Film Stability on Zn-Al-Cu Alloy in Universal Buffer

A.A. Mazhar, A.G. Gad-Allah, S.A. Salih and R.H. Tammam

Chemistry Department, Faculty of Science, Cairo University, Giza, Egypt

Abstract

The effect of some anions and pH of solution on the corrosion of Zn-Al-Cu alloy were tested by impedance, cyclic voltammetry and scanning electron micrographs in the universal buffer. The tested anions included Cl-, SO42-, IO3-, MoO42-, CrO42-, Cr2O72- and CH3COO-. In acidic medium (pH 2) Cr2O72- produces the highest passivation of the alloy surface, whereas in alkaline medium (pH 12) CrO42- is the best passivator. The presence of Cr2O72- in the solution produced a smooth surface on the alloy and minimized the number of pits formed in the universal buffer. The most protective film was formed in solutions of pH 9.7. The order of film stability is at pH 9.7 > 7.7 > 12 > 2.