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

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 mixtures, or two-stage oxidised first then H216O - N2 16O2 atmospheres. In the pre-transition, diffusion-controlled regime, mostly steam contributes zirconia formation, while nitrogen-catalysed post transition regime both oxygen contribute oxidation. These results tentatively explained by competitive adsorption at gas/solid interfaces, formation porosity oxide layers.