Mechanism of LiOH aqueous solution accelerating corrosion rate of zircaloy--4
LiOH水溶液提高Zr-4合金腐蚀速率的机理

Autoclave experiments in different water chemistry were conducted to clarify the degradation behavior of zircaloy-4 corroded in LiOH aqueous solution. It was found that the compressive stress and the tetragonal zirconia (t-ZrO2) contents in oxide films formed in different media were different; when specimens were exposed in LiOH and KOH solutions with same concentration, the penetration depth is shallower and the intensity of K+ is weaker than those of Li+, and the penetration depth of OH- corroded in KOH solution is also shallower than that corroded in LiOH solution. Based on the results, it is suggested that the growth of oxide films is a process of OH- diffusing from outside of oxide into metal/oxide interface and reacting with zirconium to form Zr02 and hydrogen. It is easy for Li+ to diffuse into oxide film because of small radius when specimen was exposed in LiOH aqueous solution, so more OH- would diffuse into oxide film deeply. The reaction between adequate OH~ and oxygen vacancies in the t-ZrO2 would promote the transformation from t-ZrO2 to monoclinic zirconia (m-ZrO2). The transformation would bring some cracks in the oxide, which relaxed the compressive stress in the oxide, degraded the protective ability of oxide films and caused an enhancement of corrosion rate of zircaloy-4 alloy.