Corrosion and corrosion inhibition of Al and some alloys in sulphate solutions containing halide ions investigated by an impedance technique

This paper reports the results of impedance measurements on the corrosion behaviour of pure Al, (Al + 6%Cu) and (Al + 6%Si) alloys in Na2SO4 solutions in the absence and presence of NaCl, NaBr and NaI under the influence of various experimental variables at the open circuit potential (OCP). We find that in the absence of halide ions the rates of corrosion of the three Al samples are enhanced with increasing concentration, acidity, and alkalinity of the Na2SO4 solution and in the presence of halide ions. The corrosion resistance increases in the order Al < (Al + 6%Cu) < (Al + 6%Si). The aggressiveness of the halide ions towards the corrosion of Al and its two alloys increases in the order: I- < Br- < Cl-. We find that the effects of Cr2O72-, CrO42-, WO42-, MoO42-, NO2- and NO3- as inorganic inhibitors on the corrosion inhibition of pure Al and its alloys in (0.5 M Na2SO4 + 0.2 M NaCl) solution (except NO3-) are to inhibit the corrosion of the three samples to an extent depending on the nature of the inhibitor. (C) 2002 Published by Elsevier Science B.V.