportional to the ferric ion concentration. The cathodic reaction was promoted by a corrosion product such as the ferric ion, which was chemically oxidized and functioned as an oxidant. Thus, the accelerated corrosion of iron in molten sulfate was explained by an autocatalytic mechanism of the corrosion product.

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