Surface Engineering and Applied Electrochemistry最新文献

Increasing 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 1410HV_0.05 to 2540HV_0.05.

In this paper, the concentration functions of electrical conductivity and pH are determined for aqueous solutions of an ionic liquid based on diethanolamine and boric acid (DEAB). Correlations between the physicochemical properties of an aqueous solution of DEAB and the processes of dissociation of the system components were established. Charge carriers in DEAB solutions are shown to be anions. It was established that an aqueous solution of DEAB has unipolar electrical conductivity and anion-exchange properties with an anion transfer number of 0.79.

It 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.

The anodic dissolution of type Kh18N10 (Cr18Ni10) chromium–nickel steel was performed in a nitrate solution (conductivity of 0.15 S/cm) under pulsed current conditions using pulse durations of 20–100 µs, current densities of 0.01–100 A/cm², and relative pulse durations of 10 to 1 (duty cycle from 10 to 100% (direct current), respectively). Different hydrodynamic conditions were implemented, and the surface temperature was measured. The results obtained are in line with the hypothesis that the process is mediated by the formation of a semiconducting anodic oxide film with point defects that can exhibit different types of conduction. The film is described within point defect model II, and the rate of its electrochemical formation is balanced under steady-state conditions by the rate of its chemical dissolution, which is why the mass decrease per unit charge reaches a limiting value of 0.16–0.18 mg/C (under the pulsed conditions), which corresponds to a current efficiency close to 100% (assuming the highest oxidation state for alloying components of the steel in solution). In going from pulsed current to direct current conditions, the thermokinetic instability of the film is observed, i.e., it forms and then undergoes breakdown due to thermal explosion. Under such circumstances, the current yield of anodic dissolution may not only reach 100%, assuming the lowest degree of oxidation of the alloying components (thermal activation), but exceeds this value as a result of chemical interaction between the film-free surface and the electrolyte.

The pack cementation method was applied for the preparation of four coatings. The pack mixtures consisting of Zn, Y₂O₃, and NH₄Cl were used in this work. The impact of adding Y₂O₃ on the appearance, the components, and the anti-corrosion action of coatings was analyzed. The appearance was observed by scanning electron microscope. The components were characterized by X-ray diffraction. The results suggested that adding Y₂O₃ increased the coatings thickness and perfected the coatings quality. Without adding Y₂O₃, the coatings obtained consisted of Zn atoms and a few Fe atoms. Minute amounts of Y atoms were detected in the coatings at adding Y₂O₃. The impact of adding Y₂O₃ on the corrosion performance of coatings was assessed by the corrosion morphology analysis and an electrochemical test. The results showed that adding Y₂O₃ increased anti-corrosion ability. When the additive amount of Y₂O₃ was 4 wt %, the coatings exhibited the largest thickness and the strongest anti-corrosion ability.

It has been found that the gas-phase diffusion of gallium and phosphorus atoms into silicon provides not only the compensation but also partial interaction of the elements with each other. Analysis under a scanning electron microscope has shown that, after diffusion and surface treatment, gallium and phosphorus atoms are present on the silicon surface in similar concentrations. Studies of the concentration distribution of charge carriers over depth have shown that, upon codiffusion, the solubility of gallium increases by an order of magnitude, while the charge carrier mobility decreases by a factor of three to four. Based on the obtained data, the concentration (~10¹⁹ cm^–3) and energy of formation (~0.62 eV) of neutral complexes [Ga^–P⁺] have been calculated. The results can be attributed to the electrostatic interaction of gallium and phosphorus ions during diffusion, which leads to a change in the concentration distribution of the impurities and the formation of quasi-neutral complexes of the [Ga^–P⁺] type in the silicon lattice.

The features of the deviation of the open circuit potential at the semiconductor–electrolyte contact where cadmium and zinc sulfides are used as semiconductor materials are considered. Models of equivalent electrical circuits that explain the observed phenomena are proposed. Some examples of devices designed on the basis of the research results are given.

Direct electrical energy storage by supercapacitors is the leading energy storage technology. The performance of supercapacitors depends mainly upon the electrode material constituents. Carbon is the preferred energy storage material for its some main properties such as a large surface area, electrical conductivity, porosity, thermal stability, etc. Sustainable, green, renewable, low-cost and environmentally friendly carbon energy storage materials can be obtained from biomass. A larger surface area and tunable micro-porosity, which are the most important advantages, could be achieved by chemical activation of K₂CO₃ and HNO₃. In this work, the effect of K₂CO₃ and HNO₃ on the porosity and the electrochemical energy storage capacity of carbon derived from biomass made from the industrial tea waste were evaluated. A carbon material with a high performance of energy storage exhibiting 460 F g^–1, with a surface area of 1261 m² g^–1, could be developed by activation of K₂CO₃ in the 1 : 1 optimum ratio (w/w). The HNO₃ treatment also increased the capacitance but to a very low degree.

The electrical conductivity and thermochemical and electrochemical properties of a system consisting of melts of aluminum trichloride and sodium-lithium chlorides taken in different ratios have been studied. In this system, the electrochemical behavior of Ni²⁺ ions via cyclic voltammetry and the electromotive force in the modes of heating and cooling of the system were studied. It was found that the melting temperature of the melts passes through a minimum at a lithium chloride (хLiCl) content from 0.23 to 0.35. A possibility of reducing the starting temperature of a nickel-chloride battery with a partial replacement of sodium chloride with lithium chloride, as well as stabilization of its operation at a minimum temperature of 240°C, is shown. An admissibility of using the optimal compositions of the system as an electrolyte in sodium–nickel-chloride batteries has been established. It was found that the composition 0.5AlCl₃–0.23LiCl–0.27NaCl has a minimum melting point (111°C), a minimum activation energy for conductivity (8.9 kJ mol^–1), and a sufficiently high electrical conductivity (0.53 S cm^–1 at 250°C).