Charge and pH effects on inhibitor performance

Work has been performed to investigate the effect of inhibitor charge and pH, in the range 3.9 to 6.5, on the efficiency of various tertiary and quaternary amines. Results have revealed that for such adsorption type inhibitors performance at a given pH depends critically upon the charge of the adsorbing species. At pH 6.5 highest efficiencies were attained when the net charge on the inhibitor was negative, while at pH 3.9 positively charged species were discovered to give better results. Based on the data obtained it is suggested that at pH 6.5 the corrosion potential is more noble than the potential of zero charge causing the metal surface to be predominantly composed of positive charges. At the other end of the spectrum (pH 3.9), the situation is thought to be reversed thus aiding better the adsorption of positively charged inhibitors.