Effect of tartrate on the electrochemical behaviour and semiconductive properties of passive film on steel in saturated calcium hydroxide

Abstract

This paper presents results of the basic study on the inhibitive action of tartrate toward chloride‐induced corrosion on carbon steel rebar in alkaline environment. Modification of the electrochemical behaviour and semiconductive properties of passive film formed on steel surface in the presence of tartrate were characterised by a range of electrochemical techniques in saturated calcium hydroxide. In the presence of tartrate in saturated calcium hydroxide with addition of 0.14 M sodium chloride pitting corrosion initiation was postponed for 622 mV up to potentials of oxygen evolution reaction. The hypothesis on the competitive adsorption between the chloride ions and tartrate anion through the surface complex formation was applied on the studied system.

Influence of the Ligands in Cu(II) Complexes on the Oscillatory Electrodeposition of Cu/Cu2O

“…The need to reach more negative potentials to initiate the deposition can suggest a surface inhibition effect, stronger when compared with lactate, caused by the adsorption of tartrate and/or its complexes. This evidence agrees with lower cathodic currents (at higher potentials in the positive sweep and lower potentials in the negative sweep) depicted in Figure a and the surface protective effect of the tartrate molecules found in the corrosion science literature. − For a detailed investigation of the pH effect on the CV and the galvanodynamic curves, please see Figures S1 and S2 in the Supporting Information, respectively.…”

Inhibition Effect of Tartrate Ions on the Localized Corrosion of Steel in Pore Solution at Different Chloride Concentrations

“…At the same time, the presence of the negative carboxylate group of the tartrate on the film surface counteracts the adsorption of the chloride ions, favoring the re-passivation. The same authors also reported that increasing the concentration of tartrate above 2.5 × 10 −3 M results in the deterioration of passive film due to the dissolution of the surface complex induced by the lowering metal/ligand ratio [42]. For this reason, the overall effect of tartrate ions on carbon steel could be to enhance the generalized dissolution of the passive film, but, at the same time, its carboxylate groups counteract the adsorption of the chlorides on the film surface, inhibiting the localized corrosion onset and propagation.…”

“…The competitive formation of soluble complexes of Fe (III) and the adsorption of the tartrate ions on the electrode surface to substitute the hydroxyl in the passive film, increases the current density in the passive range of potential, but, at the same time, inhibits the adsorption of chloride ions, and, as a consequence, the pitting initiation. In the inhibition mechanism proposed by Valek Žulj et al, the tartaric acid stabilized the Fe (III) in the passive film; as a consequence of this, the concentration of Fe (II) ions in the film decreases, and, in this way, the conductivity of the n-type semiconductor passive film is reduced, for the decreasing of the concentration of the donors, reducing the efficiency of the occluded cell in the propagation of the localized attack [42]. At the same time, the presence of the negative carboxylate group of the tartrate on the film surface counteracts the adsorption of the chloride ions, favoring the re-passivation.…”

“…All these tests were carried out in acidic solution [76]. In alkaline solution, Valek Žulj et al proposed a competitive adsorption of tartrate ions and chlorides as a mechanism of corrosion inhibition of rebar in pore solution [42]. Bazzaoui et al reported the formation of a passive layer on iron in 0.2M sodium tartrate at pH 6.8, at a potential of −0.35 V versus Ag/AgCl, according to the reaction:…”

“…Several studies have shown that the ions of organic acids with nucleophilic substituents are able to act as corrosion inhibitors; the greatest efficiency is represented by dicarboxylic acids, such as tartaric acid, which can coordinate on the metal surface with a chelating effect [38][39][40][41]. The properties of tartaric acid as a corrosion inhibitor were underlined by several authors [42,43]. However, it is a strong set retarder and its dosage must be well determined to achieve chlorides corrosion protection thus avoiding excessive retardation.…”