The influence of the organolithium reagent nature on the possibility of the O→C<Subscript>sp</Subscript> migration of the R<Subscript>3</Subscript>Si group in propynes HC≡CCH<Subscript>2</Subscript>OSiR<Subscript>3</Subscript>

A possibility of the O→C_sp 1,4-migration of the R₃Si group in silyl ethers of terminal acetylenic alcohols upon treatment with organolithium reagents (RLi) was studied. In the case of 3-trimethylsilyloxypropyne, depending on the nature of RLi, the heterolysis of the Si—O bond occurs either by the action of acetylide formed as a result of deprotonation with the formation of 3-trimethylsilylprop-2-yn-1-ol trimethylsilyl ether, or by the action of the metalation agent with the formation of propargyl alcohol. The realization of the O→C_sp 1,4-migration of the Me₃Si group requires the use of mild organolithium reagents (lithium hexamethyldisilazanide and diisopropylamide). Silyl ethers having steric hindrance at the carbon atom bonded to the reaction center or around the silicon atom do not react with the studied organolithium reagents.     

Regularities of formation of complex oxides with the fluorite structure in the ZrO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

The crystal and local structures of the complex oxides (1–x)ZrO₂ ? xY₂O₃ (YSZ) (x = 0.08–0.40) prepared by precipitation from solutions of metal salts followed by heat treatment in air were comprehensively studied by X-ray diffraction and Raman spectroscopy. Despite the same crystal structure type of the YSZ powders (cubic system, space group \(Fm\overline 3 m\) (225)), there are differences in the local structure of the samples. Comparison of the Raman spectra recorded at different laser excitation wavelengths provided the conclusion that the peaks observed in the Raman spectra of the YSZ samples with high yttrium content (x = 0.18–0.40) are likely to be due to luminescence of the powders.     

Reactivity of the oxides in the ternary V<Subscript>2</Subscript>O<Subscript>5</Subscript>-CuO-α-Sb<Subscript>2</Subscript>O<Subscript>4</Subscript> system in air

In this work it has been established which compounds finally are formed in air in the two-component CuO-V₂O₅ and CuO-α-Sb₂O₄ systems. Unknown thermal properties of CuV₂O₆, Cu₂V₂O₇ and Cu₁₁V₆O₂₆ have been established. Reactivity of the oxides and phase relations in the ternary V₂O₅-CuO-α-Sb₂O₄ system in air have been studied by using XRD and DTA methods. The results have showed the reaction of V₂O₅, CuO with α-Sb₂O₄ does not produce any compound where all the three oxides would be involved. It has been established that the α-Sb₂O₄ reacts and forms binary phases independently with CuO or V₂O₅. On the base of these results the investigated system was divided into subsidiary subsystem in which CuSb₂O₆ remains at equilibrium in the solid state with other phases formed in corresponding binary systems.     

The sensor properties of SnO<Subscript>2</Subscript> · In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocomposite oxides in the detection of hydrogen in air

The sensor properties of In₂O₃ · SnO₂ polycrystalline films having different compositions were studied in the detection of 2% hydrogen in air over the temperature range 330–530°C. Films containing 19% In₂O₃ were most sensitive to hydrogen. The temperature dependence of the sensitivity of sensors passed a maximum, the position of which depended on the composition of the film. The temperature at which sensor sensitivity was maximum decreased as the content of indium oxide increased. This temperature was 485°C for the SnO₂ film and 425°C for the In₂O₃ film. The response and relaxation times of sensors also decreased as the amount of In₂O₃ in the composite metal oxide film increased. Possible mechanisms of the sensor sensitivity of the films are discussed.     

Phase Diagram of the NaNO<Subscript>2</Subscript>—KNO<Subscript>3</Subscript> System in the 0 to 1 Molar Fraction Range of Concentrations of KNO<Subscript>3</Subscript>

The temperature dependence of the phase composition of KNO₃—NaNO₂ mixtures in the 0 to 1 molar fraction range of concentrations of KNO₃ is investigated. A phase diagram of the KNO₃—NaNO₂ binary system in the range of concentrations from 0 to 1 molar fractions of KNO₃ is drawn on the basis of DTA results. The composition of the eutectic mixture and its melting temperature is determined experimentally.     

Study of the effect of methods for liquid-phase synthesis of nanopowders on the structure and physicochemical properties of ceramics in the CeO<Subscript>2</Subscript>–Y<Subscript>2</Subscript>O<Subscript>3</Subscript> system

Two alternative chemical synthesis methods—cryotechnological coprecipitation of hydroxides and cocrystallization of salts—were used for preparing (CeO₂)_1–x (Y₂O₃) _x nanopowders (x = 0.10, 0.15, 0.20) with a mean coherent scattering domain size of ~7–11 nm and S _sp = 2.1–97.5 m²/g. From these nanopowders, ceramic nanomaterials with mean coherent scattering domain sizes of ~61–85 nm were synthesized. It was studied how the phase composition, microstructure, and electrical transport properties of the produced samples depend on the Y₂O₃ content of a CeO₂-based solid solution and on the synthesis method. It was shown that, in the series (CeO₂)_1–x (Y₂O₃) _x (x = 0.10, 0.15, 0.20), the solid solution (CeO₂)_0.90(Y₂O₃)_0.10 has the highest ionic conductivity with the ion transport number t _i = 0.73 (600°C). In its physicochemical characteristics, this ceramic can be used as a solid electrolyte of intermediate-temperature fuel cells.     

Formation of the center of ignition in a CH<Subscript>3</Subscript>Cl–Cl<Subscript>2</Subscript> mixture under the action of UV light

The dependence of temperature on time is investigated using a microthermocouple at different distances from a UV light source in a mixture of chlorine and chloromethane. These relationships give an idea of the size and location of a center of photoignition. It is found that if the size of the reaction vessel in the direction of the luminous flux is much greater than the dimensions of the ignition center, the thermal expansion of a reacting gas mixture has a huge impact on such photoignition parameters as the critical concentration limits and the critical intensity of UV radiation. It is found that by increasing the length of the vessel, some chlorinated combustible mixtures lose the ability to ignite when exposed to UV light.     

Tensimetric investigation of the CrCl<Subscript>3</Subscript>—Cl<Subscript>2</Subscript> system in the temperature range of 600–1200 K

The sublimation pressure of chromium trichloride was measured by the static method with a quartz membrane-gauge manometer in the temperature range of 875–1230 K. An approximating equation for the sublimation pressure vs. temperature was found. The enthalpy (259.4±4 kJ mol^–1) and the entropy (224.2±3.5 J mol^–1 K^–1) of sublimation at 298 K were calculated. For the process 2 CrCl₃(g) + Cl₂(g) = 2 CrCl₄(g), the following values were obtained: _r H°₂₉₈ = –207.1±11.6 kJ mol^–1 and _r S°₂₉₈ = –173.6±10 5 J mol^–1 K^–1.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1561–1564, August, 2004.     

Synthesis and investigation of the heat capacity of Sm<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> in the 346–1050 K range

Optimal conditions for the synthesis of Sm₂Sn₂O₇ with pyrochlore crystal structure by solid-phase reactions were determined. The effect of temperature (346–1050 K) on the molar heat capacity of samarium stannate was studied by differential scanning calorimetry. Thermodynamic properties of Sm₂Sn₂O₇ in the temperature range under study were determined using the experimental data.     

Specific features of the crystal and local structures of compounds formed in the Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–HfO<Subscript>2</Subscript> system

The crystal and local structures of compounds formed in the Dy₂O₃–HfO₂ system (at molar ratios from 1: 3 to 3: 1) in the course of isothermal annealing of X-ray amorphous mixed hydroxides at temperatures up to 1600°C have been studied. At the molar ratio Dy₂O₃: HfO₂ from 1: 3 to 1: 1, crystallization leads to formation of single-phase defect fluorite solid solutions nDy₂O₃ ? mHfO₂ with clearly pronounced nonequivalence of parameters of local environment of Dy³⁺ and Hf⁴⁺ cations. It has been found that Dy₂H₂O₇ (Dy₂O₃: HfO₂ = 1: 2) samples have a tendency to pyrochlore-type ordering in both the cationic and anionic sublattices.     

The effect of synthesis conditions on the structure of compounds formed in the Dy<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> system

Crystallization and phase transition processes taking place in the Dy₂O₃–TiO₂ system during the isothermal annealing of the precursors synthesized by co-precipitation were studied. The phase composition of the obtained powders is determined by not only the chemical composition of the precursor (Dy₂O₃: TiO₂ ratio) and annealing temperature but also by the procedure of precursor synthesis determining the uniformity of Dy and Ti distribution in the precursor precipitate. Higher homogeneity of precursor particles provides the formation of almost single-phase nanocrystaline dysprosium titanate (Dy₂TiO₅, Dy₂Ti₂O₇) powders at annealing temperatures of 800–1000°C.     

Quantum-chemical study of the role of conical intersections in photoisomerization processes of the [RuCl<Subscript>5</Subscript>NO]<Subscript>2−</Subscript> complex

The potential surfaces of the ground and lowest excited states of the [RuCl₅NO]_2? complex ion were studied by density functional theory. The conical intersections between the potential surfaces of the ground and lowest excited states were found and characterized. The possible routes from the conical intersection points to the ground state and metastable bond isomers were traced. A preliminary scheme, describing photoisomerizations in the complex, was suggested.     

Formation of nanocrystals in the ZrO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O system

Formation of zirconia nanocrystals in the course of thermal treatment of an X-ray amorphous zirconium oxyhydroxide was studied. It was shown that the formation of tetragonal and monoclinic polymorphs of ZrO₂ in the temperature range from 500 to 700°C occurs owing to dehydration and crystallization of amorphous hydroxide. An increase of the temperature up to 800°C and higher activates mass transfer processes and, as a result, activates the nanoparticle growth and increases the fraction of the phase based on monoclinic modification of ZrO₂ due to mass transfer from the nanoparticles with the non-equilibrium tetragonal structure. Herewith, formed ZrO₂ nanocrystals with monoclinic structure have a broad size distribution of crystallites, and the average crystallite size after thermal treatment at 1200°C for 20 min is about 42 nm.     

Study of the kinetic aspects of formation of calcium monosilicate in the model system CaSO<Subscript>4</Subscript>·2H<Subscript>2</Subscript>O-Na<Subscript>2</Subscript>O·SiO<Subscript>2</Subscript>

The possibility and kinetic aspects of formation of X-ray amorphous calcium monosilicate in the model system CaSO₄·2H₂O-Na₂O·SiO₂ at room temperature were studied.     

Effect of the sequence of chemical transformations on the spatial segregation of components and formation of periclase-spinel nanopowders in the MgO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–H<Subscript>2</Subscript>O System

Specific features of the process in which oxide nanopowders are formed in a hydrothermal treatment of coprecipitated magnesium and iron oxides were studied. It was shown that the rate at which oxide nanoparticles are formed increases when reagents structurally close to the final product are used. It was found that, with the hydrothermal treatment of coprecipitated magnesium and iron hydroxides at 450°C combined with the subsequent thermal treatment in air at temperatures of 400–600°C, it is possible to obtain a homogeneous mixture of nanocrystalline powders based on an iron-containing spinel phase and magnesium oxide.     

The characterization and property of polystyrene compounding of α-Fe<Subscript>2</Subscript>O<Subscript>3 </Subscript>in the nano-scale

-Fe₂O₃/polystyrene composite nanoparticles were synthesized in an oil/water microemulsion. Their structure was characterized by transmission electron microscopy, X-ray diffraction and Fourier transform-infrared spectrometry. An Ubbelonde viscometer, a Gouy balance and a model 283 potentiostat/galvanostat measured the molecular weight of the composite nanoparticles and their magnetic and electrical characteristics respectively.     

Regime of superhigh reactivity of the YBa<Subscript>2</Subscript>Cu<Subscript>3</Subscript>O<Subscript>6 + δ</Subscript> superconductor toward the components of air

Physicochemical features of the YBa₂Cu₃O_{6 + δ} superconductor synthesized via ceramic route and subjected to a kind of modification by long-term exposure to an atmosphere with low pH₂O have been studied by X-ray diffraction, thermal analysis, and magnetometry. The resulting material had a high degree of saturation with air components at room temperature and 30% humidity, up to 1.5 wt % in 30 days, which is not inherent in YBa₂Cu₃O_{6 + δ}.     

Photochemistry of the IrCl<Subscript>6</Subscript><Superscript>2−</Superscript> complex in aqueous solutions in the presence of the bromide anions

Laser flash photolysis (308 nm) was applied to study photochemistry of the IrCl₆ ²⁻ complex in aqueous solutions in the presence of the Br⁻ anions. The formation of the Br₂ ^·− radical anions in the reaction between the Br⁻ ion and secondary radical pair formed after the photon absorption by the initial complex was observed. The Br₂ ^·− radical anions decay both in recombination and in the reaction with the initial IrCl₆ ²⁻ complex.     

Features of high-temperature behavior in NdCaCoO<Subscript>4</Subscript>—the catalyst of the partial oxidation of methane to syngas

The peculiarities of the high-temperature (373–1173 K) behavior and transport properties of NdCaCoO₄, which is a highly active and selective catalyst of the partial oxidation of methane to syngas, were considered. A relationship between its thermal and electrophysical properties and the structure and defectiveness of the oxygen sublattice was found. The electric conductivity of this compound, which is a two-dimensional analog of perovskite, was found to be almost independent of the oxygen pressure (\(p_{O_2 } = 10^{ - 4} - 1\) atm) and to increase with temperature, reaching ～100 S/cm at 1173 K. The temperature dependence of the conductivity of the n-type semiconductor NdCaCoO₄ has two thermoactivation regions (373–573 and 573–873 K), in which the activation energy is almost doubled (0.46 and 0.81 eV, respectively). The discovered tendencies that determine the unique catalytic properties of this material are probably due to the change in the energy spectrum of this compound. The hypothetical reasons for this change are discussed.