Untitled

Abstract

The anodic polarization behavior and time dependence of anodic current of 99.999% aluminum in 0.5M NaUl solution were examined. Pitting corrosion of super high purity aluminum in 0.5M NaCl at pH 8.5 is caused by Cl-which permeates cracks at the interface of the surface film and a rhombic corrosion product. This corrosion product mainly composed of Al, Fe and Si is formed at less noble potentials than the pitting potential.The pitting corrosion is affected by chemical dissolution in 0.5M NaCl solution at pH 10, and the pitting potential becomes noble. The limiting current in the anodic polarization curves is controled by diffusion of OH-in the solutions of pH 8.5 and 10. The corrosion potential of super high purity aluminum in 0.5M NaCI is about -0.76V at pH 4, -0.73V at pH 6, -0.72V at pH 8.5 and -0.72V at pH 10.