Oxidation of 9crods exposed to supercritical water

The oxide layers formed on 9CrODS have been characterized using synchrotron radiation fluorescence and diffraction. This analysis showed a three-layer structure with an outer layer containing only Fe ₃O ₄, an inner layer containing a mixture of FeCr ₂O ₄ and Fe ₃O ₄, and a diffusion layer containing a mixture of metal grains and FeCr ₂O ₄ precipitates. A Cr ₂O ₃ ribbon formed at the diffusion layer-metal interface on the samples exposed to 600°C supercritical water for 4 and 6 weeks. Calculations of the oxidation behavior were undertaken to calculate the activation energy and the corrosion rate constant n of power law kinetics. These calculations showed that the oxidation behavior of this alloy could not be described by a power law because the oxide microstructure changed with exposure time and temperature. Additionally, the outward flow of iron was calculated and showed that not enough iron migrates outwards to be able to form the outer layer suggesting that other mechanisms might be at work. Finally, a qualitative description of the oxidation behavior of 9CrODS is displayed showing the importance of the role played by Cr ₂O ₃ in the corrosion process.