Pressure dependence of oxygen absorption by metallic zirconium with a clean surface

Abstract

The rate of oxygen absorption by metallic zirconium with a clean surface at 1073 K has been measured as a function of time by a volumetric method in u.h.v. apparatus under constant pressures of oxygen in the range 10^–1–10^–5 Pa. The electric resistivity, which is a measure of the oxygen concentration, and the effective emissivity, which is a measure of the degree of surface coverage by oxygen, are observed in parallel with the rate of oxygen absorption of the specimen. Besides being determined experimentally, the absorption rate and the electric resistivity are evaluated by numerical calculation on the basis of an appropriate model constructed for the absorption process. Good agreement is obtained between the calculated and experimental results. At 1073 K there is no evidence for formation of the oxide phase at the surface under pressures not higher than 10^–4 Pa, whereas the oxide layer is formed promptly under pressures not lower than 10^–1 Pa. The intermediate region between these two pressures represents the presence of a transient state, which would be characterized by the occurrence of the nucleation and growth of the oxide phase at the surface.