Vol 55, No 3 (2019)

This paper presents the results of a multiyear study of the dependence of the erosion of the anode in electric spark alloying (ESA) on the physicochemical properties of its material. This work has been performed using various devices, with different electric modes, using manual or mechanized treatment, and in various media. This article contains generalized data on the anode erosion of refractory compounds and hard alloys. It is shown that the refractory compounds’ erosion occurs at a substantial solid phase participation, whereas the correlation of the erosion value with thermo-physical properties for them is absent. Erosion resistance and the coefficient of the transfer of hard alloys at the ESA initial stage of treatment are both significantly larger than those of a relevant refractory compound, and they increase with the addition of bundle content to the alloy. The law of the additive property of erosion and its dependence on the content of the plastic bundle is not applicable to hard alloys. Porosity enhancements increase the erosion of the anode material.

Both intrinsic and doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films were prepared by plasma-enhanced chemical vapor deposition (PECVD) with various process parameters, such as a hydrogen dilution ratio, power, substrate temperature, and doping ratios of phosphorus or boron. The crystallization characteristics of nc-Si:H thin films grown with various process parameters were carefully and systematically investigated by Raman spectroscopy. Generally speaking, the results show that the higher the hydrogen dilution ratio and power or the lower the doping ratio, the higher the average grain size and the crystalline volume fraction of both thin films prepared and investigated here. In addition, a p-i-n type nc-Si:H thin film solar cell, which has an open circuit voltage of 660 mV and a short circuit current intensity of 13.06 mA/cm², was directly prepared on a flat transparent conductive glass substrate.

A system for controlling the process of the high-voltage high-frequency electric discharge synthesis of nanocarbon on metal surfaces in a carbon gas medium has been developed. The criteria that determine the production mode of the synthesis of nanocarbon are defined. The synthesis control is performed according to the minimax optimality criterion. It allows the current value in the range of the production mode of the synthesis of carbon nanomaterials with an onion-like structure to be maintained. The control of the movement of the metal surface sample with respect to the electrode in the course of synthesis ensures the uniformity of coating the surface with a layer of a synthesized nanocarbon material.

In this paper, the Gibbs dividing surface method is used to derive a formula to determine curvature-dependent surface tension in a system with two phases. The well-known Tolman formula is a special case of this formula. The problem of a sessile droplet is considered. The Bashforth–Adams equation analogue (in view of curvature-dependent surface tension) is obtained, and the numerical solution of the equation is carried out. It is shown that if the droplet size is not very large relative to the thickness of the surface layer (micro- or nanodroplets), the dependence of the surface tension on the curvature is very important. In addition, the case is considered where the diameters of cylindrical nanodroplets are shorter than the Tolman length.

The effects of three organic additives polyethylene glycol (PEG), sodium dodecyl sulphate (SDS), and polyvinylpyrrolidone (PVP), on the electrodeposition of chromium from trivalent chromium chloride baths were investigated. The experiments were performed based on a two-level factorial design. The effects of electrolysis parameters: pH, temperature, and current density, as well as the concentrations of the three additives, on the thickness, roughness, and corrosion current density of the chromium deposited layers were analysed. Statistical results revealed that all response models are significant. It was found that the contributions of factors in thickness and interactions in roughness and the corrosion current density are more important. The main and interaction effect studies showed that pH and current density have significant effects on all of the responses, whereas the additive concentration only has an effect on the corrosion current density, especially in the presence of PVP and PEG. The interactions of pH with the current density and the temperature with current density have the most important effects on all responses. Optimisation and technical, economic, and environmental investigations revealed that PEG is the most suitable additive for usage in technical and decorative processes. PVP and SDS could substitute PEG for decorative and technical processes, respectively.

Tetranitro cobalt phthalocyanine (TNCoPc) was used as a corrosion inhibition of mild steel in a 0.25 M hydrochloric acid medium using Tafel polarization and electrochemical impedance spectroscopy in a temperature range of 303 to 323 K. The concentration of inhibitor used was in the range of 1.25–5 mM. The surface morphology was studied using scanning electron microscopy, atomic force microscopy, and energy dispersive X-ray analysis. Inhibition efficiency was found to increase with increasing inhibitor concentration and decreasing temperature. Polarization studies revealed that TNCoPc acts as a mixed type inhibitor at all concentrations of it. The maximum inhibition efficiency of 86.48% was obtained with TNCoPc at its optimum concentration of 5 mM. Adsorption studies revealed that the adsorption of this inhibitor underwent both physisorption and chemisorption on the surface of the metal and followed the Langmuir adsorption isotherm. The kinetic and thermodynamic parameters were calculated and discussed in detail. The results obtained by both Tafel polarization and electrochemical impedance spectroscopy methods were in good agreement with each other. TNCoPc emerged as a potential inhibitor for the corrosion control of mild steel in a hydrochloric acid medium.

The characteristics of a multistage electrohydrodynamic converter (EHDC) have been studied, and the results are presented in this paper. The diagram of an experimental installation is described; the pressure head, flow rate, and current characteristics are provided as a function of time and the EHDC supply voltage. The factors determining the EHDC parameters and the methods of their regeneration are determined.

Biomaterials are used for developing implants and producing a part or facilitating a function of a human body in a safe, reliable, and economical manner. Sol–gel deposition is one of the best, simple and economical methods of surface modification. In the current work, hydroxyapatite Ca₁₀(PO₄)₆(OH)₂, a bioactive material, has been prepared and then deposited on 316L stainless steel by the sol-gel coating method. The porosity percentage of hydroxyapatite coating was found to be 0.22. Electrochemical corrosion testing was carried out for both uncoated and sol-gel coated specimens. The coated specimens were characterized by the X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and cross-sectional analysis. The results revealed that the Ca/P ratio of the sol-gel coated steel was closer to that of a real human bone. It was found that hydroxyapatite-coated samples show better corrosion resistance and better implant properties as compared to those of the uncoated 316L stainless steel.