Vol 55, No 5 (2019)

The electrospark deposition of coatings onto SPKhN–60 white cast iron samples has been undertaken in two stages. A barrier sublayer has been deposited at the first stage, using chromium and nickel electrodes, and a multifunctional protective coating was deposited at the second stage. The effect of the sublayer on coating properties upon application of STIM–40NAOKn (TiC–NiAl + \({\text{ZrO}}_{2}^{{{\text{nano}}}}\)) and STIM-11OKn (TiB₂–NiAl + \({\text{ZrO}}_{2}^{{{\text{nano}}}}\)) electrodes is studied. The coating structures are investigated. The grain size of the refractory phase is found to be smaller than 100 nm. The application of double-layer coatings increased the wear and heat resistances of white cast iron samples. Pre-deposition of a nickel sublayer enhanced the heat resistance of STIM-11OKn coating over eightfold. The full-scale tests of the rolls strengthened using SHS electrodes were carried out and positive results were obtained.

Results of the roughness studies of multicomponent hard metal layers on X12 tool steel (210Cr12/1.8–2.2% C, 12%Cr) obtained by contactless local electrospark deposition using two types hard metal electrodes (WC–TaC–Co–Al₂O₃ and WC–(Ti, Ta, Nb)C–Co–Al₂O₃) are presented here. Dense, smooth, and uniform coatings with a good repeatability of properties have been obtained. The minimal and maximal values of thickness δ, of the roughness parameter Ra, and of micro hardness HV of obtained coatings are changed by altering the stratification regimes in borders: δ = 3–12 μm, Ra = 0.8–2.2 μm and HV = 8.5–18 GPa, respectively. The influence of the process parameters and the electrode composition on the roughness of the layers obtained have been studied. Mathematical-statistical models and equations describing the roughness of the coatings have been created and worked out. They enable obtaining of coatings with a predetermined roughness by controlling regime parameters. Specific ways of obtaining coatings with reduced roughness at the maximum possible thickness, as well as recommendations for their appropriate application, have also been proposed and justified. Based on the obtained regression equations and graphical dependencies, it is possible to optimize properties of the coatings and the conditions of their deposition in order to obtain maximum tribo-effect and increased performance properties of the coated surfaces for different cases of exploitation.

In this study, a novel approach was adopted to determine the drug resistance developed due to the presence of antibiotics in industrial effluents. As a remedy, magnetic carbon nano-composites (MCNs) were prepared from waste biomass and characterized by a surface area analyzer, by SEM, EDX, XRD, FTIR, and TG/DTA. Langmuir, Freundlich and Temkin isotherms were used for the determination of adsorption parameters. The Langmuir adsorption isotherm was found to fit better the data of the equilibrium adsorption of enrofloxacin (ENR) on MCN (R² = 0.99). The effect of pH on the adsorption process was evaluated and a decline in percentage of adsorption was noted at both highly acidic and alkaline pH. The maximum percentage of adsorption was observed at pH 6–8. The effect of ionic strength and humic acid was also tested for the removal of ENR by MCNs. Various kinetic models were used to analyze the kinetics data. The best fit was obtained with a pseudo 2nd order kinetic equation. The thermodynamic parameters were also determined: ΔS° was positive (80 J mol^–1K ^–1) while ΔH° (23.57 kJ mol^–1) and ΔG° were negative with numerical values of –0.27, –1.47, and –3.07 kJ mol^–1 corresponding to temperatures 25, 40, and 60°C, respectively. MCNs were regenerated with 3% NaOH solution, methanol, and distilled water.

A solution to the problem of calculating the temporary evolution of amplitudes of capillary waves of an arbitrary symmetry on the surface of a cylindrical jet of an ideal incompressible conductive liquid moving relative to an ideal incompressible dielectric medium is offered, taking into account multimodal initial conditions. Analytical expressions for the temporary evolution of the amplitudes of waves on a jet, amplitude values of hydrodynamic potentials of velocity fields on a jet and in a medium, and the electric potential of the field in the neighborhood of the jet. An assessment of the characteristic time of a separation of a drop from a jet is performed.

The experimental technique and equipment used to study the kinetics of ion exchange in weak electric fields in the ion–exchange resins using a computer resistometric measurement method are described. In the course of ion exchange in the NaCl + NaOH model solution–ion exchanger system the chemical composition dynamics of a solution measuring the solution resistance with the help of a resistometer is measured with a flowing sensor; its signal is computer processed. The pattern of interaction between electrical and diffusion ion fields in the solid phase of the ion exchanger is discussed. It is shown that when a weak directional electric field is applied on the spherical ion exchanger particle, the spherical symmetry of the ion displacement rate is distorted, and the balance of the ion flows is changed. Thus, the exchange process is accelerated in the direction of the electric field vector. The test unit for the study of the ion exchange dynamics, which includes a convective reactor, a built-in column with a portion of the exchanger, a temperature control system, a flowing sensor of the electrical resistance of the solution, an electronic resistometer, and a potentiostat–galvanostat, is described. Three experimental methods are described: a nonstationary method with the ion exchange suspension in the enclosed volume, the nonstationary method with filtration through the ion exchanger in the column, and the method of open filtration through the column. It is shown that the speed of the ion flux in the solid phase is constant and does not depend on the saturation value of the exchanger in the suspension mode of exchange in the basic interval time of the process. This effect is caused by the operation of the electroneutrality law on two ion fluxes with the charges of the same sign but with the opposite concentration gradients.

In this work, plasma electrolytic oxidation was performed on AZ31 magnesium alloy. The electrolytes contained mixtures of sodium silicate, sodium hexamethaphosphate, potassium hydroxide, and potassium fluoride. Scanning electron microscopy, X-ray diffraction, porosity measurements, atomic analysis, and exposition in 3% NaCl were carried out to investigate the microstructure, elemental/phase composition, and corrosion resistance of the coatings. The results showed that the coating formed in both silicate- and phosphate-containing electrolyte were mainly composed of MgO, Mg(OH)₂, Mg₂SiO₄, and Mg₃(PO₄)₂ showing the most dense structure and the best corrosion resistance.

Electro-spark deposition (ESD) has been already recognized as an economically effective surface coating method. It requires a simple and low-cost equipment to run a process. Furthermore, mechanical and tribological properties of the coatings deposited using ESD are very promising, being, in many cases, improved compared to those of a substrate. When coatings are secondary treated via laser beam, they get a smoother surface and an amorphous structure. This paper reviews the investigations conducted on different substrates using different deposition materials via ESD as well as those of mechanical and tribological properties obtained. In particular, the review specifies: the role of ESD in enhancing the metal surface mechanical and tribological characteristics. It seems reasonable to apply ESD wider in order to improve mechanical and tribological properties of metal surfaces.