A. A. Chirkunov

Protection of low-carbon steel in aqueous solutions by lignosulfonate inhibitors

The corrosion and electrochemical behavior of low-carbon steel and iron in a neutral aqueous solution containing ZnHEDP, lignosulfonates LS1 and LS2, and their mixtures was studied. Corrosion tests showed that these lignosulfonates stimulate corrosion at room temperature but act as weak inhibitors at 80°C. However, adding LS1 and LS2 to ZnHEDP enhanced the steel protection by the latter; a synergism of their protective effects was observed at certain ratios of the complexonate and polymers. Although LS1 and LS2 are compounds of the same type, their effects on steel corrosion in a neutral aqueous solution containing ZnHEDP differ substantially: LS1 favors the inhibition by ZnHEDP of the cathodic reaction only, while LS2 affect both electrode reactions.

The effect of steel modifying with zinc oxyethylidenediphosphonate on its passivation in solutions of certain inhibitors

It is shown that a solution of zinc complex of 1-hydroxyethane-1,1-diphosphonic acid can be used for modifying the surface of low-carbon steel in order to enhance its passivation by aqueous solutions of other inhibitors (1,2,3-benzotriazole, sodium alkylcarboxylate, and their mixture). The results of accelerated tests of protectability of nanosized passivating coatings are compared. To assess the efficiency of steel protection by electrochemical tests, the difference in pit formation potentials ΔE = Eptin − Eptsup are determined from polarization curves in borate buffer solutions containing NaCl in the absence (Eptsup) and in the presence (Eptin) of the inhibitor. The direct corrosion tests are carried out in cells and in the G-4 humidity chamber (GOST (State Standard) 9.054–75) where the time of the appearance of first indications of corrosion on samples τcor serves as the criterion of efficient protection. Three groups of coatings can be distinguished: with weak protectability characterized by ΔE < 0.20 V and τcor < 6.25 days; with medium protectability and ΔE = 0.20–0.40 V with τcor reaching 9 days; and the with high protecting efficiency and ΔE > 0.40 V where τcor can be even longer than 25 days.

Inhibition of anodic dissolution of low-carbon steel with alkyl phosphonates in borate buffer solution

Anodic behavior of a low-carbon steel in a borate buffer solution containing CnH2n + 1PO3Na2 sodium alkyl phosphonates with n = 7–10 is studied. The passivating ability of alkyl phosphonates is shown to depend on the length of the hydrocarbon radical of the inhibitor and the exposure of the steel in the 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 (−ΔGa0) = 55.2–76.3 kJ/mol and an energy heterogeneity factor that varies from 0.91 to 2.5. The maximum value of −ΔGa0 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.

Protecting Aluminum from Atmospheric Corrosion via Surface Hydrophobization with Stearic Acid and Trialkoxysilanes

The possibility of subjecting aluminum to hydrophobization and superhydrophobization (SHP) with ethanol solutions of trialkoxysilanes and stearic acid is explored. It is shown that SHP coatings are highly effective in protecting Al against atmospheric corrosion. The thicknesses of surface SHP layers are determined via X-ray photoelectron spectroscopy and ellipsometry. The protective ability of SHP coatings is determined by polarization measurements and corrosion tests in a salt fog chamber.

Inhibition of Magnesium Corrosion by Salts of Higher Carbonic Acids

The effect of sodium salts of some higher carboxylates on anodic magnesium dissolution in the borate buffer solution (pH 7.4) has been investigated. It has been demonstrated that the best protective and passivating properties characterize sodium oleate (SOL). The high protective properties of SOL were corroborated in tests of Mg plates under conditions of humid atmosphere with daily humidity condensation. Preliminary Mg passivation in an aqueous solution of 16 mmol/L of SOL provides protection from the emergence of the first corrosion damage for 18–20 h, which is six times more efficient than the chromate treatment at the same concentration.

Inhibition of magnesium corrosion by triazoles

The inhibitive action of some azoles (1,2,4-triazole, 1,2,3-benzotriazole, 5-chlorobenzotriazole, and IFKhAN-92 corrosion inhibitor) on the corrosion of magnesium was investigated in aqueous buffer solutions and humid atmosphere. Increasing the hydrophobicity and decreasing the pKa of NH-acids enhance the protection of Mg by triazoles, that is why 5-chlorobenzotriazole and IFKhAN-92 – a mixture of substituted triazoles – are more efficient inhibitors. Small additions of dioctylphosphate increase the protection of Mg in aqueous solution by IFKhAN-92 inhibitor, and addition of trialkoxysilane to the mixed inhibitor allows one to enhance the protection of Mg in a humid atmosphere.

Improving steel passivation with aqueous solutions of [3-(2-Aminoethylamino)propyl]trimethoxysilane

It is shown by means of electrochemical measurements that small amounts of silane are capable of improving the protective properties of sodium salts of different organic carboxylates in the passivation of lowcarbon steel. The adsorption of sodium oleoylsarcosinate on both oxidized and reduced steel surfaces is studied by means of ellipsometry. It is shown that the passivation of low-carbon steel with a mixture of silane and oleoylsarcosinate at a ratio of 3 : 1 is an efficient method of protection under severely humid atmospheric conditions.

Passivation of steel with aqueous solutions of trialkoxysilanes

The passivating power of the aqueous solutions of certain trialkoxysilanes towards low-carbon steel has been studied. It has been established that aminoalkoxysilanes, as opposed to vinyltrimethoxysilane, are capable of passivating low-carbon steel in a neutral chloride-containing buffer solution. Aminoethylaminopropyltrimethoxysilane induces the passivation of steel most effectively. Its adsorption on the reduced or oxidized surface of the St3 steel studied via an ellipsometric method can be adequately described by the Frumkin equation.

Adsorption of dioctyl phosphate and inhibition of dissolution of low-carbon steel in neutral solution

The effects of temperature, exposure, and agitation of the solution on the passivating properties of sodium dioctyl phosphate are studied. It is found that passivation of steel in the presence of the salt can proceed without the formation of surface oxide.