Vol 89, No 6 (2016)

Nanocrystalline cobalt ferrite powders were synthesized by hydrothermal treatment of co-precipitated hydroxides in the conditions of an external heating of the autoclave and under microwave heating of the reaction medium. In the microwave-heating mode, the prenucleation clusters formed under ultrasonic treatment of a suspended mixture of cobalt and iron hydroxides is transformed into CoFe₂O₄ nanocrystals during the first minute of synthesis at a temperature satisfying the equilibrium-existence conditions of cobalt ferrite. In the case of a slow external heating of the autoclave, there is no effect of this kind, which is attributed to the disintegration of the prenucleation clusters before the dehydration of the hydroxides to give crystalline cobalt ferrite becomes thermodynamically favorable. The main factor determining the increase in the formation rate of crystallites of CoFe₂O₄ nanopowders and the decrease in their size is the generation of prenucleation centers in the starting mixture of cobalt and iron hydroxides.

Main technological parameters of the process of local plasmochemical etching of single-crystal quartz were optimized. The etching was performed in a gas mixture of CF₄ and H₂ under radio frequency (RF, 13.56 MHz) discharge excitation. The scientific experiment design by the Taguchi matrix method was used to examine the effect of chamber pressure, RF generator power, negative bias applied to the substrate holder, and hydrogen flow rate on the rate of the etching process. The experimental results made it possible to evaluate for the first time the influence exerted by the technological parameters on the etching rate. It was shown that the influence exerted by the technological parameters in the conditions under study decreases in the following order: pressure in the reaction chamber, bias potential, RF power, hydrogen flow rate.

Possibility of direct extraction of 0.66 g L–1 Ni(II), 0.048 g L^–1 Co(II), and 0.024 g L^–1 Zn(II) in the presence of the nine commonly accompanying elements from a model solution for underground sulfuric acid leaching of an oxidized Ni ore with a 0.4–0.6 M solution of a hydrazide of Versatic C₁₅–C₁₉ acids in kerosene was considered. The optimal conditions of extraction, extract washing to remove impurities, and re-extraction of Ni and Co were determined. It was found that the direct extraction of up to 90% of nickel, cobalt, and zinc is possible with an at least fivefold concentration in the extraction stage. The separation of Ni from Co and co-extracted Fe, Zn, and Mn is possible in the re-extraction stage by washing of the organic phase with a 0.5 M HCl solution.

Kinetic and equilibrium characteristics of the sorption of benzoic, salicylic and ortho-chlorobenzoic acids by a new cross-linked sorbent based on N-vinylpyrrolidone were studied at various pH values of the medium. It was found that the molecular sorption of aromatic carboxylic acids from aqueous solutions occurs in the mixed-diffusion mode and the sorption capacity of the polymer grows with increasing acid-base equilibrium constants of the acids. The advisability of introducing a salting-out agent into sorption systems was confirmed. Effective sorption systems and a method for concentration of aromatic carboxylic acids from aqueous solutions by the new cross-linked sorbent based on N-vinylpyrrolidone were suggested.

Nanostructured carbon materials for supercapacitor electrodes, produced by short-pulse laser treatment of a polyimide film in argon with a fiber-optic ytterbium laser, were studied. Owing to the high power density, there occurred an optical breakdown of the polyimide film and its material was destructed to give nanocrystalline graphite. The thus synthesized nanostructured carbon was used as an active electrode material for supercapacitors. The results obtained in measurements of their functional characteristics demonstrated that the materials being synthesized are highly promising.

Compatibility of the lithium-titanium spinel Li₄Ti₅O₁₂ in contact with precursors of lithium-conducting solid electrolytes of composition Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP), Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP), Li_0.5La_0.5TiO₃ (LLT) was studied. It was found that, in sintering of Li₄Ti₅O₁₂ brought in contact with LATP and LAGP, a solid-phase reaction occurs to give nonconducting phases (TiO₂ and Li₃PO₄). The conductivity of the stable composite Li₄Ti₅O₁₂/LLT (10%) is higher than that of the starting Li₄Ti₅O₁₂, which makes it possible to regard the composite as a promising anode material for lithium-ion batteries.

Thermal behavior of polymers [poly(methyl methacrylate), poly(methyl acrylate), polystyrene] prepared in the presence of tri-n-butylboron and a series of p-quinones was studied. The heat resistance of the polymers increases with an increase in the inhibition constant of the p-quinone taken for the synthesis. The enhancement of the heat resistance of the polymer is due to a decrease in the amount of weak bonds and to the formation of associates.

Composites with titanium oxide structures on the surface of a polymer matrix were prepared by preliminary plasma activation of polytetrafluoroethylene films, followed by chemical treatment with vapors of titanium tetrachloride and water. The chemical composition and structure of the modified film surface were studied by scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. The stability of the formed surface charge increases in going from the initial film to the plasma-activated film, then to the film successively treated with vapors of titanium tetrachloride and water, and finally to the plasma-activated film treated subsequently with vapors of titanium tetrachloride and water. The modified polytetrafluoroethylene films are of interest as electrets with enhanced operation characteristics.

A three-step procedure for preparing polyurethanes with mixed polyether segments was suggested. It involves preparation of the “inverse” prepolymer by the reaction of one of oligodiisocyanates with 1,4-butanediol taken in a double excess, followed by the reaction with the other oligodiisocyanate. Polyurethanes with alternating poly(tetramethylene oxide) and poly(propylene oxide) soft segments were prepared by this procedure. Such materials surpass polyurethanes prepared from a mixture of oligodiisocyanates in the strength and softening point of the hard phase. In contrast to poly(tetramethylene oxide) urethane, elastomers with mixed polyether segments do not crystallize.

A series of chalcogenide glasses of various compositions, based on the TlI–Ag₂S–As₂S₃ system, were prepared. The conductivity parameters and diffusion coefficients of silver and thallium radiotracers in the glass samples were determined. Chemical sensors with membranes of four glass compositions were prepared, and their analytical characteristics (sensitivity, selectivity, detection limit) were studied. Correlation between the ionic conductivity parameters of the ion-sensitive membranes and the analytical characteristics of chemical sensors for thallium ions in solutions was found.

Changes in the process parameters and quality of the synthesized SKI-3 isoprene rubber, caused by using a small tubular turbulent apparatus of diffuser–confuser design in the step of titanium catalyst preparation, are analyzed. The use of this apparatus in the industrial process leads to a decrease in the catalyst consumption and to an increase in the polymer yield without significant changes in the polymer characteristics.

Conditions were found for solid-phase mechanochemical activation of coals, allowing a significant increase in the yield of water-soluble humic preparations enriched in humic acids and mineral elements. The humic preparations are characterized by a decrease in the molecular mass and by changes in the ionic composition and surface activity. The physiological activity of the humic preparations was determined.

This study presents a numerical investigation on the proton exchange membrane fuel cell (PEMFC) and the solid oxide fuel cell (SOFC), using the aerothermal and electrochemistry equations to describe all phenomena included in both types of the fuel cells. The computational process is based on the implementation of the mathematical fuel cells models in FLUENT computational fluid dynamics code. This is in order to evaluate the temperature field, the production of the electricity, and the distribution of the water mass fraction in different region of the fuel cells. The obtained results show that the simulation is able to evaluate the physical and chemical parameters to explain the main phenomena in the fuel cells.

The electrochemical behavior of electric double layer capacitors (EDLCs) with tetramethylammonium bis(oxalato)borate electrolyte and electrodes based on various activated carbons (ACs) was studied. Tetraalkylammonium bis(oxalate)borate salts were synthesized by means of microwave (MW) irradiation. The specific conductivities of salt solutions were determined. It was shown that the efficiency of electric double layer capacitors increases with an increase in specific surface area and a decrease in the purity of carbon materials.

Carbon black (CB) was simply modified by tert-butylchlorodimethylsilane (TBDMCl) to form the–C–OSiR and–C–OOSiR structures on the surface of CB. The formation of–C–OSiR and–C–OOSiR structures on CB was verified by FTIR and XRD measurements. The modified carbon black (MCB) has relative high electrochemical performance, which was determined by electrochemical studies. The first charging capacity of MCB is at 343 mAh g^–1 and the conductivity of MCB is at 148.1 Sm^–1 which is similar to that of CB 155.2 Sm^–1. These results indicate that application of the obtained MCB will be promising for lithium anode materials. Meanwhile, these results can also suggest solving the overproduction problem of CB in China.

Composite electrochemical coatings modified with carbon nanotubes were produced on the basis of the zinc–nickel alloy. The functional properties (friction coefficient, protective capacity) of the composite coatings were studied in comparison with zinc–nickel alloys without a dispersed phase. It was found that, upon inclusion of carbon nanotubes particles into zinc–nickel deposits, their sliding friction coefficient decreases by a factor of 1.3–1.4 and the range of passive-state potentials becomes two times wider.