Corrosion Inhibition of Aluminum Pigments in Aqueous Alkaline Media at Different pH Values

The isoelectric point of aluminum oxide (pH 9) was studied as an important parameter for the corrosion inhibition of metallic aluminum pigments in aqueous alkaline media. The addition of chelating agents led to increased hydrogen evolution at pH 8 (below the isoelectric point) but also to better long-term stability than at pH 10 (above the isoelectric point). The high molecular-weight polyacrylic acid accelerated the corrosion reaction at pH 8, but inhibited corrosion at pH 10. Styrene-maleic acid (S-MA) copolymers were excellent corrosion inhibitors at pH 8 and 10. Analysis of the concentrations of soluble Al(III) in the corrosion media proved the formation of at least partially soluble inhibitor-Al(III) complexes. The solubility of these complexes appeared to be an important factor controlling inhibition of the corrosion reaction.