ISSN 2305-6894

Ascorbic acid as a corrosion inhibitor of steel in chloride-containing solutions of calcium hydroxide

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1 A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninsky pr. 31, 119071 Moscow, Russian Federation
2 Federal State-Funded Educational Institution of Higher Education “D. Mendeleev University of Chemical Technology of Russia”, Miusskaya sq. 9, 125047 Moscow, Russian Federation

Abstract: Due to the increasing attention to environmental protection issues, there have been reports on the use of ascorbic acid (ASC) as an environmentally safe steel corrosion inhibitor. In this publication, we investigated the effectiveness of this inhibitor for the protection of steel in a model solution of concrete pore fluid containing 3% NaCl. Visual observations of the surface condition of carbon steel samples after two weeks of exposure showed the absence of rust on the surface in the presence of ascorbic acid. Using instrumental methods such as potentiodynamic polarization, anodic polarization resistance and electrochemical impedance spectroscopy, the effect of ascorbic acid concentration on the electrochemical characteristics of this system was studied. It was shown that the protective effect is manifested at concentrations of 0.1 g/L and 0.5 g/L ASC, reaches a maximum at 1 g/L, and remains at a sufficient level for one month. When the ASC concentration is increased to 5 g/L, the protective effect decreases. Based on experimental data, adsorption isotherms corresponding to the Langmuir model were obtained and Gibbs free energy values were calculated. These values indicate that a strong bond is formed between ASC molecules and the steel surface. The mechanism of the protective action of the inhibitor in this system is discussed: ascorbic acid, being an antioxidant, reacts with active oxygen forms, reducing both their concentration in solution and the cathodic depolarization associated with them. This helps decrease the corrosion rate of steel. In addition, ascorbic acid reduces iron(III) oxides and hydroxides, causing the formation of a soluble iron(II) chelate, which leads to a decrease in the passivating properties of the surface layer at high ASC concentrations. These two counteracting factors determine the existence of an optimal ascorbic acid content in the solution.

Keywords: steel, inhibitor, ascorbic acid, model concrete pore fluid, Corrosimeter, EIS

Int. J. Corros. Scale Inhib., , 11, no. 2, 727-751
doi: 10.17675/2305-6894-2022-11-2-19

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