Monitoring the effectiveness of corrosion inhibitors by electrochemical methods. Sodium nitrite as an inhibitor for the protection of steel in a model solution of the concrete pore fluid

• V.E. Kasatkin, V.N. Dorofeeva, I.V. Kasatkina, I.G. Korosteleva and L.P. Kornienko

A.N. Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Leninskii pr. 31, 119071 Moscow, Russian Federation

Abstract: The effectiveness of steel corrosion inhibitors is investigated by the example of a model system: sodium nitrite as an additive to the electrolyte of a pore liquid of concrete with a high chloride content. Two methods were used for monitoring the state of the system during exposure in solution: the Corrosimeter method based on linear polarization resistance and Electrochemical Impedance Spectroscopy. It is shown that the results obtained by these methods are in good agreement and complement each other. These techniques made it possible to observe for nitrate all the patterns of its inhibitory action known from publications. It is shown that the inhibitory effect of nitrite increases with an increase in its concentration in solution. At a nitrite content of 10 g/l, the protective effect for steel (92–98%) can persist for at least a month. This effect is caused by the oxidizing ability of nitrite, which leads to the maintenance of the corrosion potential of steel at the level of 0…+100 mV (Ag/AgCl), i.e., under the conditions of the protective oxide γ-Fe₂O₃ formation on the surface. As the solution with the inhibitor “ages”, the protective effect decreases due to the chemical reduction of nitrite and acidification of the solution. These methods are used to carry out long-term monitoring of the state of the corrosion system with minimal disturbance of its equilibrium. This significantly distinguishes these “minimally invasive methods” from the popular method of studying inhibitors by polarization curves. Those methods can be recommended for the study of other corrosive objects in liquid media with inhibitors of various classes.

Keywords: steel, inhibitor, nitrite, model concrete pore fluid, Corrosimeter, EIS

Int. J. Corros. Scale Inhib., 2022, 11, no. 1, 198-220
doi: 10.17675/2305-6894-2022-11-1-11

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