Surface Engineering and Applied Electrochemistry最新文献

Based on mathematical modeling, the influence of the magnetic-pulse, the electric-discharge, and the combined sources of the pulsed pressure on wave fields in aluminum melt was studied. An increase in the intensity of the wave fields in the melt with an increase in the amplitude, the pulsation period, and the attenuation time of pressure pulsations created by pulsed sources was observed. The occurrence of cavitation in the melt under the action of the considered sources of pressure pulses was determined. A significant influence of the parameters of pulsed pressure sources on the change in the density of the internal energy of the melt was noted.

The paper presents the results of calculations and experiments to determine the primary amplitude and time characteristics of electrical breakdown in long air gaps in a point-to-plane double-electrode discharge system (DEDS) by a standard switching aperiodic high-voltage pulse of the time configuration, T_m/Т_p ≈ 200 μs/1990 μs, of positive polarity. Approximate calculation relations are obtained to find the breakdown time, T_d, breakdown (discharge) voltage, U_d, and breakdown strength, E_d of a strong electric field for this DEDS, averaged over a minimum length of l_min ≥ 1 m of these gaps. The proposed engineering approach to determining the values of T_d, U_d, and E_d is based on the results of an approximate calculation in a long air gap of a point-to-plane DEDS of a sharply inhomogeneous strong electromagnetic field that produces a spherical zone with a radius r_i of active impact ionization of its atmospheric air by electrons. This occurs near the lower sharp edge of the upper potential electrode point of the DEDS, wherefrom a positive discharge leader develops towards the lower grounded electrode plane of the DEDS.

The article discusses the changes occurring in polypropylene and its compositions with silicon dioxide, which occur under the influence of electro-thermal polarization. The dependence of the piezoelectric properties of polypropylene compositions on the percentage of the additive has been revealed. The present study identifies the dependence of the piezoelectric properties of polypropylene compositions on the percentage content of the additive. Furthermore, it demonstrates that the dependence of the charge of polymer compositions of polypropylene with silicon dioxide on the filler content can be described by an exponential curve with a peak at 3% filler content. Furthermore, the quasi-static piezoelectric coefficient of polypropylene compositions with 3% silicon dioxide has been examined in relation to both preload and the spectrum of thermally stimulated depolarization of the composite.

The comparative corrosion resistance and electrochemical behavior of deformed and annealed Ni–Re alloys and their components in acidic, alkaline, and neutral media has been studied. Alloying nickel with rhenium leads to a sharp hardening of the solid solution both in the deformed and annealed state. However, the corrosion resistance of the alloy decreases in 48% H₂SO₄ but increases in concentrated HCl and HNO₃. The diffusion-migration nature of the limiting current of alloys during anodic polarization in NaCl solutions (as well as during the dissolution of Ni and Co) has been revealed. Deformed metals are less resistant than metals annealed in noted media.

Surface characteristics of the clay-carbonate diatomite and its adsorption properties with respect to methylene blue (MB) were investigated. The equilibrium isotherms were modeled by the Langmuir, Freundlich, and Dubinin–Radushkevich equations. The Langmuir model more adequately described the experimental data with a correlation coefficient of 0.9783 and a maximum adsorption capacity of 112.8 mg/g. The separation factor was 0.143, indicating the favorability of the sorption process. The treatment of the experimental kinetic data showed that the pseudo second order model better describes the kinetic curves of the MB sorption. Intraparticle diffusion does not control the MB sorption rate, and film diffusion is the main contributor to the rate limitation. The activation energy for sorption, calculated using the Dubinin–Radushkevich model, was 17.4 kJ/mol, indicating the predominance of physical sorption. The results show that this sorbent can be used for the purposes of water purification from organic pollutants.

A minimal theoretical model for describing the dynamics of localization of a shared electron in a pentamer nanocluster in an external low-frequency electric field, taking into account the electron-vibrational interaction, is proposed. Based on the given model, the system of differential equations was obtained regarding the time dependences of amplitudes of the probability of finding an electron on different centers of a pentamer. This model was used to describe the pentamers of linear and square-planar configurations. For those two types of the pentamer configuration, the numerical calculations were performed at different values of model parameters. The proposed model is characterized by the fact that the centers of the nanocluster are considered as weakly tunnel-coupled, and the electron-vibrational coupling with the ligand environment on each of its centers plays a significant role. Moreover, tunneling is taken into account only between the nearest centers of the nanocluster, while the cluster centers are considered equivalent. The control role of an external electric field was revealed so that the variations of its intensity amplitude and frequency allowed for realizing the various electron localization regimes in the pentamer nanocluster. By setting up the values of those electric field parameters, the duration of the full localization of an electron at a certain cluster center (or centers) was regulated as was the rate of switching the localization of an electron to another cluster center (or centers) and the form of the overall distribution of electron density in the nanocluster.

The work contains studies on increasing the porosity of the surface layer of composite membranes. In order to increase the porosity of composite membranes, such solvents as ethanol and acetonitrile, whose boiling point is higher than that of acetone, which was used as the main cellulose acetate, were added to the polymer solution as a porogen. Based on the results of the study, samples of composite membranes were obtained and their physicochemical properties, such as total porosity, layer thickness, water absorption, and wetting angle, were studied and IR spectra of the membranes were obtained. The specific productivity and retention capacity of the obtained microfiltration membranes were also established.

Fermentation of whey facilitates the increasing of its acidity and changes its redox potential. As a result of the research, it was possible to improve the quality of whey by its electrical processing, increase its acidity, in particular, to change the pH of the medium from 4.5 to 2 under optimal process conditions.

The formation of surface Ti–Ag–Al–V alloy was carried out by compression plasma flows impact on Ti–6Al–4V titanium alloy preliminary coated by silver. The coating was deposited on the sample by the electron beam technique. The thickness of the coating was approximately 2 μm. The treatment of the system samples was carried out by three pulses of compression plasma flows in a nitrogen atmosphere (energy density absorbed by the surface varied from 26 to 43 J/cm² per pulse). The phase and elemental composition, structure, surface roughness, and microhardness were investigated. It has been established that the action of compression plasma flows on Ag/Ti–6Al–4V system results in the formation of TiAg, Ag, and δ-TiN in the surface alloyed layer. Increase of the energy absorbed by the surface during plasma impact (26–43 J/cm²) led to a decrease in Ag concentration (20.0–6.9 wt %) in the analyzed layer. The change of phase composition and structure results in modification of the microhardness. A microhardness increase up to 4.8 GPa (1.3 times in comparison with initial Ti–6Al–4V alloy) was found after compression plasma flows’ treatment at 43 J/cm².

In this paper, an attempt is made to know the changes that occur in the optical properties of WO₃ and TiO₂ nanopowders after forming WO₃@TiO₂ Core-shell nanopowder. Using the anodizing method, WO₃ and TiO₂ nanopowders were synthesized. WO₃@TiO₂ powder was formed using the hydrothermal method. Analytical techniques including SEM, TEM, XRD, and UV-VIS diffuse reflectance spectra were used to characterize each of the three samples. Reflectance percentage, absorbance percentage as well as Absorption, Scattering, and Extinction cross sections for all samples were studied. The energy band gaps were calculated for all samples, they were 2.72, 3.57, and 3.6 eV for WO₃, TiO₂, and WO₃@TiO₂, respectively. A material with better absorption and a longer spectrum response than each material alone is created by WO₃@TiO₂, which combines the characteristics of both WO₃ and TiO₂.