<i>Ortho-substituted </i>aniline-N-salicylidenes as corrosion inhibitors for zinc in sulphuric acid

Abstract

The corrosion of zinc in sulphuric acid containing different <i>o</i>-substituted aniline-N-salicylidenes has been studied with respect to inhibitor and acid concentration, period of exposure and temperature. All the five compounds studies show high (95-97%) inhibitive efficiency. At 0.5% inhibitor concentration in 0.5 <i>M </i>acid, the order of efficiency is: <i>o-</i>HNS<i> </i>(95.5%) < <i>o-</i> CNS (96.8%) < <i>o-</i>AnNS<i> </i>(99.7%) ≤<i> o</i>-TNS (99.8%) ≤ ANS (99.9%). The activation energies are higher in inhibited than in uninhibited acid. It appears that an efficient inhibitor is characterized by a relatively greater decrease in the free energy of adsorption. Galvanostatic polarization studies indicate that these are mixed type inhibitors with predominant action on the local cathodes. Cathodic protection in the presence of these inhibitors has been studied. The inhibitors appear to function through adsorption due to the presence of the imine (-C=N-) group and conjugated double bonds.