Determination of the enthalpy of fusion of K<Subscript>3</Subscript>TaO<Subscript>2</Subscript>F<Subscript>4</Subscript> and KTaF<Subscript>6</Subscript>

Areas of fusion and crystallization peaks of K₃TaO₂F₄ and KTaF₆ were measured using the DSC mode of a high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities, considering the temperature dependence of the calorimeter sensitivity, values of the fusion enthalpy of K₃TaO₂F₄ at the fusion temperature of 1181 K of (43 ± 4) kJ mol⁻¹ and of KTaF₆ at the fusion temperature of 760 K of (8 ± 1) kJ mol⁻¹ were determined.     

Thermochemical properties of the Fe-analogue of cryolite, Na3FeF6

Relative enthalpies for low-and high-temperature modifications of Na₃FeF₆ and for the Na₃FeF₆ melt have been measured by drop calorimetry in the temperature range 723–1318 K. Enthalpy of modification transition at 920 K, δ_trans H(Na₃FeF₆, 920 K) = (19 ± 3) kJ mol⁻¹ and enthalpy of fusion at the temperature of fusion 1255 K, δ_fusH(Na₃FeF₆, 1255 K) = (89 ± 3) kJ mol⁻¹ have been determined from the experimental data. Following heat capacities were obtained for the crystalline phases and for the melt, respectively: C _p(Na₃FeF₆, cr, α) = (294 ± 14) J (mol K)⁻¹, for 723 = T/K ≤ 920, C _p(Na₃FeF₆, cr, β) = (300 ± 11) J (mol K)⁻¹ for 920 ≤ T/K = 1233 and C _p(Na₃FeF₆, melt) = (275 ± 22) J (mol K)⁻¹ for 1258 ≤ T/K ≤ 1318. The obtained enthalpies indicate that melting of Na3FeF6 proceeds through a continuous series of temperature dependent equilibrium states, likely associated with the production of a solid solution.      

Enthalpy of formation of BaCe<Subscript>0.9</Subscript>In<Subscript>0.1</Subscript>O<Subscript>3−δ</Subscript>(s)

Enthalpy of formation of the perovskite-related oxide BaCe_0.9In_0.1O_2.95 has been determined at 298.15 K by solution calorimetry. Solution enthalpies of barium cerate doped with indium and mixture of BaCl₂, CeCl₃, InCl₃ in ratio 1:0.9:0.1 have been measured in 1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe_0.9In_0.1O_2.95 has been calculated as −1611.7±2.6 kJ mol⁻¹. Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium cerate doped by indium from the mixture of binary oxides is Δ_ox H ⁰ (298.15 K)=−36.2±3.4 kJ mol⁻¹.     

Hydrothermal synthesis and thermodynamic properties of 2CaO·3B<Subscript>2</Subscript>O<Subscript>3</Subscript>·H<Subscript>2</Subscript>O

2CaO·3B₂O₃·H₂O which has non-linear optical (NLO) property was synthesized under hydrothermal condition and identified by XRD, FTIR and TG as well as by chemical analysis. The molar enthalpy of solution of 2CaO·3B₂O₃·H₂O in HCl·54.572H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HCl·54.501H₂O and of CaO in (HCl+H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s), and H₂O(l), the standard molar enthalpy of formation of −(5733.7±5.2) kJ mol⁻¹ of 2CaO·3B₂O₃·H₂O was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method.     

Quantum-chemical modelling of nanotubes of titanium silicocarbides Ti<Subscript>2</Subscript>SiC,Ti<Subscript>3</Subscript>SiC<Subscript>2</Subscript>, and Ti<Subscript>4</Subscript>SiC<Subscript>3</Subscript>

Atomic models are proposed for nanotubes of the titanium silicocarbides Ti₂SiC, Ti₃SiC₂, and Ti₄SiC₃, and their electronic structure and interatomic interactions are investigated by the density functional tight-binding method (DFTB) in comparison with the corresponding crystalline phases. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 2, pp. 88-92, March-April, 2009.     

Hydrothermal synthesis of one-dimensional (1D) Na<Subscript>x</Subscript>TiO<Subscript>2</Subscript> nanostructures

Nanorods of sodium titanium dioxide bronze Na_xTiO₂ were synthesized by the hydrothermal treatment of the amorphous TiO₂·nH₂O gel with 10 M NaOH followed by ultrasonication in 0.1 M HCl and thermal treatment (500°C, 10 h). The thermal treatment of the nanorods does not change the morphology of the particles. According to the electron diffraction data, the Na_xTiO₂ nanorods grow along the c axis.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 71–73, January, 2005.     

Molar heat capacity and thermodynamic properties of crystalline Ho(Asp)Cl<Subscript>2</Subscript>·6H<Subscript>2</Subscript>O

The molar heat capacity, C _p,m, of a complex of holmium chloride coordinated with L-aspartic acid, Ho(Asp)Cl₂·6H₂O, was measured from 80 to 397 K with an automated adiabatic calorimeter. The thermodynamic functions H _T-H _298.15 and S _T-S _298.15 were derived from 80 to 395 K with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimeter (DSC) and thermogravimetric (TG) technique, and the mechanism of thermal decomposing of the complex was determined based on the structure and the thermal analysis experiment.     

Determination of the enthalpy of fusion of K3TaF8 and K3TaOF6

The areas of the fusion and crystallization peaks of K₃TaF₈ and K₃TaOF₆ have been measured using the DSC mode of the high-temperature calorimeter (SETARAM 1800 K). On the basis of these quantities and the temperature dependence of the used calorimetric method sensitivity, the values of the enthalpy of fusion of K₃TaF₈ at temperature of fusion 1039 K: Δ_fusH_m(K₃TaF₈; 1039 K) = (52 ± 2) kJ mol⁻¹ and of K₃TaOF₆ at temperature of fusion 1055 K: Δ_fusH_m(K₃TaOF₆; 1055 K) = (62 ± 3) kJ mol⁻¹ have been determined.     

Theoretical study on the reaction mechanism of (CH<Subscript>3</Subscript>)<Subscript>3</Subscript>CO<Superscript>.</Superscript> radical with NO

The reaction mechanism of (CH₃)₃CO^. radical with NO is theoretically investigated at the B3LYP/6-31G* level. The results show that the reaction is multi-channel in the single state and triplet state. The potential energy surfaces of reaction paths in the single state are lower than that in the triple state. The balance reaction: (CH₃)₃CONO⇔(CH₃)₃CO^.+NO, whose potential energy surface is the lowest in all the reaction paths, makes the probability of measuring (CH₃)₃CO^. radical increase. So NO may be considered as a stabilizing reagent for the (CH₃)₃CO^. radical.     

Formation of Composites Based on CsHSO<Subscript>4</Subscript> and Cs<Subscript>5</Subscript>H<Subscript>3</Subscript>(SO<Subscript>4</Subscript>)<Subscript>4</Subscript> and Mechanism of Their Protonic Conduction

Vibrational spectra of finely divided amorphous CsHSO₄,Cs₅H₃(SO₄)₄ · H₂O, and composites based on these are measured and analyzed. An analysis of the spectra indicates the occurrence of substantial changes in the system of hydrogen bonds and in the spectral range of the sulfate group of acid sulfates in the composites. Structural dynamics of the SO₄ tetrahedrons is in full conformance with protonic conduction and the data of x-ray diffraction analyses accompanied by differential scanning calorimetry. It is shown that mobility of protons in the composites increases. A mechanism of the formation of the composites and their conduction is proposed.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 640–645.Original Russian Text Copyright © 2005 by Ponomareva, Lavrova, Burgina.     

Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> powders by the complex polymerization method: synthesis,characterization and morphology

Lanthanum-modified bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂, BLTO) powders were prepared by the complex polymerization method. The structure and morphology of BLTO powders were investigated by X-ray diffraction and scanning electron microscopy. The complexation of citric acid with the metallic cations was detected by Fourier transformed infrared (FT-IR). The thermal analyses of obtained gels were investigated by differential thermal gravimetric (DTG). The pure and normally stoichiometric phase of BLTO powders could be obtained at relatively low temperature of 550–700 °C even if the bismuth content is not excess in the starting precursors, while the secondary phase could be detected at lower and higher calcination temperatures. The shape of the BLTO grains is similarly to platelet in Bi-layer structure and stoichiometry BLTO was detected by the analysis of energy dispersive spectrometry.     

Electronic structure and chemical bonding in K<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>8</Subscript>

The calculations of the electronic structure of layered polyvanadate K₂V₃O₈ were made employing the spin-polarized tight-binding LMTO method. Calculated magnetic moment for K₄V₆O₁₆ compound phase equals 1.97 μ_B. V-O interactions were established to be dominating in the chemical bonding generation in this polyvanadate according to the estimated crystal orbital overlap population. The covalent bonds V(2)-V(2) in V(2)₂O₇ groups and electron density localization on vanadium atoms in isolated pyramids V(1)O₅ were found.     

Catalytic Activity of WO<Subscript>3</Subscript> and MoO<Subscript>3</Subscript> with Pt and Pd Additives in Oxidation of Hydrogen

We have shown that WO₃ and MoO₃ with Pt or Pd additives exhibit high catalytic activity in the reaction of H₂ oxidation. In the temperature range 313 K to 353 K, we have studied the kinetic behavior of the reaction on 0.1 mass % Pt(Pd)/WO₃ and Pt(Pd)/MoO₃ samples. We have established that the kinetics of H₂ oxidation on these catalysts correspond to an Eley - Rideal mechanism. __________ Translated from Teoreticheskaya i Eksperimental'naya Khimiya, Vol. 41, No. 5, pp. 313–316, September–October, 2005.     

Synthesis of ammonia from natural gas at atmospheric pressure with doped ceria–Ca<Subscript>3</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>–K<Subscript>3</Subscript>PO<Subscript>4</Subscript> composite electrolyte and its proton conductivity at intermediate temperature

A new type of oxide–salt composite electrolyte, yttrium doped ceria YDC–Ca₃(PO₄)₂–K₃PO₄, was developed and demonstrated for its promising use for ammonia synthesis. Using this composite electrolyte, ammonia was synthesized from nitrogen and natural gas at atmospheric pressure in the solid-state proton conducting cell reactor, and the optimal condition for ammonia production was determined . The evolved rate of ammonia is up to 6.95×10⁻⁹ mol s⁻¹ cm⁻².     

Magnetorheological characteristics of aqueous suspensions that contain Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanoparticles

This investigation examines the magnetorheological (MR) characteristics of Fe₃O₄ aqueous suspensions. Magnetite particles (Fe₃O₄) were synthesized using a colloidal process and their sizes were determined to be normally distributed with an average of 10 nm by TEM. Experimental results reveal that the MR effect increases with the magnetic field and suspension concentration. The yield stress increases by up to two orders of magnitude when the sample is subjected to a magnetic field of 146 Oe/mm. In comparison with other published results, concerning a concentration of approximately 10–15% v/v, this study demonstrates that the same increase can be obtained with a concentration of nano-scale particles as low as 0.04% by volume. The viscosity was increased by an order of magnitude while the shear rate remained low; however, the increase decayed rapidly as the shear rate was raised. Finally, the MR effect caused by DC outperformed that caused by AC at the same current.     

Preparation of novel visible-light-driven In<Subscript>2</Subscript>O<Subscript>3</Subscript>–CaIn<Subscript>2</Subscript>O<Subscript>4</Subscript> composite photocatalyst by sol–gel method

Novel visible-light-activated In₂O₃–CaIn₂O₄ photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In₂O₃–CaIn₂O₄ composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm). The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed that the In₂O₃–CaIn₂O₄ composite samples with different In₂O₃ and CaIn₂O₄ content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light activity for decomposition of methyl orange. The significant enhancement in the In₂O₃–CaIn₂O₄ photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in the In₂O₃ and CaIn₂O₄ coupling semiconductors.     

Temperature dependence of the polarization resistance of the O<Subscript>2</Subscript>,Au/La<Subscript>0.88</Subscript>Sr<Subscript>0.12</Subscript>Ga<Subscript>0.82</Subscript>Mg<Subscript>0.18</Subscript>O<Subscript>2.85</Subscript> electrode system

The impedance of a porous gold electrode in contact with solid electrolyte La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 and the effect of the manufacture conditions on its polarization resistance are studied at 600–800°C in air. The overall oxygen reaction rate on a gold electrode is described as the sum of two partial constituents, namely, the oxygen exchange at the gas/electrolyte interface at the gold/gas/electrolyte triple-phased boundary.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 190–197.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Khlupin, Beresnev.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.     

Phase relations in the CoO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> system in subsolidus area

Thermal properties of Co₂FeV₃O₁₁ have been reinvestigated. It has been proved that this compound does not exhibit polymorphism. It melts incongruently at the temperature of 770±5°C and the phase with lyonsite type structure is the solid product of this melting. Phase relations in the whole subsolidus area of the CoO–V₂O₅–Fe₂O₃ system have been determined. The solidus area projection onto the component concentration triangle plane of this system has been constructed using the DTA and XRD methods. 15 subsidiary subsystems can be distinguished in this system.     

Two color up-conversion emissions of Er<Superscript>3+</Superscript>-doped Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanopowders prepared by non-aqueous sol-gel method

Er³⁺-doped Al₂O₃ nanopowders have been prepared by the non-aqueous sol-gel method using the aluminum isopropoxide as precursor, acetylacetone as a chelating agent, nitric acid as a catalyzer, and hydrated erbium nitrate as a dopant under isopropanol environment. The different phase structure, including three crystalline types of (Al, Er)₂O₃ phases, α, γ, θ, and an Er–Al–O stoichiometric compound phase, Al₁₀Er₆O₂₄, was observed for the 0.01–0.5 mol% Er³⁺-doped Al₂O₃ nanopowders at the sintering temperature of 1,000 °C. The green and red up-conversion emissions centered at about 523, 545 and 660 nm, corresponding respectively to the ²H_11/2, ⁴S_3/2→⁴I_15/2 and ⁴F_9/2→⁴I_15/2 transitions of Er³⁺, were detected by a 978 nm semiconductor laser diodes excitation. With increasing Er³⁺ doping concentration from 0.01 to 0.1 mol%, the intensity of the green and red emissions increased with a decrease of the intensity ratio of the green to red emission. When the Er³⁺ doping concentration rose to 5 mol%, the intensity of the green and red emissions decreased with an increase of their intensity ratio. The maximum intensity of both the green and red emissions with the minimum of intensity ratio was obtained, respectively, for the 0.1 mol% Er³⁺-doped Al₂O₃ nanopowders composed of a single α-(Al,Er)₂O₃ phase. The intensity ratio of the green emission at 523 and 545 nm increased monotonously for all Er³⁺ doping concentrations. The two-photon absorption up-conversion process was involved in the green and red up-conversion emissions of the Er³⁺-doped Al₂O₃ nanopowders.     

Calorimetric study of melts in the System KF - K<Subscript>2</Subscript>NbF<Subscript>7</Subscript>

The relative enthalpies of melts in the system KF - K₂NbF₇ were measured by drop-calorimetry at the temperatures 1058, 1140 and 1208 K as a function of composition. Heat capacities of melted mixtures and enthalpies of mixing were determined using the experimental data. The molar heat capacity of melts diverges slightly from additivity. The molar enthalpy of mixing of melts shows small negative deviation from ideality which decreases with decreasing temperature. The thermal effect at mixing was assigned predominantly to association reactions producing more complex fluoroniobate anions.