Magnetochemical study of iron molybdates obtained from precursor precipitates with different Mo- and Fe-content

The calcination, above 350°C, of precursor precipitates with well-defined stoichiometry and different fixed Mo-to-Fe ratios leads to the formation of undistinguishable, by X-ray diffractometry, crystal iron molybdates. At Mo-to Fe ratios higher than 1.5 a phase of MoO₃ appears. The parameters describing the temperature dependence of the magnetic susceptibility and the EPR-lines belonging to the iron molybdates depend on the initial-precipitate composition. This is an evidence for the presence of some structural differences in iron molybdate phases.     

不同结构稀土掺杂铝酸锶的合成与发光性能研究

采用燃烧法成功合成了稀土掺杂铝酸锶长余辉发光材料.XRD结果表明,当铝锶n(Al)∶n(Sr)=2时,发光基质中只存在SrAl2O4相结构.随着Al∶Sr比值的增大,出现新相Sr4Al14O25.当Al∶Sr比值增大到4时, SrAl12O19相开始形成.而Al∶Sr比值增大到12时,全部为SrAl12O19相.光致发光测量结果表明,发光样品SrAl2O4∶Eu2 ,Dy3 发射谱峰值位于519nm,而发光样品SrAl12O19∶Eu2 ,Dy3 的发射峰位于512nm.余辉检测结果表明,不同结构铝酸锶发光样品的衰减都是由初始的快衰减过程和其后的慢衰减过程组成,但是不同结构铝酸锶发光样品的初始亮度和发光衰减快慢不同.     

Preparation and properties of active submicronic solids and new metastable phases obtained via a metal-organic precursor method

The mixing of constituent ions on an atomic scale accomplished in single phase metal-organic precursors facilitates the occurrence and completion of the reactions such as decomposition, oxidation and reduction at reduced temperatures and in shorter times. This has been particularly shown for the first series of transition metals and for the lanthanide elements for which simple, and mixed oxides or their oxide solid-solutions have been prepared via decomposition and treatment of their respective organic salt precursors. The method gives compounds with increased homogeneity, purity and reactivity and allows isolation of submicronic solids and sometimes of new metastable phases, which could not have been obtained by high-temperature reactions. The morphological and other application properties of these submicronic solids and of new metastable phases can be widely modified and regulated by varying the composition and treatment given to the metal-organic precursors.     

Synthesis and photoelectrochemical properties of thin bismuth molybdates film with various crystal phases

Bismuth molybdate films with various phase structures including α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, γ-Bi₂MoO₆, and γ′-Bi₂MoO₆ are fabricated on the indium-tin oxide glass substrates from an amorphous heteronuclear complex via the dip-coating method by appropriate adjustment of the reaction conditions. α-Bi₂Mo₃O₁₂, β-Bi₂Mo₂O₉, and γ-Bi₂MoO₆ film can be obtained at 400 °C, 500 °C, and 500 °C for 1 h, respectively. At 500 °C, γ′-Bi₂MoO₆ can be obtained for 4 h. Film formation process is proposed based on the experimental results. Thin γ-Bi₂MoO₆ films exhibit high photoresponse under visible light irradiation. Incident photon to current conversion efficiency of thin γ-Bi₂MoO₆ film starts to increase near 450 nm. And, it can reach 4.1% at 400 nm. The top of the valence band and bottom of the conduction band are roughly estimated to be − 0.71 and 1.69 eV, respectively. In contrast, γ′-Bi₂MoO₆ generated weak photocurrent; α-Bi₂Mo₃O₁₂ and β-Bi₂Mo₂O₉ film has no photoresponse under visible light irradiation. The reason for the difference in the visible light response was discussed.     

Investigation on crystalline phases and mechanical properties of TZP ceramics prepared from sol-gel powders

Y₂O₃-stabilized tetragonal zirconia polycrystalline (TZP) ceramics containing 1–5 mol% Y₂O₃ were prepared by hot pressing and pressureless sintering of sol-gel-derived powders. Sintered ceramics were evaluated for their density, grain and crystallite size, width of transformation zone, crystalline phases and mechanical properties. Variation in the values of fracture toughness and flexural strength has been explained on the basis of crystallite size and proportion of transformable tetragonal phase, which are influenced by the concentration of Y₂O₃ in TZP ceramics. Correlation of the data has indicated that the transformable tetragonal phase is the key factor in controlling the fracture toughness and strength of ceramics.     

Ionic-liquid-assisted synthesis of YF3 with different crystalline phases and morphologies

YF₃ with different crystalline phases and morphologies have been prepared via a facile hydrothermal route assisted by imidazolium ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate (C₄mimBF₄) or 1-butyl-3-methylimidazolium hexafluorophosphate (C₄mimPF₆). The microstructures and morphologies of YF₃ particles were characterized by X-ray powder diffraction, X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), high resolution electron microscopy (HRTEM) and field emission scanning electron microscopy (FESEM). Cubic and orthorhombic YF₃ were selectively synthesized by adjusting the molar ratio of the reagents and using C₄mimBF₄ as the fluoride source, while only orthorhombic YF₃ was obtained using C₄mimPF₆, indicating that the crystalline phases and morphologies of the products were significantly influenced by fluoride source and reaction media.     

Zeta potential of alumina powders with different crystalline phases in simulated body fluids

The zeta potential of alumina (Al₂O₃) powder with different crystalline phases, prepared by heat treatment of boehmite, was measured in simulated body fluids in order to discuss the mechanism on in vivo formation of a calcium and phosphorus (CaP)-rich layer on bone cement containing δ-Al₂O₃-based bead powder. γ, δ, and θ-Al₂O₃ powders were obtained by heat treatment of boehmite powder at 600 °C, 900 °C, and 1025 °C, respectively. It was found that δ-Al₂O₃ gave a negative zeta potential in an acidic simulated body fluid, whereas γ-Al₂O₃ and θ-Al₂O₃ gave a positive potentials. During the bone fracture healing process, acidic conditions are maintained at the site of fracture for several days. Consequently, it is speculated that the negative surface potential of δ-Al₂O₃ in an acidic body fluid, similar to the fracture site, might be responsible for the in vivo formation of the CaP-rich layer on the overlying bone cement, given that the negatively charged surface of δ-Al₂O₃ would attract calcium ions from the surrounding body fluid, thereby facilitating the formation of the CaP-rich layer.     

BiVO4晶体的制备及其光学性能

在无氨水调节pH值条件下采用液相沉淀法制备了纳米晶BivO4粉体。通过XRD、SEM、紫外-可见分光光度计、色差仪和FITR等手段综合分析了煅烧前后BiVO。相结构和微粒形貌及其光学性能。结果表明：未煅烧的BiVO4具有四方相和单斜相两种结构，而500℃煅烧后为单一的等轴状的单斜相结构。与混合相粉体相比，纯单斜相的BiVO4具有较好的光学性能，亮度值81．7、黄品值85．9及色饱和度86．5％。     

Microemulsion-mediated solvothermal synthesis and photocatalytic properties of crystalline titania with controllable phases of anatase and rutile

Titanium oxide with different ratios of anatase to rutile has been prepared by the microemulsion-mediated solvothermal method. The resulting samples were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-vis diffuse reflectance spectra, transmission electron microscopy and Brunauer-Emmett-Teller analysis. The contents of anatase and rutile in the TiO₂ particles have been successfully controlled by simply adjusting the amount of urea in the aqueous phase of the microemulsion. Both the degradation of Rhodamine B in aqueous solutions and mineralization of TOC revealed that the catalyst containing 47.6% anatase have presented the highest photocatalytic activity. A proposed mechanism is discussed to interpret the evolution of the phases based on the effect of different amount of urea.     

淀粉基碳包覆铁纳米胶囊的合成及其磁学性能

以淀粉为碳源，通过热解炭化铁／淀粉复合物，成功制备出碳包覆铁（Fe@C）纳米胶囊。在这一过程中淀粉有双重作用，既是碳源又是铁纳米颗粒的稳定剂。采用透射电镜、X射线衍射及振动样品磁强计研究了（Fe@C）纳米胶囊的结构和磁学性能。发现Fe@C纳米胶囊具有完美的铁核（bcc-Fe）／碳壳（石墨层片）包覆结构，其尺寸介于30nm～40nm之间；Fe@C纳米胶囊在室温下有低的剩磁比（Mr／Ms=0．11），表明它在室温下具有超顺磁性。     

Preparation and characterization of ceria nanoparticles using crystalline hydrate cerium propionate as precursor

Ceria nanoparticles were synthesized simply by pyrolysis method using hydrate cerium propionate as precursor. The effect of pyrolysis temperature on the physical properties of ceria was investigated. It was found that the large crystals of precursor cracked to many nano-sized ceria particles on heating, and the medium particle sizes D₅₀ determined by laser scattering (LS) method decreased firstly and then increased with minimum value around 460 nm at calcination temperature of 1000 °C. SEM observations showed that the average particle size of synthesized ceria powders ranged from 20 to 50 nm.     

Preparation and properties of exfoliated graphite modified with iron compounds

Using the anodic oxidation of graphite in Fe(NO₃)3-HNO₃ mixed electrolytes, followed by heat treatment, we obtained exfoliated graphite modified with iron oxides. All of the samples obtained were characterized by X-ray diffraction, M?ssbauer spectroscopy, and scanning electron microscopy. The results demonstrate that the proposed approach allows one to produce exfoliated graphite containing up to 14% Fe in the form of oxides and hydroxides, whose composition depends on the exfoliation temperature.     

Preparation and properties of iron molybdates. I-investigation on the interaction between Mo(VI) and Fe(III) as a function of pH of the paramolybdate solution

The equilibrium processes of formation of various forms of polymolybdate ions during alkaline hydrolysis of diluted ammonium paramolybdate solutions have been investigated. The discrete existence of certain polymolybdate ions has been established by a study of the precipitation processes with Fe(III) ions using three pre-fixed Mo/Fe atomic ratios. Chemical analysis and UV spectroscopy measurements of the equilibrium filtrates have been made and the Mo/Fe atomic ratios in the equilibrium precipitates have been determined. A conclusion has been drawn about the existence of a homologous series of iron molybdates.     

Growth of nano-particles of Al2O3, AlN and iron oxide with different crystalline phases in a thermal plasma reactor

The paper presents the experimental results showing that the crystalline phase of the nano-particles, synthesized in a DC transferred arc thermal plasma reactor, critically depend on the operating pressure in the reaction zone. The paper reports about the changes in crystalline phases of three different compounds namely: aluminium oxide (Al₂O₃), aluminium nitride (AlN) and iron oxide (Fe_xO_y) synthesized at 760 Torr and 500 Torr of operating pressures. The major outcome of the present work is that the phases having higher defect densities are more probable to form at the sub-atmospheric operating pressures. The variations in the crystalline structures are discussed on the basis of the change in the temperature during the nucleation process, prevailing at the boundary of the plasma, on account of the ambient pressures. The as-synthesized nano-particles were examined by X-ray diffraction analysis and transmission electron microscopy. In addition, the confirmatory analysis of the crystalline phases of iron oxides was carried out with the help of Mössbauer spectroscopy.     

Preparation of iron boride-silica core-shell nanoparticles with soft ferromagnetic properties

A one-pot aqueous chemical synthesis for silica-passivated ferromagnetic nanoparticles is presented. The average size of these particles is 84 ± 20?nm. The x-ray and electron diffraction experiments revealed that the nanoparticles are mainly composed of polycrystalline iron boride. The broad x-ray diffraction peak leads to an average crystallite size of 1.8?nm, which is much smaller than the overall size of the particles, and is consistent with the polycrystalline nature of the samples. M?ssbauer spectroscopy and magnetization experiments were used to establish the room temperature magnetic properties as well as the chemical nature of the particles. Fe(2)B dominates the composition of the nanoparticles, having a hyperfine field broadly distributed in the 10-33?T range. Alpha iron, the second ferromagnetic material identified in the particles, amounts to 4.6% of the composition. Finally, a paramagnetic phase accounting for approximately 14.6% of the material of the particles was also detected. These nanoparticles contain a core with soft ferromagnetic properties surrounded by a passivating silica layer, and are suitable for magnetically targeted drug delivery and electromagnetic induction heating applications.     

Effect of precipitation conditions on the phase composition, particle morphology, and properties of iron(III,II) hydroxide precipitates

The phase composition and particle shape of amorphous iron hydroxide-iron oxide precipitates were correlated with the oxidation state of iron in the starting solution, Fe₂O₃ : FeO ratio, and precipitation procedure (coprecipitation or successive precipitation) using Mössbauer spectroscopy, atomic absorption, lowtemperature nitrogen BET, and electron microscopy data. A correlation was established between the amount of iron(II) in the starting solution, the amount of the metastable phase γ-Fe₂O₃ in the precipitate, particle shape, and the activity of the final heat-treatment products—α-Fe₂O₃ and mixed oxides of iron.     

Preparation and performance of intermediate-temperature fuel cells based on Gd-doped ceria electrolytes with different compositions

In this work, the effect of two frequently used Gd_xCe_1−xO_2−x/2 electrolytes (x = 0.1 and x = 0.2) on the performance of fuel cells operated at intermediate temperature was studied. The microstructures of ceria electrolytes responsible for the performance were discussed. Electrochemical measurements of as-prepared cells showed that the cell with Gd_0.2Ce_0.8O_1.9 electrolyte had a better performance than that of Gd_0.1Ce_0.9O_1.95. It can be concluded that the increase of grain boundary conductivity of Gd_0.2Ce_0.8O_1.9 electrolyte contributes to its better cell performance.     

Preparation and properties of YAG nano-sized powder from different precipitating agent

Yttrium aluminum garnet (YAG) nano-sized powder was prepared by co-precipitation method assisted by ultrasonic display using different precipitating agent. The precursor powder can crystallize into YAG phase after being calcined at 900 °C for 2 h, because of the uniformly distribution of Al and Y elements. DTA–TG and IR measurements on the precursor powder obtained were performed to improve the synthesis process. X-ray diffraction was conducted on the powder calcined at different temperatures to investigate the effect of reaction conditions on particle size and phase composition. The powder about 15 nm in diameter with pure YAG was obtained at lower temperature (900 °C) by controlling the pH value, precipitating agent and doping agent.     

Preparation and catalytic properties of tungsten oxides with different morphologies

Tungsten oxides with different morphologies including platelet-like sheets, nanobelts, and nanoparticles have been successfully prepared by changing the ions in the synthetic solution. Transmission electron microscopy, X-ray diffraction, Fourier-transform infrared analysis and N₂ adsorption were employed to reveal the morphological evolution, and results show that the morphological evolution can be attributed to the alteration of coordination environment of tungstenic cations contained in the synthetic solution. Furthermore, these products have been applied into hydrodesulfurization measurement to investigate the relationship between the morphologies of tungsten oxides and their catalytic properties. It is concluded that the catalysts originating from nanobelt-like tungsten oxides have highest catalytic activity and excellent selectivity due to their scrolled character and strong metallic edges.     

Preparation and photoluminescence properties of dye doped polymerization crystalline colloidal arrays

Polymerization crystalline colloidal arrays (PCCA) were fabricated by light polymerization method. Microstructures of polymerization crystalline colloidal arrays were observed by SEM. The results show that the microspheres in the PCCA form into a face-centered cubic structure with (111) plane parallel to the surface of the quartz cell. In addition, the influence of photonic band gap on photoluminescence of dyes was also investigated in the PCCA. Suppression of the emission was observed if the photonic band gap overlapped with the dyes emission band in the PCCA. Suppression of the emission was attributed to the photon trapping of the Bragg reflection in the PCCA.