Schiff bases of ethylenediamine as corrosion inhibitors of zinc in sulphuric acid

The work described here deals with the performance of ethylenediamine N,N'-dibenzylidene, ethylenediamine N,N'-di(p-methoxybenzylidene), ethylenediamine N,N'-disalicylidene as corrosion inhibitors for zinc in sulphuric acid. The effect of various parameters on the efficiency of these inhibitors has been studied. Ethylenediamine N,N'-di(p-methoxybenzylidene) and ethylenediamine N,N'-disalicylidene give 99% protection under a variety of conditions. Activation energies in the presence and absence of inhibitors have been calculated. It appears that an efficient inhibitor is characterized by a relatively greater decrease in free energy of adsorption, relatively lower entropy of adsorption and relatively lower heat of adsorption. Galvanostatic polarisation studies indicate that these are basically cathodic inhibitors. Cathodic protection in the presence of these inhibitors has been studied. With an efficient inhibitor, cathodic protection is achieved at potentials much less negative than that required for plain acid. The difference between protective potential and corrosion potential appears to be less for an effective inhibitor. Mechanism of the action of inhibitors has been provided. (C) 2003 Published by Elsevier Ltd.