Surface Engineering and Applied Electrochemistry最新文献

The work is devoted to the study of the features of mass transfer, structure, and properties of electrospark coatings on substrates made of the chromium alloy grade VKh1-17A using SHS-electrode ceramics of the compositions ZrSi₂–MoSi₂–ZrB₂ and HfSi₂–MoSi₂–HfB₂. The coatings were studied using X-ray diffraction, scanning electron microscopy, energy-dispersive analysis, and tribological tests using the “pin-on-disk” test; nanoindentation was also carried out. The kinetics of the mass transfer and heat resistance of coatings were determined by the gravimetric method. In accordance with the Palatnik criterion, the formation of coatings occurred in the form of an alloy of anode (electrode) and cathode (substrate) materials, which ensures high adhesion of the surface layer. The maximum weight gain on the cathode was observed after the first minute of treatment, and a decrease in the mass of the cathode was subsequently noted. As a result of electrospark deposition, coatings with 100% continuity and a thickness of 10–20 µm were deposited on the surface of the chrome alloy VKh1-17A. Zirconium-containing coatings are characterized by a hardness of 18.2 GPa and an elastic modulus of 274 GPa, and coatings obtained using the HfSi₂–MoSi₂–HfB₂ electrode were characterized by a hardness of 16.9 GPa and an elastic modulus of 332 GPa. The use of SHS-electrodes made it possible to increase the hardness of the surface layer of the chromium alloy by four times, wear resistance by 1.5 times, and oxidation resistance by 1.6 times at 1000°C for 30 h of testing.

The article deals with the study of the influence of additives of unsaturated rubbers and low-molecular reactive compounds (LMRCs) on the structure and properties of modified ethylene propylene rubbers (EPRs). Synthesis methods involve the introduction of those components into the vulcanization process in order to improve the key characteristics of polymer materials. The results of the analysis of rheological, thermal, and mechanical properties of modified EPRs are presented. During the experiments, it was established that the introduction of unsaturated rubbers and low-molecular reactive compounds leads to significant changes in the structure of the polymer matrix. The resulting composites exhibit improved mechanical properties, including increased strength and elasticity. The rheological analysis revealed changes in the viscoelastic properties of the material, indicating modification of the internal polymer network. The presented results expand the understanding of elastomer modification processes and also highlight the potential of those additives to create polymer materials with optimized properties. The practical significance of the obtained results may shed light on new ways to develop advanced polymer composites with improved performance and durability.

Corrosion in steel leads to significant resource waste. With that in view, three kinds of anti-corrosive Zn-based coatings were prepared on carbon steel, including electrodeposited Zn and Zn–Ni coatings, and as-sprayed Zn + Al coating. The microstructure, morphology, chemical composition, phase structure, and microhardness of the coatings were investigated using scanning electron microscopy, energy-dispersive spectroscopy, X-ray diffraction, and a Vickers microhardness tester. The wettability of the coatings was determined using a contact angle tester. The corrosion resistance of the coatings was evaluated through electrochemical impedance and dynamic polarization. The results revealed that Zn coatings consisted of the Zn phase with a hexagonal close-packed crystal structure. Zn–Ni coatings were composed of the Zn and Ni₅Zn₂₁ alloy phases. The as-sprayed Zn + Al coatings consisted of the Zn phase and the Al phase. The grain size of Zn coatings was 78.4 nm, and the grains were relatively large and irregular in shape. Zn–Ni coatings had a small grain size of 54.96 nm and exhibited some pinholes on the surface. Zn + Al coatings showed a flake-like structure with some micropores. The average microhardness values of Zn, Zn–Ni, and Zn + Al coatings were 112.6 ± 8.2 HV_0.5, 249.7 ± 9.8 HV_0.5, and 140.9 ± 7.6 HV_0.5, respectively. Zn and Zn + Al coatings exhibited hydrophilicity, while Zn–Ni coatings demonstrated hydrophobicity, which can effectively slow down the penetration of corrosive media. Zn–Ni coatings exhibited the best corrosion resistance, followed by Zn + Al coatings, while Zn coatings exhibited the poorest corrosion resistance.

In this study, for the first time, an electrochemical sensor has been developed by synthesizing CoFe₂O₄/MCM-41 nanocomposite and incorporating it into a carbon paste matrix. The simultaneous measurement of 4-aminophenol (4-AP), acetaminophen (APAP), and mefenamic acid (MA) was performed using this sensor. Scanning electron microscopy, elemental analysis, and X-ray diffraction were used to analyze the properties of the produced nanocomposite. By using the techniques of chronoamprometry, cyclic voltammetry, impedance spectroscopy, and differential pulse voltammetry, the electrochemical behavior of the modified electrode in aqueous solutions was investigated. When compared to а bare carbon paste electrode (CPE), the peak current response of the 4-AP, APAP, and MA was significantly improved at the CoFe₂O₄/MCM-41 nanocomposite modified СРЕ (CoFe₂O₄/MCM-41/CPE). Also, using differential pulse voltammetry (DPV) method, the linear range of 4–240, 3–200 and 2–180 μM and the limit of detection (LOD) (S/N = 3.0) 1.20, 1.05 and 0.52 μM were obtained for 4-AP, APAP, and MA, respectively. The ability of CoFe₂O₄/MCM-41/CPE to detect 4-AP, APAP, and MA in waste water, tablets, urine, and tap water has been confirmed by real sample analyses results.

A method was presented to calculate the parameters of a high-voltage discharge channel (pressure, radius, expansion rate) of electric-discharge machines for the destruction of nonmetallic materials. This method made it possible to study the effect of the parameters (inductance, voltage, and capacitance) on the hydrodynamic parameters of the discharge channel and the generated pressure wave. With an increase in inductance, the pressure and expansion rate of the discharge channel decrease and the voltage increases, which leads to an expansion of the active characteristics of the discharge channel; increasing inductance also causes an increase in capacitance, which leads to an increase in the discharge current; the pressure and expansion rate of the discharge channel remain unchanged. An effective destruction zone was determined, which depends on the cycling parameters, the strength characteristics of the material being destroyed, and the electrical conductivity of the discharge medium. Recommendations were proposed for choosing the process conditions of electric-discharge machines for the disintegration of nonmetallic materials.

The temperature and frequency dependences of the dielectric constant and electrical conductivity of FeGa_0.4In_1.6Se₄ crystals on alternating current have been studied. In the FeGa_0.4In_1.6Se₄ crystal, normal dispersion occurs in the frequency range 2 × 10²–10⁴ Hz, and the lifetime distribution of defects obeys the law n(τ) ~ τ−^1.75. With increasing temperature, the reason for an increase in the value of the real part of the dielectric constant is an increase in the concentration of defects. The experimentally observed monotonic decrease in the imaginary part of the dielectric constant depending on frequency indicates the presence of relaxation dispersion in the FeGa_0.4In_1.6Se₄ crystal. It has been established that, in the temperature range 294.5–343 K at frequencies 2 × 10²–10⁶ Hz, the law σ ~ f ^S (0.1 ≤ S ≤ 1.0) is satisfied for electrical conductivity. It was shown that the conductivity in those crystals is characterized by a band-hopping mechanism. Activation energies were determined from the (log sigma sim frac{{{{{10}}^{3}}}}{T}) dependencies.

The influence of the phase composition of zeolite rocks and their modification under the influence of an electromagnetic field in an environment of ferromagnetic particles on the physical properties and sorption of heavy metals has been studied. The results of water purification from heavy metals using activated zeolite in a magnetic fluidized bed are presented.

Electrodeposition of wear-resistant compositions on the surfaces of parts makes it possible to increase the reliability and durability of machines. Studies have been carried out on the process of applying Fe-WC composite galvanic coatings (CGC) from a suspension electrolyte containing 550–600 g/L FeCl₂·H₂O and microabrasive tungsten carbide powder. A high incorporation of dispersed phase particles into the coating was obtained. The properties of Fe-WC composite coatings were studied. A relationship has been established between the concentration of tungsten carbide particles in the electrolyte and the current efficiency of the composition as well as the WC content in the coating. Some physical and mechanical properties of CGC have been determined without their mechanical pretreatment, in particular, microhardness and wear resistance. The roughness of Fe-WC compositions was studied in comparison with Fe–Al₂O₃ coatings.

For the first time the electrophoretic deposition method was used to deposit multilayer oxides on iron discs for gamma attenuation. The following powders: W₁₀O₂₉, Bi₂O₃, and Pb-PbO, were deposited separately on both sides of iron discs. Eleven coated Fe discs with an oxide were put on each other and preserved by pouring epoxy on them to form three multilayer samples: Fe coated plates with W₁₀O₂₉, with Bi₂O₃, and with Pb-PbO. Another group (mixture samples), was prepared by mixing each oxide separately with micro Fe particles (instead of the Fe plate) and epoxy. The weights of each component for the second group were the same as those for the first one. The characterization of powders was investigated by the X-ray diffraction tests. The scanning electron microscopy images showed that the particle sizes averages for W₁₀O₂₉, Bi₂O₃, and Pb-PbO were 60, 40, and 66 nm, respectively. The transmission factor percentage, the radiation protection efficiency, and theoretical as well as experimental linear attenuation coefficient of multilayer and mixture samples have been experimentally determined for five different gamma energies emitted from the Eu-152 radioactive source by using a gamma spectrometry system with a NaI(Tl) detector. The percentage of the transmission factors of multilayer samples was lower than that of uncoated Fe layers and mixture samples. At a low gamma energy, for both groups (multilayer and mixture samples) there was a mismatch between the practical and theoretical linear attenuation coefficient curves. Those Fe coated with Pb-PbO had a higher linear attenuation coefficient than other samples. All multilayer samples had greater buildup factor values-around 121 keV, and lower buildup factor values in the high and low energy ranges.

Abstract—Samples of n-type germanium (doped with three different impurities) with and without an oxygen impurity have been studied. To reveal the interaction of oxygen in n-Ge crystals with As, Sb, and Bi impurities, the effect of transverse magnetoresistance (very sensitive to the presence of complexes in the crystal) was chosen as a research method. It was shown that, in the germanium samples doped with antimony and bismuth, low-temperature annealing leads to the formation of electrically active impurity complexes that affect both the magnitude and the form of the dependence of the transverse magnetoresistance Δρ_⊥/ρ₀ on the magnetic field strength H. The insensitivity of the oxygen-enriched germanium crystals with an arsenic impurity (in contrast to the accompanying impurities of antimony and bismuth) to low-temperature thermal annealing has been revealed. This fact is of not only scientific but also practical interest since such annealing is in many cases one of the inalienable technological operations in the creation of a wide class of semiconductor devices, and the absence of oxygen in germanium (used for those purposes) is not always guaranteed by the supplying companies. It was shown that the use of impurity with a large tetrahedral radius in n-Ge crystals (at a practically equal concentration of charge carriers) is accompanied not only by a decrease in the tensoresistance ρ_X/ρ₀ in the saturation region but also by a decrease in the rate of an increase in ρ_X/ρ₀ with increasing pressure. The latter circumstance finds its manifestation in a decrease in the slope of the curves ρ_X/ρ₀ = f (X).