Effect of inorganic inhibitors on the corrosion behavior of 1018 carbon steel in the LiBr plus ethylene glycol + H2O mixture

The effect of inorganic inhibitors on the corrosion behavior of 1018 carbon steel in the mixture LiBr (55%) + ethylene glycol + H2O at room temperature has been evaluated. Used inhibitors included LiNO3 (Lithium Nitrate), Li2MoO4 (Lithium Molybdate) and Li2CrO4 (Lithium Chromate) at concentrations of 5, 20 and 50 ppm. Electrochemical techniques included potentiodynamic polarization curves, electrochemical noise resistance (EN) and electrochemical impedance spectroscopy (EIS) measurements. Additionally, adsorption isotherms were calculated. The results obtained showed that both, the corrosion rate and the passive current density decreased with inhibitors, and, in general terms, inhibitors efficiency increased with inhibitor concentration, except in the case of Li2CrO4. where the highest efficiency was obtained with 20 ppm of inhibitor. Pitting potential with 5 ppm of inhibitor, regardless its chemical composition, was more active than in absence of inhibitor, increased at 20 ppm, especially with Li2CrO4, and remained unaltered with 50 ppm. EN measurements showed that at 5 ppm of inhibitor, the number of film rupture/repassivation events was higher than that obtained at 20 or 50 ppm. Adsorption isotherms suggested a different adsorption mechanism for each inhibitor, whereas EIS results suggested that the corrosion process when nitrates were added was under charge transfer control, but in the case of molybdates or chromates was under diffusion control. (C) 2008 Elsevier Ltd. All rights reserved.