TRANSIENT OXIDE FILM GROWTH ON ZIRCONIUM IN HIGH TEMPERATURE AQUEOUS SOLUTIONS

摘要

Transients in current density and film thickness of the passive film formed on zirconium in 0.1M boric acid + 0.001M lithium hydroxide solution at 250℃ and 900psi (62bar) have confirmed that the rate law afforded by the Point Defect Model (PDM) adequately describes the growth and thinning of the passive film at high temperatures. The experimental results demonstrate that the kinetics of oxygen or hydrogen vacancy generation at the metal/film interface control the rate of film growth when the potential is displaced in the positive direction, whereas the kinetics of dissolution of the barrier layer at the barrier layer/solution interface control the rate of passive film thinning when the potential is stepped in the negative direction. The dissolution rate of the passive film formed in the hydrogenated solution is lower than that formed in the solution without hydrogen. An electron charge transfer phenomenon was observed when changing the hydrodynamic conditions of the solution in contact with the sample. The current density measured in the hydrogenated electrolyte increases with increasing rotation rate of the impeller, which indicates that the hydrogen oxidation reaction may occur in parallel with the oxidation of zirconium.