Reaction Of WO3 Research Articles

Anomalous photo-thermoelectric effects of platinum and tungsten trioxide bilayers

We attempted to deposit a platinum (Pt) layer onto a tungsten trioxide (WO3) thin film (Pt/WO3). The Pt layer deposited on WO3 was oxidized by calcining Pt/WO3 in air to form PtOx/WO3. An n-type anomalous photo-thermoelectric (photo-TE) effect was confirmed for Pt/WO3 and Pt/HyWO3−x. HyWO3−x is a protonated WO3 after the gaschromic (GC) reaction of WO3 in Pt/WO3. The anomalous photo-TE effect was that both the electrical conductivity (σphoto) and the absolute value of the Seebeck coefficient (Sphoto) increased under UV light or visible light irradiation. After stopping the irradiation, σphoto and Sphoto decreased. In contrast, an n-type normal photo-TE effect was observed for PtOx/HyWO3−x after the GC reaction of PtOx/WO3, in which σphoto increased and the absolute value of Sphoto decreased under ultraviolet (UV) light irradiation, and vice versa after stopping the irradiation. These findings indicate that Pt was responsible for the anomalous photo-TE effect due to the electron accumulation capability of Pt, to which electrons were transferred from the conduction band of HyWO3−x. In contrast, electrons could not energetically transfer from HyWO3−x to PtO2, which existed in PtOx particles at the surface. Therefore, PtOx/HyWO3−x behaved similar to sole HyWO3−x, indicating the normal photo-TE effect.

Deposition of nano-crystalline tungsten carbide powders from gaseous WO2(OH)2

Lower WC grain sizes in the nanometer range have positive effects on the properties of hardmetals (e.g., hardness), but the established production processes of WC are limited to grain sizes of about 150 nm. To produce WC powder with grain sizes in the lower nanometer range, an alternative WC production process based on the chemical vapor transport (CVT) reaction of WO3 and H2O forming gaseous WO2(OH)2 at about 1100 °C, followed by a carburation reaction with H2/CH4-gas mixtures was investigated. The influences of different process parameters such as furnace temperature, humidity and gas flows were investigated to improve the process. With the right set of parameters the produced powder consisted mainly of agglomerated WC grains with a size of about 5 nm. Beside the common hexagonal WC phase, the cubic WC1−x phase was stabilized due to the small crystallite sizes. In addition, a thin layer of amorphous carbon was present on the powder surface due to the catalytic methane decomposition on the WC surface. The amount of oxidic and metallic residues in the product powder was minimized with the parameter optimization and the powder yield was increased up to about 50%. With further optimization of the process parameters and usage of improved flow breakers, the purity and yield of the product powder can be further improved. Since an application in the hardmetal section is not realistic at the moment, applications in the catalysis sector could be considered due to the small grain size and good catalytic activity of the cubic WC1−x phase.

Structure and Thermal Transformations of Methylammonium Tungstate

AbstractMethylammonium paradodecatungstate, (CH3NH3)10[H2W12O42] ⋅ nH2O, was prepared by the reaction of WO3 or H2WO4 in aqueous methylamine, followed by drying. The [H2W12O42]10− anion consists of two HW3O13 groups containing three edge‐sharing WO6 octahedra and two W3O14 groups having two edge‐sharing connections. On drying the produced material at 70 °C, some lattice water was released, but this did not affect the [H2W12O42]10− structure, although there was a decrease in the unit cell volume. By adding water, the loss of lattice water and structural changes were reversed. The existence of paradodecatungstate anions was confirmed by single‐crystal and powder X‐ray diffraction, Fourier transform infrared, Raman, 183W nuclear magnetic resonance, and ultraviolet‐visible spectroscopy. When the methylammonium paradodecatungstate was heated to more than 150 °C, CH3NH2 and H2O were released, and amorphous WO3 was observed as an intermediate product and monoclinic WO3 as the final product. These results reveal the structure of methylammonium tungstate, which was first reported in 1909 and now is used as an important negative staining reagent for virus observation, is methylammonium paradodecatungstate.

Synthesis, crystal structure and catalytic activity of an oxo-diperoxo tungsten(VI) complex containing an oxazine ligand for selective oxidation of sulfides

A novel oxo-diperoxo tungsten(VI) complex, [WO(O2)2(Hphox)], was prepared by reaction of WO3 in H2O2 with an oxazine-type ligand, 2-(2′-hydroxylphenyl)oxazine (Hphox). The complex was characterized by FTIR, 1H NMR and elemental analysis. The single-crystal X-ray diffraction studies revealed a seven-coordinate tungsten center with a distorted octahedral geometry. The [WO(O2)2(Hphox)] complex was applied as a catalyst in efficient and selective oxidation of sulfide to sulfoxide using 30% H2O2 or UHP (urea hydrogen peroxide) as oxidants. This catalyst showed excellent catalytic activities and high selectivities in producing a variety of aryl and alkyl sulfoxides under mild conditions. To get an insight into the mechanisms of oxidation of sulfides, the mechanistic studies were monitored by UV–Vis spectroscopy.

Surface-Mediated Chemical Dissolution of Two-Dimensional Nanomaterials toward Hole Creation

Chemically engineered holes on two-dimensional (2D) nanomaterials may significantly increase the number of edge sites to tune their intrinsic properties to achieve promising performance. Here, we report a general and mild approach to the convenient creation of holes on atomically thin nanosheets for engineering bandgaps and enhancing properties of 2D materials. Through surface blocking, controlled dissolution, and chemical stabilization, WO3 nanosheets are readily treated to create holes in the presence of bovine serum albumin (BSA) via the reaction of WO3 with OH– ions at pH 8. Arising from the increased bandgaps and more edge sites as demonstrated experimentally and theoretically, the resulting holey WO3 nanosheets exhibit enhanced photocurrents and much better performance during selective adsorption and photocatalytic degradation compared with those of bulky WO3 and nonporous nanosheets. Also, this approach is further extended to the convenient creation of holes on more 2D nanomaterials such as MoS2 an...

Photo-electrochemical properties of WO3 particulate layers

Monoclinic tungsten trioxide particle layers were prepared on FTO glass substrates by the sedimentation method and further annealing at different temperatures to improve the adhesion of WO3 particles to substrate. Linear voltammetry of these layers was measured within the periodically chopped light illumination [very narrow single peaks at 314, 365 and 404nm and the standard solar illumination (AM1.5G)]. An optimal amount of WO3 in the layer was found for each light source. Back side illumination is more advantageous only for thick layers and visible light source. Better adhesion at higher annealing temperatures resulted in more stable layers with the higher photocurrent. The increase of annealing temperature above 500°C caused the formation of undesirable crystal phases (produced by the reaction of WO3 and FTO layer) and the significant decrease in photocurrent.

Intrinsic Kinetics of Chlorination of WO3 Particles With Cl2 Gas Between 973 K and 1223 K (700 °C and 950 °C)

Chlorination is one of the methods applied in extractive metallurgy for the treatment of minerals to obtain valuable metals, such as titanium and zirconium. The possibility of applying chlorination metallurgy to other metals such as tungsten was the major aim of this study. The kinetics of the chlorination of tungsten oxide (WO3) particles has been investigated by thermogravimetry between 973 K and 1223 K (700 °C and 950 °C) and for partial pressures of chlorine ranging from 15 to 70 kPa. The starting temperature for the reaction of WO3 with chlorine is determined to be about 920 K (647 °C). The influence of chlorine diffusion through the bulk gas phase and through the particle interstices in the overall rate was analyzed. In the absence of these two mass-transfer steps, a reaction order of 0.5 with respect to chlorine partial pressure, and an activation energy of 183 kJ/mol were determined. For tungsten oxide particles of less than 50-μm size, a complete rate expression has been obtained.

Synthesis of potassium tungstate in the K2CO3-KNO3-WO3 system

The interaction of the components in the potassium carbonate-potassium nitrate-tungsten(VI) oxide system was studied. The reaction of WO3 with a potassium carbonate-potassium nitrate mixture was found to occur at a higher rate than the reaction with pure potassium carbonate at the same temperature. A variant of the synthesis of high-purity potassium tungstate with a high yield of the target product was developed on the basis of the obtained data.

Synthesis of sodium tungstate from the system Na2C2O4-NaNO3-WO3

The physicochemical basis of the heterogeneous reaction between the components of the system (sodium oxalate)-(sodium nitrate)-(tungsten(VI) oxide) has been studied. The reaction of WO3 with sodium oxalate-nitrate mixtures occurs at a lower temperature and at a higher rate than the reaction with pure sodium carbonate. A high-yield process for the synthesis of high-purity sodium tungstate has been developed on the basis of this study.

The synthesis and antiwear action of tungsten dithiolate

AbstractTungsten dithiolate was synthesised by the reaction of WO3 with toluene‐3,4‐dithiol (abbreviated to H2TDT), and its extreme‐pressure and antiwear properties were investigated on a four‐ball tester. The results showed that it possesses fairly good extreme‐pressure and antiwear abilities. Based on analytical results obtained by Scanning Auger Microprobe and Scanning Electron Microscopy, as well as Electron Ionisation Mass Spectra fragments, the antiwear mechanism of WTDT suggested that a permeating layer containing WC, WS2, and WO3 played an important role in the antiwear and friction‐reducing action.

Studies on Direct Carburization of WC form the Mixture lf WO3 and Carbon

The reason why WC powder of good quality cannot be obtained by the process of heating the WO3 and C mixture in H2 was examined by simple experiments. The authors obtained the following conclusions so that the 2 stage-carburization was adequate to solve the problem.1) The reduction by H2 occurs preferentially to the reduction by C when the mixture of WO3 and C is heated in H2.2) The H2O formed by the reaction of WO3+H2 reacted with carbon at the reacting zone. The quantity of the H2O depends upon both the way of charging and heating conditions, affecting the carbon content of WC.3) WC crystals of abnormal shape were found when the coarse WO3 powder was used. The reason was discussed.4) The WC powder of good quality was obtained when the H2O was either completely removed or not formed and when fine WO3 powder was used.