Oxidation kinetics of Zircaloy-4 and Zr–1Nb–1Sn–0.1Fe at temperatures of 700–1200 °C

The oxidation characteristics for the Zircaloy-4 and Zr–1.0Nb–1.0Sn–0.1Fe alloys were investigated in the temperature ranges of 700–1200 °C for 3600 s under steam supply conditions, using a modified thermo-gravimetric analyzer. The oxidation at these temperatures generally complied with the parabolic rate law for the examined duration up to 3600 s. However, the parabolic rate was not obeyed in the temperature ranges of 800–1050 °C. The oxidation kinetics were changed depending on the oxidation temperatures due to the phase transformations of the base metal and its oxide. The oxidation rate exponents of the Zr–1.0Nb–1.0Sn–0.1Fe alloy at all the temperatures were higher than those of Zircaloy-4. Considering the data controlled by the parabolic rates at 700, 1100, 1150, and 1200 °C, the oxidation rate constants were the same slopes as the Baker–Just relationship. The rate transition at 800 °C could have resulted from the phase transformation of the base metal and those at 1000 and 1050 °C could have resulted from the lateral cracks in the oxide due to the ZrO2 phase transformation from a monoclinic structure to a tetragonal structure.