Vol 53, No 1 (2017)

The study investigates the influence of electrolyte compositions containing acetone, glycerol, sucrose, ethylene glycol and ammonium chloride on the properties of VT22 titanium alloy in the process of the anode plasma electrolytic treatment (PET). An X-ray diffractometer and a scanning electron microscopy (SEM) were used to characterize the phase composition and morphology of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a pin-on-disc tribometer under lubricated testing conditions. The effect of electrolyte compositions on the corrosion resistance of the PET samples was examined by means of potentiodynamic polarization in a solution of Na₂SO₄. It was assumed that the PET provides the saturation of titanium alloy with oxygen and carbon and formation TiO₂ with a rutile structure and carbon solid solution in titanium. The anode PET in an electrolyte with glycerol results in an increase in microhardness to 540 HV and a decrease in the corrosion current density by 2.4 times. The friction coefficient of the treated samples in anelectrolyte with sucrose can be reduced 7.5 times. The anode PET in all electrolytes enables todiminish the wear rate of the titanium alloy samples by 3 orders of magnitude and the surface roughness, too, due to the anode dissolution of titanium.

Methylammonium lead-halide perovskites are very promising for applications as solar light-harvesting materials. This paper presents a study on the methylammonium iodide and iodide-chloride perovskite films prepared by spin coating from a liquid precursor. The powder diffraction spectroscopy has detected 10 lattice plane reflections common to a perovskite of a tetragonal crystal structure. The calculated cell parameters are a = 8.85 Å and c = 12.60 Å. The preparation conditions and their impact on the crystallization process and film morphology are discussed. A red shift of photoluminescence bands at low temperatures was evidenced. A photoelectrical study of perovskite films has revealed their high sensibility to illumination, especially in the visible spectrum, which gives a hint on their applications in photovoltaics.

The structure of EHD flows in a wire-plane electrode system have been computer simulated using the injection mechanism of spatial charge formation, and the results are presented in this paper. The injection mechanism of charge formation makes it possible to explain the threshold nature of EHD flows, the patterns of an undeveloped and developed EHD flow, the band structure of EHD flows, the dependence of the EHD flow structure on the low-voltage conductivity of a liquid, and the weak dependence of the structure and properties of an EHD flow on the geometrical dimensions of an electrode.

The inhibition effect of a newly synthesized pyrimidine derivative, namely 3-(2-(4-(hydroxymethyl)-1H-1,2,3-triazol-1-yl)ethyl)-2-methyl-6,7,8,9-tetrahydropyrido[1,2-a]pyrimidin-4-one, on the corrosion of mild steel in 1.0 M HCl medium was investigated using the weight loss, the Tafel extrapolation technique and the AC impedance spectroscopy. The effect of the inhibitor concentration, temperature and concentration of the acid mixture media on the inhibitor action was also studied. It was observed that the anti-corrosion efficiency increases with an increase in the inhibitor concentration, but decreases with an increase in temperature. Thermodynamic parameters for the dissolution process were determined. The adsorption of the pyrimidine derivative on the mild steel surface was found to obey the Langmuir adsorption isotherm.

The instability of the dc operating point in the pH-sensitive ion-selective field effect transistors (ISFETs) has been ascribed to a chemical ageing at the electrolyte–insulator. This instability, commonly referred to as a drift, is believed to involve formation of a chemically-modified insulator surface layer as a result of hydration of the insulator material. A kinetic model for hydration of the amorphous insulator material is presented. The kinetics of hydration is limited by the hopping and/or trap-limited transport mechanism known as dispersive transport, the key characteristic of which is a power-law time dependence of the diffusion coefficient. The power-law time dependence of the diffusion coefficient will be shown to lead to a stretchedexponential decay in the form exp[–(t/τ)^β] for the excess density of sites or traps occupied by the hydrating chemical species undergoing dispersive diffusion, where τ is the time constant associated with a structural relaxation and β is the dispersion parameter satisfying 0 < β < 1. The kinetics associated with a hydration reaction limited by the dispersive diffusion has been shown to lead to a hydrated layer thickness exhibiting a time dependence in the form {1–exp[–(t/τ)^β]}. The first order rate equation describing the kinetics of the hydration reaction is characterized by the time-dependent rate coefficient.

The effect of electromagnetic radiation of an extremely high frequency on the productivity and biosynthetic activity of Saccharomyces cerevisiae CNMN-Y-18 and Saccharomyces cerevisiae CNMN-Y-20 yeast strains, depending on the duration of irradiation, has been revealed. It was established that at the irradiation with millimeter waves with a frequency of 53.33 GHz during 10 and 20 minutes the amount of biomass, carbohydrates, mannoproteins, β-glucans, proteins gets the maximum and the catalase activity is the highest. For the first time, procedures to increase the content of mannoproteins and β-glucans using the electromagnetic radiation of an extremely high frequency as stimulating factor, are proposed.

Enrofloxacin uptake and removal from aqueous solutions using illite and synthetic zeolite X prepared from illite, were studied in batch experiments under varying pH, contact time, and initial enrofloxacin concentrations. The X-ray diffraction and Fourier transform infrared spectroscopy caracterization were used to analyse the enrofloxacin adsorption in order to elucidate the adsorption mechanisms. It was found that enrofloxacin could be efficiently removed at pH 7 and pH 8 for clay and zeolite X, respectively. In addition, the second order model of kinetics is more adopted for the two samples. The isotherms of adsorption of enrofloxacin by illite and zeolite X show that the latter has the twice higher adsorption capacity of the clay. Equilibrium data fit well with the Langmuir and Freundlich isotherms. Moreover, the cation exchange, the electrostatic interaction, the cation bridging and the formation of bidentate ligands were the possible mechanisms of the enrofloxacin retention.

The process of the conversion of capacitor bank energy as a result of a high-voltage electrical discharge in water that fills a closed discharge chamber into the plasma, liquid, and solid energy is studied. Mathematical modeling in a coupled geometrically and physically nonlinear statement of electrodynamic, hydrodynamic, and elastic–plastic wave processes in the discharge chamber is used as the main research method. We determine the distribution of the capacitor bank energy transferred into a plasma, liquid, and solid body through their contact boundaries in accordance with the parameters of the dynamic system.