Structural relaxation of PbO–WO3–P2O5 glasses

The structural relaxation of three compositional series of PbO–WO₃–P₂O₅ glasses with composition (0.5 ? x/2)PbO·xWO₃·(0.5 ? x/2)P₂O₅, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5; 0.5PbO·xWO₃·(0.5 ? x)P₂O₅, x = 0, 0.1, 0.2, and 0.3; and (0.5 ? x)PbO·xWO₃·0.5P₂O₅, x = 0, 0.1, 0.2, 0.3, 0.4, and 0.5 was studied by thermomechanical analysis. The structural relaxation was studied in the transformation region using the Tool–Narayanaswamy–Moynihan’s and Tool–Narayanaswamy–Mazurin’s models. The relaxation function of Kohlrausch Williams and Watts was used. The parameters of both models were calculated by nonlinear regression analysis of thermodilatometric curves measured by thermomechanical analyzer under the constant load. Both models very well describe the experimental data. It was found that the modulus is increasing with increasing amount of WO₃ in all glasses. On the contrary, the width of the spectrum of relaxation times is decreasing with increasing amount of WO₃ in all studied glasses. Both models possess the values of metastable melt thermal expansion coefficient equal to their experimental value.     

Impedance spectroscopy of V2O5–Bi2O3–BaTiO3 glass–ceramics

The glasses within composition as: (80 − x)V₂O₅/20Bi₂O₃/xBaTiO₃ with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition (T_g) increases with increasing BaTiO₃ content. Synthesized glasses ceramic containing BaTi₄O₉, Ba₃TiV₄O₁₅ nanoparticles of the order of 25–35 nm and 30–46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO₃ content by impedance spectroscopy measurements. The hopping frequency, ω_h, dielectric constant, ε′, activation energies for the DC conduction, E_σ, the relaxation process, E_c, and stretched exponential parameter β of the glasses samples have been estimated. The, ω_h, β, decrease from 51.63 to 0.31 × 10⁶ (s⁻¹), 0.84 to 0.79 with increasing BaTiO₃ respectively. Otherwise, the E_σ, increase from 0.279 to 0.306 eV with increasing BaTiO₃. The value of dielectric constant equal 9.5·10³ for the 2.5BaTiO₃/77.5V₂O₅/20Bi₂O₃ glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined.     

Raman spectroscopic study of CuO–V2O5–P2O5–CaO glass system

In order to evidence the structural changes induced by CuO and V₂O₅ in the phosphate glass network and their modifier or former role, x(CuO·V₂O₅)(100 − x)[P₂O₅·CaO] glass system was prepared and investigated using Raman spectroscopy (0 ≤ x ≤ 40 mol%).Raman spectra of the studied glasses present the specific bands of the phosphate glasses at low concentration of transition metal (TM) ions, but at higher concentration (x > 7 mol%) a strong depolymerization of the phosphate network appears; non-bridging oxygen atoms are involved in VOP and CuOP bonds and new short units are formed. For a high concentration of V₂O₅ (x > 10 mol%) the Raman bands of V₂O₅ prevail in the spectra; this fact suggests that vanadium oxide imposes its structural units in the network acting thus as a network glass former.2D correlation analysis was also applied for the concentration-dependent Raman spectra in order to verify the assignments of the vibration modes and to find correlations in the changes induced by TM ions content. 2D correlation maps indicate a good correlation between the bands at ∼705 cm⁻¹ assigned to POP stretching vibration and at ∼1175 cm⁻¹ assigned to PO₂ groups which suggest the depolymerization of the phosphate network. The correlation between the 1270 cm⁻¹ and 930 cm⁻¹ bands also suggests that V₂O₅ oxide is responsible for PO bonds breaking and POV formation.     

Phases in the subsolidus area of the system CuO–V2O5–Fe2O3

The phase equilibria in the solid state in the system FeVO₄?CCu₃V₂O₈ and FeVO₄?CCuO have been determined. Based on the obtained DTA and XRD analysis results and some additional research, a phase diagram in the whole subsolidus area of the system CuO?CV₂O₅?CFe₂O₃ has been worked out. Eighteen subsidiary subsystems can be distinguished in this ternary system. Basic properties of the obtained phases with howardevansite- and lyonsite-type structure have been investigated by DTA, IR, and SEM methods.     

Phase Equilibria in the System Fe2O3–V2O5 –WO3 in the Solid State

DTA and X-ray phase diffraction methods were used to construct a solidus area projection onto the component concentration triangle plane of the system Fe₂ O₃-V₂ O₅-WO₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase Equilibria in The System La2O3–K2O–P2O5

The ternary system La₂O₃–K₂O–P₂O₅ has been examined by thermal, X-ray, IR and microscopic methods. The existence of three double potassium-lanthanum phosphates, K₃La(PO₄)₂, KLa(PO₃)₄ and K₂La(PO₃)₅ has been confirmed, and the phase diagram of the ternary system La₂O₃–K₂O–P₂O₅ over the composition range LaPO₄–K₃PO₄–P₂O₅ has been determined. This revised version was published online in August 2006 with corrections to the Cover Date.     

Phase equilibria in the oxide system Nd2O3–K2O–P2O5

A phase equilibria diagram of the partial system NdPO₄–K₃PO₄–KPO₃ has been developed as part of the research aimed at determining the phase equilibrium relationships in the oxide system Nd₂O₃–K₂O–P₂O₅. The investigations were conducted using thermoanalytical techniques, X-ray powder diffraction analysis and reflected-light microscopy. Three isopleths existing between: K₃Nd(PO₄)₂–K₄P₂O₇, NdPO₄–K₅P₃O₁₀ and NdPO₄–K₄P₂O₇ have been identified in the partial NdPO₄–K₃PO₄–KPO₃ system. Previously unknown potassium-neodymium phosphate “K₄Nd₂P₄O₁₅” has been discovered in the latter isopleth section. This phosphate exists in the solid phase up to a temperature of 890 °C at which it decomposes into the parent phosphates NdPO₄ and K₄P₂O₇. Four invariant points: two quasi-ternary eutectics, E₁ (1057 °C) and E₂ (580 °C) and two quasi-ternary peritectics, P₁ (1078 °C) and P₂ (610 °C), occur in the NdPO₄–K₃PO₄–KPO₃ region.     

V2O5负载量对V2O5/Al2O3氧化活化正庚烷催化裂解反应的影响

采用X射线衍射, 低温氮气吸脱附, 氨气程序升温脱附和吡啶吸附红外光谱分析方法对不同活性组分负载量V2O5/Al2O3的性质进行了表征. 根据表面VOx单元密度, 推测V2O5负载量为20%-25% (w)对应着V2O5/Al2O3表面达单层覆盖状态; V2O5的负载使Al2O3表面Lewis酸量减少, 并出现Br?nsted酸, 对应着氧化态VOx单元中的V―OH; 随着负载量的增加, Brφnsted酸量增加至负载量为20%时达到最大值. 对V2O5/Al2O3中活性组分负载量对其氧化活化正庚烷催化裂解反应的影响进行了考察. 结果表明, 在V2O5负载量为20%-25%时,V2O5/Al2O3的引入对正庚烷在HZSM-5平衡剂上催化裂解反应的促进作用最明显, 此时VOx单元在V2O5/Al2O3表面形成单层覆盖状态, 可提供最大量的表面晶格氧, 因而对正庚烷具有最强的氧化活化作用; V2O5负载量继续增加形成体相的V2O5和AlVO4, 不利于晶格氧参与正庚烷的转化, 因而反应性能有所下降.     

Synthesis and structural investigation of a unique columnar phase in the Bi2O3–TeO2–V2O5 System

A new columnar phase Bi(11.65)Te(1.35)V(5)O(34-δ) (δ ～ 1.3) containing VO(4) tetrahedra has been identified for the first time in the Bi(2)O(3)-TeO(2)-V(2)O(5) system. The phase formation and the extent of substitution of Te(4+) for Bi(3+) ions in order to stabilize V(5+) in this composition have been confirmed by the single crystal analysis, combined with the powder X-ray diffraction of the solid state synthesized bulk crystalline samples. The oxide crystallizes in a monoclinic crystal system, space group P2/c, with unit cell parameters a = 11.4616(7) ?, b = 5.7131(3) ?, c = 23.5090(18) ?, β = 101.071° (6) (Z = 2). The structure retains the basic features of the columnar oxides with the presence of [Bi(10.65)Te(1.35)O(14)](n)(9.35n+) columns along the (010) direction, surrounded by (VO(4)) tetrahedra placed in the planes parallel to (100) and (001), with an isolated bismuth atom in between the columns. The composition with a limited Te(4+) substitution, Bi(11.65)Te(1.35)V(5)O(34-δ) (δ ～ 1.3), exists with a surprisingly high oxygen deficiency as compared to the stoichiometrically known columnar oxides such as Bi(13)Mo(4)VO(34), Bi(12)Te(1)Mo(3)V(2)O(34), and Bi(11)Te(2)Mo(2)V(3)O(34). The structure of this interesting member of the columnar family of oxides based on the single crystal X-ray diffraction and the Raman spectroscopic studies indicates the possibility of the distribution of the oxygen vacancies among the VO(4) tetrahedral units. Further confirmation for the formation of vanadium stabilized columnar structures has been provided by the successful preparation of Bi(11.65)Te(1.35)V(4)CrO(34-δ) (δ ～ 0.83) and Bi(11.65)Te(1.35)V(4)WO(34-δ) (δ ～ 0.83) phases. Preliminary investigation of the photocatalytic efficiencies of the oxides Bi(11.65)Te(1.35)V(5)O(34-δ), Bi(11.65)Te(1.35)V(4)CrO(34-δ), and Bi(11.65)Te(1.35)V(4)WO(34-δ) revealed moderate photocatalytic activities for the decomposition of the dyes such as Rhodamine B under UV-vis light irradiation.     

Kinetics of nonisothermal crystallization of Cs2O–Fe2O3–P2O5 glasses

The crystallization kinetics of Cs₂O–Fe₂O₃–P₂O₅ glasses containing 12.5–27 mol% Cs₂O were studied by using differential scanning calorimetry under nonisothermal conditions. Strong dependence of activation energy with temperature was observed, indicating the complex nature of the crystallization process. The various crystallization products were identified by X-ray diffraction technique. CsFeP₂O₇ was found to be the major crystalline phase in all cases. The overall activation energy obtained by classical model-free kinetic method was compared with that of isoconversional method; and from the results, the dependence of activation energy on extent of reaction and average temperature was delineated.     

Physical–chemical and catalytic properties of deposited MoO3 and V2O5

The deposition of molybdenum and vanadium oxides onto fumed silica, titania, and alumina as supports through dry milling has been carried out. The structure of prepared compositions has been investigated by means of XRD, DTA?CTG, FTIR, and UV?CVis spectroscopy, nitrogen adsorption. The deposited crystal phases are sufficiently uniformly distributed on support surface. The supported oxides are subjected to dispersion in process of milling to the state of oligomeric or isolated species. Milled bulk and deposited MoO₃ (first of all, on alumina) possesses improved catalytic performance in process of epoxidation of 1-octene. Vanadium pentoxide also has higher activity in this process.     

V2O5-MoO3体系的电子探针分析

V_2O_5—MoO_3体系是重要的氧化催化剂体系之一.许多作者分别用X射线衍射对V_2O_5—MoO_3体系进行了物相分析,测定了有关的晶体结构,用热分析或熔点显微镜研究其相图等.据文献报道,V_2O_5—MoO_3体系中当MoO_3含量低于约40mol％时,可形成MoO_3在V_2O_5中的固溶体相;当 MoO_3含量在约50mol％或稍高时,可形成中间化合物相;当MoO_3含量更高时,则以MoO_3相为主.但是,文献中对于V—Mo—O中间化合物相的化学组成的认识存在着分岐,有些作者归结为V_2MoO_8,另一些作者则归结为V_9Mo_6O_(40).这两种分子式表示法的差异首先在于V和Mo的原子比不     

Phase Relations in The System Al2(MoO4)3–V2O5

The phase equilibria established in the system Al₂ (MoO₄ )₃ –V₂ O₅ throughout the whole component concentration range up to 1000°C were investigated by DTA and XRD methods. The results are presented in the form of a phase diagram. This revised version was published online in August 2006 with corrections to the Cover Date.     

Adsorption of Chlorobenzene on V2O5/γ-Al2O3 Catalyst

Isotherms of chlorobenzene adsorption on V₂O₅/-Al₂O₃ catalyst within the 0.07-18 Pa range of adsorbate partial pressure were measured, and certain thermodynamic characteristics of adsorption were found.     

异丁烷脱氢V2O5/γ-Al2O3催化剂的研究

五氧化二钒;异丁烷脱氢V2O5/γ-Al2O3催化剂的研究     

The effect of mechanical activation on the thermal reactions of P2O5–Al2O3–Fe2O3–Na2O phosphate glasses

The effect of mechanical activation on the structure and thermal reactions of glasses has been studied on the example of Na–Al–Fe phosphate glasses. These glasses are used in nuclear technology for immobilization of radioactive waste. The glasses were activated by grinding in a planetary mill. Mechanical activation causes a decrease of the T _g temperature as well as of the glass crystallization temperature. The type of crystalline phases formed and the quantitative proportions between them are changing. Analysis of inter-atomic interactions in the structure of glass was applied to explain the observed regularities governing the crystallization of the activated glasses.     

V2O5/γ-Al2O3和V2O5/SiO2负载型催化剂对异丁烷的催化脱氢性能

V2O5/γ-Al2O3和V2O5/SiO2负载型催化剂对异丁烷的催化脱氢性能;V2O5/γ-Al2O3; V2O5/SiO2; 异丁烷; 脱氢     

Adsorption of benzene on the V2O5/γ-Al2O3 catalyst

Adsorption of benzene on the V₂O₅/-Al₂O₃ catalysts was studied in the temperature interval from 443 to 493 K and at partial pressures of the adsorbate ranging from 1 to 400 Pa. The adsorption isotherms were plotted. The isosteric heats and various entropy characteristics of adsorption were determined. Mobility of benzene in the adsorption layer is restricted compared to the model of ideal dimeric gas. The adsorbed amounts of benzene and chlorobenzene are compared.     

Reinvestigation of Phase Equilibria in the V2O5–ZnO System

A diagram of phase equilibria established in a two-component oxide system V_{2 5}–ZnO has been worked out applying differential thermal analysis and X-ray phase analysis as well as depending on investigations carried out with the aid of high-temperature X-ray attachment and scanning electron microscope linked to an X-ray microanalyser. This revised version was published online in July 2006 with corrections to the Cover Date.