P-substituted phenols as corrosion inhibitors for aluminium-copper alloy in sodium hydroxide

Abstract

The inhibition of corrosion of B26S aluminium (Al-4% Cu alloy) in solutions of sodium hydroxide has been studied by weight loss and galvanostatic methods. At constant alkali concentration the inhibitor efficiency increases with increase in the concentration of the inhibitor (except hydroquinone), and at constant inhibitor concentration the efficiency decreases with increase in alkali concentration. At 2.0% inhibitor concentration in 0.1 M NaOH, the efficiency of the inhibitors increases in the order: p-hydroxydiphenyl (65.3%) < p-aminophenol < p-bromophenol < hydroquinone < p-chlorophenol < p-cresol < p-hydroxyacetophenone < p-nitrophenol < phenol (∼ 100%). An increase in exposure period or temperature does not appear to have any marked effect on percentage inhibition which, in most of the cases, remains constant or shows a slight tendency to decrease. The average activation energy in inhibited NaOH in the temperature range 20–50°C is found to be 55 kJ/mole, which is almost the same as that in uninhibited alkali. Polarization data indicate that the inhibitors act as mixed inhibitors with greater effect on the anode reaction.