A. V. Syugaev

Electrochemical behavior of Co3C carbide

The electrochemical properties of the Co3C carbide have been studied. In contrast to metallic cobalt, its carbide is characterized by higher electrocatalytic activity in the hydrogen evolution reaction and low rate of anodic oxidation in acidic sulfate solutions. The oxidation in borate solutions (pH = 6.3–9.0) results in the formation of oxide films different in phase composition. In the case of metallic cobalt, a passive film consisting of CoO and Co(OH)2 forms, while the cobalt carbide oxidation results in the formation of the Co3O4 film. The oxidation of cobalt carbide is an irreversible process accompanied by the accumulation of carbon on the surface.

Electrochemical properties of iron silicocarbide and cementite in acidic and neutral environments

Voluminous specimens of individual Fe5SiC iron silicocarbide and Fe3C iron carbide phases were produced by mechanical alloying with subsequent pressing and considered as models of nonmetallic inclusions in carbon steels and siliceous cast irons. In an acidic sulfate solution, silicocarbide is highly active in hydrogen reduction and iron ionization in the active dissolution range. Therefore, the corrosion resistance of silicocarbide in acids is lower compared to iron and cementite, which is caused by the peculiarities of its crystal structure. In a neutral borate solution both on silicocarbide and cementite, two anodic peaks are observed that are caused by the dissolution of the corresponding phase and the additional oxidation of the passive film, which is characterized by the heightened defectiveness because of the carbon accumulation. Silicocarbide has lower dissolution currents compared to cementite and a higher resistance to the local activation and depassivation, which is caused by the presence of a superficial layer enriched in SiO2.

Corrosion-electrochemical properties of α-Fe + Fe3C + TiC nanocomposites in neutral environments

The corrosion-electrochemical properties of α-Fe + Fe3C + TiC three-phase nanocrystalline composites in borate solutions with pH 6.3–9.0 both with and without NaCl are studied. α-Fe + Fe3C + TiC composites are found to have heightened resistances at active-oxidation potentials of α-Fe and cementite due to the formation of xFeO · yTiO2 mixed surface oxides. The protective properties of passive films based on xFeO · yTiO2 and their resistance to local activation are worse than those of Fe3O4/γ-Fe2O3 (γ-FeOOH) passive films formed on iron and α-Fe + Fe3C composites.

Electrochemical properties of α-Fe + Fe3C nanocrystalline composites in acidic environments

Regularities of the physicochemical behavior of α-Fe + Fe3C nanocomposites in a concentration range of cementite from 9 to 92 wt % in sulfate and chloride solutions are studied. Nanocrystalline state (∼40 nm) is found to intensify the active dissolution of α-Fe + Fe3C alloys and not noticeably affect the hydrogen evolution in acidic environments. With an increase in the cementite content or when it forms a reticular structure, the catalytic activity of α-Fe + Fe3C nanocrystalline composites with respect to the hydrogen evolution increases. Cementite manifests a higher overpotential of dissolution in both sulfate and chloride solutions.

The electrochemical properties of Ni3C carbide

The electrochemical properties of Ni3C was studied. In acidic sulfate solutions, the carbide is characterized by high overpotential of its oxidation as compared with nickel. In the case of carbide oxidation, the anodic reaction orders with respect to anions are low, indicating a weak dependence of the rate of the anodic process on the solution composition. Significant differences in the kinetics of the anodic processes indicate different mechanisms of the oxidation of nickel and its carbide. The rate and kinetic parameters of the hydrogen evolution reaction are comparable on Ni and Ni3C. In neutral and alkaline solutions, the metal and carbide samples were similar in their electrochemical characteristics. The anodically grown oxide film is thinner on nickel carbide than on nickel metal, and the oxide formed on the carbide is more readily reduced under cathodic polarization. This film is also more resistant to the pitting attack than the oxide film on nickel metal.

Structural-phase composition, structure of the surface, magnetostatic and microwave properties of powders produced by milling of Fe in polystyrene with additions of surfactants

The effect of additions of surfactants (stearic and perfluorononanoic acids, stearylamine, and of their mixtures) on the morphology, structural-phase composition, structure of the surface, and magnetostatic and microwave properties of ferromagnetic powders obtained by the joint high-energy milling of Fe and polystyrene has been investigated. It has been shown that the use of a mixture of stearic and perfluorononanoic acids during milling made it possible to obtain particles of plate-like shape with minimum changes in the phase composition and to produce shells on their surface that consist of the surfactant molecules. All of these factors have positively affected the microwave properties of the composites prepared from thus obtained powders.

Chemical modification of iron particles in mechanical activation with polydienes

Ultrafine iron particles prepared via mechanical activation in a planetary ball mill in polydiene solutions with surface-active substances (SASs) are studied in this work. It is shown that carbides are disposed in the particle bulk, whereas an organic layer with modified (oxidized) polymer molecules and SASs is formed at the surface of particles. Adsorption of polydienes on the particle surface is due to alcohol and carboxyl groups. It is established that modification of iron particles with polybutadiene leads to the formation of a polymeric film with a maximum protective effect.

The influence of the ultrafine-grained structure on passivation of copper

The influence of ultrafine-grained structure on passivation of copper in borate solutions was studied. Ultrafine-grained cooper was prepared by the equal channel angular extrusion. It was shown that, under the conditions of anodic oxidation, an oxide film with improved protective properties is formed on the ultrafine-grained sample. This film is characterized by a small thickness, low roughness, and high content of copper(I) oxide.

Formation of interfacial layer in Fe-polystyrene system during mechanochemical synthesis in the presence of alkyl surfactants

The structure of surface organic layers formed during the mechanical milling of Fe with polystyrene and alkyl surfactants is studied using NEXAFS and FT-IR spectroscopies. It is shown that the main constituents of the layers formed are condensed aromatic structures (products of the dehydrogenation of an organic medium) that contain covalently bound polystyrene fragments.

Cathodic evolution of hydrogen on carbides of iron-family metals

The activity of carbides of iron-family metals with respect to hydrogen evolution in acidic solutions is found to be much higher than the activity of the corresponding metals and increase in the sequence Ni3C < Co3C < Fe3C. Of the carbides studied, cementite has the highest activity, which is comparable to that of a Pt electrode.