Substituted benzotriazoles as inhibitors of copper corrosion in borate buffer solutions

The adsorption of substituted 1,2,3-benzotriazoles (R-BTAs) onto copper is measured via ellipsometry in a pure borate buffer (pH 7.4) and satisfactorily described by Temkin’s isotherm. The adsorption free energy (?ΔG _a ⁰ ) values of these azoles are determined. The (?ΔG _a ⁰ ) values are found to rise as their hydrophobicity, characterized by the logarithm of the partition coefficient of a substituted BTA in a model octanol–water system (logP), grows. The minimum concentration sufficient for the spontaneous passivation of copper (C _min) and a shift in the potential of local copper depassivation with chlorides (E _pt) after an azole is added to the solution (i.e., ΔE = E _pt ⁱⁿ ? E _pt ^backgr characterizing the ability of its adsorption to stabilize passivation) are determined in the same solution containing a corrosion additive (0.01М NaCl) for each azole under study. Both criteria of the passivating properties of azoles (logC _min and ΔE) are shown to correlate linearly with logP, testifying to the role played by surface activity of this family of organic inhibitors in protecting copper in an aqueous solution.     

Formation of passivating layers by 1,2,4-triazole derivatives on copper in aqueous solutions

Ellipsometry and electrochemical measurements are used to study the adsorption of some substituted 1,2,4-triazoles on copper and their effect on dissolution of copper in aqueous buffer solutions at pH 7.4. It is found that the adsorption of triazole compounds on copper is polymolecular at potential Е = 0.0 V, in relation to a normal hydrogen electrode. The first layer is described by the Temkin equation with free adsorption energy (−ΔG_a⁰) = 55.2–76.3 kJ/mol and an energy heterogeneity factor that varies from 0.91 to 2.5. The maximum value of −ΔG_a⁰ is found for an acid and a hydrogen sulfide corrosion inhibitor that is a mixture of triazole derivatives. The same inhibitor is the one least sensitive to the energy heterogeneity of the surface of a copper electrode, due to its high chemical reactivity and ability to be adsorbed on different active sites. This inhibitor is likely chemisorbed on copper and forms an ultrathin coating in an aqueous solution that is vastly superior to similar coatings produced by the familiar corrosion inhibitors of triazole group compounds in protecting against atmospheric corrosion.

     

Adsorption and protecting properties of 1,2,3-benzotriazole on MNZh 5-1 alloy in neutral solutions

1,2,3-Benzotriazole (BTA) stabilizes the passive state of the MNZh 5-1 alloy in a chloride borate buffer with pH 7.40 at c _BTA = 0.5 mM, which is lower than for the metal components of the alloy. The adsorption of BTA on the surface of MNZh 5-1 is polymolecular. The free energy of adsorption ?ΔG _a ⁰ for monolayer BTA coverage of the alloy was higher than for the alloy component metals (Fe, Ni, Cu).     

Inhibition of copper dissolution in water solutions of triazoles

The influence of the chemical structure of certain triazoles on the inhibition of copper dissolution in water solutions at pH 7.40 is studied by electrochemical and ellispometric means. It is established that adsorption of the studied triazoles on copper at potential E = 0.0 V relative to a normal hydrogen electrode is polymolecular, the first layer is described by the Frumkin equation with values of the free adsorption of energy values (?ΔG _a ⁰ ) = 50.5–70.1 kJ/mol. In addition, possible orientations of triazole molecules with respect to a surface of oxidized copper are revealed.     

On co-adsorption on passive iron from aqueous 1,2,3-benzotriazole and sodium phenylundecanoate

Passivation of iron and low-carbon steel in borate buffer solution (pH 7.40) was studied in the presence of 1,2,3-benzotriazole (BTA) and its equimolar mixture with sodium phenylundecanoate (SPU). As was shown BTA is an ineffective stabilizer of the passive state, while SPU has a better efficiency in this function. However, the stabilizing effect of BTA can be improved by forming its adsorption layer on the electrode surface pre-modified with SPU anions at anodic potential E = 0.2 V or by its co-adsorption with SPU. The analysis of attraction between the adsorbed particles of these inhibitors enabled to suggest that their co-adsorption on oxidized iron (E = 0.2 V) yields associates of SPU and BTA anions.