Oxidation of Zircaloy by steam

The oxidation of Zircaloy by steam and by steam-hydrogen mixtures was studied experimentally from 1100–1600°C using the continuously-recording gravimetric method. Parabolic kinetics based on oxygen diffusion in the solid were followed at low temperatures but steam starvation, nonisothermal behavior, and finite medium effects dominated at temperatures above about 1500°C. The effect of high dilution of the steam by hydrogen was to accelerate oxidation initially because of the heat released by hydrogen absorption in the metal. At high temperatures, oxygen uptake kinetics were nonparabolic and required analysis by a fundamental diffusion model in which the initial effects are incorporated.