High temperature Zircaloy-4 oxidation in water vapour-containing environments examined with Raman imaging and labelled oxygen

Abstract High Temperature oxidation of Zircaloy-4 was studied in N2–O2–H2O gas mixtures using labelled 18O2, thermogravimetry, Raman imaging and mass spectrometry. Samples were either exposed to N2–18O2–H2O gas mixtures, or two-stage oxidised first in 18O2, then in H216O - N2 or 16O2 - N2 atmospheres. In the pre-transition, diffusion-controlled regime, mostly steam contributes to the zirconia formation, while in the nitrogen-catalysed post transition regime both oxygen and steam contribute to the oxidation. These results were tentatively explained by competitive adsorption of oxygen and steam at the gas/solid interfaces, and the formation of porosity in the oxide layers.