This review presents an electrode-kinetic model of the origin of aluminum pitting corrosion, taking into account the charge of the metal surface, the adsorption of chloride ions on the oxide surface, their penetration through the oxide film using oxygen vacancies and the initiation of pitting corrosion at the metal/oxide interface. It is shown that the critical potential of pitting formation is a function of the potential of a thin layer of a metal (aluminum) surface coated with an oxide, and the value of the pitting potential of binary surface alloying is related to the isoelectric point of the oxide of the alloying element in the binary alloy. An electrode-kinetic model of the occurrence of pitting is described, which is used to explain the effect of surface alloying on the occurrence of pitting in binary alloys. A method for changing the surface charge is proposed, including the formation of foreign surface organosilicon nanolayers carrying both negatively and positively charged groups. It is shown that four characteristics (charge (q), surface potential (Ψ1), critical pitting potential (E_pit) and metal's tendency to depassivation) depend on the nature of ion-exchange groups, the degree of their acid dissociation and ion-chemical interaction with activator ions.

One of the corrosion prevention methods is to add chemical compounds called inhibitors in corrosive environments. Inhibitors can be inorganic or organic compounds. However, these compounds are dangerous for human health and environment because of their toxicity effects. In addition to obtain them is difficult and expensive. For this reason, corrosion inhibitors that are non-toxic, biocompatible, not harmful to human health and the environment, and which can be obtained easily and cheaply, are the subject of many researches in recent years. Scientists have focused on a new class of inhibitors such as plant extracts, fruit and vegetable extracts and essential oils. Plant extracts are the most studied class of these inhibitors, called green inhibitors. The protection effects of plant extracts are due to the adsorption of their molecules on the metal surface. They provide the metal with a protective film by blocking the active sites. The formation of film provides the metal surface with a physical barrier from corrosive media, and supplies protection effects from corrosive attacks. Copper is noble metal and as a result of this property, it shows to resist against to corrosion. However, certain conditions can cause corrosion on copper, such as polluted air, oxidizing acids, oxidizing heavy metal salts, sulfur ammonia and some sulfur and ammonia compounds. Therefore, the investigation of copper corrosion is significant. In this review, studies are summarized with plant extracts, which have an inhibitory effect on the corrosion of copper.

The adsorption, protective and passivating effect of the sodium salt of methylenesuccinic acid and its composition with 2-mercaptobenzothiazole on the oxidized surface of copper and copper alloy MNZh5-1 in a neutral solution has been studied. Adsorption measurements show a higher free energy of adsorption (-∆G⁰_a) = 65,4 kJ/mol on copper than on the MNZh5-1 alloy (-∆G⁰_a) = 58,3 kJ/mol at E = 0,0 V. These values (-∆G⁰_a) indicate the chemisorption interaction of the organic anion with the oxidized electrode surface. Corrosion tests in a chloride solution of copper and its alloy for 7 days showed that the maximum degree of protection (Z = 90–100%) is observed for a 3 mmol/L composition of the investigated dicarboxylate with the sodium salt of 2-mercaptobenzothiazole.

The effect of cyclic electrochemical polarization on the corrosion properties of oxide-ceramic coatings consisting of transition metal oxides, boron carbide, and boron nitride was studied. The coatings were applied by laser melting of powder mixtures on the surface of low-carbon unalloyed steel using a fiber-optic laser. The resulting coatings feature enhanced tribological properties. The composition, surface condition, and resistance of samples to electrochemical corrosion were studied. Voltammetric curves were recorded in a neutral buffer solution. It was shown that the presence of boron nitride in the coating composition leads to depassivation of the steel surface. The conceptual possibility of enhancing the corrosion resistance of samples coated with B₄C-BN-Bi₂O₃-MnO₂ by cyclic polarization was shown.

Combining a conversion coating with subsequent application of an inhibitor film is an effective and widely used method for increasing the corrosion resistance of metal products. This work compares the structure and protective properties of oleic acid films formed on the oxidized surface of magnesium Mg90 from alcohol solutions and from hot acid vapors. Using the ellipsometry method, it was shown that both methods lead to the formation of thin (up to 100 nm) layers on the surface, increasing the protective properties of the oxide coating. The maximum protective effect was demonstrated by the film obtained by one-hour treatment in an alcohol solution containing 8 mM acid. Voltammetric studies have shown that such a film suppresses anodic dissolution. Using electrochemical impedance spectroscopy, a mixed blocking-activation mechanism of protective action was determined.

At more negative Е_c values, an increase in the duration of cathodic polarization reduces the intensity of steel local corrosion in the unbuffered chloride solution. This effect is explained by blocking of the pit nucleation centers on the metal surface by a layer of steel dissolution products formed in the near-electrode electrolyte layer with a high pH. Significant fluctuations in the cathodic protection potential under the influence of stray currents lead to the formation of local types of corrosion of steel structures operating in soils and seawater. The potential fluctuations induced by both alternating and direct current sources can be modeled by cycling a square potential stage. In this paper, the effect of cyclic potential pulse (CIP) on the general and local corrosion of low-carbon steel in 3.5% NaCl solution with borate buffer (pH 6.7) and without it is studied. A decrease in the cathodic half-period potential (E_c) of the CIP inhibits general corrosion and accelerates local corrosion of steel in both solutions, which is associated with an increase in the amount of hydrogen in the metal. An increase in the duration of the cathodic half-period of the CIP increases the density and total area of the pitting at less negative values of the E_c. At more negative Е_c values, an increase in the duration of cathodic polarization reduces the intensity of local.

The effect of Fe(III) salts on the protection of low carbon steel in solutions of sulfuric and phosphoric acids (20 and 60°C) by corrosion inhibitors (VNPP-2, INVOL-2 m. A, Catapin A, Catapin BPV, PKU-E, Soling m. Z, Soling m. L and NORUST CM 150 C) has been studied. None of the individual corrosion inhibitors studied can provide efficient protection of steel in 2 M H₂SO₄ and 2 M H₃PO₄ if significant amounts of Fe(III) salts are accumulated in them. In 2 M H₃PO₄ containing Fe(III) phosphate, efficient protection of steel can be obtained by the formulation comprising 2 g·L^-1 VNPP-2+0.5 mM KNCS+200 mM urotropin as the corrosion inhibitor. The same formulation protects steel in 1 M H₂SO₄+1 M H₃PO₄ (20 and 60°C) with up to 0.10 M Fe(III) cations accumulated in it. Solutions of a H₂SO₄+H₃PO₄ mixture inhibited by the formulation of 2 g·L^-1 VNPP-2+0.5 mM KNCS+200 mM urotropin can be an alternative to inhibited solutions of individual H₂SO₄ in case of potential accumulation of Fe(III) sulfate in them.

The effect of titanium surface treatment on the formation of the oxide layer nanostructure was studied. This layer was formed by electrochemical oxidation in an acidic solution containing fluoride ions. The structures and properties of the oxides obtained on the titanium surface were studied by means of electrochemical impedance spectroscopy, cyclic voltammetry and atomic force microscopy. Preliminary formation of a hydride sublayer on the titanium surface does not allow for the formation of a regular nanotubular oxide structure.

The application of polymerizable and alkoxide gels for the formation of porous coatings on metals has been investigated. The basic principles of construction of polymerizable gels and their advantages over partial gels, which are obtained from highly dispersed metal oxides, are noted. The morphology and chemical composition of the surface of steel and magnesium alloys modified with the help of gels have been studied by means of X-ray photoelectron spectroscopy. It was found that when styrene-acrylic dispersion interacts with magnesium alloy, a porous structure consisting of organomagnesium and polymer structures is formed on its surface. A uniform polymer coating with good adhesion to the substrate is formed on the surface of low carbon steel. The mechanism of formation of porous titanium dioxide structures on the steel surface obtained by sol-gel technology is considered. It is shown that the inclusion of organosilanes in the composition of porous titanium dioxide gel significantly increases the mechanical strength of the coating and its adhesion to the steel surface.

The effect of mixed inhibitors based on octanoic acid and nitrogen compounds with a negative degree of oxidation on the corrosion properties of a ceramic oxide coating of the composition B4C–BN–Bi2O3–MnO2 has been studied. The coating was synthesized by laser sintering of a powder mixture on the surface of low-carbon non-alloy steel. As a result of laser treatment, an oxide-ceramic layer is formed on the metal surface, which has antifriction properties and high hardness. The phase composition and surface relief of the resulting composite are investigated. A decrease in the corrosion resistance of the resulting composite under conditions of electrochemical corrosion in a neutral buffer solution medium compared with untreated steel has been established. To increase the corrosion resistance, an inhibitory treatment method was applied. The following compositions were used as inhibitors: octanoic acid, octanoic acid–hexamethylenetetramine, octanoic acid– hydrazine hydrate and octanoic acid-2,4-dinitrophenylhydrazine. The inhibitors were applied by impregnation methods followed by heating of the samples to 120°C. All the studied compound inhibitors increased the corrosion resistance of the material to electrochemical corrosion in a neutral borate buffer solution.