Adsorption and corrosion inhibition of polyacrylic acids on aluminium pigment

摘要

The inhibition of the hydrogen corrosion of aluminium pigment at pH 8 and 10 by polyacrylic acidsand their adsorption is strongly influenced by the isoelectric point (IEP) of aluminium oxide (pH≈9). Approximately polyacrylic acids are completely dissociated at both pH values. As expected, at pH8 (below the IEP) polyacrylic acids are adsorbed significantly stronger as at pH 10 (above the IEP).Furthermore, the adsorbed fraction of polyacrylic acid increases with increasing molecular mass; butthe protective value of polyacrylic acids decreases with increasing molecular mass. There is thesurprising result that with increasing adsorption of polyacrylic acids their corrosion inhibiting effectdecreases. A partial explanation of this result is the high content of carboxylat groups (calculated acidnumber 780 mg KOH/g) in alkaline medium, which may be responsible for specific ionic interactionswith the aluminium oxide surface.