Solid-state phase equilibria in the V2O5−Fe8V10W16O85 system

Phase equilibria being established in the solid state in the system V₂O₅?Fe₈V₁₀W₁₆O₈₅ were examined by X-ray phase powder diffraction and DTA. It has been found that the system of interest is a real two-component system with an eutectic temperature 620±5°C.     

Phase equilibria up to the solidus line in the system Fe2O3−Fe8V10W16O85

Phase equilibria up to the solidus line in the system Fe₂O₃?Fe₈V₁₀W₁₆O₈₅ were determined by means of X-ray phase powder diffraction and differential thermal analysis. This system is one of the intersections of the three-component system Fe₂O₃?V₂O₅?WO₃. The studies revealed that this is not a real binary system, even in the solid state.     

Phase equilibria up to the solidus line in the system Fe2WO6−Fe8V10W16O85

Phase equlibria in the solid state in the system Fe₂WO₆?Fe₈V₁₀W₁₆O₈₅ were studied by means of X-ray phase powder diffraction and differential thermal analysis, This system is one of the intersections of the three-component system Fe₂O₃?V₂O₅?WO₃. The investigation demonstrated that the system is not a real two-component system even below the solidus line.     

Reaction Mechanism of Fe8W10W16O85 Synthesis

The reaction mechanism of the synthesis of Fe₈V₁₀W₁₆O₈₅ was studied by means of XRD, IR spectroscopy and DTA techniques. It was found that the intermediate in the reaction may be either FeVO₄ or FeVO₄ admixed with an unidentified phase X, depending on the reaction temperature. The IR spectrum of the phase Fe₈V₁₀W₁₆O₈₅ is reported for the first time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Formation and properties of the Fe<Subscript>8</Subscript>V<Subscript>10</Subscript>W<Subscript>16–x</Subscript>Mo<Subscript>x</Subscript>O<Subscript>85</Subscript> type solid solution

Solid solution phases of a formula Fe₈V₁₀W_16–xMo_xO₈₅ where 0≤x≤4, have been obtained, possessing a structure of the compound Fe₈V₁₀W₁₆O₈₅. It was found on the base of XRD and DTA investigations that these solution phases melted incongruently, with increasing the value of x, in the temperature range from 1108 (x=0) to 1083 K (x=4) depositing Fe₂WO₆ and WO₃. The increase of the Mo⁶⁺ ions content in the crystal lattice of Fe₈V₁₀W₁₆O₈₅ causes the lattice parameters a=b contraction with cbeing almost constant. IR spectra of the Fe₈V₁₀W_16–xMo_xO₈₅ solid solution phases have been recorded.     

Phase Equilibria in the System V2O5–Fe8V10W16O85 and Some Properties of the Fe8V10W16O85 Phase

A phase diagram of the V₂O₅–Fe₈V₁₀W₁₆O₈₅ system were carried out using XRD and DTA methods. In addition, an indexing of Fe₈V₁₀W₁₆O₈₅ powder diffraction pattern was made and its basic crystallographic parameters were determined. Finally, the phase was studied using IR spectroscopy. This revised version was published online in July 2006 with corrections to the Cover Date.     

Subsolidus area of the system CdO - V2O5 - Fe2O3

Phase diagrams in the subsolidus area of the systems FeVO₄ - CdO and FeVO₄ - Cd₂V₂O₇ have been deduced using the results of XRD and DTA analyses. On the basis of these diagrams and some additional verifying research, a projection of the subsolidus area of the CdO - V₂O₅ - Fe₂O₃ system onto the plane that comprises the components’ concentration triangle has been presented. The H-type phase is the only phase formed in this system. It co-exists at equilibrium with other phases in six subsidiary subsystems.      

Study of phase equilibria established up to the solidus line in the system Fe2V4O13−WO3

The phase equilibria established up to the solidus line in the system Fe₂V₄O₁₃−WO₃, one of the intersections of the three-component system Fe₂O₃−V₂O₅−WO₃, have been studied. The system appears not to be a real two-component system.

---

Zusammenfassung Es wurde eine Untersuchung des Phasengleichgewichtes durchgeführt, welches bezüglich der Solidus-Linie im System Fe₂V₄O₁₃−WO₃, einer der Zwischenbereiche im Dreikomponentensystem Fe₂O₃−V₂O₅−WO₃, nachgewiesen wurde. Dieses System scheint kein echtes Zweikomponentensystem zu sein.

     

Synthesis of γ-Fe2O3 by Thermal Decomposition of Ferrous Gluconate Dihydrate

Ferrous gluconate dihydrate (FeC₁₂H₂₂O₁₄⋅2H₂O), was prepared and its thermal decomposition was studied by means of simultaneous thermal analysis, supplemented with a two probe d.c. electrical conductivity measurements under the atmospheres of static air, dynamic air and dynamic nitrogen. Under all the atmospheres final product was found to be α-Fe₂O₃ with FeO, γ-Fe₂O₃, Fe₃O₄ etc. as probable intermediates. γ-Fe₂O₃ was formed under the atmosphere of dynamic air containing water vapour. γ-Fe₂O₃ thus synthesised was characterised for its structure, morphology, thermal and magnetic behaviour. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effects of doping on the thermal stability of spindle-shaped γ-Fe2O3 particles

Spindle-shaped α-FeOOH particles were synthesized using the chemical coprecipitation method in Fe(CO₃)_x(OH)_2(?x) suspensions system by adding metallic ions. The spindle-shaped γ-Fe₂O₃ particles were obtained by dehydration of α-FeOOH, and subsequent reduction and oxidation. Its thermal stability was investigated by differential thermal analysis (DTA). It was found that the transition temperature of γ-Fe₂O₃→α-Fe₂O₃ of samples doped with metallic ions is higher than that of the pure γ-Fe₂O₃ and increasing with increase of the size of the metallic ions, and γ-Fe₂O₃ by doping with two or more different metallic ions together has even higher thermal stability. The origin of the improved thermal stability was discussed. Additionally, the magnetic properties of γ-Fe₂O₃ were measured.     

Electrochemical synthesis of Fe3O4-PB nanoparticles with core-shell structure and its electrocatalytic reduction toward H2O2

The Fe₃O₄-Prussian blue (PB) nanoparticles with core-shell structure have been in situ prepared directly on a nano-Fe₃O₄-modified glassy carbon electrode by cyclic voltammetry (CV). First, the magnetic nano-Fe₃O₄ particles were synthesized and characterized by X-ray diffraction. Then, the properties of the Fe₃O₄-PB nanoparticles were characterized by CV, electrochemical impedance spectroscopy, and superconducting quantum interference device. The resulting core-shell Fe₃O₄-PB-modified electrode displays a dramatic electrocatalytic ability toward H₂O₂ reduction, and the catalytic current was a linear function with the concentration of H₂O₂ in the range of 1 × 10⁻⁷~5 × 10⁻⁴ mol/l. A detection limit of 2 × 10⁻⁸ (s/n = 3) was determined. Moreover, it showed good reproducibility, enhanced long-term stability, and potential applications in fields of magnetite biosensors.     

The Al2O3-Fe2O3 Mixed Oxidic System, II. Catalytic Decomposition of N2O

N₂O decomposition was examined over a series of Al₂O₃-Fe₂O₃ mixed oxidic solids with composition ranging from 0 to 100% of Fe₂O₃. The catalytic activity of the solids runs parallel to the number of atoms of iron in the Al_2−x Fe_xO₃ solid solution phase. Two compensation effects are present. The first corresponds to catalysts rich in alumina, and the second one to catalysts rich in hematite. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phase equilibria in the system NiO-V2O5-Fe2O3 in subsolidus area

Reactivity of FeVO₄ towards Ni₂V₂O₇ and Ni₃V₂O₈ in the solid state was investigated. On the base of XRD and DTA results, phase diagrams in subsolidus area of the FeVO₄-Ni₂V₂O₇ and FeVO₄-Ni₃V₂O₈ intersections of the ternary system NiO-V₂O₅-Fe₂O₃ have been worked out and the phase diagram of this ternary system in subsolidus area in the whole component concentration range has been verified. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effect of sodium oxide doping on solid-solid interactions between V2O5 AND Al2O3

A V₂O₅/Al₂O₃ mixed solids sample was prepared with a molar ratio of 0.41 Na₂O (4 and 10 mol%) was added in the form of sodium nitrate prior to calcination in air in the temperature range 500–1000C. Solid-solid interactions between V₂O₅ and Al₂O₃ were studied using DTA and TG curves and their derivatives together with XRD techniques.The results obtained showed that Na₂O interacted with V₂O₅ at temperatures starting from 500C to yield a sodium/vanadium compound, Na_0.3V₂O₅ which remained stable and decomposed in part by heating at 1000C. V₂O₅ exists in orthorhombic and monoclinic forms in the case of pure mixed solids and those containing 4 mol% of Na₂O and preheated at 500C, and in monoclinic form in the case of the mixed solid doped with 10 mol% of Na₂O.Heating of pure and doped mixed oxide solids at 650C resulted in the conversion of most of the V₂O₅ into AlVO₄. Doping with sodium oxide enhanced the solid-solid interaction between V₂O₅ and Al₂O₃ at 650C to produce AlVO₄. The produced AlVO₄ decomposed completely on heating at 700C to form -Al₂O₃ and V₂O₅, (orthorhombic and monoclinic forms).The presence of Na₂O was found to decrease the relative intensity of the diffraction lines of -Al₂O₃ (corundum) produced at 750C which indicated some kind of hindrance of the crystallization process.Heating of pure and doped mixed solids at 1000C resulted in a further crystallization of acorundum together with V₂O₅ and sodium vanadate, Na_0.3V₂O₅. However, the intensities of diffraction lines relative to those of the sodium vanadium compound were found to decrease markedly by heating at 1000C, indicating partial thermal decomposition into vanadium and aluminium oxides.     

Thick Fe2O3, Fe3O4 films prepared by the chemical solution deposition method

Fe₂O₃, Fe₃O₄ films have been prepared from Fe(OCH₂CH(CH₃)₂)₃–(CH₃)₂CHCH₂OH–2.2′-diethanola- mine (DEA)–poly(vinylpyrrolidone) (PVP) solutions by the spin-(SC) and dip-coating (DC) technique on SiO₂ and Si substrates. The maximum film thickness achieved without crack formation has been increased by incorporation of PVP (relative molecular weights 40000 and 360000) into the precursor solution. The stability of the precursor solutions was remarkably increased by addition of DEA. Compact, dense, and crack-free Fe₂O₃ films with thicknesses 900 nm (DC), 450 nm (SC), have been obtained via single-step deposition cycle. Higher-molecular-weight PVP has been more effective in increasing the thickness. The minimum concentration of DEA, which results in pronounced increase of solutions stability, is about R _P (n(DEA)/n(Fe) = 0.1). The high content of carboneous residue in the pyrolysed Fe₂O₃ films promotes the formation of Fe₃O₄ films via reduction in a gas flow of H₂/N₂ gas mixture. Microstructure, surface morphology, and magnetic properties of the films have been also investigated using SEM, AFM, and SQUID, respectively.     

IR-spectral investigation of the structure of glasses in the Fe2O3-V2O5 system

The structure of glasses in the Fe₂O₃-V₂O₅ system in the 0–50 mol% Fe₂O₃ range is studied by IR-spectroscopy. It is found that the introduction of Fe₂O₃ favours the transformation of the VO₅-groups into VO₄ ones. This effect may be shown with the aid of IR-spectra, owing to the fact that these glasses are characterized by two high-frequency bands at 1020 and 930 cm^–1. The first is determined by the vibrations of the short V=O nonbridging bonds in the VO₅-groups, while the second is assigned to the vibrations of the V—O-bonds in deformed VO₄-tetrahedra.

---

IR-spektroskopische Strukturuntersuchung von Gläsern des Systems Fe₂O₃-V₂O₅

Zusammenfassung Die Struktur von Gläsern des Systems Fe₂O₃-V₂O₅ in dem Bereich von 0–50 Molprozent Fe₂O₃ wurde mit Hilfe der IR-Spektroskopie untersucht. Zusatz von Fe₂O₃ begünstigt die Umwandlung der VO₅- in VO₄-Gruppen. Das kann in den IR-Spektren durch zwei Banden bei 1020 und 930 cm^–1 festgestellt werden. Die erste wird durch Schwingungen der kurzen V=O-Nichtbrücken-bindungen in den VO₅-Gruppen verursacht, die zweite wird auf Schwingungen der V—O-Bindungen in dem deformierten VO₄-Tetraeder zurückgeführt.

     

Characterization and application of Fe3O4/SiO2 nanocomposites

A sol-gel procedure was used to cover Fe₃O₄ nanoparticles with SiO₂ shell, forming a core/shell structure. The core/shell nanocomposites were synthesized by a two-step process. First, Fe₃O₄ nanoparticles were obtained through co-precipitation and dispersed in aqueous solution through electrostatic interactions in the presence of tetramethylammonium hydroxide (TMAOH). In the second step, Fe₃O₄ was capped with SiO₂ generated from the hydrolyzation of tetraethyl orthosilicate (TEOS). The structure and properties of the formed Fe₃O₄/SiO₂ nanocomposites were characterized and the results indicate that the Fe₃O₄/SiO₂ nanocomposites are superparamagnetic and are about 30 nm in size. Bioconjugation to IgG was also studied. Finally, the mechanism of depositing SiO₂ on magnetic nanoparticles was discussed.     

纳米γ-Fe2O3粉体的合成与磁性增强研究

采用微乳法合成出氧化铁的前驱体——纳米β-FeOOH, 分别以β-FeOOH与添加剂壬基酚聚氧乙烯醚(NP-4)以物质量的比(n)为4, 5, 100添加NP-4, 混合煅烧. 采用拉曼光谱分析了样品中炭含量及分布, 并且用透射电镜观测产物的形貌和粒径, 采用磁强计观测产物磁性的变化. 结果得出, 对n＝5或破乳所得凝胶煅烧, 所得样品皆为分散均匀的四方形颗粒状, 且为磁性明显增强的纳米氧化铁γ-Fe₂O₃. 还分别讨论了样品中炭含量以及颗粒形状对比饱和磁化强度σ_s、矫顽力、矩形比的影响.     

Reactivity of Zn3V2O8 Towards ZnMoO4 in the Solid State

The reactivity of Zn₃ V₂ O₈ towards ZnMoO₄ was investigated by using DTA and XRD methods. A new compound of the formula Zn_2.5 VMoO₈ was found. It crystallises in an orthorhombic system. The melting temperature was determinated to be 845±5°C. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of capping and particle size on Raman laser-induced degradation of γ-Fe2O3 nanoparticles

Diol capped γ-Fe₂O₃ nanoparticles are prepared from ferric nitrate by refluxing in 1,4-butanediol (9.5 nm) and 1,5-pentanediol (15 nm) and uncapped particles are prepared by refluxing in 1,2-propanediol followed by sintering the alkoxide formed. X-ray diffraction (XRD) shows that all the samples have the spinel phase. Raman spectroscopy shows that the samples prepared in 1,4-butanediol and 1,5-pentanediol and 1,2-propanediol (sintered at 573 and 673 K) are γ-Fe₂O₃ and the 773 K-sintered sample is Fe₃O₄. Raman laser studies carried out at various laser powers show that all the samples undergo laser-induced degradation to α-Fe₂O₃ at higher laser power. The capped samples are however, found more stable to degradation than the uncapped samples. The stability of γ-Fe₂O₃ sample with large particle size (15.4 nm) is more than the sample with small particle size (10.2 nm). Fe₃O₄ having a particle size of 48 nm is however less stable than the smaller γ-Fe₂O₃ nanoparticles.