Aminophenols as Corrosion Inhibitors for Aluminium-Magnesium Alloy in Phosphoric Acid

Abstract

The corrosion of aluminium alloys 2S(99·8% Al), 3S (Al–1·3% Mn), B26S (Al-3·9% eu) and M57S (A1–2·2% Mg) and their inhibition in solutions of phosphoric acid has been studied. The general order of corrodibility of the alloys in phosphoric acid is: 2S < B26S < 3S < M57S. Additions of aminophenols decrease the corrosion, the protection given by the inhibitors to the various alloys increasing in the order: 3S < B26S <2S M57S. For M57S aluminium, at constant acid concentration, the inhibitive efficiency of aminophenol increases with increase in inhibitor concentration, but decreases with increase in acid concentration and also with a rise in temperature. At an inhibitor concentration of 0·01–0·1 M in 0·033–0·33 M H₃PO⁴, the efficiency increases in the order: p-aminophenol < m-aminophenol <O-aminophenol.

The inhibitors appear to function through adsorption, following the Langmuir adsorption isotherm. From galvanostatic polarisation data all three compounds appear to be mixed type inhibitors with preferential action on local anodes.