Vol 61, No 10 (2016)

HfB₂–SiC ceramic samples containing 10, 15, and 20 vol % silicon carbide were prepared by spark plasma sintering. The samples were characterized by X-ray powder diffraction, SEM, and other methods. Their densities and calculated porosities were determined. The behavior of the materials under heating by a subsonic dissociated air flow was studied on a VGU-4 high-frequency inductive plasmatron. The average surface temperatures of the 10 and 15 vol % SiC samples were shown to increase up to 2550–2675°C during heating, due to the generation of surface localities having temperatures of 2600–2700°C (the initial surface temperature was ~1700–1900°C) and the progressive growth of these regions in area. The overall time during which the average surface temperatures of these samples were higher than 2000°C, was about 31–32 min. For the 20 vol % SiC sample, heat removal (when the sample touched a water-cooled holder) was shown to influence the surface temperature and surface temperature distribution. The variation in gas-phase composition over the central area of the sample surface during an experiment was studied using emission spectroscopy. Explanations are proposed to the variation of boron and silicon concentrations in the course of exposure to high-enthalpy flows. The elemental and phase compositions were determined and the microstructures were studied on the surface and sections of samples after long-term (~40-min) exposure to high-enthalpy air flows.

Methods for producing aluminum nitride nanopowder were reviewed. It was shown that an azide technology of self-propagating high-temperature synthesis using sodium azide as a solid nitriding agent produces quite a cheap nano- and ultradispersed AlN powder by the combustion of a Na₃AlF₆–3NaN₃–nAl powder mixture. This AlN powder is of interest for electronics, light-emitting diode technology, and reinforcement of modification of aluminum alloy. A nanostructured aluminum nitride powder forms by the combustion of a Na₃AlF₆–3NaN₃. With increasing the aluminum content of the initial mixture, the aluminum nitride yield increases, but so does the average powder particle size.

Potentially hexadentate phosphoryl podands 1,2-bis[2-((2-diphenylphosphorylmethyl)phenoxy) ethoxy]cyclohexane (L), 1,2-bis[2-((2-diphenylphosphoryl)phenoxy)ethoxy]cyclohexane (L¹), and 1,2-bis[2-((2-diphenylphosphorylmethyl)phenoxy)ethoxy]benzene (L²) are synthesized. Stability constants of complexes formed by L, L¹, and L² with alkali-metal 2,4-dinitrophenolates in mixed THF—CHCl₃ solutions (4: 1 by volume) are determined. Electroanalytical characteristics of ion-selective electrodes with hexadentate phosphoryl podands having different structures used as active components of their plasticized membranes are compared for cations of alkali and alkaline-earth metals. The IR spectra are described. The crystal structure of L is studied by X-ray diffraction.

The results of simulation of oxidation reactions of ethylene derivatives with different substituents (F atoms, CH₃O and CH₃ groups) and butadiene molecule with participation of ¹O₂ (¹Δg) have shown the possibility to realize different routes for the majority of the considered reactions. The largest product variety is obtained for butadiene and CH₃ derivatives of ethylene. For butadiene, along with 1,2-cycloaddition reactions resulting in four-membered dioxetane (which is realized in all cases), the possibility to form six-membered cyclic epidioxides (1,4-addition) and diepoxide products with two three-membered rings (epoxidation) has been found. The formation of hydroperoxide forms along with 1,2-addition reactions is also possible for all CH₃ derivatives of ethylene. Formation conditions and relative stability of the noted products have been analyzed for each case and certain features of the revealed reaction pathways with the transfer of two oxygen atoms have been discussed.

In this investigation, we have designed a series of benzene and borazines containing chromophores for employing in dye-sensitized solar cells (DSSCs). The optimized structures and photo-physical properties of these molecules have been explored by using the density functional theory method (B3LYP/6-311++G(d,p)). These dyes consist of electron-donor (benzene, borazine, fluorinated borazine) and -acceptor/anchoring (tricyanovinyl), connected by the π-conjugated linker as an electron spacer. The Natural Bond Orbital (NBO) analysis has also been employed for studying the origin of charge transfer. The time-dependent density functional theory (TD-DFT) method has also been used to calculate the electronic absorption spectra of these molecules. The maximum absorption wavelengths assign to HOMO → LUMO transition. The electronic coupling constant, electron injection and light harvesting efficiency have been computed by first principle researches. This revealed that the studied molecules would be efficient photosensitizers.

Clusters of atmospheric gases (N₂, CO, Ar) of different composition comprising 11 and 13 molecules have been systematically studied by means of MP2(full)/6-311+G** calculations. The effect of a meduim (a nitrogen or carbon monoxide atmosphere) on the properties of the gas molecule dimers has been revealed, and general trends in the formation of large clusters have been determined.

Vaporization of the complex between sodium dipivaloylmethanate and o-phenanthroline Na(thd)(phen) is studied using the Knudsen effusion method and mass spectral analysis of the gas-phase composition. Sublimation of the compound is found to occur congruently. Saturated vapor predominantly consists of o-phenanthroline molecules C₁₂H₈N₂, trimeric molecules Na₃(thd)₃, and a minor amount of Na₄(thd)₄ and Na(thd)(phen) molecules. The absolute partial pressures and enthalpies of sublimation of the gas-phase components, as well as the Δ_fG⁰(T) of formation of the complex from Na(thd)(s) and Phen(l), are calculated. The standard enthalpy of dissociation of gaseous Na(thd)(phen) into Na₃(thd)₃(g) and Phen(g) is estimated.

The gel formed in the synthesis of Mg(Fe_0.8Ga_0.2)₂O₄ powder from corresponding metal nitrates and glycine was studied by thermal and IR spectral analyses. Being a bidentate ligand, glycine was established to initiate the gel combustion reaction resulting in the oxide of the above composition. Based on the data on ΔH₂₉₈° and Cp of the reagents and reaction products, the thermodynamic parameters of this process were calculated.

Metal–carbon nanocomposites that represent FeCo alloy nanoparticles uniformly distributed over the carbon matrix, were prepared by the IR pyrolysis of precursors comprising polyacrylonitrile (PAN), iron acetylacetonate, and cobalt acetate (the metal ratio in the precursors was Fe: Co = 1: 1, 3: 1). The composition of FeCo alloy nanoparticles satisfies the tailored ratio Fe: Co. The FeCo phase is formed at synthesis temperatures in the range 500–600°С; at T ≤ 500°С only FCC-Co-base solid solutions are observed. The nanocomposites prepared at T ≥ 600°С simultaneously contain FeCo intermetallic nanoparticles and an insignificant amount of a FCC-Co phase or a cobalt-base solid solution phase. The saturation magnetization of FeCo/C metal–carbon nanocomposites is determined by the mean nanoparticle size and the alloy composition, and ranges from 36 to 64 (A m²)/kg (when Fe: Co = 1: 1) and from 35 to 52 (A m²)/kg (when Fe: Co = 3: 1) at synthesis temperatures in the range 600–800°С.

The NaCl–KI–K₂CrO₄ stable triangle was studied by differential thermal analysis. The melting temperature, melt composition, and specific melting enthalpy corresponding to the ternary eutectic were determined in the system. The compositions of crystallizing phases in the eutectic were confirmed by X-ray diffraction.

Phase formation in the system Li₂MoO₄–MgMoO₄–Sc₂(MoO₄)₃ was studied by X-ray powder diffraction analysis and differential thermal analysis. Ternary molybdate LiMgSc(MoO₄)₃ was synthesized, which crystallizes in the triclinic system (space group P\(\bar 1\)). In the Li₂Mg₂(MoO₄)₃–Li₃Sc(MoO₄)₃ section, a continuous solid solution in the rhombic system was found to form (space group Pnma).

Interfacial distribution of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y between aqueous solutions of their salts and solutions of functionalized ionic liquid, 1,11-bis(1-methylimidazol-3-yl)-3,6,9-trioxaundecane bis(hexafluorophosphate) has been studied. The stoichiometry of extracted complexes has been determined, the effect of HNO₃ concentration in aqueous phase on the efficiency of rare earth elements(III) recovery into organic phase has been considered.