Abstract
Sulfation studies were conducted on CoO samples coated with a thin film of Na2SO4 and exposed at 600 to 900 °C in O2-SO2-SO3 environments containing 0.02 to 2 pct (SO2+SO3). Within this range of conditions, Co3O4 (s), CoSO4 (s), and liquid Na2SO4-CoSO4 solutions were observed as reaction products. At lower concentrations of SO3 where CoSO4 (s) was unstable, the reaction product consisted of a thick Co3O4 layer close to the CoO, a layer of Na2SO4-CoSO4 liquid, and large Co3O4 particles at the gas/salt interface. At higher concentrations of SO3, the reaction procuct was a two phase mixture of solid CoSO4 and an Na2SO4-CoSO4 liquid. In gas mixtures containing 0.15 pct and 1 pct (SO2+SO3), the highest reaction rates were observed at about 750 to 800 °C. Some of these results are quite similar to those observed during low temperature hot corrosion of cobalt-base alloys. The overall reaction mechanism has been described in terms of two processes: oxidation of CoO to Co3O4 and sulfation of cobalt oxides.
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Luthra, K.L. Mechanism of oxidation-sulfation reactions of coo in the presence of na2so4 . Metall Trans A 13, 1647–1654 (1982). https://doi.org/10.1007/BF02644805
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DOI: https://doi.org/10.1007/BF02644805