The corrosion of zinc in sulphamic acid containing various isomer of toluidines has been studied. In plain sulphamic acid, the corrosion increases with the acid concentration and temperature. An increase in the concentration of the inhibitor increases the inhibition efficiency the order of inhibition efficiency in 0.1 M sulphamic acid containing 5 mM inhibitor being: o-toluidine (62%) < m-tolui-dine < p-toluidine (72%). Plot of log a/(1-a) versus log C results in a straight line suggesting that

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... the inhibitors cover both the anodic as well as cathodic regions through general adsorption following Langmuir isotherm. Zinc shows a corrosion potential of-920,-880 and-875 mV versus Ag/ AgCl reference electrode in 0.1, 0.5, and 1.0 M sulphamic acid. Galvanostatic polarization curves show both anodic and cathodic polarization in the case of all inhibitors studied. I • Zinc is one of the most vital non-ferrous metal, having extensive use in metallic coating. Zinc, like aluminium is amphoteric in its behaviour towards acids and alkalies 1. Sulpharnic acid is a strong acid (NHzS03H) and it is used as a cleaner for rust, algae and hard water scale from cooling tower and condensorsz. Desaj3 studied the effect of arnisaldehyde and ethylene diarnine as inhibitor for the corrosion of zinc in sulpharnic acid. Water4 stated that corrosion of zinc and zinc plated surfaces, like boilers or pipe systems during scale removal by treatment with sulpharnic acid was inhibited by addition of benzyl quinolinium chloride and cinnarnic acid. In the present work, the corrosion of zinc by sui-pharnic acid containing ortho-, meta-and para-toluidine has been reported. E:xperimental Procedure Rectangular specimens (5.5 x 2.5 x 0.2 em) of zinc with a small hole of-3 mm diameter near the upper edge were used for the determination of the corrosion rates. The chemical composition of test specimen was found to be: 98.5% Zn, 0.03% Pb, 0.02% Cd and 0.01% Fe. All the spci-mens were cleaned by buffing to obtain a ml.rror like finish. A specimen, suspended by a glass hook was immersed in each beaker containing 230 mL of the test solution at 28 ± 1°C and left exposed to the ail for 24 h period. After the test, the specimens • Author to whom correspondence should be addressed. were cleaned with saturated solution of ammoni-um acetate5,6. Duplicate experiments were performed in each case and the mean values of the weight losses were calculated. To study the effect of temperature on corrosion of zinc in 0.1 M sulphamic acid, the specimen were immersed in 230 mL of the corrosive solution and weight losses were determined at solution temperatures of 40, 50 and 60°C for an immersion period of 3 h with and without inhibitors. For polarization study, metal specimens of circular desWI, having an area of 7.7 cm2 exposed to corrosive solutions. The volume of corrosive medium was 100 mL. Auxiliary platinum electrode was placed in a corrosive media through which external current was supplied from a regulated power supply. A silver-silver chloride reference electrode was placed in a saturated KCI solution which remains in contact with the corrosive solution via salt bridge. The change in potential was measured by potentiostatl galvanostat (Model-273) against the refe.rence electrode. Calculations The inhibition efficiency (I.E. %) due to inhibi-tors has been calculated on a percentage basis 7• w-w I.E. % = U 1 X 100 Wu where If., is the weight loss of the metal in uninhibited acid and ~ is the weight loss of metal in inhibited solution.