Water vapour effects on corrosion of Ni-Cr alloys in CO2 gas at 650 °C

Binary Ni-Cr alloys containing 5-30 wt% Cr were oxidized in Ar-20CO2-20H2O gas at 650 °C. Weight gain kinetics for alloys reacted with electropolished surfaces generally increased with increasing Cr content up to 25 wt%. All alloys underwent both internal oxidation and outer NiO formation. The NiO developed as separated, isolated growths on all alloys. Internal oxide zones on high chromium alloys underwent buckling. Weight gain and internal oxidation rates were slower than in dry Ar-20CO2. These differences are discussed in terms of altered diffusion processes in NiO in the presence of H2O, and displacement of metal from the internal oxidation zone.