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.     

Facile synthesis of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/TiO<Subscript>2</Subscript> core–shell nanobelts

We report a facile chemical approach for the synthesis of one-dimensional V₂O₅/TiO₂ core–shell nanobelts. The coated V₂O₅ nanobelts are synthesized by a hydrothermal method which is feasible for large-scale production. V₂O₅ nanobelts coated with a thin layer of TiO₂ sol are formed before sintering, and after sintering one-dimensional V₂O₅/TiO₂ core–shell nanobelts, composed of single-crystalline V₂O₅ nanobelts cores uniformly coated with anatase TiO₂ nanoparticle shells are obtained. The influences of the synthetic parameters, such as sintering temperature and titanium/vanadium mole ratios, on the morphology of the resulting products are investigated. Interestingly, the shape of single-crystalline of V₂O₅ nanobelts is totally preserved after sintering; the morphology can be readily controlled to be smooth or rough by altering the sintering temperature of the shells and titanium/vanadium mole ratio.     

The effect of gelatin as a chelating agent on the synthesis and characterization of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders prepared via sol–gel method

In this research, LiMn₂O₄ nanopowders were synthesized by the sol–gel method using gelatin as a chelating agent. Three categories of samples with various weight ratios of gelatin to the final product, 1:1, 2:1, and 3:1, have been synthesized. The produced gel was dried in a controllable oven with a slow slope up to 250??C and calcined at different temperatures. The results show that the amount of gelatin affects the structural properties such as the formation temperature of the spinel structure, the homogeneity of the size distribution and size of the particles. The sample with the weight ratio of 3:1 of gelatin to the final product has a lower temperature for the formation of LiMn₂O₄ with more homogeneity, and smaller particles with the average size of 70?nm, which is calcined at 750??C, while the samples with the weight ratios 2:1 and 1:1 have the average particle sizes of 75 and 89?nm, respectively.

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Hydrothermal synthesis and microstructure of α-Zn<Subscript>2</Subscript>SiO<Subscript>4</Subscript>:V crystal phosphor

A morphologically uniform single-phase crystal phosphor α-Zn₂SiO₄:V was prepared by one-pot hydrothermal synthesis. Energy dispersive analysis showed that a zinc silicate-base solid solution was formed with a vanadium content of 10 ± 1 at %. Its luminescence spectrum was a broad luminescence band in the region 400–700 nm with a peak near 540 nm.     

The effect of temperature on the formation of titanium dioxide structures on γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> surface

The effect of calcination temperature of hydrated gamma-aluminum oxide on the phase formation of surface structures and the content of titanium in them in the course of successive treatment of the initial matrix with TiCl₄ and H₂O was determined.     

Adsorption of chlorobenzene vapor on V<Subscript>2</Subscript>O<Subscript>5</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst under dynamic conditions

Adsorption dynamics of chlorobenzene vapors on a 5% V₂O₅/Al₂O₃ catalyst has been investigated using the frontal chromatography technique. The uptakes of chlorobenzene have been measured as a function of vapor concentration and adsorption equilibrium has been found to follow formally the Langmuir isotherm. The breakthrough time proved to be a linear function of the column length as expected. Breakthrough profiles have been reported for different experimental conditions and quantitatively fitted by a reduced lumped diffusion model. This model provides an analytical solution that facilitates engineering calculations. Model parameters show complex behavior as functions of stream characteristics and depend on column length. When empirical expressions relating model mass transfer coefficients with influencing variables are found the model demonstrates good accuracy in predicting column performance.     

Calorimetric studies on 2TeO<Subscript>2</Subscript>–V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Glasses of the composition 2TeO₂–V₂O₅ were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The glass transition and crystallization parameters were evaluated under non-isothermal conditions using DSC. X-ray diffraction studies confirmed the presence of partially oriented crystallites in the heat-treated glasses. Kauzmann temperature (lower bound for the kinetically observed glass transition) was deduced from the heating rate dependent glass transition and crystallization temperatures.     

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.     

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.     

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.     

Balance,uniformity, and asymmetry of the structure of volborthite Cu<Subscript>3</Subscript>(OH)<Subscript>2</Subscript>(V<Subscript>2</Subscript>O<Subscript>7</Subscript>)·2H<Subscript>2</Subscript>O

Four structural models of volborthite Cu₃(OH)₂(V₂O₇)·2H₂O (a = 10.646(2) Å, b = 5.867(1) Å, c = 14.432(2) Å, β = 95.19(1)°, V = 897.7(5) ų, Z = 4, R/R _w = 0.038/0.046) calculated in the space groups determined from the systematic absences are compared. Based on the structure balance and the similarity of constituting polyhedra, values of the R factor, and isotropic thermal parameters, the space group Ia is found to be preferable, which is the only possible asymmetric and uniform variant. Hydrogen atoms of OH-groups, oxygen atoms and, partially, hydrogen atoms of water are localized.     

Phase equilibria in the Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–CdO system and the thermal stability of Cd<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and CdNb<Subscript>2</Subscript>O<Subscript>6</Subscript>

Phase equilibria were studied in the Nb₂O₅–CdO system in the Nb₂O₅-rich region including CdNb₂O₆ and Cd₂Nb₂O₇. It was determined that CdNb₂O₆ and Cd₂Nb₂O₇ in air are stable to 1150 and 1120°C, respectively, and that, above these temperatures, there is solid-phase decomposition of niobates with CdO release in the gas phase. Along with the cadmium oxide evaporation, the Cd₂Nb₂O₇ decomposition is accompanied by the formation of cadmium metaniobate CdNb₂O₆ and the CdNb₂O₆ decomposition results in the formation of niobium oxide Nb₂O₅. No thermal events were observed in the differential thermal analysis curve for a 1: 1 CdNb₂O₆–Cd₂Nb₂O₇ mixture heated to 1100°C in air, which suggests that there are neither phase transformations in cadmium niobates, nor a eutectic within this temperature and concentration ranges. A study of the morphology of compacted samples of niobates determined specific conditions for producing dense composite ceramics, a mixture of niobates, that is suitable for using as a dielectric material.     

V<Subscript>3</Subscript>O<Subscript>7</Subscript> · H<Subscript>2</Subscript>O oxide nanostructures: Synthesis and study

Nanorods of orthorhombic V₃O₇ · H₂O with the parameters a = 16.805 Å, b = 9.428 Å, and c = 3.660 Å are prepared under hydrothermal conditions (T = 180–190°C, τ = 30–40 h) from the V₂O₅ · nH₂O/H₂C₂O₄ · 2H₂O composite. The particle diameter is 40–70 nm, and the length is several micrometers. The IR spectra, electric conductivity, and thermal properties of the nanorod powder are studied. In air V₃O₇ · H₂O begins to decompose at temperatures above 150°C, and at 350°C nanobelts V₂O₅ 40–100 nm wide and 40 µm long are formed. A mechanism of nanostructure formation is suggested.     

Effects of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> on the crystallization and structure of CaO–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass ceramics

Radiation-induced degradation of the weakly and strongly 4-vinylpyridine basic ion exchange resins by gamma radiolysis was investigated in the presence of air and liquid water. This study is focused on evaluating the radiolytic gases (H₂, CO, CO₂ and CH₄) and liquid products (water-solute TOC and NH₄ ⁺). The weakly basic resin yielded lower amounts of H₂ and CO and higher amounts of CO₂ than those of the strongly basic resin. Moreover, the strong basic resin tended to yield greater amounts of NH₄ ⁺. Resins were characterized by the FTIR spectroscopy technique and the results showed that the resins structures are relatively stable.     

Thermoelectric power and electrochemical studies on CdI<Subscript>2</Subscript>–Ag<Subscript>2</Subscript>O–V<Subscript>2</Subscript>O<Subscript>5</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> system

A quaternary super-ion-conducting system, 20CdI₂ − 80[xAg₂O − y(0.7V₂O₅ − 0.3B₂O₃)] where 1 ≤ x/y ≤ 3, has been prepared by melt quenching technique. The electrical conductivity measured was the order of 10⁻⁴  S/cm at room temperature. The values of silver-ion transport number obtained by electromotive force technique are nearly unity. The thermoelectric power and electrochemical studies were done on the CdI₂–Ag₂O–V₂O₅–B₂O₃ system. The discharge and polarization characteristics were examined for different cathodes to evaluate the utility of these cells as power sources for low energy applications.     

Investigation on properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–MWCNTs composites as cathode materials

An effective method to prepare the composites of multi-wall carbon nanotubes (MWCNTs) and vanadium pentoxide (V₂O₅) was presented. Vanadyl-triisopropoxide (VO(OC₃H₇)₃) was used as the starting material, MWCNTs pretreated with acids by a two-step process was used as the conductive ingredient. V₂O₅–MWCNTs composites were synthesized via a sol–gel method with solvent exchange and an ambient pressure drying technique. The samples were characterized by SEM, TEM, XRD, BET, Raman spectra and electrical resistivity measurement respectively. The experimental results indicate that the V₂O₅–MWCNTs nanocomposite has a fiber-like and tri-dimensional network structure. Its surface area is up to 189.7 m²/g when the MWCNTs’ content is 15 wt%. And MWCNTs are dispersed homogeneously in the composites. The electrical resistivity of the composites decreases from 1,239 to 765 Ω·cm when the MWCNTs’ content increases from 0 to 10 wt%. Thus MWCNTs can improve properties of V₂O₅ aerogels as the cathode material in lithium batteries.     

Synthesis and heat capacity study of stannates Dy<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> and Ho<Subscript>2</Subscript>Sn<Subscript>2</Subscript>O<Subscript>7</Subscript> in the range 370–1000 K

Stannates Dy₂Sn₂O₇ and Ho₂Sn₂O₇ are produced by solid-phase synthesis from Dy₂O₃ (Ho₂O₃)–SnO₂ stoichiometric mixtures by calcining at 1473 K. The molar heat capacity of holmium and dysprosium stannates is measured by differential scanning calorimetry (DSC) in the temperature range 370–1000 K. The experimental data are used to calculate thermodynamic properties (enthalpy change H°(T)–H°(370 K), entropy change S°(T)–S°(370 K), and the reduced Gibbs free energy Φ°(T)) of the synthesized compound.     

Supported MgO–V<Subscript>2</Subscript>O<Subscript>5</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for oxidative propane dehydration: Effect of the molar Mg : V ratio on the phase composition and catalytic properties of samples

The physicochemical properties of V₂O₅/Al₂O₃ and MgO–V₂O₅/Al₂O₃ supported catalysts (Mg : V = 1 : 1, 2 : 1, and 3 : 2) obtained by consecutive impregnation of the support with solutions of vanadium and magnesium precursors are studied using a complex of mutually complementary methods (XRD, Raman spectroscopy, UV–Vis spectrometry, and TPR-H₂). The effect of the formation of surface magnesium vanadates of various composition and structure on the catalytic properties of the supported vanadium oxide catalysts in the oxidative dehydrogenation of propane is studied. The introduction of magnesium in the samples and an increase in its content, accompanied by a change in the structure of the surface vanadium oxide phases from polymeric VO₆/VO₅ species to surface metavanadate species, magnesium metavanadate, and further to magnesium divanadate, significantly affects their catalytic properties in the reaction of the oxidative dehydrogenation of propane to propylene.     

Preparation,characterization and catalytic studies of V<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> xerogel composite

In this work, we report the synthesis, characterization and catalytic properties of a vanadium oxide–silicon oxide composite xerogel prepared by a soft chemistry approach. In order to obtain such material, we submitted a vanadium pentoxide gel previously synthesized via protonation of metavanadate species to an “in situ” progressive polycondensation into silica gel. The material has been characterized by X-ray diffraction, infrared spectroscopy, thermogravimetric analysis and scanning electron microscopy. Further, the catalytic activity of this material was evaluated for the epoxidation of styrene and cyclooctene using iodosylbenzene, hydrogen peroxide and m-chloroperbenzoic acid as the oxidizing agent.     

Targeted synthesis ultrafine α- and γ-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> having different morphologies

Reactions of nitric acid solutions of bismuth with alkalis have been studied. The effect caused by coprecipitation conditions in the presence of additional agents (EG, PEG 400, or PEG 8000) and without on the phase composition and morphology of α- and γ-Bi₂O₃ has been determined.