Detrimental role of LiOH on the oxide film formed on Zircaloy-4

To understand the degradation behavior of Zircaloy-4 corroded in LiOH aqueous solution, X-ray diffraction was performed to analyze the crystal structure of Zircaloy-4 oxide formed in three different media. Second ion mass spectrometry (SIMS) was utilized to measure the penetration of Li+ and OH− into the oxide film when Zircaloy-4 is exposed in LiOH aqueous solution. It was found that the SIMS depth profile of OH− in the oxide film is in accord with that of Li+, which indicates that there exists OH− in the oxide film. Based on the results, it is put forward that OH− diffuses faster than O−2 in the oxide films, which can enhance the corrosion rate of Zircaloy-4 and the transformation from tetragonal zirconia (t-ZrO2) to monoclinic zirconia (m-ZrO2). OH− plays a detrimental role on the oxide film formed on Zircaloy-4.