Electrochemical Measurements on Zirconium and Zircaloy-2 at Elevated Temperatures

Abstract

Rates of film growth in oxygenated dilute sulfuric acid have been measured on zirconium and Zircaloy‐2 at temperatures from 200° to 300°C using electrochemical methods. The resulting rate‐time plots were analyzed according to logarithmic and cubic kinetics. The kinetic constants obtained from these results, and those of other investigators, were correlated with respect to temperature. The calculated activation energy for the cubic rate constant was 29.7 kcal/mole. The reduction of oxygen was studied as a function of film thickness. The results showed two polarization regions, a high current region with a Tafel slope about and a low current region with a Tafel slope decreasing with film thickness from . The oxygen evolution reaction was also studied at 295°C. The observed Tafel slope ranged between . The anodic process in the over‐all corrosion reaction was postulated to be a field‐dependent ionic transport of oxygen ions. The Tafel slope for this process increased with film thickness from . At 295°C, a steady‐state anodic rate independent of potential was observed. This result suggests that at steady‐state the film dissolution rate is equal to the rate of film formation. The weak‐field approximation to the conventional anodizing equation is postulated for the film formation reaction. The film dissolution reaction is not postulated.