Composition and formation kinetics of strontium polyvanadates in vanadium(IV,V) solutions

The phase and chemical compositions of the precipitates forming in the Sr(VO₃)₂-VOCl₂-H₂O system in the V⁴⁺/V⁵⁺ = 0.11–9 range at 80–90°C are reported. At pH 1–3 and V⁴⁺/V⁵⁺ = 0.25−9, the general formula of the precipitated compounds is Sr _x V _y ⁴⁺ V_12−y ⁵⁺O_31−δ·nH₂)(0.37 ≤ x ≤ 1.0, 1.7 ≤ y ≤ 3.0, 0.95 ≤ δ ≤ 2.1). Polyvanadates containing the largest amount of vanadium(IV) are obtained at an initial V⁴⁺/V⁵⁺ ratio of 9 and pH 1.9. Precipitation from solutions at pH 3 takes place only in the presence of the VO²⁺ ion, and the highest precipitation rate is observed at V⁴⁺/V⁵⁺ = 0.11. The process is controlled by a second-order reaction on the polyvanadate surface. Under hydrothermal conditions at 180°C, Sr_0.25V₂O₅·1.5H₂O nanorods are obtained from solutions with a V⁴⁺/V⁵⁺ molar ratio of 0.1 at pH 3. The nanorods, 30–100 nm in diameter and up to 2–3 μm in length, have a layered structure with an interlayer spacing of 10.53 ± 0.08 ?.     

Potassium Vanadates of Mixed Valence as Sulfuric Acid Catalyst Precursors

The kinetics of hydrolytic precipitation of potassium vanadates K_xV₁₂O_31-δ ·nH₂O(0 < x ≤ 2.25; 0 <δ ≤ 1.15) from a KVO₃ solution at pH = 1.7 and 80°C in the presence of K₂SO₄ and VOSO₄ is controlled by second and third order reactions respectively occurring on the precipitate surface. This difference is due to the effect of VO²⁺ ions on the polymer anion [V₁₂ O_31-δ]ⁿ formation. Potassium vanadates K_xV₁₂O_31-δ ·nH₂O and K_xV₃O_8-δ·nH₂O (1.02 ≤ x ≤ 1.91; 0 ≤ δ ≤ 0.22) can be used as vanadium-containing precursors for sulfuric acid catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Composition and formation kinetics of sodium polyvanadates in vanadium(IV, V) solutions

We study how VO²⁺ ions affect the composition and formation kinetics of polyvanadate precipitates in solutions with 1 ≤ pH ≤ 3 at 80–90°C. The compounds have the general formula Na_2.1?x H_xV _y ⁴⁺ V _12?y ⁵⁺ O_31?δ. nH₂O (0 ≤ x ≤ 1.1, 0.2 ≤ y ≤ 2.3, 0.1 ≤ δ ≤ 1.4). The maximal vanadium(IV) concentration in the precipitates y = 2.2 and 2.3) is achieved for the V⁴⁺/V⁵⁺ ratio in the solution equal to 0.5 and 0.3 and pH of 1.7 and 3.0, respectively. The polyvanadate precipitation at pH 1.7 has a long induction period, which is not observed when V⁴⁺/V⁵⁺ > 0.02. In the solutions with pH 3.0, the precipitation occurs only when VO²⁺ are added. The processes are controlled by second-order reactions on the polyvanadate surface.     

Hydrolytic precipitation of calcium polyvanadates from vanadium(IV) and vanadium(V) solutions

The effect of VO²⁺ ions on the composition and kinetics of calcium polyvanadate precipitation from solutions with 1.5 ≤ pH ≤ 9 at 80–90°C has been studied. For 1,5 ≤ pH < 3 and V⁴⁺/V⁵⁺ = 0.11–9, the precipitated compounds have the general formula Ca _x V _y ⁴⁺ V _12?y ⁵⁺ O_31?δ · nH₂O (0.8 ≤ x ≤ 1.06, 2 ≤ y ≤ 3, 0.94 ≤ δ ≤ 1.5). The maximum vanadium(IV) proportion (y = 3) in the precipitates is achieved when V⁴⁺/V⁵⁺ = 0.5?1.0 in the solution and pH is 3. Polyvanadate precipitation at pH 1.7 has a long induction period (up to 30 min), which is not observed for V⁴⁺/V⁵⁺ > 0.1. Precipitation in solutions with pH 3 occurs only when VO²⁺ ions are added, with a maximum rate near V⁴⁺/V⁵⁺ = 0.2 and in presence of chloride ions. The processes are controlled by a secondorder reaction on the polyvanadate surface.     

Phase formation in the system Zn(VO<Subscript>3</Subscript>)<Subscript>2</Subscript>–HCl–VOCl<Subscript>2</Subscript>–H<Subscript>2</Subscript>O

The phase and chemical compositions of precipitates formed in the system Zn(VO₃)₂–HCl–VOCl₂–H₂O at pH 1?3, molar ratio V⁴⁺: V⁵⁺ = 0.1?9, and 80°C were studied. It was shown that, within the range 0.4 ≤ V⁴⁺: V⁵⁺ ≤ 9, zinc vanadate with vanadium in a mixed oxidation state forms with the general formula Zn_xV⁴⁺ _yV⁵⁺ _2-yO₅ ? nH₂O (0.005 ≤ x ≤ 0.1, 0.05 ≤ y ≤ 0.3, n = 0.5?1.2). Vanadate Zn_xV₂O₅ ? nH₂O with the maximum tetravalent vanadium content (y = 0.30) was produced within the ratio range V⁴⁺: V⁵⁺ = 1.5?9.0. Investigation of the kinetics of the formation of Zn_xV₂O₅ ? nH₂O at pH 3 determined that tetravalent vanadium ions VO2+ activate the formation of zinc vanadate, and its precipitation is described by a second-order reaction. It was demonstrated that, under hydrothermal conditions at pH 3 and 180°C, zinc decavanadate in the presence of VOCl₂ can be used as a precursor for producing V₃O₇ ? H₂O nanorods 50–100 nm in diameter.     

Synthesis and photocatalytic activity of Ti[1 ? x]VxO[2 ? y]Cy whiskers in hydroquinone oxidation in aqueous solutions

Ti_1−x V _x O_2−y C _y (0 ≤ x ≤ 0.10 and x = 0.50) whiskers having the anatase structure were synthesized via thermolysis of vanadium-doped titanium glycolate of composition Ti_1−x V _x (OCH₂CH₂O)₂ (0 ≤ x ≤ 0.10 and x = 0.50). The starting reagents used to prepare Ti_1−x V _x (OCH₂CH₂O)₂ were mixtures of coprecipitated titanium and vanadyl hydroxides, which were heated in ethylene glycol at T ≤ 200°C: (1 − x)TiO(OH)₂ + xVO(OH)₂ + 2HOCH₂CH₂OH = Ti_1−x V _x (OCH₂CH₂O)₂ + 3H₂O↑. Thermolysis of vanadium-doped titanium glycolate in various gas media over a wide range of temperatures is useful to prepare titania samples doped with both vanadium and carbon to form a phase of the general composition Ti_{1 − x} V _x O_{2 − y} C _y whiskers prepared by thermolyzing Ti_{1 − x} V _x (OCH₂CH₂O)₂ in air at 450°C were found to have a high photocatalytic activity in hydroquinone oxidation in aqueous solutions irradiated in the UV spectral range; the photocatalyst’s activity increases with increasing vanadium concentration. When hydroquinone was irradiated in the blue, the maximal catalytic activity was discovered in a sample of composition Ti_0.50V_0.50O_2−y C _y . Quantum-chemical calculations support experimental data that the double doping of titania (Ti_1−x V _x O_2−y C _y ) enhances its photocatalytic activity compared to undoped anatase or anatase doped in one sublattice: Ti_1−x V _x O₂ and TiO_2−y C _y .     

Synthesis and thermolysis of substitutional solid solutions (Cu1?yMy)2(OH)PO4·xH2O (x = 0.1?0.2; M = Zn, Co, Ni)

Substitutional solid solutions (Cu_1−y Zn _y )₂(OH)PO₄·xH₂O (0 ≤ y ⩽ 0.26, x = 0.1−0.2), (Cu_1−y Co _y )₂(OH)PO₄·xH₂O (0 ≤ y ≤ 0.10, x = 0.1−0.2), and (Cu_1−y Ni _y )₂(OH)PO₄·xH₂O (0 ≤ y ≤ 0.08, x = 0.1−0.2) were synthesized. The unit cell parameters of the resulting phosphates were determined, and their IR absorption spectra were measured. The reactants were H3PO4 and mixtures of hydrous carbonates of the appropriate metals. Thermolysis of the solid solutions was examined with (Cu_1−y Co _y )₂(OH)PO₄·xH₂O (0 ≤ y ≤ 0.10, x = 0.1−0.2) as an example.     

Y2O3 and MgO co-doped ceria based electrolytes

Electrolytes of Ce_1-x-y Y _x Mg _y O_2-0.5x-y were prepared with citrate method and were characterized by inductively coupled plasma-atomic emission spectrometry, energy dispersive spectrometry, powder X-ray diffraction, and impedance spectroscopy. The effect of composition on the structure, conductivity, and stability of the electrolytes were investigated. When 0≤x≤ about 0.2 and 0≤y≤ about 0.05, the electrolytes were all single phase materials of ceria-based solid solution. However, when y> about 0.05, the electrolytes became two-phase materials, Y³⁺ and Mg²⁺ co-doped ceria-based solid solution and free MgO. The sample with nominal composition of Ce_0.815Y_0.065Mg_0.12O_2-d showed ionic conductivity at 973 K close to or even a little higher than that of similarly prepared Ce_0.9Gd_0.1O_1.95, but had lower cost of raw materials and a little better stability in reducing atmosphere. The existing of free MgO improved the stability of the electrolytes in reducing atmosphere, but too much free MgO reduced the conductivity.     

Existence region, structure, and properties of YBa(Cu1? x Fe x )2O5+δ and (Y1? y Ba y )2 CuFeO5+δ solid solutions

We study the effect of Y³⁺ ↔ Ba²⁺ and Cu²⁺ ↔ Fe³⁺ substitutions on the structure, thermal expansion, electrical conductivity, and thermal e.m.f. of layered ferrocuprate YBaCuFeO_{5 + δ} · YBa(Cu_1−x Fe _x )₂O_{5 + δ} solid solutions with 0.45≤x≤0.55 are formed. The unit cell parameters, thermal expansivity, and oxygen nonstoichiometry index of the YBaCuFeO_{5 +δ} phase (δ) are almost independent of variations in the cationic composition of this phase. The electrical conductivity of layered yttrium barium ferrocuprate increases, whereas the activation energy of conductivity decreases in response to Ba²⁺ → Y³⁺ and Cu²⁺ → Fe³⁺ substitutions (with increasing copper(III) proportion in samples). The thermal e.m.f. of ceramics decreases when composition deviates from the cationic stoichiometry (YBaCuFeO_{5 +δ}). Original Russian Text ? A.I. Klyndyuk, E.A. Chizhova, V.M. Kononovich, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1672–1676.     

Synthesis and Properties of The Solid Solutions Formed in The Fe2V4O13–Cr2V4O13 System

DTA and XRD studies of the Fe₂V₄O₁₃–Cr₂V₄ O₁₃ system have shown that continuous solid solutions of a Fe_2–xCr_xV₄O₁₃ type, bearing a Fe₂ V₄ O₁₃ structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe₂ V₄ O₁₃ structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe_2–x Cr_x V₄ O₁₃ type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr³⁺ ion incorporation. The solid product of melting Fe_2–x Cr_x V₄ O₁₃ solid solutions for 0.2<x >1.2 is the Fe_1–x Cr_x VO₄ solution phase, and for x ≤0.2 and x ≥1.4 – the Fe_1–x Cr_x VO₄ phase as well as FeVO₄ or CrVO₄ , respectively. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of Ln1 ? xSrxGa0.5 ? y/2Al0.5 ? y/2MgyO3 ? δ (Ln = La, Pr, Nd; x, y = 0.10, 0.15)

Phase composition, electroconductivity, oxygen ion transport number, and microhardness of samples of Ln_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} (Ln = La, Pr, Nd; x, y = 0.10, 0.15) synthesized by a ceramic methods are studied. Methods of x-ray diffraction analysis and scanning electron microscopy reveal the La-containing samples to be homogeneous and have a perovskite structure. Magnesium does not dissolve in Pr-and Nd-containing systems but forms an individual phase based on magnesium oxide. Apart from magnesium oxide, in these systems there form extrinsic phases, specifically, LnSrGa₃O₇ and an unknown phase. The electroconductivity of La_{1 − x} Sr_xGa_{1 − y} Mg_yO_{3 − δ} decreases after substituting Al for Ga. Ceramic La_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_3−δ is a purely ionic conductor in the temperature interval 500 to 1000°C; Nd_xSr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} has predominantly ionic conduction; and the predominant type of conduction in Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} is electronic below 700–800°C, with the contribution of ionic conduction increasing at higher temperatures. Substituting Al for Ga raises the hardness of ceramics under study. Among the compositions studied, La_0.85Sr_0.15Ga_0.45Al_0.45Mg_0.10O_{3 − δ} and La_0.85Sr_0.15Ga_0.425Al_0.425Mg_0.15O_{3 − δ} exhibit a combination of electroconductivity and hardness that is optimal for application as electrolyte at reduced temperatures (600–800°C). The Pr_{1 − x} Sr_xGa_{0.5 − y/2}Al_{0.5 − y/2}Mg_yO_{3 − δ} system possesses mixed ionic-electronic conduction and high hardness, which makes it appealing for application as oxygen-penetrable membranes. Original Russian Text ? Yu.V. Danilov, A.D. Neuimin, L.A. Dunyushkina, L.A. Kuz’mina, N.S. Zybko, Z.S. Martem’yanova, A.A. Pankratov, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 1, pp. 57–65.     

Structural features of the formation of La1?xCaxFeO3?δ (0 ≤x ≤ 0.7) hetero valent solid solutions

A synthesis method with the use of polymer-salt compositions (calcination temperature 800°C) provides the preparation of various solid solutions of a La_1−x Ca _x FeO_3−δ series in the 0≤ x≤ 0.7 range, which belong to the perovskite structure type. A morphotropic phase transition occurs from the orthorhombic perovskite modification (0≤ x ≤ 0.4) to the cubic one (0.5 ≤ x≤ 0.7). A growing number of microdistortions in the perovskite structure and the formation of a microblock structure in the morphotropic phase transition region are observed with increasing degree of calcium substitution for lanthanum. Calcination of solid solutions with x = 0.6 and 0.7 at temperatures above 1000°C in the air or under conditions of reduced oxygen partial pressure (laboratory vacuum of 10⁻³ Torr) results in the formation of a nanostructured state with coherently grown blocks of perovskite and Grenier phase, which is due to irreversible oxygen loss.     

Volume and compressibility effects in the formation of metal-EDTA complexes

We used precise measurements of ultrasonic velocity and density to study the complexation of ethylendiaminetetraacetic acid (EDTA) with Mg²⁺, Ca²⁺, Sr²⁺, and Ba²⁺ at 25‡C and pH 12. From these measurements we obtained the changes in the molar concentration increment of the ultrasonic velocity δA, the apparent molar adiabatic compressibility δK_sΦ, and the apparent molar volume δV_Φ of complex formation. The hydration contributions δ(AV_h) to the volume effect of binding range from 39.6 to 46.6 cm³-mol^-1 while the hydration contribution to the adiabatic compressibility change in the binding, δ(δK_h), ranges from 103.9X 10^-4 to 131.1 X 10^-4 cm³-mol^-1-bar^-1. These data are interpreted in terms of dehydration of interacting molecules,i.e., transfer of water molecules from the hydration shells of cations and EDTA into the bulk water. The ratio δ(δV_h)/ δ(δV_h) is in the range 0.35 to 0.38 bar, indicating a dominant contribution from the dehydration of charged atomic groups in the volume and the compressibility effects of complex formation.     

The homogeneity range of lyonsite-type phase existing in the CrVO4 - Co3V2O8 system

In the work presented here, the way of obtaining the phase with general formula Co_3+1.5xCr_2–x(VO₄)₄ (0 ≤ × < 0.4) is demonstrated. A new phase is detected in CrVO₄ - Co₃V₂O₈ that is formed in one of the intersection of the ternary CoO - V₂O₅ - Cr₂O₃ system. Monophasic Co₃Cr₂(VO₄)₄ (Co_3+1.5xCr_2−x(VO₄)₄, where × = 0) was obtained from both a mixture comprising CrVO₄ and Co₃V₂O₈ as well as from the mixture of CoV₂O₆ with CoCr₂O₄. The Co_3+1.5xCr_2−x(VO₄)₄ is isotypic with the those demonstrating the lyonsite-type structure. The temperature of melting for the new compound was established using the DTA methods.      

Typical data of a new microporous material obtained from gels with titanium and silicon

The aim of this work is the synthesis and the characterization of a microporous material obtained from gels with titanium and silicon: NTS (titanosilicate). The structure of NTS zeotype is similar to that of AM-1 and JDF-L1 (titanosilicates). The synthesis were carried out with gels of composition: 3.5Na₂O–yTiO₂–4.48HCl–xSiO₂–110H₂O with 1.0≤x≤12.0 and 0.2≤y≤0.7. The temperature of reaction was 190±2°C.     

Homogeneity regions of yttrium and ytterbium manganites in air

Homogeneous solid solutions and heterogeneous systems of the general formula R_{2 − x} Mn _x O_{3 ± δ} (0.90 ≤ x ≤] 1.10 for R = Y and 0.88 ≤ x ≤ 1.14 for R = Yb; Δx = 0.02) were produced by ceramic synthesis from oxides in air within the temperature range 900–1400°C. The solubility boundaries of simple oxides R₂O₃ (R = Y, Yb), Mn₃O₄, and binary oxide RMn₂O₅ in yttrium and ytterbium manganites RMnO_{3 ± δ} were determined X-ray powder diffraction of these solutions and systems. The results were presented as fragments of phase diagrams of the systems Y-Mn-O and Yb-Mn-O in air. The solubility of Y₂O₃ and Mn₃O₄ in YMnO_{3 ± δ} was found to increase with increasing temperature, and the solubility of Yb₂O₃ and Mn₃O₄ in YbMnO_{3 ± δ} to be insensitive to varying temperature. It was suggested that the solubility of Y₂O₃ and Mn₃O₄ in YMnO_{3 ± δ} and of Yb₂O₃ and Mn₃O₄ in YbMnO_{3 ± δ} is caused by crystal structure defects of yttrium and ytterbium manganites and their related oxygen nonstoichiometry. In dissolving RMn₂O₅ in RMnO_{3 ± δ} (R = Y, Yb) in air within a narrow (∼20°C) temperature range adjacent to the RMn₂O₅ = RMnO₃ + 1/3Mn₃O₄ + 1/3O₂ equilibrium temperature, the solubility of RMn₂O₅ in RMnO_{3 ± δ} ecreases abruptly until almost zero. Conclusion is made that structural studies are necessary necessary to determine the oxygen nonstoichiometry δ of R_{2 − x} Mn _x O_{3 ± δ} solid solutions as a function of x and synthesis temperature; together with the results of this work, these studies will allow one to construct unique crystal-chemical models of these solid solutions.     

Hydrothermal synthesis, structure and property of nano-BaTiO3-based dielectric materials

A series of Ba_1-xSr_xTi_1-yZr_yO₃ (0≤x≤0.5, 0≤y≤0.4) and BA_1?xZn_xTi_1?ySn_yO₃ (0≤x≤0.3, 0≤y≤0.3) solid solutions were synthesized by low-temperature/low-pressure hydrothermal method below 170°C, 0.8 MPa. XRD pattern and cell parameters-composition figures of these prepared powders demonstrated that they are completely miscible solid solutions based on BaTiO₃. Furthermore, TEM showed that they have a shape of uniform, substantially spherical particles with an average particle size of 70 nm in diameter. The sintered ceramics of those powders doped by Sr²⁺ and Zr⁴⁺ or Zn²⁺ and Sn⁴⁺ have dielectric constant twelve times higher than and dielectric loss 1/6 those of pure BaTiO₃ phase at room temperature.     

Electrochemical properties and state of paramagnetic centers in copper-modified complex vanadium and titanium oxides

Complex vanadium and titanium oxides modified by copper ions are studied by the electrochemical and ESR methods. Oxides Cu _x V_2?y Ti _y O_5?δ·nH₂O (0<y<1.33) have a layered structure and oxides Cu _x Ti_1?y V _y O_5+δ·nH₂O (0<y<0.25), an anatase structure. The intercalation of cations Cu²⁺ into the hydrates leads to oxidation of V⁴⁺. According to ESR data, V⁴⁺ exists in the oxides in the form of VO²⁺ and an octahedral surround of oxygen (V⁴⁺?O₆), respectively. The electroreduction of ions of d-elements and chemisorbed oxygen in the oxides is analyzed. The intercalation of cations Cu²⁺ alters the content of V⁴⁺ and the chemisorption ability of the oxides. Possible reasons for this phenomenon are discussed.     

Calculations of chemical equilibria in heparin-arginine-H<Subscript>2</Subscript>O-NaCl and MCl<Subscript>2</Subscript>-heparin-arginine-H<Subscript>2</Subscript>O-NaCl systems (M = Ca<Superscript>2+</Superscript>, Mg<Superscript>2+</Superscript>) in a physiological solution

Chemical equilibria in the high-molecular-weight heparin (Na₄hep)-arginine (HArg)-H₂O-NaCl and MCl₂-Na₄hep-HArg-H₂O-NaCl systems of electrolytes (M = Ca²⁺, Mg²⁺) were calculated by the method of mathematical simulation of chemical equilibria from representative planned pH-metric titration experiment at 2.30 ≤ pH ≤ 10.50 in a physiological solution medium in the presence of 0.154 M NaCl as a background electrolyte at 37°C. The initial concentrations of the basic components were n × 10⁻³ M (n ≤ 4).