Showing papers on "Tungstate published in 2011"
TL;DR: In this article, a template-free synthetic approach based on hydrothermal reaction that leads to the formation of nanoparticles and microspheres with the change in concentrations of ammonium tungstate used as a dopant precursor was proposed.
240 citations
TL;DR: In this article, aqueous solution of nickel nitrate and ammonium tungstate and calcined in air at 500°C for 2h was used in the oxidative dehydrogenation of ethane.
105 citations
TL;DR: In this article, a co-precipitation method was used to synthesize Mg-Al layered double hydroxides, loaded with tungstate anions, and the obtained compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy/energy-dispersive Xray spectrography (SEM/EDS), inductively coupled plasma (ICP), and transmission electron microscope (TEM), respectively.
83 citations
TL;DR: In this paper, a facile hydrothermal process was utilized to synthesize bismuth tungstate (Bi2WO6) hierarchical nano/microstructures, by which various morphologies could be achieved, including caddice clew-like, nestlike, flower-like and plate-like nanostructures.
83 citations
TL;DR: In this paper, the effects of different variables on the digestion of scheelite, and on the evaporation of the crude sodium tungstate leach solution, have been investigated.
81 citations
TL;DR: WO 3 /TiO 2 composite films were prepared by plasma electrolytic oxidation in electrolytes containing different tungstate concentration as discussed by the authors, and morphology, topography, compositions, crystal structure and photophysical properties of films were characterized by SEM, AFM, EDX, XRD, XPS, UV-vis DRS and PL, the surface acidity of films was investigated by ATR-IR.
80 citations
TL;DR: The photoluminescence characteristics of compounds ALn(MO4)2, with A = Li, Na, K; Ln = Y, La, Gd, Lu, M = Mo, W, are analyzed as a function of their structure as mentioned in this paper.
75 citations
TL;DR: In this paper, the effect of postdeposition thermal treatment on reactively cosputtered copper tungstate (CuWO4) thin films and its impact on photoelectrochemical performances was reported.
Abstract: In this Article, we report the effect of postdeposition thermal treatment on reactively cosputtered copper tungstate (CuWO4) thin films and its impact on photoelectrochemical performances. This stu...
73 citations
TL;DR: In this article, an organic-inorganic type composite cation-exchanger poly-o-toluidine Zr(IV) tungstate was chemically prepared and the physico-chemical properties of the material were studied using FTIR, TGA, X-ray, SEM and EDX studies.
73 citations
TL;DR: A divalent wolframite-structure zinc tungstate (ZnWO4) was synthesized using a facile hydrothermal process at 180 °C, with pH adjustment to drive the preferential growth along the [100] direction as discussed by the authors.
Abstract: A divalent wolframite-structure zinc tungstate (ZnWO4) was synthesized using a facile hydrothermal process at 180 °C, with pH adjustment to drive the preferential growth along the [100] direction, ...
72 citations
TL;DR: In this article, single crystals of the tungstates Ba2MgWO6 and Ba2ZnwO6 have been grown for the first time using molten potassium carbonate acting as a flux.
TL;DR: In this article, Tungsten trioxide (WO 3 ) nanoparticles have been successfully synthesized by thermal decomposition of ammonium tungstate loading on g-C 3 N 4.
TL;DR: Two complementary methods, the Rietveld method and PDF analysis, reveal that both LiEu(WO(4))(2) and NaEu-(4) afford the same local surroundings of Eu(3+), which well account for the observed luminescent properties.
Abstract: The effect of alkali-metal ions on the local structure and luminescence properties for alkali-metal europium double tungstate compounds AEu(WO4)2 (A = Li, Na, K) has been investigated by a dual-space structural technique, atomic pair distribution function (PDF) analysis, and the Rietveld method of powder X-ray diffraction. The compounds AEu(WO4)2 (A = Li, Na) crystallize in the isostructure with the tetragonal space group I41/a (No. 88) and show the same luminescence properties in spite of the different doped alkali metals. However, KEu(WO4)2 crystallizes in monoclinic symmetry with the space group C2/c (No. 15). Compared with the two other counterparts, KEu(WO4)2 exhibits a more effective charge-transfer excitation, a larger Stokes shift, and a broader 612 nm emission band. This phenomenon is ascribed to the lower crystal symmetry in KEu(WO4)2, which influences bond distances and the coordination number of Eu3+. Two complementary methods, the Rietveld method and PDF analysis, reveal that both LiEu(WO4)2 ...
TL;DR: The use of sulfated tungstate as an efficient and reusable catalyst for the preparation of amides from alcohols and nitriles via the Ritter reaction pathway is discussed in this paper.
TL;DR: A ceramic coating on the surface of Mg-14Li-1Al (LA141) alloy for corrosion protection via plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte with tungstate as an additive is presented.
Abstract: Superlight Mg–Li alloy is a promising structural materials in aerospace, automobile, and electronics because of its excellent properties such as low density, high ductility, superior strength-to-weight ratio, and good damping ability. The fabrication of compact plasma electrolytic oxidation coatings with excellent corrosion resistance is valuable for the widespread application of Mg–Li alloy. Here we present a ceramic coating on the surface of Mg-14Li-1Al (LA141) alloy for corrosion protection via plasma electrolytic oxidation (PEO) in an alkaline silicate electrolyte with tungstate as an additive. X-ray photoelectron spectroscopy and thin film-X-ray diffraction analysis of coatings show that the surface coating is mainly comprised of Mg2SiO4, MgO and WO3. Scanning electron microscopy observations have revealed that the dense and compact coating formed in the presence of tungstate has less structural imperfections in comparison to the control one fabricated without use of tungstate. The effect of oxidatio...
TL;DR: In this article, the authors studied the dielectric properties of scheelite ceramics in terms of their syntheses, sintering, solubility in water, and dielectrics response after storing them in dry and moist atmospheres.
Abstract: MWO4 (M=Ca, Sr and Ba) scheelite ceramics were studied in terms of their syntheses, sintering, solubility in water, and dielectric response after storing them in dry and moist atmospheres. Of the studied scheelites, the CaWO4 possessed the most promising dielectric properties (ɛ=10.9, Q × f=105 600 GHz), which were stable under the influence of humidity. BaWO4 and SrWO4 exhibited ɛ=9.0 and Q × f values of 32 200 and 62 600 GHz, respectively. The most detrimental effect of the moisture was observed for SrWO4. A sodium impurity present in the SrCO3 reagent (0.35 wt%), which was used for the synthesis of the SrWO4, was found to lower the sintering temperature, enhance the grain growth, and change the other properties of the ceramics, such as humidity susceptibility and solubility in water. The evident tendency of the ceramics to attract water and the increased dissolution of tungstate were observed for all MWO4 scheelite ceramics, which were sintered with the help of Na2CO3 or Li2CO3 (0.5 wt%) sintering aids. The results of the present study suggest that the physical and chemical properties of the ceramics should be carefully considered in the case of using of alkaline-containing sintering aids.
TL;DR: In this article, a density-functional theory has been employed to study the electronic and magnetic properties of copper tungstate CuWO4, as well as its optical characteristics in the ultraviolet region, up to 40 eV.
TL;DR: Tissue distribution in mice following oral exposure to sodium tungstate confirmed most of what has been published on tungsten tissue distribution and showed that the brain is relatively protected from oral exposure, although further studies are necessary to clarify the findings in splenic tissue.
Abstract: Heavy metal tungsten alloys have replaced lead and depleted uranium in many munitions applications, due to public perception of these elements as environmentally unsafe. Tungsten materials left in the environment may become bioaccessible as tungstate, which might lead to population exposure through water and soil contamination. Although tungsten had been considered a relatively inert and toxicologically safe material, recent research findings have raised concerns about possible deleterious health effects after acute and chronic exposure to this metal. This investigation describes tissue distribution of tungsten in mice following oral exposure to sodium tungstate. Twenty-four 6-9 weeks-old C57BL/6 laboratory mice were exposed to different oral doses of sodium tungstate (0, 62.5, 125, and 200 mg/kg/d) for 28 days, and after one day, six organs were harvested for trace element analysis with inductively coupled plasma mass spectrometry (ICP-MS). Kidney, liver, colon, bone, brain, and spleen were analyzed by sector-field high-resolution ICP-MS. The results showed increasing tungsten levels in all organs with increased dose of exposure, with the highest concentration found in the bones and the lowest concentration found in brain tissue. Gender differences were noticed only in the spleen (higher concentration of tungsten in female animals), and increasing tungsten levels in this organ were correlated with increased iron levels, something that was not observed for any other organ or either of the two other metals analyzed (nickel and cobalt). These findings confirmed most of what has been published on tungsten tissue distribution; they also showed that the brain is relatively protected from oral exposure. Further studies are necessary to clarify the findings in splenic tissue, focusing on possible immunological effects of tungsten exposure.
TL;DR: In this paper, the correlation between the crystal structure and luminescent properties of Eu3+-doped metal tungstate phosphors for white LEDs was investigated, and the results confirmed that these phosphors exhibited a strong absorption in the near UV to green range.
TL;DR: In this article, a study has been made on the corrosion protection performance of tungstate doped polyaniline containing vinyl coating on steel, which has been found to offer protection more than 60 days in salt spray and immersion in 3% NaCl.
TL;DR: In this paper, a novel ion conductor comprising magnesium hafnium tungstate (MgHf(WO4)3) was developed as a solid electrolyte for future metal-air batteries.
Abstract: We have developed a novel ion conductor comprising magnesium hafnium tungstate (MgHf(WO4)3) as a solid electrolyte for future metal-air batteries. The conductivity of this material measured as 2.5 × 10−4 S/cm at 600°C is about one order of magnitude higher than that of existing ion conductor with similar structure, such as Sc2(WO4)3. We have also elucidated for the first time that MgHf(WO4)3 has an intrinsic crystal structure, forming one-dimensional (1-D) alignments of individual Mg2+ and Hf4+ ions alternating within quasi-layered WO42– units at Sc3+ sites in Sc2(WO4)3. The structure observed by HAADF-STEM clearly coincides with the results obtained by first principle calculation. The mechanism for high ion conductivity is discussed from the viewpoints of its ordered structure and physical property of negative thermal expansion.
TL;DR: Aluminium exchanged heteropoly tungstate (AlTPA) supported on titania catalysts were used for benzylation of anisole with benzyl alcohol as discussed by the authors.
Abstract: Aluminium exchanged heteropoly tungstate (AlTPA) supported on titania catalysts were prepared and characterized by FT-Infra red, X-ray diffraction, Laser Raman, temperature programmed desorption of ammonia and X-ray photo electron spectroscopy. The catalytic properties of the catalysts were evaluated for benzylation of anisole with benzyl alcohol. The catalysts showed high activity for anisole benzylation and the catalyst with 20 wt% of AlTPA exhibited highest activity. The presence of Al resulted in generation of Lewis acidic sites. Acidic property and chemical structure of AlTPA on different supports also evaluated by supporting AlTPA on Nb 2 O 5 , ZrO 2 and SnO 2 . The catalytic activity of these catalysts is in the order of AlTPA/TiO 2 > AlTPA/SnO 2 > AlTPA/ZrO 2 > AlTPA/Nb 2 O 5 . The benzylation activity and selectivity towards benzylated product also depends on the reaction temperature, catalyst weight and anisole to benzyl alcohol ratio.
TL;DR: In this paper, a quasi-ternary system of LuAl3(BO3)4 (LuAB) and Li2WO4-B2O3 flux has been investigated for the first time, where the thermal expansion coefficients along two crystallographic directions in the temperature range of 30-800 °C were determined to be α1 = 3.38 × 10-6 K-1 and α3 = 10.4 × 10 -6 K -1.
Abstract: Single crystals of LuAl3(BO3)4 (LuAB) have been grown with the top-seeded solution growth method from a new tungstate based flux Li2WO4–B2O3. The crystallization region of LuAB is revealed in a quasi-ternary system of LuAB–Li2WO4–B2O3. Correlation between the crystallization region of LuAB and an excess of Al2O3 in the flux system has been identified for the first time. Compared with the commonly used K2Mo3O10–B2O3 flux at 1100 °C, the Li2WO4–B2O3 flux has lower volatility with lower incorporation of tungstate into the crystals. Thermophysical properties of the crystal have been investigated for the first time, where the thermal expansion coefficients along two crystallographic directions in the temperature range of 30–800 °C were determined to be α1 = 3.38 × 10–6 K–1 and α3 = 10.4 × 10–6 K–1. The specific heat was about 0.65 J/(g·K) at room temperature. The thermal conductivities at room temperature were 12.47 W/(m·K) and 10.443 W/(m·K) along the a and c axes, respectively, and the Vickers hardness value...
Patent•
11 Nov 2011TL;DR: In this article, a method for extracting tungsten from scheelite, which comprises: introducing mixed acid consisted of sulfuric acid and phosphoric acid into a decomposition reactor, heating to 70-100?, and then adding scheelsite, maintaining the solid-liquid ratio at 3:1-8:1L/kg.
Abstract: Disclosed is a method for extracting tungsten from scheelite, which comprises: introducing mixed acid consisted of sulfuric acid and phosphoric acid into a decomposition reactor, heating to 70-100?, and then adding scheelite, maintaining the solid-liquid ratio at 3:1-8:1L/kg, filtrating after 1-6h of reaction, crystallizing the obtained filtrate which is compensated with sulfuric acid consumed by the reaction to obtain phosphotungstic acid crystal, dissolving phosphotungstic acid crystal in water and transforming it to obtain ammonium tungstate solution containing 200-300g/L of WO3, which is used for preparing APT, while returning the obtained crystal mother liquor for ore leaching after being compensated with phosphoric acid and water to the initial level. The invention saves cost of phosphorus-removal reagent and loss of Tungsten; is capable of high efficient scheelite leaching at normal pressure, and overcomes the problems such as Cl- corrosion and heavy volatilization of HCl in traditional acid decomposition process; realizes the recycling of phosphoric acid in general, and greatly reduces the cost of leaching and the quantity of wastewater discharging; and has short flow process, convenient operation, and is adaptive for industrial application.
TL;DR: A WO 3 /TiO 2 composite film was in-situ prepared in tungstate electrolyte and characterized by Electron microscopy, X-ray diffraction, UV-Vis spectrophotometer and Photoluminescence.
Patent•
21 Sep 2011
TL;DR: In this paper, the authors proposed a method for preparing ethylene glycol from polyols, including cellulose, starch, hemicellulose, sucrose, glucose, levulose and levan.
Abstract: The invention provides a method for preparing ethylene glycol and propylene glycol from polyols, including cellulose, starch, hemicellulose, sucrose, glucose, levulose and levan. The method is realized in a way that: polyols are used as reaction raw materials; oxides of transition metals in Families VIII, IX and X, including iron, cobalt, nickel, ruthenium, rhodium, palladium, iridium, platinum and tungsten, tungstic acid, tungstate and heteropoly tungstate are used as catalytic active components to form a composite catalyst; and one-step catalytic conversion is carried out at 120-300 DEG C under the hydrogen pressure 1-13 MPa under hydrothermal conditions, thereby preparing the ethylene glycol and propylene glycol from polyols at high efficiency, selectivity and yield. The reaction provided by the invention has the advantages of renewable raw materials and atom economy. Compared with other technologies for preparing polybasic alcohols by using biomass as the raw material, the invention has the advantages of simple reaction process, high yield of target product, and low cost, and the catalyst preparation process is simple to implement.
TL;DR: In this article, the structural, dielectric and ferroelectric properties of tungsten (W) substituted SrBi 2 (Ta 1− x W x ) 2 O 9 (SBTW) samples were studied as a function of sintering temperature.
Abstract: Structural, dielectric and ferroelectric properties of tungsten (W) substituted SrBi 2 (Ta 1− x W x ) 2 O 9 (SBTW) [ x =0.0, 0.025, 0.05, 0.075, 0.1 and 0.2] have been studied as a function of sintering temperature (1100–1250 °C). X-ray diffraction patterns confirm the single-phase layered perovskite structure formation up to x =0.05 at all sintering temperatures. The present study reveals an optimum sintering temperature of 1200 °C for the best properties of SBTW samples. Maximum T c of ∼390 °C is observed for x =0.20 sample sintered at 1200 °C. Peak-dielectric constant ( e r ) increases from ∼270 to ∼700 on increasing x from 0.0 to 0.20 at 1200 °C sintering temperature. DC conductivity of the SBTW samples is nearly two to three orders lower than that of the pristine sample. Remnant polarization ( P r ) increases with the W content up to x ≤0.075. A maximum 2 P r (∼25 μC/cm 2 ) is obtained with x =0.075 sample sintered at 1200 °C. The observed behavior is explained in terms of improved microstructural features, contribution from the oxygen and cationic vacancies in SBTW. Such tungsten substituted samples sintered at 1200 °C exhibiting enhanced dielectric and ferroelectric properties should be useful for memory applications.
TL;DR: In this article, a solvothermal approach was used to synthesize tungsten oxide nanobrushes in the presence of citric acid and hexadecylamine as surfactants.
Abstract: Tungsten oxide nanobrushes were synthesized using a solvothermal approach that lead to self-branching in the presence of citric acid and hexadecylamine as surfactants. Our synthetic approach yielded branched nanorods of tungsten oxide in a single synthetic step. Based on our results, we propose a phenomenological pathway for the formation, branching, and assembly of these tungsten oxide brushes. The formation of tungsten oxide brushes proceeds by thermal decomposition of ammonium tungstate in the presence of citric acid and hexadecylamine. The pale blue powder obtained after solvothermal reaction was analyzed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The field emission (FE) properties of the tungsten oxide nanostructures which can be tailored by their aspect ratio and the hierarchical nanostructures follow a Fowler–Nordheim behavior.
TL;DR: In this article, the authors solved the structure of Y2WO6 using ab-initio methods from X-ray powder diffraction data and showed that the Eu3+ dopants preferentially entered the 2a site.
TL;DR: In this article, the effects of tungsten material used as a highvoltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated.
Abstract: The effects of tungsten material used as a high-voltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated. A reactor of needle?plate electrode geometry was used. The erosion of the tungsten electrodes by the discharge was evaluated. The yields of H2O2 production and the decomposition of DMSO by the discharge, which were obtained using the tungsten electrodes, were compared with those determined for titanium electrodes. The electrode erosion increased significantly with an increase in the solution conductivity. A large fraction (50?70%) of the eroded tungsten electrode material was released into the solution in dissolved form as tungstate ions. A correlation between the amount of eroded tungsten material released into the solution and the chemical effects induced by the discharge was determined. Lower yields of H2O2 and a higher degradation of DMSO by the discharge were obtained using the tungsten electrodes than were determined using titanium electrodes. Tungstate ions were shown to play a dominant role in the decomposition of H2O2, which was produced by the discharge using a tungsten electrode. The higher degradation of DMSO that was determined for tungsten was attributed to the tungstate-catalyzed oxidation of DMSO by H2O2, in addition to the oxidation of DMSO by OH radicals. Such a mechanism was supported by the detection of degradation by-products of DMSO (methanesulfonate, sulfate and dimethyl sulfone). The catalytic role of tungstate ions in the plasmachemical activity of the discharge generated using a tungsten electrode was also demonstrated on a pH-dependent decomposition of H2O2 and DMSO.