AbstractThe influence of the grain size of tungsten carbide in tungsten-cobalt hard alloy, received as anode material for the electro-spark deposition (ESD) of steel 35, on its erosion resistance, on the weight gain of the substrate material, and on the coefficient of electro-mass transfer is studied. It is shown that a pressing charge with additives of 0.4% Cr3C2–0.4% VC grain growth inhibitors and grinding in alcohol and argon atmosphere at a grinding time of 20 to 320 min was used in the preparation of new anode materials with different structure, density, porosity, fracture strength, and grain size of tungsten carbide. The results of the erosion resistance and the use of the obtained new anode materials in the ESD of steel 35 are shown. When performing kinetic studies, a number of indicators of the efficiency of the formation of the doped layer were identified taking into account the obtained values of the of additional weight of the cathode, the time of the ESD, the specific surface area of 1 cm2, and the coefficient of electro-mass transfer at the ESD of the studied anode materials. The results of the studies of the structure, thickness, composition of the doped layer, and of the heat resistance and wear resistance of the coating are shown. It was revealed that, among the created new anode materials, the best oxidation resistance of the coating after ESD with the selected processing modes were obtained using a new nanodispersed anode material WC8%Co–0.4%Cr3C2–0.4%VC, with an average grain size of 0.8 microns WC.

AbstractThe paper presents a theoretical study of the behavior of an ionic boundary layer that occurs in the process of a steady proton exchange in a benzoic acid melt contacting with the surface of a lithium niobate crystal. The penetration of protons into a crystal promotes the injection of oppositely charged ions (lithium and benzoate) from the surface of lithium niobate in the surrounding acid. The transfer of the reaction products and their interaction in benzoic acid is studied numerically. The proposed mathematical model includes the effect of recombination in the volume so that the ions with different charge signs approach each other and form a neutral lithium benzoate. The results of the numerical simulations demonstrate that there are exponential-like concentration profiles of two types of ions, and a non-uniform electric field and pressure distributions develop in the boundary layer under steady-state conditions. In this process, the total charge of the system remains zero. It is shown how the concentration, recombination, and activity of lithium and benzoate ions and the diffusion coefficients affect the profile shapes and the process intensity.

AbstractIn this work, the surface oxidation of commercially pure titanium (CP-Ti grade 4) was performed by means of a Nd:YAG in a continuous wave mode in an air environment. The morphology, structure and chemical composition of the formed layers were analyzed by different characterization techniques, such as X‑ray diffraction, scanning electron microscope coupled to an electron microprobe, optical microscopy, and optical profilometry. The diffusion of light atmospheric elements (oxygen and nitrogen) was also investigated. The corrosion resistance of the treated samples was examined in 3.0 wt % NaCl solution using potentiodynamic polarization measurements. The results were compared with those obtained from untreated CP-Ti tested under the same conditions. The analysis indicates that ultra-short pulses (in a nanosecond scale) from a Nd:YAG laser effectively enhanced the corrosion resistance of the studied alloy in 3.0 wt % NaCl (simulated marine environment). An improved corrosion resistance was obtained due to the microstructural changes caused by rapid solidification after laser treatment. A notable enhancement in hardness was reached as well.

Abstract—The article discusses electromagnetic radiation generated by capillary oscillations of zeroth and first modes of a droplet in an external electrostatic field. It is assumed that the droplet is an ideal, incompressible, electrically conductive fluid with a zero net charge and is charged in an external uniform electrostatic field by induced charges of opposite signs. The discussed radiation is detected in analytical asymptotic calculations of second order of magnitude with respect to the dimensionless amplitude of the droplet oscillations in the external electrostatic field. Analytical expressions for the intensity of the electromagnetic radiation associated with the zeroth and first mode oscillations are found as are dependencies of the radiation intensity on the strength of the field, size of the droplet, and surface tension coefficient.

AbstractIt has been shown that the state of manganese atoms in the silicon lattice can be controlled with a view to varying the state and pattern of the magnetoresistance of the material. The laws governing changes in the magnetoresistance of silicon with manganese atoms (single atoms and clusters) as a function of temperature, illumination, and electric field have been determined.

Abstract—Experimental study of the anodic dissolution of titanium and its alloys over a wide range of current densities, including pulsed currents (up to 100 A/cm2), under controlled hydrodynamic conditions and surface temperature in nitrate and chloride solutions, showed that the process is mediated by electrochemical formation of an anodic oxide film (AOF), which undergoes chemical dissolution. The AOF has a bilayer structure (two barrier films: at the interface with the metal and solution). It is described by PDM-III (Point Defect Model). Under certain conditions, it is possible to achieve a steady state in which the film growth rate is compensated by the rate of its chemical dissolution (during a pulsed treatment). In this case, there is a 100% current efficiency in terms of titanium ionization in the oxidation state of four. Under the conditions of the described experiments, i.e., when using direct current, the rate of the AOF electrochemical formation exceeds that of its chemical dissolution, which leads to a decrease in the current efficiency, which does not exceed 75%. Due to the temperature dependence of the electrical resistance of the barrier film at the interface with the solution, which determines its thickness, the current efficiency increases with an increase in the flow rate of the electrolyte. When the thermokinetic instability (TKI) of the AOF is reached (thermal explosion caused by positive feedback: the rate of electrochemical reaction–surface temperature–the rate of electrochemical reaction), the interaction of electrolyte components with the surface free from the film leads to “anomalous” anodic dissolution of the AOF with a current efficiency exceeding 100%. Regardless of the nature of the electrolyte, the TKI conditions are reached at ~1 A/cm2. It has been shown that the dissolution rate in nitrate solutions for certain pulsed treatment parameters (relative pulse duration of 2, dc = 50%) (and the displacement of cathode tool in electrochemical machining) may exceed the machining rate with direct current of the same density by more than a factor of two.

AbstractIt is experimentally shown that a meniscus is raised under the action of pulsed-periodic spark discharges between the electrode and the meniscus in a capillary formed by two vertically fixed cylindrical rods. The recorded effect can be applied, for example, to intensify technological processes of the fabric impregnation.

AbstractThe effects of electrical conductivity of magnetic fluids both in the presence and absence of an external magnetic field are studied. It is shown that magnetic fluids based on magnetite (Fe3O4) magnetic nanoparticles coated with surfactant additive oleic acid contain current conducting ions that are formed because of oleic acid molecules involved in dissociation and electrochemical processes. The key role of the electrochemical reactions of oleic acid molecules on the surface of chemically active Cu electrodes in producing the injection conductivity is proved. The anisotropy of the electrical conductivity of the magnetic fluid in an external magnetic field is analyzed for chemically active and inert electrodes. The nonstationary ion processes in near-electrode layers, which determine the kinetics of magnetic nanoparticles and autowaves in thin magnetic fluid films, are interpreted.

AbstractThree nonionic gemini surface active agents on the base of sebacic acid with different propoxylated units were prepared for this research work, and their forms were studied using infra-red and hydrogen nuclear magnetic resonance spectroscopy. The surfactants physical characteristics were determined. They were found to be inhibitors of the corrosion for carbon steel in a HCl solution. In this investigation, the weight loss and the electrochemical techniques were applied. All of the studied agents were shown to be persuasive inhibitors of corrosion, with inhibition efficiency values exceeding 99%. The efficiency of the inhibition was shown to improve as the surfactant concentration and the exposure time increased, as well as the number of propylene units per a surfactant molecule. The studied surfactants acted as mixed-type inhibitors, according to polarization studies. Surfactants were found to protect steel from acidic corrosion by physically adsorbing their molecules onto the steel surface and forming a protective barrier between the metal and the corrosive liquid, decreasing the corrosion rate. Surfactants adsorption followed the Langmuir adsorption isotherm. Atomic force spectroscopy was used to investigate the surface of the carbon steel as blank specimen and in an acidic solution. The acquired images, as well as the surface properties measured, agree with the results obtained via other techniques used.

Abstract—The composite coatings on the surface of tin bronze substrates were formed by electro-spark deposition applying alternately the soft materials of silver and the alloy Babbitt B83. The effect of their deposition on the mass transfer, the surface roughness, the coating thickness, the surface morphology, the cross-sectional morphology, the elemental composition, and the tribological properties of the composite coatings was investigated using electronic scales, a 3D optical profilometer, a tribometer, and such techniques as scanning electron microscopy, and energy dispersion spectroscopy. The results show that the studied composite coatings were dense, with grains refined and uniformly distributed, and they functioned via the metallurgical fusion with the substrate. The silver and Babbitt B83 optimal process parameters were obtained as follows: the voltage of 60 and 30 V, the duty cycle of 30 and 30%, and the efficiency of 1 and 3 min/cm2, respectively. Under the optimal process parameters, the mass transfer was 125.2 mg, the surface roughness of the composite coatings was 19.43 μm, and the maximal thickness of the layers was 80 μm. The minimum friction coefficient of the composite coatings was about 0.177 after the running-in stage. The main wear mechanisms of the composite coatings prepared under the optimal process parameters were plastic deformation and abrasive wear accompanied by slight polishing.

AbstractThe electrochemical kinetics and mechanism of the electroless deposition of silver were studied in varying concentrations of [Ag(NH3)2]+ and [N2H4]—within moderate to high. The partial cathodic and anodic polarisation curves obtained from the steady state dual cell as well as under the potentiodynamic conditions were superimposed to generate the mixed potentials and the mixed currents. The real rate of silver deposition was determined gravimetrically and then compared with the mixed current obtained under the same bath conditions. The current values of mA/cm2 obtained from the mass deposited in gravimetric study and those of the mixed current were close to each other. At moderate [Ag+] of 0.001 M and [N2H4] of 0.1 M, the position of the mixed potential was in the Tafel region of both cathodic and anodic polarization curves. The mechanism of the reaction was therefore indicated to be under a mixed control. At higher [Ag+] of 0.025 M and [N2H4] of 1 M, the mixed potential was located in the cathodic Tafel and anodic limiting current regions. The mechanism was therefore under the anodic diffusion control. The analysis of the partial polarization plots and the values of the mixed potential confirmed that irrespective of [Ag+] the cathodic reaction was under an activation control, and the anodic reaction was shifted from the activation to the diffusion control mechanism by varying moderate to high [N2H4]. The deposits were characterised by the X-ray diffraction and scanning electron microscopy to confirm that there was the formation of agglomerated Ag particles with crystal faces of (111), (200), and (311) planes and a uniform distribution of the nano spherical clusters of silver deposit. The agglomerated particles were of a relatively higher size in the electroless bath containing very high levels of [Ag+] and [N2H4] than when both ions were at a moderate level of concentration.

AbstractThe fabrication of an electrochemical sensor based on a screen-printed electrode modified by ZnO/Al2O3 nanocomposite for sensing hydrochlorothiazide is described and discussed here. The electrochemical behavior of this sensor was evaluated through the differential pulse voltammetry, cyclic voltammetry, and chronoamperometry. The electrochemical studies revealed that modification with ZnO/Al2O3 nanocomposite leads to an increment of current response through the synergistic augmentation. The used modified electrode showed a detection limit of 8.0 × 10–8 M in the concentration range of 0.1 to 100.0 μM, which is promising in sub-micromolar detection of hydrochlorothiazide.

AbstractIncreasing the hardness and wear resistance of powder alloys and coatings through the use of ultrafine-grained powders and metastable phases is a promising way in powder metallurgy. This paper presents results of the studies of the process of obtaining ultrafine powders by the electrical discharge erosion of the cemented carbide waste WC–5TiC–10Co on a special installation. An empirical model that describes the dependence of the productivity of the process on the discharge energy and properties of a liquid is provided. The dependence of the chemical and phase compositions of the obtained powders on the compositions of the used liquids and the specific energy consumption was investigated. The effect of the discharge energy on the morphological composition and the average particle diameter was examined. It was revealed that the formation of a metastable solid solution (W,Ti)C and a decrease in the concentration of cobalt induce an increase in the hardness of the resulting spherical particles from 1410HV0.05 to 2540HV0.05.

Abstract—The process of chemical etching of Cu98Be alloy in solutions of various compositions was studied. The dilution rate of beryllium bronze in the solutions examined was determined, and its change with time was analyzed. The selectivity of Cu98Be components’ dissolution during the long-term etching in solutions with different electrolytes was established. A possibility of obtaining a Cu98Be uniform etching by varying the composition of the etching solution was shown. The concentrations of metal ions in the etching solutions used were determined, and the capacitance of those solutions was calculated. The compositions of solutions with a high capacity for both of the alloy components during long-term etching were determined. The optimal compositions of etching solutions ensuring the high-quality etching of beryllium bronze according to several criteria, such as a high process rate, uniform dissolution of the alloy components, and high capacity for both alloy components, were proposed. The morphology of the Cu98Be electrode surface after etching in solutions ensuring uniform dissolution for both alloy components was studied. The absence of surface passivation after chemical etching in those solutions was shown. The chemical nature of the compounds formed in the shape of small inclusions on the etched surface of the electrode was established. The obtained results are of great importance for the practical use because they allow selecting the appropriate composition of the etching solution, which, in turn, facilitates optimization of the technological etching process.

AbstractThe separation of oil–water emulsion with cellulose acetate membranes modified with a unipolar corona discharge at a voltage of 5–25 kV and time of 1–5 min was investigated. Decrease in the filter roughness after the impact of the corona discharge was determined using atomic-force microscopy. The results of X-ray diffraction analysis and of electrostatic field parameters’ measurements showed a decrease in crystallinity from 0.29 to 0.27 and the formation of positive charges on the surface of the sample, while the formation of a double electric layer according to dielectric spectrometry data was not detected. During the separation of the model oil–water emulsion, an increase in efficiency was revealed as 80 to 98% and the separation productivity from 15 to 35 dm3/(m2 h) after treatment in the field of a unipolar corona discharge of cellulose acetate membranes, which is explained by a change in the supramolecular and chemical structure of the latter.

AbstractMany industries face corrosion problems caused by the medium containing chloride ion due to its aggressive nature. The implementation of corrosion inhibitors has been recognized to be the easiest and most inexpensive approach for corrosion mitigation. Plant extracts as inexpensive, nontoxic, and biodegradable materials are found abundantly in nature. The heteroatoms, and polyfunctional groups of the active constituents present in plant extracts, make them potential candidates as corrosion inhibitors for metals. The present review includes a compilation of to-date investigations of aqueous extracts of various parts of plants for the corrosion inhibition of mild steel in the NaCl medium only. The inhibition efficiency of various plant extracts was reported based on electrochemical techniques. The type of action, the mode of adsorption, and the mechanism of inhibition were also explored. The surface characterization and theoretical accepts are explained briefly as a support to the experimental results.

AbstractThe efficiency of the electrohydrodynamic (EHD) cooling and thermostating systems of electronic and electrical devices is investigated. A design of electroconvective cooling of an X-ray generator is proposed, the effectiveness of which is confirmed on laboratory models and full-scale samples. The anode temperature was reduced by a factor of two, the duration of the emitter operation increased, and the reliability of the device improved. Various methods of cooling a high-voltage transformer are presented allowing one to increase the specific power, to reduce the weight and size parameters and the temperature of the coolant, and to augment the resource. Studies have been conducted to establish the possibility of thermostating the heat-emitting element (block) by EHD methods when both external and internal conditions change. The design of an EHD thermostat with an automatic thermal stabilization system has been developed and tested (the temperature is maintained with an accuracy of ±0.05°С). A frame with an EHD liquid circuit and an EHD thermostat has been designed, which allows one to significantly reduce the longitudinal temperature differences and its deformation. The high efficiency of EHD cooling methods is shown by an example of a block of light-emitting diodes, small elements and components of electronic equipment, and the use of electrodes—wires with a perforated insulating coating when cooling flat heat-emitting surfaces; a sevenfold increase in the heat-transfer coefficient is achieved.

Abstract—The results of experimental studies on the electrode degradation caused by the electrochemical reactions under high voltage fields are presented. Technical hydrocarbon and polymethylsiloxane (PMS) liquids and their solutions with iodine (I2) at chemically active (Cu) and indifferent (Ti) electrodes were examined. It was shown that, in hydrocarbon Cu, electrodes interact intensively with I2 and, moreover, the cathodic degradation is more intense than that of anodic. Titanium electrodes do not degrade; however, the I2 physical adsorption occurs in hydrocarbons on them and the polymer film forms on them in the PMS. The degradation kinetics in time was studied.

Abstract—The issue of processing secondary resources of the dairy industry, whey, which is produced in large volumes during the production of cottage cheese and cheese, has been studied. The results of studying the process of organic compound extraction during fractionation of whey by vacuum distillation are presented. It was found that it is advisable to process concentrated whey. Processing whey by fractionated vacuum distillation allows for the separation of organic acids of the required purity and necessary concentration. The direction of profitable processing of whey that combines the concentration of whey by fractionated distillation and subsequent electroprocessing is considered. This process allows for the separation of organic substances from whey and further concentration of the resulting products towards the formation of separate organic compounds.

AbstractTo understand the corrosion of bent steel bars exposed to sand soils the physicochemical properties were tested and corrosion rates measurements were made in the laboratory as a function of the type of sand used in the production and reinforcement of concrete, of the exposure time, and of a drastic condition (a saturated sand soil simulating a wet concrete by moisture content). Some assumptions were involved in the investigation of activated concretes containing beach and/or pit sand to correlate the corrosion rate of a steel bar measured in laboratory conditions to that used in the field works. The paper presents four techniques to measure the corrosion rate; thus, a comparison of corrosion rates data via electrochemical and weight loss methods was carried out. The analysis of the obtained results suggested that the corrosion susceptibility was almost doubled for a bent steel bar exposed to the saturated pit sand after 74 days of exposure (the corrosion rate was found to be 0.136, 0.010, 0.025, and 0.026 mm/year by using linear polarization resistance, charge transfer resistance of the Tafel plots, and gravimetric measurements, respectively), in comparison with a not bent steel bar. The deviation of corrosion rates was attributed to a more conductive corrosion products resulting in a more active interface with respect to the experimental variables used in the electrochemical and weight loss measurements. The Tafel and weight loss measurements that were close between them must be useful in determining steel bars susceptibility to corrosion in drastic conditions simulating active concretes, to be applied to systems such as construction industries.