A. N. Maratkanova

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 (pHu2009=u20096.3–9.0) 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.

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.

Microwave properties of powders produced by high-energy milling of iron with paraffin

The structural and phase composition and magnetostatic and microwave properties of powders produced by simultaneous milling of carbonyl iron and paraffin taken in volume ratios ranging from 10 : 90 to 80 : 20 have been studied. It has been shown that the shape of the powder particles depends substantially on the amount of Fe in the mixture. At an Fe content of 30 vol %, the particles acquire a platelet shape; at an Fe content of more than 40 vol %, the agglomeration of the particles is observed. At an Fe content above 30 vol %, the Fe3C phase is formed in the particles, which leads to an increase in the coercive force and a decrease in the specific saturation magnetization of the powder. The frequency dependences of the microwave magnetic and dielectric permeabilities of the composite materials containing the prepared powders have been measured, and the frequency dependences of the intrinsic magnetic permeability of these powders have been determined. It has been shown that the static magnitude of the intrinsic magnetic permeability reaches a maximum in powders containing 30 vol % Fe in the initial mixture.

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.

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.

Corrosion-electrochemical properties of nanocomposites of α-Fe+Fe3C+VC in acidic and alkaline sulfate solutions

This work studies corrosion-electrochemical properties of three-phase composites of α-Fe+ Fe3C + VC in acidic and alkaline sulfate solutions. Nanosize carbide inclusions are characterized by a high level of activity in the reaction of cathodic hydrogen evolution and result in a high rate of composite dissolution in acidic solutions. The presence of carbides and carbon has a negative effect on passivation of the iron matrix. The resistance of vanadium carbide inclusions to anodic oxidation increases upon a decrease in the amount of carbon in the carbide.

Microwave Properties of Mechanosynthesized Fe-Paraffin Nanocomposites

The structure and microwave properties of composites consisting of paraffin as a dielectric host matrix and Fe particles as inclusions have been studied. The composites were prepared by the mechanochemical synthesis and contain 7.7% vol. concentration of the inclusions. The microwave properties were studied in 0.1 to 6 GHz frequency range. The microwave properties of the composites are shown to depend mostly on the size and shape of the inclusions, with the phase composition of the inclusions exerting only a slight effect. With decreasing the inclusions size, the low-frequency peak (300−400 MHz) attributed to the domain wall motion diminishes.

Molecular orientation in electrodeposited polypyrrole films

The molecular arrangement in electrodeposited polypyrrole films was studied by means of linear dichroism in the near-edge X-ray absorption fine structure (NEXAFS) spectra measured at the K absorption edges of carbon and nitrogen. It has been found that the change of the exciting radiation incidence from normal to grazing leads to an increase in the intensity of π*-related resonances with simultaneous decrease in the intensity of σ*-related resonances in the spectra. Similar changes in the spectra measured for both absorption edges indicate a pronounced conjugation of π-bonds in the polypyrrole chains in the grown films. Preferential in-plane orientation of pyrrole rings relative to the substrate surface is observed for all the deposited films. The linear dichroism is more pronounced at the initial stages of deposition (2D growth) than at later stages characterized by “cauliflower”-like morphology of the grown film.