Surface Engineering and Applied Electrochemistry最新文献

Using the example of stamping a box-shaped part from high-strength sheet steel by a pulsed electro-hydraulic method, the limiting possibilities of its shaping, taking into account the springing of the material, are studied. The influence of the radius of the curvature and the shape of the surface of the corners of the part on the change in the structure of high-strength steel DP780 and the appearance of defects in it is determined. Relations between the radius of the curvature of the surface of the part and the thickness of the workpiece at which there are no defects in the structure of DP780 steel and the limiting possibilities of its deformation are achieved with minimal springing of the material are obtained.

This research explores the heightened sensitivity of the electrochemical formaldehyde detection achieved by incorporating a modified graphene paste electrode with a titanium dioxide-silver (TiO₂/Ag) composite (GTA). The G-TiO₂ matrix was augmented with varying masses of silver modifiers, namely, 0.2, 0.4, 0.6, and 0.8 g, aiming to establish the most effective composition for formaldehyde detection. Characterization through scanning electron microscopy and energy-dispersive X-ray spectroscopy confirmed the material’s composition, revealing GTA electrode nanocomposites consisting of carbon, oxygen, titanium, and silver with the compositions of 77.05, 19.46, 2.39, and 1.11%, respectively. An electrochemical analysis was conducted to assess the efficacy of the developed electrode in a 1 M K₃[Fe(CN)₆] solution. Furthermore, a real sample testing was performed to evaluate the practical utility of the electrode gauging its efficiency through the calculation of percentage recovery before and after treatment. The GTA electrode with a 0.4 g Ag modifier exhibited the optimal performance, as evidenced by a Horwitz Ratio stability test result of 1.38% and a limit of detection of 0.0168 µg/L. This research highlights the promising potential of the GTA electrode for the precise and sensitive formaldehyde detection, particularly in processed food products.

A special case of equality of the conduction current density and the displacement current density in a homogeneous nonmagnetic conducting medium was used to consider the results of approximate calculation estimation of the relative permittivity ε_r of nonmagnetic conducting materials (metals and alloys), which are extensively used in electrical power engineering, electric power industry, and high-voltage pulse technology under the influence of variable (pulsed) electric currents and electromagnetic fields (EMF) with various amplitude–time parameters. It was demonstrated that, in the investigated case, at low frequencies f₀ of conduction current and EMF (at a frequency on the order of 10² Hz) in the range of extremely low-frequency electromagnetic waves (EMW), the materials under consideration exhibit extremely high values of the electrophysical parameter ε_r (on the order of 10¹⁵). For extremely high frequencies f₀ of current and EMF (at a frequency on the order of 5 × 10¹³ Hz) in the infrared range of EMW, these conducting materials are characterized by ε_r values on the order of 10²–10⁴, and in terms of the electrophysical parameter ε_r, they approach solid dielectrics and ferroelectrics.

Deposition of protective coatings improves the corrosion resistance and tribological behavior of the surfaces of metallic components. However, surface preparation prior to coating application increases the cost per unit area of the coating. Substrates made of St3 steel with surface roughness R_a ranging from 0.01 to 0.597 μm were prepared, including those with a layer of rust, and were subjected to electro-spark deposition of Cr–Fe–Cu coatings. The performed studies led to the conclusion that the initial surface roughness of St3 steel does not affect the nature of material deposition during the electro-spark alloying (ESA) and the structure of the deposited coatings. This is unequivocally confirmed by the data on heat resistance and tribological properties of the coatings. Electro-spark treatment can promote self-cleaning of the rust layer; however, complete elimination is not achieved, and large pores are formed in the coating. This significantly reduces the heat resistance and wear resistance of the coating.

High voltage silicone insulators that are placed close to coastal marine areas have the problem of salt fog depositing on their surfaces in the form of conductive droplets. Under the influence of an electric field, those droplets initiate partial discharges, which leads to the degradation of the hydrophobic properties of silicone rubber. This phenomenon, in which droplets serve as the cause of partial discharges, has been studied in considerable detail elsewhere. However, it remains unclear whether the droplets themselves, as moisture-laden areas, affect the properties of silicone rubber. The current work is focused on studying the combined effect of an AC electric field (E = 17 kV/cm) and a 4% solution of sodium chloride on the water-repellent properties of silicone rubber in the absence of electrical discharges. The results of the study show that the influence of moisture and an electric field leads to slowing down the droplet runoff from the inclined sample of Powersil 310 rubber. An AC electric field did not have a noticeable effect on the rate of water runoff; the slowdown was due to the pre-treatment of the sample with the solution.

Electric, energy, and hydrodynamic characteristics of high-voltage electrochemical explosion (HVECE) in confined liquid volumes were experimentally investigated with varying the charging voltage, the stored electrical energy, and the mass of the burnt exothermic mixture. A comparison with other methods of initiating an electrical discharge under similar conditions was conducted. The obtained results showed that HVECE allows achieving a high-voltage electrical discharge with low energy losses (less than 9%) and implementing an electrical breakdown mode close to aperiodic. It was found that HVECE generates compression waves with amplitudes up to 37% and specific impulse up to 45% higher (at a charging voltage of 25 kV and above) than in the case of electrical explosion of an initiating metallic conductor under identical initial conditions. It was revealed that increasing the charging voltage leads to a linear increase in the amplitude and specific impulse of the generated compression wave. A comprehensive analysis of the dependences of energy and hydrodynamic characteristics showed that both the stored electrical energy and the interrelation of electrical parameters of the discharge circuit with the mass of the burning exothermic mixture have a significant influence on the formation of the specific impulse of the compression wave in HVECE, determining the shape of the discharge characteristics.

The influence of the synthesis conditions on the surface morphology, phase composition, and electrocatalytic activity of materials in oxygen and hydrogen evolution reactions was investigated. For instance, the slopes in the potential verses the logarithm of the current density dependencies during oxygen evolution were 221 and 109 mV/dec for TiO₂ nanotubes and platinum-coated layers, respectively. In the latter case, small deviations may be attributed to the structural heterogeneity of the material or the developed surface of the coating. As for pristine TiO₂ nanotubes, an atypical Tafel slope was observed, almost twice the theoretical value, indicating the presence of a semiconductor component in the electrode capacitance. Studies showed that the materials are n-type semiconductors. The cathodic polarization stage leads to the formation of titanium suboxides in the nanotube recovery phase, contributing to an increase in the material electrical conductivity. This also allows for the creation of a porous developed surface matrix for the electrodeposition of catalytic metal layers. Tafel slopes were calculated for the investigated materials in the hydrogen evolution reaction. For TiO₂ nanotubes, a slope of 175 mV/dec was observed. The material surface was partially blocked by hydroxides, resulting in a low number of active centers for the hydrogen evolution, and the polarization curve had a steep slope. In the case of TiO₂ nanotubes coated with a platinum layer, a high number of cationic vacancies in the matrix and a deficit of oxygen ions facilitated the mobility of platinum atoms, leading to the emergence of a large number of active centers for the hydrogen evolution. As a result, the Tafel slope of the polarization curve was found to be 30 mV/dec.

This paper describes the study of corona electrets made of a polyethylene terephthalate (PET) laminate film with an aluminum oxide nanolayer with a protective coating based on acrylic copolymers. Those films showed rather high and stable electret properties. Furthermore, dipole polarization prevailed at the acrylic layer due to the orientation of oxygen-containing groups of atoms and macromolecular segments under the corona discharge, while injected charge carriers were located predominantly in polyethylene terephthalate layer at interfaces of both PET-aluminum oxide and amorphous-crystalline regions of the polymer.

The comparative corrosion resistance and electrochemical behavior in acidic, alkaline, and neutral media of both pure metals and the Ni–Re alloys doped with zirconium, hafnium, tungsten, and palladium were investigated. A positive effect of zirconium on the corrosion resistance of the Ni–Re alloy in all studied media was demonstrated. It is shown that the Ni–Re alloy doped with hafnium also improves corrosion resistance and compensates its reduction at introduction to a tungsten alloy. It is shown that the Ni–Re alloy doped with zirconium together with palladium has the maximum corrosion resistance.

The influence of temperature on the properties of nanocrystalline Co–W coatings obtained from a citrate electrolyte at pH 6.7 and deposited under natural convection conditions was studied. The influence of the electrolyte temperature on the morphology, composition, structure, and roughness of coatings, as well as their corrosion and tribological properties, is demonstrated. It is shown that the structure of the coating can change from the X-ray amorphous to the crystalline one when the deposition temperature of the coating is increased to 90°С. The average value of the mass wear of Cо–W coatings formed at 80°С and measured under the linear friction condition of 0.08 mg is 62 times lower than that of a Cr coating (4.95 mg) and 84 times lower that at the surface of steel SK-5 (6.71 mg). When testing by the reciprocating wear method, the value of the volumetric wear of Co–W coatings obtained in the 50–70°С temperature range was 0.00109 mm³, which is 55 times lower than the wear value of a Cr coating (0.0596 mm³) and 41 times lower than that of the steel SK-5 surface (0.0449 mm³). The paper also shows a slight decrease in the currents of corrosion coatings and a decrease in the dispersion values of the corrosion potentials obtained after mechanical polishing of the surface of the coatings at temperatures in the range of 20–90°С. Under the corrosive effect of 3.5% sodium chloride, an increase in the deposition temperature of the coating is accompanied by a slight increase in the corrosion current.