No 1 (2023)

The effect of reductive treatment on the phase composition, morphology, and electrochemical parameters of δ-MnO2 produced by the hydrothermal method from KMnO4 at a temperature of 160°C in the presence of HNO3 was studied. δ-MnO2 processing with 3 M NaBH4 aqueous solution leads to partial reduction of Mn(IV) to Mn(III) and Mn(II). The electrochemical characteristics of the obtained electrode materials were examined by cyclic voltammetry, galvanostatic charge–discharge measurements, and impedance spectroscopy. Reductive treatment increases the specific capacitance of δ-MnO2 in 1 M Na2SO4 up to 204 F g–1 at a current density of 0.1 A g–1, and also reduces diffusion limitations during cycling due to an increase in the specific surface area. The loss of specific capacitance after 2000 charge–discharge cycles does not exceed 2.6%, which confirms the high electrochemical stability of the obtained electrode materials.

The high-temperature strength properties of silicon carbide-based ceramic materials reaction-sintered in air and vacuum are proved by experimental data. The ultimate bending strength of pressed and cast ceramic material samples at temperatures up to 1400°C was measured as a criterion. High-temperature tests demonstrate the guaranteed strength of ceramics above 100 MPa. An example of the manufacture of a complex shaped ceramic product using the hot slip casting processing under pressure into additive water-soluble forms is given. An approval of the combined technology makes it possible to manufacture bladed ceramic elements with a thickness of about 1 mm.

A procedure was suggested for voltammetric determination of streptomycin from the catalytic current on a glassy carbon electrode with a composite based on reduced graphene oxide and gold–nickel binary system. The working conditions of the electrode modification (volume of the graphene oxide and chitosan suspension, duration of the electrolytic reduction of immobilized graphene oxide and electrodeposition of the gold–nickel binary system) and the conditions for recording the catalytic current in the flow injection system were determined. The procedure for streptomycin determination in a flow, compared to the determination under stationary conditions, is more sensitive, reproducible, and rapid. The streptomycin detection limit was 0.45 nmol, and the productive capacity of the analysis was 60 samples per hour. The streptomycin determination procedure passed trials in analysis of cow milk.

The study assessed the coagulating ability of copolymers N,N-diallyl-N,N-dimethylammonium chloride with acrylamide and maleic acid when separating styrene/butadiene and nitrile/butadiene rubbers from latexes. The effect of the consumption of these cationic polymers, the concentration of the dispersed phase and temperature on the completeness of rubber separation was studied. It was established that the completeness of styrene/butadiene rubber separation from latex is achieved at a 0.5 kg t–1 consumption of cationic copolymer with acrylamide, and that of butadiene/nitrile rubber is achieved at 22 kg t–1. The introduction of maleic acid units into the cationic copolymer ensures the complete separation of styrene/butadiene and nitrile/butadiene rubber from latex at a consumption of 0.3 and 8 kg t–1, respectively. Vulcanizates obtained from rubbers isolated using copolymers meet the requirements of State Standard GOST 15627–2019.

Procedures were developed for forming hollow cylindrical structures with the wall thickness in the micrometer range (microtubes) from chitosan solutions in citric, lactic, and glycolic acids. The procedures are based on the phase-transfer neutralization induced by the transport of ions (hereinafter, ion-induced reaction), occurring at the liquid–liquid or solid–liquid interface, namely, on the polymer-analogous conversion of the salt form of the polymer to the base form in a NaOH or triethanolamine medium or formation of a water-insoluble polyelectrolyte complex with sodium dodecylbenzenesulfonate. Comparative analysis of the dependences of the morphological, structural, elastoplastic, physicomechanical, and biological properties of the structures on the reaction conditions and kind of the organic acid and neutralizing agent was made. The microtubes prepared from a chitosan solution in glycolic acid by ion-induced neutralization at the solid–liquid interface in a NaOH or triethanolamine medium exhibit the optimum levels of strength and elasticity, comparable with those of a fragment of human carotid artery and xenopericardial patch. The hemo- and biocompatibility and controlled biodegradation of these materials make them promising as analogs of biodegradable blood vessel implants.

To ensure the safety of the arabinogalactan sulfation process, the thermal effect of the reaction (148.26 kJ) was determined by the thermal flux balance method. The dependence of the dynamic viscosity of the reaction medium on the way of introducing the sulfating agent and on its particle size was studied by phase rheology. The stirring process was calculated to substantiate the optimum stirrer design and determine the quality parameters of stirring of the reaction medium. The data obtained allow optimization of the process for producing Agsular® substance in scaling of the production technology.

A mathematical model is presented that describes the movement of gas in a direct-flow cyclone. The equations of motion of the gas phase were solved and profiles for the tangential and axial components of gas velocity were derived based on them. The results obtained are compared with the results of numerical simulation. The latter was carried out in the FlowVision software using the SST turbulence model. Via numerical calculations the change in the tangential and axial components of the gas velocity was determined at distances of 110, 150, 200, and 250 mm from the plate turbulator, or cyclone swirler.