Surface Engineering and Applied Electrochemistry最新文献

For the first time, the principled possibility of forming oxide layers on the vanadium surface using the VNM-1 alloy by plasma electrolytic treatment (PET) has been experimentally demonstrated. A clarified formulation of the valve materials’ definition has been proposed. The features of PET for the VNM-1 alloy in different electrolytes were studied, the adhesive and cohesive properties of the formed layers were discussed. It was proven that PET technology, along with and in competition with other methods, can be used to obtain vanadium oxides intended for multipurpose usages.

The paper studies the structural and physicochemical properties of binary polymer mixtures based on ethylene-propylene copolymer (EPDN) and nitrile-butadiene rubber (NBR) in order to improve their technological and thermal stability. A comprehensive analysis of the influence of composition and plasticization conditions on the processes of crosslinking, structure formation, and thermal-oxidative destruction was carried out. It was experimentally established that an increase in the proportion of NBR promotes the development of a spatial network due to radical reactions activated by double bonds and polar groups. Optimal viscosity, elasticity, and gel content are achieved with an EPDN to NBR ratio of 60 : 40. The results are confirmed by both spectral and rheological analyses as well as by calculating the degree of crosslinking using the Flory–Rehner equation. The work demonstrates the potential of targeted modification of EPDSN-containing compositions using reactive elastomers to create heat-resistant and durable polymeric materials.

The paper proposes a method of constructing an ultrasonic system that determines the stability of thermosonic microwelding of gold wire with a diameter of 17.5–50 µm when assembling electronic products in metal-ceramic enclosures. A simulation of waveguide was conducted at the standard frequency of ultrasonic oscillations of 66 kHz and an increased frequency of 136 kHz.

The electrodeposition and properties of the Co–W alloy obtained from concentrated gluconate electrolytes were studied. It was shown that high-quality alloy coatings with a high current efficiency are formed by variating the precursors from 0.1 to 0.5 M at a concentration ratio of the Cit ligand and alloy-forming components ({text{C}}{{{text{o}}}^{{2 + }}}{text{/WO}}_{4}^{{ - 2}}) of 5 : 1. Based on the results of the X-ray structural analysis, it was concluded that the Co–W alloy can be formed as a polycrystalline substitutional solid solution and a thermodynamically stable Co₃W compound, which, depending on the content of the alloying element tungsten, can be either polycrystalline or finely dispersed. High values of microhardness of the alloy of 800 kg/mm² obtained at a current density of 1 A/dm² can be associated with the electrochemical deposition of the Co₃W intermetallic compound, which has a high microhardness.

The aim of the research was to study the effect of the electrode material and the electrolyte composition on cathode and anodic overvoltages during electrolysis. The relevance of the present work is due to the widespread use of electrolysis in the production of hydrogen, chlorine, and alkalis and other areas where overvoltages caused by kinetic constraints are a key factor in energy losses, reducing the economic feasibility of technologies. The methodology included a comparative analysis of the electrode materials (Pt, ORTA, graphite, AISI 430, Fe, Ni, Cu, Al) in solutions of H₂SO₄, NaOH, Na₂SO₄, and Na₂S with the construction and analysis of the anode and cathode Tafel curves to determine kinetic parameters. The results presented by the polarization curves showed a significant dependence of overvoltages on the nature of materials and the composition of electrolytes. Platinum showed the lowest overvoltage values. The ORTA material exhibited ambiguous behavior with a sharp decrease in efficacy in alkaline solutions. Graphite, despite its consistently high overvoltage, confirmed its chemical inertness. Metal electrodes have shown a complex dependence on the electrolyte. The most effective solution was found to be the combination of the AISI 430 stainless-steel cathode with the ORTA anode, which provides the optimal ratio of efficiency and economy. The correct choice of materials and electrolyte significantly increases the energy efficiency of the process.

This paper discusses the features of synchronous regulation of inverter blocks in two topologies of transformer-based photovoltaic installations with two or three three-phase voltage source inverters operating in a specific overmodulation zone characterized by increased inverter modulation indices that are close to maximum values. It is shown that, in the case of a two-range inverter control strategy in overmodulation mode, modified algorithms of a synchronous pulse-width modulation, including the use of specialized correction coefficients for each sub-range of the overmodulation zone, allowed for the continuous synchronization and symmetry of the basic voltage waveforms on the inverter-side windings of the power transformers of photovoltaic systems throughout the entire inverter overmodulation zone. Modeling the processes in the systems confirms the absence of harmonic components of even order and of subharmonics of the fundamental frequency of photovoltaic stations in the spectra of the basic voltages of the analyzed photovoltaic installations over the entire range of two-stage regulation of inverters in the overmodulation zone. This improvement in the harmonic composition of basic voltages decreases losses and increases the efficiency of photovoltaic installations based on inverters with synchronous modulation, which is particularly important for high-power systems characterized by a relatively low switching frequency of the power switches of inverters.

A possibility of the plasma electrolytic treatment of a heat-resistant nickel alloy ChN77TiAlB, which leads to the removal of edge cracks, a decrease in hardness, and an increase in wear resistance, is shown. The volt-ampere and volt-temperature characteristics of the plasma electrolytic treatment, typical for anodic processes, are revealed. Changes in the morphology and roughness of the surface and the structure and microhardness of the surface layers are considered. It was established that the treatment in an electrolyte based on carbamide and ammonium chloride leads to the formation of nitrocarburized layers without the formation of compounds. The combined effect of both high-temperature oxidation and anodic dissolution on the morphology and roughness of the surface was determined. Tribological tests were conducted using the ball-on-disk scheme, which showed the best results after treatment at 900°C (reduction in volumetric wear by 15.7 times), when a reduction in roughness (by five times) and the presence of thick oxide layers determine a uniform running-in period, reaching a lower value of the friction coefficient, and homogenization of the alloy, accompanied by the removal of cracks, determines a softer wear mechanism. Positive results were obtained in abrasive wear tests: after treatment at 600 and 900°C, volumetric wear decreased by 2.6 and 2.2 times, respectively.

The effect of γ-irradiation on the electrophysical parameters of silicon doped with nickel during growth from melt according to the Czochralski method was studied. Experimental results obtained by scanning electron microscopy showed that clusters of Ni atoms ~6–8 μm in size with a surface density of ~(5–8) × 10³ cm^–2 were formed in nickel-doped silicon during cultivation. It was established that, during irradiation with γ-quanta ⁶⁰Co of the control samples not doped with nickel, material compensation occurs due to the generation of deep centers of radiation origin. In silicon samples doped with nickel, when irradiated with γ‑quanta, the size of the clusters decreased, and the concentration of free charge carriers changed slightly: when the fluence increased to F ≥ 3 × 10⁸ rad, and the resistivity decreased by no more than 30%. Such a change in the parameters of Si〈Ni〉 samples is due to the formation of acceptor centers because of an increase in the concentration of electrically active nickel atoms. It was shown that nickel atoms diffuse from clusters into the silicon matrix during irradiation, whereupon interaction with radiation-generated vacancies interstitial nickel atoms Ni_i pass into electrically active position in the Ni_s crystal lattice unit. Those impurity defect centers (Ni_s) were thermally stable to at least an annealing temperature of 600°C.

The influence of the modes and conditions of laser surface alloying of the corrosion-resistant 95Cr18 steel (440C, 440B—analogues in the United States) was investigated. The structure, quality, and geometric parameters of the surface layers created as a result of laser exposure were studied. Powders of chemical compounds, such as B₄C, WC, TiB₂, W₂B₅, TiSi₂, and HfSi₂, were used for alloying; processing in an argon medium was carried out using a fiber laser with a wavelength of 1.06 microns. During the experiments, optimal parameters, such as the beam focusing size, scanning speed, and radiation output power, were selected. With increasing power, the volume of the melt bath increased as did both the depth and width of the alloying zone. Thus, with a laser power of 2 kW, the width of the doping zone reached ~3 mm. The depth of the alloyed layers on the surface of that steel was 400–700 microns in the power range of 1–2 kW. The microhardness of the alloy zones of 95Cr18 steel could be at the level of 4500–12 000 MPa. At the same time, with a decrease in the depth of the alloyed layer, the microhardness may increase due to an increase in the concentration of alloying components. For boron carbide in the solid phase quenching zone, the maximum increase in the microhardness of the surface layer reached 14 000 MPa.

The current state of agricultural land makes us think about the need to search for new, innovative methods of weed control since relying only on intensive chemical and historically justified mechanical processing of soil areas is not always justified today, due to the fact that nature is cumulatively inflicted with environmental damage and humus, and organic matter reserves in the soil continue to be uncontrollably depleted. It is proposed to use electropulse weeding as a technologically and ecologically justified alternative to traditional methods. The conducted studies on the electrical conductivity of the weed plant tissue and processing current flow circuits, identifying the option of supplying electrical energy and damaging doses of energy, made it possible to justify the structure of the unit, consisting of a mover (a wheeled tractor) and an electrotechnological unit, as well as to evaluate the economic and agro-technological efficiency of its use in agricultural technologies. In principle, the unit consists of three main structural blocks: a movement power unit (a universal row-crop wheeled tractor), a power source, and an electrode system. In order to achieve lower cost of the device and greater maneuverability of the unit, it is preferable to choose the option with a trailer generating unit and mounted units for increasing voltage, forming pulses and an electrode system. Analysis of the total energy costs during the electric pulse treatment of soil areas from weeds and unwanted plants, and their assessment during cultivation of winter wheat of the Mironovskaya Yubileynaya variety on the black fallow on the lands of Volgograd oblast made it possible to reasonably consider such treatment to be less energy-intensive compared to mechanical cultivation and chemical weeding on an area of 100 hectares, and also implemented with a minimal negative impact on the environment.