Corrosion Inhibition of Carbon Steel by Blends of Gluconate/Benzoate at Temperatures Up to 60°C

Abstract

The inhibition of carbon steel in solutions of mixtures of calcium- and zinc-gluconate with sodium benzoate was investigated in the temperature range from 25° to 60°C, under atmospheric conditions in stagnant solutions prepared with the tap water. The efficiency and the mechanism of inhibition were estimated by potentiodynamic polarization measurements. The influence of the concentration and the ratio of gluconate/benzoate on the anodic reaction and an observed cathodic effect, indicating slowing down the oxygen reduction process, relevant to the concentration of zinc ions, have been demonstrated. The performed inhibition of carbon steel, as shown by polarization data, may be attributed to the adsorption of gluconate along with benzoate or/and to the formation of a low soluble iron gluconate complex on the metal surface. The inhibition is enhanced by the cathodic polarization mechanism resulting in the precipitation of a zinc hydroxide film, due to the local cathodic gradient of hydroxyl ions. Gluconates act also as sequestring agents preventing a deposition of calcium carbonate from hard waters. Results obtained by electrochemical measurements were confirmed by immersion tests, and could be of interest for the application in cooling water treatement systems, and for the injection water in oil and gas recovery. Investigated compounds are environmentally acceptable being non-toxic and non-polluting.