Surface Engineering and Applied Electrochemistry最新文献

Approximate calculations were made to identify the main features of the propagation of standing transverse electromagnetic waves (EMWs) and standing longitudinal de Broglie electron waves in a homogeneous non-massive non-magnetic metallic conductor of finite dimensions (radius r₀ and length l₀ ⪢ r₀) with axial alternative conduction current i₀(t) of different amplitude–time parameters. Relations were obtained for the calculation estimation of averaged propagation velocities of standing transverse EMWs and standing longitudinal de Broglie electron waves in the metal (alloy) of the specified conductor. It was demonstrated that quantized standing transverse EMWs emerging in the finite-sized metallic conductor significantly differ from ordinary transverse EMWs propagating in conducting media of unlimited dimensions. An important characteristic of the standing transverse EMWs in the considered conductor is that their axial electric field intensity leads in phase their azimuthal magnetic field intensity by an angle of π/2. It was found that, in the standing transverse EMWs in the investigated conductor, the energy of the electric field is only converted into the energy of their magnetic field and vice versa. Therefore, the standing transverse EMWs do not transfer electromagnetic energy fluxes along the metal (alloy) of the considered conductor.

The aluminum metal matrix composite (AMMC) is now occupying an irreplaceable space in various industries due its advantages such as a great strength to the weight ratio, good wear resistance, and a reduced density. In this paper, the AMMC was developed using aluminum 7075 reinforced with 5 and 10% boron carbide. The L₁₈ orthogonal array was used for conducting the electrochemical micromachining experiments. The AMMC was a wire cut into thin sheets; and specimen 1 designates the AMMC with 5% boron carbide, and specimen 2 designates the AMMC with 10% boron carbide. The tool electrode was of a diameter of 0.5 mm, and sodium nitrate was used as an electrolyte. The technique for order of preference by similarity to ideal solution and the principal component analysis were utilised in order to find out the best parameter combination on the machining speed, the diametral overcut, and the delamination factor. The electrolyte concentration of 35 g/L, the voltage of 11 V, and the duty cycle of 70% were found to be the optimal combination for the machining speed, the diametral overcut, and the delamination factor in specimen 1. The ANOVA analysis results showed that the duty cycle is a significant factor, with its 53.5% contribution.

The results of experimental and theoretical studies of the electrical conductivity of weakly concentrated solutions of liquid dielectrics (LDs) with a chemically active impurity and associated electrohydrodynamic (EHD) flows are presented. The studies are carried out on the basis of a multi-ion model of electrical conductivity, which makes it possible to adequately describe both the dissociation–recombination interactions of ions and the electrochemical injection of ions from the electrode surface. It is shown that the recombination processes in the volume of the LD lead to a slow disappearance of the space charge with a characteristic time of hours and days, which does not allow for significantly reducing the distribution of the space charge in the LD that reduces the intensity of EHD flows. Numerical calculations based on the obtained theoretical and experimental data on the electrical conductivity were carried out, and they confirmed the results of observations concerning the development and structure of EHD flows and current characteristics.

This study was aimed at developing an electrochemical sensor for the detection of phenol, a harmful organic pollutant for both humans and the environment. The sensor was developed by investigating metal oxide and conductive polymer modifiers on graphene electrodes to enhance the sensitivity for the phenol detection. In this research, the production of an electrode is discussed that is very sensitive to phenolic compounds using a composite of zinc oxide and polyaniline modified graphene (Gr/ZnO@PANi). The Gr/ZnO nanocomposite synthesis was carried out using a simple hydrothermal method and modification of PANi on the electrode surface by the electropolymerization method. It was found that the Gr/ZnO@PANi composite electrode can detect phenol effectively, with an efficient electron transfer occurring at a low oxidation potential. Additionally, it was observed that the electrode sensitivity to the phenol concentration was remarkably linear within a range of 10^–6–10^–1 M, and its limit of detection was as low as 0.0515 μM. Furthermore, the Gr/ZnO@PANi composite electrode exhibited excellent stability in detecting phenolic compounds, as indicated by the low stability coefficients of the relative standard deviation for reproducibility (0.37%) and the randomized strategic demand reduction (1.02%). Those findings suggest that the new Gr/ZnO@ PANi composite electrode is a promising tool for the sensitive detection of phenol in the environment, which could contribute to mitigating its negative impacts on human health and ecosystems. Future studies could explore the potential applications of this sensor for detecting other types of pollutants as well.

The volume of the discharge chamber has a great influence on the pressure field in the water filling it and on the efficiency of many technological processes; therefore, the study of the relationship between the volume of the chamber and the pressure in it is an urgent task. However, at present, the role of the volume of the discharge chamber in the formation of the pressure field in it has been insufficiently studied. The purpose of this work is to fill the gap. The study was carried out on the basis of a previously developed mathematical model of an electric discharge in water, the adequacy of which was substantiated via a comparison of the simulation results with experimental data. It is determined that the closed volume of the discharge chamber with rigid walls significantly affects the formation of the pressure field in the water filling it. In this case, the interaction of waves reflected from the walls of the discharge chamber with the surface of the discharge channel in water and the vapor-gas cavity is of decisive importance. The reflected waves determine the period and amplitude of the pulsation of the discharge channel and the vapor-gas cavity, thereby influencing the electrical characteristics of the discharge. This influence increases with decreasing the chamber volume.

A study was made of the kinetics of the adsorption of the methylene blue dye from an aqueous solution on the photocatalyst DDT (nanosized titanium dioxide in the anatase phase, deposited on diatomite) and its components: diatomite D and anatase TiO₂. The effect of the initial concentration and pH of the methylene blue solution on the rate of the adsorption process was investigated. The kinetic data of adsorption were processed using two simplified kinetic models, one of the pseudo-first-order and the other of pseudo-second-order. To investigate the adsorption mechanism, a model of intraparticle diffusion kinetics was employed. The adsorption kinetics of methylene blue on the surfaces of D, TiO₂, and DDT was found to be best described by the pseudo-second-order model. It was shown that the adsorption of methylene blue on the D and DDT adsorbents is a multistep process involving adsorption on the external surface and inside particles, with the limiting step being a chemical reaction. For the adsorption on TiO₂, the limiting step is the external diffusion.

The results of the studies of electroactivation, an emerging method of nonwaste processing of secondary dairy products, namely, whey with a medium protein content, in order to recover whey proteins into protein mineral concentrates, are presented. Processing was carried out in electrolyzers with different ratios of the volume of the processed whey to the surface of the electrode/cathode with different constructive and geometric parameters, which influences the specific energy consumption per unit volume. The main purpose was the maximum recovery of whey proteins into protein mineral concentrates at low energy costs, and the exclusion of “dead” or inefficient zones of diaphragm electrolyzers. The degree of the recovery of whey protein depending on the pH values, the redox potential, and the temperature during electroactivation was analyzed. This justifies the optimization of the technical parameters of electrolyzers for whey with a medium protein content.

The results from investigations of obtaining the L(+) optical isomer of lactic acid from different types of whey are presented: of the initial, fermented, and concentrated in an electrolysis-type apparatus with a separating diaphragm. The rate of obtaining the L(+) isomer of lactic acid in the anode chamber of the electrolyzer was determined depending on the concentration of whey.

It was demonstrated that the concentration of nickel atoms near the surface of solar cells (SCs) is higher by 2–3 orders of magnitude in comparison with the bulk material, resulting in a significantly increased gettering rate in the former case. Experiments determined the optimal gettering conditions for nickel clusters (nickel diffusion temperature 800–850°C and additional thermal annealing temperature 750–800°C) and the structure of a silicon SC that enhances its efficiency by 25–30% in comparison with the reference structure. Physical mechanisms were identified for the effect of the diffusion of nickel impurity atoms and additional thermal annealing on the state of nickel atoms near the surface and the SC base and, consequently, on SC parameters. Physical models were developed for the structure of a cluster of nickel atoms in silicon and for the gettering process of fast-diffusing impurities by clusters of nickel atoms. The binding energy of fast-diffusing impurity atoms with a nickel cluster was estimated to be approximately 1.39 eV. Calculations showed that nickel doping can increase the minority carrier lifetime and the collection coefficient by factors of 2–4 and 1.4–2, respectively. Experiments demonstrated a twofold increase in minority carrier lifetime and a 25–30% improvement in the efficiency of SCs.

The results of the research related to the establishment of basic features of transfer and heat (Joule) losses of electromagnetic energy in a uniform two-wire overhead power line with the metal wires of finite sizes (r₀ in radius and l₀ ⪢ r₀ in length) and alternating (pulse) electric conduction current i₀(t) of different amplitude and time parameters are presented. In view of the quantum-wave nature of the electric conduction current i₀(t), it was found that, in the metal wires of studied overhead lines, there appear the standing transverse electromagnetic waves (EMWs) that cannot transfer electromagnetic energy over a distance. It is demonstrated that, due to a weak dissipation of the quantized longitudinal electronic de Broglie half-waves on the crystal lattice sites of a metal (alloy) of the wires of the studied line, the heat losses of energy are released on those lattice sites. The features of the influence of the traveling transverse EMWs in the air environment of the studied lines on the process of transmission of electromagnetic energy in the overhead power lines over a distance are established.