Stress Generated on Aluminum During Anodization as a Function of Current Density and pH

Abstract

Anodic oxidation is accompanied by stressgeneration during the growth of the oxide. The presentstudy focuses on the stress-generation mechanism onaluminum as a function of the applied current density in acidic solutions of sulfuric acid ofdifferent strengths giving variable pH. Abeam-deflection technique was utilized for thedetermination of the magnitude and direction of stressesgenerated during the anodic oxidation process. Generally,thickness of the oxide determines whether the stress iscompressive or tensile in nature. The results have beeninterpreted in terms of the formation and annihilation of anion (O2-) and cation(Al3+) vacancies. A reduction in thealuminum-ion vacancy concentration (V Al 3 ) results in a compressive stressdeflection, whereas tensile-stress deflection isintroduced by an increase in the oxygen vacancy(Vo2+) concentration. The mechanism isfurther elucidated by current-density jump/dropexperiments. The results show that stress in this caseis affected by the dissolution of the oxide at the oxide-electrolyteinterface.