Amines as Corrosion Inhibitors for Aluminium-Manganese Alloy in Phosphoric Acid

Abstract

The corrosion of 3S aluminium (Al-Mn alloy) and its inhibition in solutions of phosphoric acid has been studied. The extent of corrosion increases with increase in acid concentration and with the length of the period of immersion. At 0·5% inhibitor concentration the efficiency of the inhibitors increases in the order: triethylamine < dicyclohexylamine < diethylamine < di-n-propylamine < cyclohexylamine < n-butylamine < ethylamine < trimethylamine < ethylenediamine < hexamine < isopropylamine < dimethylamine < methylamine < n-propylamine. At constant acid concentration the inhibitor efficiency increases with increase in the concentration of the inhibitor, whereas at constant inhibitor concentration the efficiency decreases with increase in the concentration of the acid. Very little correlation appears to exist between the pK_b values or the molecular weight of the inhibitor and the extent of inhibition. Maximum inhibition is achieved in those cases where the pH of the inhibited solution lies in the range 4·5 to 8·5, but where the solution is required for use at low pH values, then hexamine appears to be the most suitable inhibitor.