Effect of Some Organic Phosphorus Compounds on the Corrosion of Low Carbon Steel in Hydrochloric Acid Solutions

Electrochemical measurements were made on low carbon steel wire in various concentrations of 1 N hydrochloric acid at 25, 50, 60 and 75 C and in solutions up to 9 N at 60 C. Effect of various concentrations of organic phosphorus compounds, some containing sulfur or selenium were measured by hydrogen evolution to determine their efficiency in reducing corrosion rates. Tests showed adsorption of inhibitors followed the isotherm of Freundlich and that the adsorption process was influenced by adsorbing strength and resistance hindering diffusion of inhibitor molecules. Compounds containing selenium were more effective than those containing sulfur. The chemisorption theory explains the effect of inhibitors on HCl corrosion of iron.