Tungsten Blue Oxide Research Articles

A separation between oxygen removal and phase transition: A new path for preparing nano-scale tungsten carbide powder

In this work, adopting tungsten blue oxide (TBO, W10O29 as main phase) as precursor, nano tungsten powder and nano tungsten carbide powder were successfully prepared through two steps of hydrogen reduction and carbonization. In tungsten powder preparation, it was found that the essence of β-W transition was a separation between oxygen removal and phase transition. Based on nucleation energy control, nano tungsten powder with a BET value as high as 25.55 m2/g was prepared. On this basis, nano tungsten carbide powder with a BET value of 3.87 m2/g, which is at a leading level, was obtained by adopting a high temperature-short time process.

Prepration and Properties of Blue Tungsten Oxide Nanopowders by High Energy Ball-Mill

The purpose of this study is to prepare WO3 nanopowders by high-energy milling in mixture gas (7 % H2+Ar) with various milling times (10, 30, and 60 min). The phase transformation, particle size and light absorption properties of WO3 nanopowders during reduction via high-energy milling are studied. It is found that the particle size of the WO3 decreases from about 30 μm to 20 nm, and the grain size of WO3 decreases rapidly with increasing milling time. Furthermore, the surface of the particles due to the pulverization process is observed to change to an amorphous structure. UV/Vis spectrophotometry shows that WO3 powder with increasing milling times (10, 30, 60 min) effectively extends the light absorption properties to the visible region. WO3 powder changes from yellow to gray and can be seen as a phenomenon in which the progress of the color changes to blue. The characterization of WO3 is performed by high resolution X-ray diffractometry, Field emission scanning electron microscopy, Transmission electron microscopy, UV/Vis spectrophotometry and Particle size analysis.

Tungsten Blue Oxide as a Reusable Electrocatalyst for Acidic Water Oxidation by Plasma-Induced Vacancy Engineering

In contrast to alkaline water electrolysis, acidic water electrolysis remains an elusive goal due to the lack of earth-abundant, efficient, and acid-stable water oxidation electrocatalysts. Here, w...

Preparation of high-purity and ultrafine WC-Co composite powder by a simple two-step process

In this study, high-purity and ultrafine WC-6%Co composite crystallites was synthesized by a simple two-step process consisting of the precursor-formation of the mixture of blue tungsten oxide (WO2.9) and cobaltic oxide (Co2O3) and the following deep reduction and carburization with CH4-H2 mixed gases. The experimental results revealed that after the first carbothermic reduction stage at 1050 or 1150 °C, a mixture of W, WO2 and Co7W6 was obtained, which was further carburized to the WC and Co phases by CH4-H2 mixed gases at 900 °C. With the increase of C/WO2.9 molar ratio, the particle sizes of first-stage precursor and carbonized product were both decreased. The particle sizes of final products are mainly determined by C/WO2.9 ratio and reaction temperature at the first stage. When the C/WO2.9 ratio was in the range of 2.3–2.7, the high-purity WC-6%Co composite powder with the average particle sizes of 160–410 nm could be obtained.

Preparation and tribological properties of WS2 and WS2/TiO2 nanoparticles

Abstract A method was developed to prepare WS2 and WS2/TiO2 nanoparticles. A blue tungsten oxide precursor was synthesized from Na2WO4, CH3CSNH2, and HCl. WS2 nanoplatelets was produced after sulfurizing the precursor at 300 °C. Nano-TiO2 could be activated by HCl and provide active sites for the deposition of the precursor to produce WS2/TiO2 nanoparticles after sulfurization. The as-prepared two nano-additives slightly affected the friction reduction of diisooctyl sebacate (DOS), but they, especially WS2/TiO2, remarkably improved the wear resistance of DOS. Compared with the pure DOS, the 0.75% WS2/TiO2-containing DOS decreased the wear volume by ∼81%. The anti-wear performance of WS2/TiO2 is ascribed to the formation of a lubricating film and the synergistic lubrication effect of WS2 and TiO2.

Correlations between Reduction Degree and Catalytic Properties of WO x Nanoparticles.

Degrading organic dyes via catalytic processes for waste water purification is an important research topic from the environmental conservation point of view. Herein, the catalytic performance of tungsten blue oxide (WOx) nanoparticles was investigated systematically by varying the reduction temperature. The optimum reduction temperature to obtain the most stable WOx phase was obtained when plasma-synthesized WO3 nanoparticles were thermally reduced at 425 °C. The as-synthesized nanoparticles had an average diameter of 10 nm and a calculated band gap of 2.37 eV, which is lower than that of the WO3 nanoparticles (2.61 eV). The WOx nanoparticles exhibited an excellent performance in degrading rhodamine B under dark conditions and visible light irradiation, with a reaction rate constant 93 times higher than that of the WO3 nanoparticles.

Transformation/dissolution characterization of tungsten and tungsten compounds for aquatic hazard classification.

The transformation/dissolution protocol (T/DP) for metals and sparingly soluble metal compounds was applied to determine the transformation/dissolution (T/D) characteristics of yellow tungsten trioxide, WO3 ; blue tungsten oxide, WOx, x taken as 2.9; tungsten disulphide, WS2 ; tungsten metal, W; 3 samples of tungsten carbide, WC; sodium tungstate, Na2 WO4 · 2H2 O; ammonium paratungstate (APT), (NH4 )10 (H2 W12 O42 ) · 4H2 O; and ammonium metatungstate (AMT) (NH4 )6 (H2 W12 O40 ) · 3H2 O. The T/D data were used to derive aquatic hazard classification outcomes under the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS) and European Union Classification, Labelling and Packaging of Substances and Mixtures (EU CLP) schemes by comparing the data with selected acute and chronic ecotoxicity reference values (ERVs) of 31 and 3.37 mg W/L, respectively. In addition to the concentration of total dissolved tungsten (W), the T/D solutions were analyzed for the concentration of the tungstate anion, because speciation can be an important factor in establishing the ecotoxicity of dissolved metals. Results show that the tungstate anion was the predominant W-bearing species in solution for all substances examined at pH 6 and 8.5. It was found that the 100 mg/L loadings of both the yellow WO3 and the blue WOx exceeded the 31 mg/L acute ERV, so they would classify as Acute 3-Chronic 3 under the UN GHS scheme but they would not classify under the EU CLP. An effect of pH on the reactivity of the W metal was observed with 3% and 16% W dissolution at pH 6 and 8.5, respectively. Tungsten metal would not classify under either the UN GHS or EU CLP schemes nor would the WS2 . The WCs were the least reactive in terms of the 1% or less dissolution of the contained W at pH 6. A critical surface area for WC was calculated. The sodium tungstate, APT and the AMT all yielded, at pH 8.5, total dissolved W concentrations that would result in UN GHS Acute 3-Chronic 3 classifications. Integr Environ Assess Manag 2018;14:498-508. © 2018 Her Majesty the Queen in Right of Canada. Integrated Environmental Assessment and Management © 2018 SETAC.

Fine Tungsten Powder Obtained with Blue Tungsten Oxide through the Hydrogen Reduction

Fine tungsten powder is prepared with blue tungsten oxide (BTO) through the hydrogen reduction. The samples were characterized with the scanning electron microscope (SEM), fisher sub-sieve sizer (FSSS) and the particulate size description analyzer (PSDA). Fine tungsten powder is easily obtained when the reduction temperature is low. With the increasement of the reduction temperature, the grain size of tungsten powder becomes coarse. The increase of the weight of BTO in the ceramic boat leads to the increasement of the thickness of its bed. Therefore, the weight of BTO in the ceramic boat ought to reduce if fine tungsten powder is prepared. Fine tungsten powder can be obtained when the hydrogen flow increases.

Facile one-pot synthesis of tungsten oxide (WO3−x) nanoparticles using sub and supercritical fluids

Tungsten oxide (WO3) and tungsten blue oxide (WO3−x) were synthesized using sub and supercritical water and methanol. Crystalline tungsten oxides were formed with subcritical water at 250°C, which shows lower production temperature compared to conventional solid-state methods. Glycerol hydrothermal reduction and supercritical methanol were both found to be effective in obtaining crystalline tungsten blue oxides and this is a great advantage since hydrogen is not required in the process. The synthesized particles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and near edge X-ray absorption fine structure (NEXAFS). NEXAFS results showed that sub and supercritical methanol was more effective in reduction of tungsten oxides compared to glycerol hydrothermal reduction.

Selective photocatalytic oxidation of aromatic alcohols into aldehydes by tungsten blue oxide (TBO) anchored with Pt nanoparticles

Hypostoichiometric Pt/WO3 shows efficient, selective and stable conversion of aromatic alcohols into corresponding aldehydes under simulated sunlight in aqueous solution.

Tungsten oxide by non-hydrolytic sol–gel: effect of molecular precursor on morphology, phase and photocatalytic performance

The synthesis, characterisation and photocatalytic water splitting activity of blue tungsten oxide materials prepared from W(vi) and W(iv) precursors is reported.

A Dissolution‐Regeneration Route to Synthesize Blue Tungsten Oxide Flowers and their Applications in Photocatalysis and Gas Sensing

Tungsten oxide (WO3) has unique physicochemical properties. Although various synthetic methods have been proposed to fabricate tungsten oxide with different morphologies, methods of tailoring the tungsten oxide nanostructure toward new morphologies are still needed. In this work, a self‐assembled WO3·0.33H2O nanoflower is synthesized using a dissolution and regeneration method. In such a two‐step synthetic process, temperature, solvent, and reaction times are found to be the main parameters affecting the morphology of WO3·0.33H2O. The synthesized WO3·0.33H2O nanoflower exhibits a localized surface plasmon resonance effect and a high photocatalytic activity, which can be explained by the doping of W5+ and its morphology. Furthermore, this WO3·0.33H2O nanoflower can also be used as a gas sensor and has good selectivity and linearity towards acetone vapor in the range of 50–500 ppm.

Effect of blue tungsten oxide on skeleton sintering and infiltration of W–Cu composites

A novel W-skeleton sintering process was introduced by adding blue tungsten oxide (BTO). The effect of BTO on skeleton sintering and infiltration of W–Cu composites was investigated. The microstructural study, analyses of thermal diffusivity, as well as copper- and oxygen concentration of W–Cu composites were carried out using a combination of scanning electron microscopy (SEM), laser flash method and chemical composition analysis respectively. The results indicate that the addition of BTO can increase the porosity of the W-skeleton. As a consequence, copper concentration can be increased in W–Cu composites. The other beneficial effect is the formation of an open pore structure with the addition of BTO. The relative density is higher than 99% for W–25Cu composites with the addition of BTO and the corresponding theoretical thermal conductivity is 231W/(mK). Furthermore, the BTO addition does not result in any increase of oxygen content of the W-skeleton.

Development Of Worker Inhalation Derived No Effect Levels For Tungsten Compounds

Under the European Community (EC) Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH), the risk to humans may be considered controlled if the estimated exposure levels to a substance do not exceed the appropriate derived no-effect level (DNEL). In order to address worker exposure, DNELs are derived for the worker population. The most significant route of exposure to workers to both soluble and sparingly soluble tungsten substances is through inhalation. In order to meet the REACH registration requirements, occupational long-term inhalation DNELs were developed according to the European Chemical Agency (ECHA) REACH guidance on characterization of dose-response for human health. The inhalation DNELlong-term for sodium tungstate, from which all other soluble tungsten substance DNELs were derived, is 3 mg sodium tungstate/m3 (1.7 mg W/m3), and the inhalation DNELlong-term for tungsten blue oxide, from which all other sparingly soluble tungsten substance DNELs were derived, is 7.3 mg tungsten blue oxide/m3 (5.8 mg tungsten/m3). Although derived using different methodologies and supported by different studies, the occupational inhalation DNELslong-term for soluble and sparingly soluble tungsten compounds are similar to the current National Institute for Occupational Safety and Health (NIOSH) recommended exposure level (REL) and the American Conference of Industrial Hygienists (ACGIH) threshold limit value (TLV) 8-h time weighted average (TWA) of 1 mg tungsten/m3 for soluble tungsten compounds and 5 mg tungsten/m3 as metal and insoluble tungsten compounds.

Toxicologic evaluation of tungsten: 28-day inhalation study of tungsten blue oxide in rats

The toxicity and toxicokinetics of tungsten blue oxide (TBO) were examined. TBO is an intermediate in the production of tungsten powder, and has shown the potential to cause cellular damage in in vitro studies. However, in vivo evidence seems to indicate a lack of adverse effects. The present study was undertaken to address the dearth of longer-term inhalation toxicity studies of tungsten oxides by investigating the biological responses induced by TBO when administered via nose-only inhalation to rats at levels of 0.08, 0.325, and 0.65 mg TBO/L of air for 6 h/day for 28 consecutive days, followed by a 14-day recovery period. Inhaled TBO was absorbed systemically and blood levels of tungsten increased as inhaled concentration increased. Among the tissues analyzed for tungsten levels, lung, femur and kidney showed increased levels, with lung at least an order of magnitude greater than kidney or femur. By exposure day 14, tungsten concentration in tissues had reached steady-state. Increased lung weight was noted for both terminal and recovery animals and was attributed to deposition of TBO in the lungs, inducing a macrophage influx. Microscopic evaluation of tissues revealed a dose-related increase in alveolar pigmented macrophages, alveolar foreign material and individual alveolar foamy macrophages in lung. After a recovery period there was a slight reduction in the incidence and severity of histopathological findings. Based on the absence of other adverse effects, the increased lung weights and the microscopic findings were interpreted as nonadverse response to exposure and were not considered a specific reaction to TBO.

Preparation of Medium-Sized Tungsten Particles via the New Method

Medium-sized tungsten particles are obtained through circulatory oxidation-reduction twice. The samples are characterized by laser particle size analyzer and scanning electron microscope (SEM). Blue tungsten oxide (BTO) is prepared with ammonium paratungstate (APT) in the argon gas. Tungsten powders are obtained with BTO through deoxidation in the hydrogen gas (Rate of purity: 99.99%, dew point: -40°C), and tungsten powders are oxidized in the air. Tungsten oxide WO3) is reduced into tungsten powders in hydrogen gas again. The routes are repeated. The volume percent content of medium-sized tungsten powders between 3 μm and 10 μm is 83.86 %.

Fine Cemented Carbide Particles Prepared with Activated Tungsten Oxide

Fine cemented carbide in the diameter of less than 1 μm is obtained activated tungsten oxide. The samples are characterized by laser particle size analyze, electron microscope and sclerometer. The experimental results show that the size of tungsten particles and tungsten carbide prepared with activated tungsten becomes small remarkably, and coarse tungsten particles decrease. The properties of cemented carbide prepared with activated tungsten oxide are better than those of cemented carbide made with blue tungsten oxide. Especially, the hardness of cemented carbide prepared with activated tungsten oxide increases by about 7 %.

Tungsten Oxide Nanopowders and Nanorods Prepared by a Modified Plasma Arc Gas Condensation Technique

Tungsten oxide nanopowders and nanorods were synthesized by using a modified plasma arc gas condensation technique that involved the introduction of a mixed gas with controllable partial O2 pressure into a gas condensation system. Experimental results showed that yellow and blue tungsten oxide nanopowders, prepared under an Ar to O2 ratios of 1:1 and 100:1, exhibited a major WO3 phase and W19O55 phase, respectively. The nanopowders grew into W5O14-phase nanorods along the [001] direction when H2 was used as the reduction gas.

Direct carburation of tungsten blue oxide in a fluidized bed reactor

The demand for tungsten carbide powders with grain sizes below 1 μm has significantly increased during the last two decades by the further development of improved cemented carbides. Therefore, the production of tungsten carbide powders by direct carburation of tungsten blue oxide in a fluidized bed reactor was investigated. The intention was to produce fine tungsten carbide powders from tungsten oxides by gas phase carburation with hydrogen/carbon monoxide gas mixtures in a single step process. The carburation time depends on the conditions of the experiment, essentially on the temperature and the gas/solid-ratio. Furthermore, the necessary time for a complete carburation without the formation of free carbon is acceptable.

In situ HT‐XRD Study on the Formation of Hexagonal Ammonium Tungsten Bronze by Partial Reduction of Ammonium Paratungstate Tetrahydrate

AbstractHexagonal ammonium tungsten bronze, (NH4)0.33–xWO3–y, is a possible constituent of the intermediate “tungsten blue oxide” in non‐sag (NS) tungsten production and a material of chromogenic and sensor interest. Its formation has been studied by in situ high‐temperature powder X‐ray diffraction (HT‐XRD) accompanied by semiquantitative phase analysis through the partial thermal reduction of ammonium paratungstate tetrahydrate, (NH4)10[H2W12O42]·4H2O, in flowing 10 % H2/He. The effect of the heating program on the formation of the title compound has been discussed. Highly crystalline, monophasic hexagonal ammonium tungsten bronze prepared by partial reduction of ammonium paratungstate tetrahydrate has been characterised by high‐precision powder XRD, X‐ray photoelectron spectroscopy (XPS), chemical analysis and solid‐state 1H NMR spectroscopy (1H‐MAS‐NMR). (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)