Corrosion of 3 S Aluminium by Mixtures of Alkalis and its inhibition by oxo‐anions

The corrosion of 3 S aluminium (Al‐1.3% Mn) in solutions of NaOH, Na 3 PO 4 , Na 2 CO 3 and NaHCO 3 , either alone or as binary mixtures, has been studied. The corrosivity of the substances studied increased in the order: NaHCO 3 < Na 2 CO 3 < Na 3 PO 4 < NaOH. In the case of mixtures those containing NaOH were most corrosive, followed by those containing Na 3 PO 4 and Na 2 CO 3 . The general order of inhibitive efficiency of the compounds studied at 0.1–1.0% concentration in the mixtures containing Na 3 PO 4 and Na 2 CO 3 was found to be: K 2 Cr 2 O 7 > KMnO 4 > K 2 CrO 4 > Na 2 B 4 O 7 > K 2 S 2 O 8 > H 2 O 2 . The increase in the corrosion potential of aluminium in inhibited solutions indicates that all the six inhibitors predominantly act on local anodes; this is confirmed by polarization data.