Surface Engineering and Applied Electrochemistry最新文献

Pure nickel (Ni) coatings and nickel–vanadium pentoxide (Ni–V₂O₅) nanocomposite coatings have been developed on the mild steel substrates by the direct current (DC) and pulse current (PC) methods of electrodeposition using a sulfamate electrolyte bath by optimizing all of the suitable parameters. The surface morphology and texture characterization of pure Ni coatings and Ni–V₂O₅ nanocomposite coatings were analyzed by spectroscopic techniques such as scanning electron microscopy (SEM) equipped with an attachment for energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) spectroscopy analyses. The SEM study confirmed surface morphology of the pure Ni coating was changed by the incorporation of V₂O₅ nanoparticles in the nickel metal matrix and chemical composition of all the coatings was determined by EDS. The XRD study proved highly corrosion resistant nanocomposites show preferred orientation towards (111) plane. The corrosion rate of all the coatings was investigated in a 3.5% corrosive medium using electrochemical techniques such as Tafel extrapolation and AC impedance. The coatings developed by PC showed an enhanced corrosion resistance behavior compared to that of the coatings developed by DC. The 0.125 g/L Ni–V₂O₅ nanocomposite coating obtained by PC showed more widened semicircles with a high R_p value and a more positive shift with high corrosion resistance during the AC impedance and Tafel extrapolation analyses respectively. The coatings developed by PC showed improved microhardness compare to that of the coatings developed by DC during microhardness testing of all studied coatings.

The results of a study into the electrical and optical characteristics of an overvoltage nanosecond atmospheric pressure discharge between electrodes made of a superionic conductor (SIC) (Ag₂S) in krypton are presented. The destruction of electrodes in the discharge and the introduction of Ag₂S vapor into the interelectrode gap occurred due to the microexplosions of inhomogeneities on the working surfaces of polycrystalline electrodes (the formation of ectons) in order to synthesize thin films based on this compound on the surface of a dielectric substrate mounted near the electrodes. Numerically solving the Boltzmann kinetic equation for the electron energy distribution function, the temperature and the electron density in the discharge, the specific discharge power losses for the main electronic processes, and the rate constants of the electronic processes depending on the parameter E/N for the plasma of vapor-gas mixtures based on krypton and silver sulfide have been calculated. Homogeneous thin films based on silver sulfide are synthesized on the quartz substrates by the gas-discharge method under conditions of ultraviolet assisted discharge plasma.

The characteristic sizes and charges of droplets formed during the realization of the electrostatic instability of a uniformly charged, charge-induced flat surface of an electrically conductive liquid are calculated on the base of the principle of the least energy dissipation in the Onsager nonequilibrium processes. It was found that the droplets of the same size and charges are emitted when the electrostatic instability of a flat liquid surface is realized. The surface should be infinitely extended along both axes of the Cartesian coordinate system of the liquid, and the axes should be perpendicular to the direction of gravity. If to compare the same characteristics of the charged droplet disintegration, unstable to its own charge, then there will be a number of differences, i.e., in the number of emitted progeny droplets, in their sizes and charges, and in the tendency of all parameters to change with an increase in the ordinal number of the progeny droplet. The paper considers the progeny droplets to be initially unstable to the electric charge which is located on them.

In this paper we present the results of studies into the frequency and temperature dependences of the dielectric loss tangent and the real and imaginary parts of the permittivity in MnGaInSe₄ single crystals in an alternating electric field. The main type of dielectric losses in MnGaInSe₄ single crystals in the frequency range of 8 × 10³–3 × 10⁵ Hz is established to be electrical conductivity losses, while the conductivity is characterized by the zone-hopping mechanism. The activation energies of current carriers of single crystals are determined. The real and imaginary parts of the permittivity are found to undergo significant dispersion, which is of a relaxation nature.

This paper presents the theory of surface electronic states induced by a high-voltage field and considers applications of the theory of surface electrons (SEs) to electrohydrodynamic flows. Theoretical considerations are carried out within the framework of a one-electron quantum mechanical model. It is shown that SEs initiate the injection of negative charges from the cathode into a liquid dielectric containing an electron-acceptor impurity, for example, molecular iodine. The comparison of the theoretic and experimental data is satisfactory.

A statistical study was made of the microgeometry parameters of the surface of vertical walls of an object of building by additive manufacturing using electron beam melting, and the effect of conditions of building and parameters of hatching mode on surface roughness was estimated. It was determined that the parameters of hatching mode affect the roughness of the lateral surface when building samples with vertical walls. It was shown that the average height of surface roughness, Rz, increases as the energy of hatching mode is intensified. A physical model was proposed to describe the effect of parameters of hatching mode on the roughness of vertical walls, which is based on the hypothesis that a melt microflow can penetrate during hatching onto the external surface of the contour. It was demonstrated that the distribution of surface roughness values of vertical walls is non-Gaussian, and the curves are typically right-skewed (the mode is located to the left of the center of size grouping), which indicates the influence of non-random factors whose number or values systematically change over time.