Inhibitive Effect of an Onium Compound on the Dissolution of Steel in Hydrochloric Acid

Abstract

An onium compound has been found to be an effective inhibitor for the dissolution of mild steel in hydrochloric acid in all practical conditions. Adsorption studies based on weight loss measurements show that adsorption of onium obeys the Freundlich adsorption isotherm. Rectilinear Arrhenius plots were obtained both in the presence and absence of inhibitor, but the activation energy is(paradoxically) much lower in the presence of the inhibitor. Onium polarises both the anode and cathode, the extent of the polarisation increasing with inhibitor concentration. The exchange current is considerably reduced in the presence of the inhibitor, inhibitor efficiencies calculated from this reduction agreeing well with values calculated from weight loss measurements. The combined use of KI and onium shows a synergistic effect.