Vol 55, No 7 (2019)

Electrostatic nature of the relationship of zero-charge potentials and critical passivation potentials of IV –VI and VIII group transition metals of the periodic system in a series of proton donor and aprotic solvents, whose adsorption on the metal surface initiates transition of metal to passive state at a particular shift of potential relative to E_{q = 0}, is considered.

Under the effect of the surface discharge in air at atmospheric pressure, the edge of the electrode exposed in the plasma undergoes significant changes (oxidation, erosion, local melting, redeposition of oxides from the gas phase, etc.). The degradation of the working electrode, in the cases, e.g., aluminum or copper electrodes, can cause a continuous change in the electrical characteristics of the device, the executive part of which is the surface discharge system. This work presents the results of an experimental study of the effect of surface discharge plasma products excited by a sinusoidal voltage of 20 and 110 kHz in ambient air on steel X03Cr23Ni6Mo4Cu3NbN (after ESR) acting as an exposed electrode. It is shown that, despite the occurrence of microdamages on the surface of the sample and the formation of local oxide layers, the discharge energy during 4 h of exposure to the plasma products remains unchanged.

The method of reflective ellipsometry has been used to study the adsorption of the IFKhAN-92 inhibitor that is a triazole derivative on 12Kh18N10T nickel–chromium steel from dilute solutions of HCl and H₂SO₄ (t = 20 ± 2°C). It is shown that the adsorption process of this inhibitor is satisfactorily described by Temkin isotherm; its parameters are calculated. The values of free energy of adsorption of the inhibitor determined on the basis of this isotherm are ≈55 kJ/mol, which allows one to conclude about the chemisorption nature of the interaction of triazole molecules and the metal surface. An increase in the adsorption of the IFKhAN-92 inhibitor on chromium–nickel steel in H₂SO₄ solution with the addition of rhodanide-anions has been noted.

The data on adsorbability of oleamides and hexylamine, cyclohexylamine, morpholine, piperidine, and piperazine salts of oleic acid are systematized in this study. The protective mechanism of these compounds is studied in order to reveal a correlation between the inhibiting ability and the calculated parameters of the molecules. A procedure for measuring the Volta potential difference using a Poverkhnost-II high-sensitivity digital electrometer under the conditions when water- and hydrocarbon-soluble corrosion inhibitors interact with the steel and copper surface is elaborated. It has been proven that a high-efficiency corrosion inhibitor can be designed based on the data on its donor properties and adsorbability.

Electrochemical and adsorption behavior of porphyrin derivatives—dimegin and depocolin—on the surface of nickel from aqueous borate buffer solution with рН 7.4 have been studied. Both porphyrins shifted the pitting formation potential positively. According to the ellipsometric and XPS data, the porphyrins’ adsorption layer thicknesses were nearly equal and amounted to 0.6–0.8 nm, which corresponded to the molecule position at an angle of ~45° to the surface. Molecules are bound to the nickel surface by the oxygen atoms of carboxyl groups, whereas the porphyrin ring was not involved in the bond formation with nickel.

In this work, the effectiveness of three industrial bactericides and urotropine in inhibiting corrosion and hydrogen embrittlement of steels in 0.5% NaCl solution at different H₂S concentrations and pH values was investigated. The capability of the studied substances for chemical inactivation of hydrogen sulfide was also experimentally evaluated. It has been shown that bactericides effectively inhibit corrosion only if at least 50 mg/L of H₂S are presented in the medium.

Technologies of plasma electrolytic oxidation (PEO) make it possible to form coatings on magnesium alloys possessing a high adhesion to a substrate. Therefore, PEO-coatings can be considered as an efficient underlayer for polymer coatings. It also offers the possibility of addressing the problem of a high porosity of resulting PEO-coating. In this work, the opportunity of improving the protective properties of PEO-coating of different thicknesses on MA8 alloy through their treatment with water-soluble polymers was studied. It was shown that for the coatings with the thickness exceeding 50 μm, the best result was achieved upon the treatment with a polyurethane water-soluble polymer.

Protective properties of polymer coatings are mainly determined by their adhesion properties. Organosilanes represent the most commonly applied adhesion promoters; they are also capable of decelerating corrosion processes. In this study, the possibility of applying organosilanes in the function of inhibitors of cathodic peeling-off of polymer coatings has been investigated. It has been established that the introduction of vinyl silane to the coating results in the inhibition of cathodic peeling-off due to higher compatibility of vinyl with the components of the bitumen-polymer coating.

Mass transfer of phosphorus-containing corrosion inhibitors in epoxy matrices, which form the layers of anticorrosion primers and coatings, has been investigated. It has been shown that diffusion profiles of phosphonic acid distribution are stepwise, which has been previously observed in a broad range of mineral and organic acids. Penetration rate constants λ of phosphonic acids are comparable with the values that are intrinsic for inorganic acids. The acid-to-water ratio in internal solution in polymer is higher than in outer diffusant solution upon diffusion of phosphonic acids to amine-hardened epoxy matrices. A selective diffusion of phosphate anions has been observed in the solutions of acidic monosubstituted phosphates.

The effect of nickel, cobalt, and iron sulfates’ additives in the alkali-silicate electrolyte for microarc oxidation on the element composition and electrochemical behavior of MAO-coatings formed on titanium has been studied. It has been established that these additives were incorporated into an oxide layer. The increase of the content of these components in the electrolyte resulted in the decrease of their content (along with silicon) in the coating and the increase of the titanium content. This dependence can be related to the MAO process mechanism specifics and, first of all, to changes in temperature–time characteristics of microarc discharges.

It has been shown that treating a zinc surface with phenols (phenol, 2,6-di-tert-butyl-4-methylphenol (ionol), hydroquinone, pyrocatechol, 3,5-di-tert-butyl-pyrocatechol) increased the corrosive damage of the metal caused by microorganisms. It has been suggested that corrosion stimulation was caused by radical processes involving phenols adsorbed on the metal surface and products of oxygen biotransformation by microorganisms.