Vol 91, No 3 (2018)

In this work Molecular layer deposition (MLD) technique used to synthesize titanium-vanadium (TiV_xC_yO_z) and aluminum-vanadium (AlV_xC_yO_z) hybrid organic-inorganic films via alternating surface reactions of titanium tetrachloride (or trimethylaluminum), vanadium oxochloride, and ethylene glycol. Using in situ monitoring it was found that the surface reactions were self-limiting at temperatures of 90 and 115°C. The coating thickness per molecular layer deposition cycle (growth rate) at 115°C on a silicon substrate varied from 5.8 to 11.4 Å/cycle, and the film densities, from 1.7 to 2.0 g cm^–3. An analysis of the samples obtained at 115°C revealed their amorphous structure. A thermal treatment of titanium-vanadium films at 450°C in air resulted in formation of highly structured coatings. These coatings were composed of nanowires of single-crystal vanadium oxide (V₂O₅) and mixed nanostructures of titanium and vanadium oxides. Increase in thermal treatment temperature to 500°C resulted in elongation of the V₂O₅ nanowires up to tens of micrometers and in their separation from the substrate. A thermal treatment of aluminum-vanadium films in air resulted in formation of a low-density film. Pyrolysis of the films in an inert gas yielded composite coatings containing domains of graphitized carbon. These films can be potentially useful in modern devices for energy storage, electronics, medicine and other promising fields of technology.

X-ray diffraction analysis and transmission electron microscopy were used to demonstrate that hydroxyapatite produced by the precipitation method is a powder composed of anisometric particles with longitudinal size of 70–100 nm and transverse size of 7–9 nm. The particles are constituted by crystallites with longitudinal sizes of 22–24 nm and transverse sizes of 8–10 nm. At a temperature of 600°C, the crystallite sizes grow, and the volume porosity and specific surface area decrease. Synthetic hydroxyapatite has a low thermal stability as compared with hydroxyapatite of biological origin.

Desorption of rare-earth metals (REMs) (lanthanum, yttrium, and ytterbium), as well as iron and aluminum, from the KU-2 sulfocation exchanger phase with solutions of mineral acids and ammonium nitrate and sulfate of various concentrations was studied. New data on the distribution of REMs in these systems were obtained. It was found that it is the most rational to use an ammonium nitrate solution with concentration of 300 g L^–1. It is recommended to precipitate a concentrate of REMs from the resulting desorbate with ammonium carbonate, with the subsequent separation of the suspension by the electrofl otation method.

Composite electrochemical coatings based on the zinc–nickel alloy and modified with carbon nanotubes were produced in the pulsed mode. The functional properties (friction coefficient, protective capacity) of the composite coatings were examined in comparison with zinc–nickel alloys without a dispersed phase. It was found that, as carbon nanotube particles are incorporated into zinc–nickel deposits, the sliding-friction coefficient decreases by a factor of 1.30–1.40, and the range of passive-state potentials becomes 1.55–1.65 times wider.

New composite materials based on polylactide and graphene, suitable for creating three-dimensional objects using the 3D printing technology, were prepared. Introduction of the nanoadditive into the matrix of the biodegradable polymer enhances the tensile strength of the materials by more than 57%. In addition, the composites exhibit high electrical conductivity, reaching 0.9 S cm^–1 for the composite with 3 wt % filler, which determines the possibility of using them for the development of various electrotechnical devices and tissue engineering structures.

Film and composite membranes with a separating layer based on an interpolyelectrolyte complex of polyethylenimine and copolyamide, synthesized from isophthaloyl dichloride and two diamines, 4,4′-(2,2′-disulfonate sodium)diaminodiphenyl and 4,4′-(2,2′-disulfonate sodium)diaminodiphenylethylene, were prepared. Their mass-exchange properties in pervaporation separation of a water–isopropanol mixture were studied. The relationship between the degree of conversion in the interpolymer reaction and composition of the interpolyelectrolyte complexes, on the one hand, and membrane characteristics, on the other hand, was revealed. The interpolyelectrolyte complexes of nonstoichiometric composition, enriched in the sulfonate-containing aromatic copolyamide, show the highest performance in pervaporation separation of water–alcohol mixtures. The infl uence of the copolyamide composition on the separation characteristics of the membranes was considered. Combination of good mechanical and mass-exchange properties allows the sulfonate-containing aromatic copolyamides to be classed with promising polyanion components for interpolyelectrolyte complexes used in hydrophilic pervaporation.

Blends of polylactide with low-density polyethylene and of poly-3-hydroxybutyrate with synthetic ethylene–propylene rubber with the component weight ratios of 30 : 70, 50 : 50, and 70 : 30 were prepared and studied in comparison with the pure components. The thermal characteristics of these blends were determined by differential scanning calorimetry. The melting point of polyhydroxybutyrate and polylactide in the blends changes insignificantly, by 1–2°C. The dependence of the morphology on the composition for both polymer systems was examined by scanning electron microscopy. The physicomechanical properties of the samples are determined by the major phase. The blends undergo biodegradation in soil at 20 ± 3°С. The process occurs faster for blends of polyhydroxybutyrate with ethylene–propylene rubber of all the compositions studied.

The reduction of zirconium oxide with nanofibrous carbon to obtain highly dispersed zirconium carbide was studied. The optimum reduction conditions were determined. The reaction products were identified using modern physicochemical methods (scanning electron microscopy, low-temperature nitrogen adsorption, sedimentation analysis, differential scanning calorimetry). The product obtained appeared to be single-phase zirconium carbide containing no more than 2 wt % impurities. The powder particles are aggregated (mean diameter 14.9–15.0 μm, specific surface area 1.5–1.7 m² g^–1). The oxidation of zirconium carbide starts at 480°С and is complete at 800°С.

New improved process for the catalytic oxidation of dissolved hydrogen with the use of palladiumcoated sorbents was suggested, described, and performed. To implement the suggestion of the authors in accordance with the scheme of the experimental setup, dissolved hydrogen formed as a result of radiolysis of water is removed from a water heat-carrying agent by the method of catalytic oxidation on the surface of a palladium-coated sorbent when the heat carrier is filtered through a mixed-type ion-exchange filter to which a catalytic sorbent is added. The decrease in the concentration of hydrogen dissolved in the heat-carrying agent rules out its evolution into the gas phase in amounts forming explosive mixtures.

Nanofibers of semiconducting oxides SnO₂, ZnO, WO₃, produced by the electrospinning method, were tested as sensitive materials for detection of products formed in pyrolysis of polyvinyl chloride in conditions simulating the smoldering of electrically insulating materials upon occurrence of a short-circuit failure in electrical circuits. The method of thermal analysis with mass-spectroscopic determination of gaseous products demonstrated that, in pyrolysis of polyvinyl chloride in the temperature range 200–400°C corresponding to the invisible-smoke stage, the main component of the gas mixture being formed is HCl. It was shown that the materials synthesized can be used to develop gas sensors for early fire warning.

New polytetraurethane diepoxides were prepared from oligo(tetramethylene oxide)diols of various molecular masses, various diisocyanates, and glycidol. High-strength frost-resistant cold-curable elastic compounds were prepared on their basis. The use of aminoethylpiperazine as a curing agent allows the cured materials to be prepared in 24 h at room temperature. The elastomers based on isophorone diisocyanate exhibit higher mechanical and thermal characteristics than those based on 2,4-toluene diisocyanate, which is due to higher degree of microphase segregation of soft and hard blocks of elastomers based in isophorone diisocyanate.

Anion-radical salts of 7,7,8,8-tetracyanoquinodimethane (TCNQ) with N-methyl-2-amino-5-chloropyridinium and N-methyl-2-chloro-3-aminopyridinium cations of simple and complex compositions were synthesized and studied. The salt (N‒CH₃‒2‒Cl₃NH₂‒Py)(TCNQ) is electrically conducting and thermally stable up to 340°C. This enables use of this anion-radical salt in electronics of organic materials.

Magnesium-cadmium hydroxyapatite [(Mg-Cd)HAP] and novel multi-wall carbon nanotubes Mg-Cd hydroxyapatite (CNTs/(Mg-Cd)HAP) composites were synthesized by a co-precipitation method. The synthesized sorbents were characterized using BET surface area measurements, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). They have possessed specific surface area of 34.85 and 60.41 m² g^–1 for (Mg-Cd)HAP and CNTs/(Mg-Cd)HAP, respectively. Furthermore, the synthesized sorbents were applied in removal of Eu(III) ions from aqueous solutions. Sorption performance of the synthesized sorbents towards Eu(III) ions was studied under different sorption parameters such as equilibration time, sample mass, solution pH and ionic strength. Sorption of europium reached equilibrium within 6 h at pH 2.5. The maximum sorption capacity (Q_max) was 137.31 and 151.47 mg g–1 for sorption of Eu(III) onto (Mg-Cd)HAP and CNTs/(Mg-Cd) HAP, respectively. Kinetically, the sorption process followed the pseudo-second-order model and both film and pore diffusions participated in ruling the diffusion of Eu(III) ions. Equilibrium sorption data of Eu(III) were analyzed using Freundlich and Langmuir isotherm models. The thermodynamic parameters (ΔG°, ΔH°, and ΔS°) for sorption of Eu(III) onto the synthesized sorbents were determined and the reaction is found to be feasible, spontaneous and endothermic process.

Mechanism of electrodeposition and stripping of Zn‒Ni‒Mn alloys deposited at different time intervals from aqueous sulfate media were investigated. The corrosion properties of coatings on steel substrate were studied by using different techniques. It might have been established that the attained Zn‒Ni‒Mn alloy exhibits a superior corrosion resistance at low plating times. Also, the ternary Zn‒Ni‒Mn alloy shows finer-grain size, more homogeneous, more uniformity, adherence, hardness, and compactness with respect to the alloy electrodeposited at high plating times. Alloys of the high content of Ni have been obtained at very low deposition times indicating that the initial layer of alloy plating is nickel, as the more noble metal than Zn or Mn, which deposits preferably during the first few seconds. As a result, the coatings obtained at low deposition times have more noble corrosion potentials than those obtained at high deposition times.

The effect of a mixture of halogen-containing fl ame retardants based on chloroparaffins and 1,1,9-trihydroperfl uorononanol-1 immobilized on a montmorillonite carrier on the character of reducing the fl ammability of polyurethane was studied. Using X-ray diffraction and sol-gel analysis, the structural and morphological features of the elastomers obtained were studied. It has been revealed that intercalation of macromolecular chains of a matrix amorphous polymer into the intralayer spaces of a fl uorine-containing organoclay occurs with an increase in a degree of structural perfection of the macromolecular system that contributes to an increase in the fire resistance of the resulting polyurethane composites.