Iron oxide fluxing and precipitation in sulphate deposits during heat-resistant alloy corrosion in simulated combustion gas

Two ferritic alloys, Fe-25Cr and Fe-25Cr-2Mn-1Si, and two austenitic alloys, Fe-25Cr-20Ni and 310SS, coated with a thin film of Na2SO4-K2SO4 mixture were exposed to a flowing wet CO2 gas at 650 and 750 C for up to 300 h. In addition to oxide scaling, a new manifestation of Fe oxide fluxing into the salt layer was observed. The effects of alloy composition and reaction temperature on this phenomenon were determined. The process is attributed to formation of a low melting Na2O-Na2SO4 solution in the early stages of reaction, followed by basic fluxing of FeO and/or Fe3O4.