The oxidation kinetics and the structure of the oxide film on Zircaloy before and after the kinetic transition

Oxidation kinetics of Zircaloy-4 have been measured using a micro-balance technique in CO–CO2 gas mixtures between 450°C and 600°C. Oxidation kinetics of Zircaloy-4 obeyed a cubic rate law with time at 450–600°C up to 24 h. At 600°C, the kinetic transition occurred after about 36 h. After the transition, oxidation kinetics obeyed a linear rate law. X-ray diffraction patterns for the samples oxidized at 600°C showed that the volume fraction of tetragonal phase of zirconia decreased with time until the kinetic transition occurred and was almost constant after that. In addition, stresses in the oxide films were found to be larger for the pre-transition samples than for the post-transition ones.