Corrosion characteristics of a nickel-base alloy C-276 in harsh environments

The oxidation behaviors of alloy C-276 in two harsh environments: high-temperature air and supercritical water (SCW), respectively representing the working conditions of the external and internal surfaces of reactors for SCW gasification biomass to produce H₂, were investigated. In two environments, all oxidation kinetics followed parabolic laws, while the corrosion rate of alloy C-276 exposed to supercritical water gasification (SCWG) environments was 2.5–3 times higher than that in high-temperature air. The oxide scale formed in air at 500 °C consisted of an outer Fe-rich layer (Fe₂O₃ and NiCr₂O₄) and an inner layer of Cr₂O₃ and NiCr₂O₄, while the outer Fe-rich layer disappeared as the temperature increased to 550 °C. Compared to the scales formed on nickel-base alloys in near-pure SCW, the absence of NiO and Ni(OH)₂ phases within the scales formed on the C-276 samples in present SCWG environment may be due to higher molar proportion of hydrogen.