Abstract
The calcium sulfate-induced corrosion behavior of binary FeCr alloys has been studied at a temperature of 1223 K under an oxygen partial pressure of 10−11.2 atm, generated using a CO/CO2 gas mixture. These conditions are intended to simulate the oxygen activities in the low oxygen partial pressure locations in the fluidized-bed combustor. Under this low oxygen activity, the presence of calcium sulfate induces sulfidation/oxidation corrosion, and breakaway corrosion was observed for an Fe-20Cr alloy. The formation of internal Cr-rich sulfide/oxide particles in the underlying alloy below an inner Cr-rich oxide layer was generally observed. The reaction products between the oxide and the calcium salts formed at the external surface of scale on iron-chromium alloys, such as a eutectic CaO-Cr2O3 oxide mixture, appear to be insignificant in controlling the overall degradation process. The corrosion mechanism appears to be a sulfidation/oxidation process consistent with the low oxygen partial pressure and the relatively high sulfur activity calculated from the CaOS equilibria.
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