A Study by Nuclear Microanalysis and 18O Tracing of the Growth of Anodic Oxide Films on Zirconium: II . Oxide Growth Mechanism

Abstract

18O tracer techniques were used to study the microscopic growth mechanism of anodic oxides on zirconium. Depth profiles of 18O in oxides first formed in water and further oxidized in water were determined using the 2 keV wide resonance at 629 keV of the reaction. It is shown that during anodic oxide growth on zirconium the oxygen migrates in regions of higher ionic conductivity (easy paths). The easy path distribution is not determined once and for all by the oxide structure, but changes during the growth. We interpret this phenomenon assuming that the easy paths are structure defects generated in the crystallites, by the migrating species. According to this interpretation the volume of the easy paths in the oxide regions near the oxide surface depends on the rate of the electrochemical reactions at the electrolyte‐oxide interface. The rate of change of the easy path distribution with the additional oxide thickness may also depend on the formation conditions (current, pH).