Surface Charge Considerations in the Pitting of Ion‐Implanted Aluminum

Abstract

The relationship between the pitting potential of an oxide-covered metal, and the pH of zero charge of its oxide, pHpzc, was studied by ion implanting aluminum (99.999 % purity) with elements whose oxides were of known pHpzo (Mg, A1, St, Cr, Zr, Nb, Mo, and Zn). The results showed that all the implants chosen because of the low PHpzc of their oxides (St, Cr, Zr, Nb, and Mo) produced binary surface alloys that had higher (more positive) pitting potentials than aluminum. The im-plants chosen because of the high pHpzc of their oxides (Zn and Mg) produced binary surface alloys that had pitting poten-tials that were either lower than (Zn) or the same as (Mg) that of aluminum. The Mg-A1 surface alloy results are explained by selective leaching of the Mg from the oxide. The implantation of aluminum into aluminum had no effect on the pitting potential, indicating that the increased and decreased pitting potentials observed for the other implants was a chemical effect. Alt~minum alloys are widely used because of their light weight, high strength, and good resistance to uniform cor-rosion. Aluminum, being an inherently active metal, owes its stability to the formation of a protective oxide film: The major corrosion problem with aluminum is the localized