Vol 54, No 1 (2018)

UHMWPE/SiO₂ composites were obtained from a homogeneous mixture of ultrahigh-molecular- weight polyethylene (UHMWPE) and silicon dioxide (α-SiO₂) by hot pressing. The temperature dependence (20–170°C) of their conductivities σdс prior to and after γ irradiation (D = 200 kGy), the effect of absorbed dose on the σ_dс value (dose dependence), the behavior of the function logσ_dc = f(T) under heating–cooling conditions, and the frequency dependences (25–106 Hz) of the real (ε') and imaginary (ε'') parts of the complex dielectric constant were studied. The logσ_dc = f(T) dependence was shown to have in both cases a complex pattern: “breaks” due to phase transitions were observed. With an increase in the concentration of α-SiO₂, the ε' and ε'' (tanδ) values in the matrix increased and the frequency dependences of these values corresponded to an exponential rule.

An analysis is carried out on the electromagnetic radiation of an uncharged drop oscillating in an electrostatic field using nonlinear asymptotic calculations for two small parameters (the value of a dimensionless stationary deformation of an initially spherical drop and the amplitude of its capillary oscillations). In the external electrostatic field, on the top of the drop, electric charges with the opposite signs are formed, to which the “effective” charges located on the drop’s symmetry axis are added relatively. Since the distance between those “effective” charges is about the length of the drop’s radius, they form a dipole, which at the distances much longer than the sizes of the drop creates a similar electric field as the drop itself. During the oscillation of the drop surface, the dipole will also oscillate, which will generate the electromagnetic waves of the dipole type.

The determination of the electrocatalytic activity and selectivity of electrodes with respect to the target process is considered to be of interest both in the theoretical aspect for the development of electrocatalysis theory and in application for efficient electrocatalysts which can be used in electrochemical systems for wastewater treatment. The purpose of the given work was to identify the relationship between the chemical and phase composition of materials based on lead dioxide, their physicochemical properties, and their electrocatalytic activity. The main research methods were quasi-stationary polarization and impedance spectroscopy, photocolorimetry, fluorescent and spectrophotometry in the UV and visible regions, atomic absorption spectroscopy, and high performance liquid chromatography (analysis of the solutions). It was shown that the modification of lead dioxide by ionic additives results in significant changes in the electrocatalytic activity of the system in respect to the oxygen evolution reaction and electrochemical oxidation reactions of organic compounds. It was found that, at low polarizations, the oxygen evolution reaction is limited by the electrochemical desorption step (the second electron transfer), and its overpotential at PbO₂-modified electrodes increases in the order that coincides with the dependence in which the number of oxygen-containing particles strongly bound to the electrode surface increases. It was found that the rate of oxidation of organic substances on the anode materials involved is directly proportional to the amount of oxygen-containing radicals formed on the electrode during the water oxidation.

Mesoporous iron phosphates were synthesized using sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) as surfactants. The material synthesized in the presence of SDS was not applied as a positive electrode active material of a lithium battery. The results show that the obtained FePO₄ has a mesoporous structure with a specific surface area of 70 m² g⁻¹ and a dominant pore diameter of 3 nm. Those mesoporous were characterized by different microstructural and electrochemical analyzes. Among the materials studied under different conditions, those calcined at 450°C preserve mesoporous structures and exhibit the best electrochemical performance when used as active materials of the positive electrodes of lithium batteries. Effectively, a relatively high specific capacity of 135 and 122 mAh g⁻¹ was registered at C/20 collected experimentally by the samples synthesized in the presence of SDS and CTAB, respectively.

The effect of surface condition down to 120 and 1000-grit finish, corresponding to 1.47 and 0.06 microns RMS (Root Mean Square), respectively, on the pitting corrosion behavior of sensitized and mill-annealed AISI (American iron and steel institute) 304 stainless steel was studied in 3.5% NaCl solutions at 23 and 50°C by electrochemical methods. The polarization curves have revealed a clear dependence of pitting corrosion on the surface finish, on the degree of sensitization, as well as on the test temperature. Surface condition has made a significant contribution to pit initiation in that the pitting potential was lowered as the surface roughness increased. The deleterious effect of surface roughness on the pitting potential of the AISI 304 stainless steel alloy in 3.5% NaCl is more pronounced on sensitized samples and becomes more evident with increasing sensitization time and test temperature.

The peculiarities of the cathode reduction of ClO^– and ClO^–₃ ions in a membraneless electrolyzer for the synthesis of sodium hypochlorite solutions to be used in human and veterinary medicine are studied. It is shown that, under the galvanostatic conditions of the electrolysis, the rate of hypochlorite ion reduction depends on the cathode current density, and it is hardly influenced by the cathode material. It is possible to decrease greatly the loss of ClO^– on the cathode, especially at high volume current densities, using electrolysis at a cathode current density over 40 mА/сm². It is demonstrated that, for a flow-through coaxial cell, the most suitable material for the cathode is VT1-0 titanium with polished surface.

A method for computer processing of the results of conductometric measurements for a mixture of solutions of two electrolytes that differ in specific electrical conductivity is developed. This method makes it possible to determine the concentration of certain components taking into account the measurements of specific electrical conductivity and temperature. The method is based on approximations of theoretical dependences of electrical conductivity of electrolytes on concentrations according to the Robinson–Stokes and Kohlrausch equations and reference data on the dependence of electrical conductivity on temperature. In the region of concentrations of C ≤ 0.02 М and temperatures of 15–25°С, the dependences are well approximated by algebraic polynomials up to the third order. The system of approximation functions describes a 3D region χ = f(C₁, C₂, T) inside of which there is a point that corresponds to the result of the measurements. This method is verified by the system of NaCl–NaOH and is applicable for the solutions of any concentrations by way of dilution of a sample to the required level. Two algorithms of processing of experimental data are studied. A simplified algorithm is based on the independence of molar electrical conductivity of the concentrations of the diluted solutions. The result of the processing of the experimental data has an overestimated systematic error from 1 to 5% in the mixtures with a high content of alkali. A more precise algorithm is based on the approximation of functions of dilution by the Kohlrausch equation. The systematic error of the specified algorithm is less than 0.05% in the mixtures with the highest electrical conductivity, and it is commensurable with the sensitivity of the conductometric measuring method.