2016年1月15日星期五

Analysis of Tungsten Oxide Nanowires Film


In the past few years, an increasing interest has been put on the tungsten oxide films due to their potential applications in smart windows, gas sensors, photocatalytic reactions, and optoelectronic devices etc. The unique properties of the tungsten oxide films were usually determined by the oxygen defects and the valence states of tungsten ions. Besides, it is very important to improve the properties of tungsten oxide films and other oxide films by controlling their morphologies and crystalline phases,which mainly depend on the preparation technologies and thermal treating temperatures and atmospheres.
Thin Film

When the temperature of the source and substrate changes, the growth of the tungsten oxide nanowires changes with regularity. i.e., as the temperature of the source of evaporation and substrate increases, the diameter of tungsten oxide nanowires increases gradually and its diameter increases faster than its height; as the temperature of the substrate increase, the height of the tungsten oxide also increases gradually and its height increases faster than its diameter.

A Facile Route to Tungsten Oxide Nano Materials

Nano-sized materials and products have been used widely in many applications because of their outstanding properties, different from those of the bulk materials. In early investigations into nanotechnology, the arc discharge technique was the first well-developed method used to manufacture nanoproducts.

However, owing to difficulties involved in controlling the manufacturing parameters, the purity and quality of nanoproducts synthesized by arc discharge called for improvement. The inert gas condensation (IGC) system was thus established by Gleiter. Because there are no catalysts or containments, it is considered the cleanest method of producing high quality products. In this system, metals are first placed in a tungsten or graphite boat and evaporated. The metal vapor is then cooled under an inert gas atmosphere (e.g. helium or argon) to condense into clusters or nanoparticles.
Yellow Tungsten Oxide

Although the arc method has a higher production rate than IGC system, the latter produces larger particles. Hence, a modified technique based on the IGC system was developed, in which blowing gases were introduced to obtain finer particles with better particle size distribution. To retain the benefits of both the arc discharge method and the IGC system, a plasma arc is used as the heat source and blowing gas is applied to quench the evaporated materials in this modified system. A simplified manufacturing process that enhances the purity of the as-prepared products is required. Therefore, an effective method, namely, the modified plasma arc gas condensation technique has been proposed.

A modified plasma arc gas condensation technique was successfully used to synthesize various nano-sized tungsten oxide nano materials with morphologies and structures that may be tuned by controlling the experimental parameters. Various non-stoichiometric WO3−x nano materials could be prepared by tuning the oxygen content during the process. W18O49nanotubes and nanorod bundles were also prepared by He plasma arc with different Ar/O2 ratios. In addition, W18O49/TiO2 core–shell nanoparticles were prepared by evaporating a dual target. In the present study, we addressed the feasibility of the plasma arc gas condensation technique and confirm its potential for nanomaterial fabrication.

Tungsten Oxide Mesoporous Structure Factors

Composites calcined in the silica pores of silica acid is converted to form the influential tungsten oxide, tungsten oxide calcination temperature of crystallization and its mesoporous structure. This paper explores at 550-950 ℃ between different calcination temperature impact of mesoporous tungsten oxide structure. Ethanol as a dispersant, and silicotungstic acid silica mesoporous material than m (WO3) / m (SiO2) 3/1, after calcination at different temperatures HF treated tungsten oxide. When the calcination temperature at 550 ℃, almost no diffraction peaks in the small, indicating the degree of structural ordering poor, while N2 adsorption - desorption characterization of the specific surface area of ​​42.7m2 • g-1, and after more than 600 ℃ calcined surface area of ​​68.0m2 • g-1 there were significant decreases when the calcination temperature is 600-750 ℃ ​​when, in the vicinity of 2θ = 1 ° there is a clear diffraction peaks, indicating that the tungsten oxide upon calcination crystalline SiO2 is preferably within the hard model , ordered mesoporous structure after HF treatment of tungsten oxide is preferably, but in a small angle diffraction, no diffraction peaks were observed secondary peaks, indicating that the mesoporous structure is not a good long-range order in the calcination temperature reached 850 and 950 ℃, the structure of the degree of order is poor, there may be caused by high temperature volatile part of the tungsten oxide, thus affecting its structure degree of order.

Small angle XRD patterns of ethanol as a dispersing agent in a different material than silicon tungsten acid mesoporous silicon when, 600 ℃ calcination and get treated by HF tungsten oxide mesoporous materials can be seen when the silicon and silicon-mediated acid hole material ratio m (WO3) / m (SiO2) is 2:1, the figure in the small-angle XRD diffraction peaks, showing that structural order is poor, while the N2 adsorption - desorption characterization of the specific surface area of ​​40.7m2 • g-1, and calcined at 600 ℃ than the surface area of ​​68.0m2 • g-1 significantly decreased compared to when the material ratio 3/1 and 4:1, there is a distinct diffraction peaks near the (211), Description In this mass ratio is preferably within a range of structures can be prepared tungsten oxide mesoporous material. When silicotungstic acid and mesoporous silicon material ratio 5:1 when, in the small-angle XRD pattern of the diffraction peaks is not obvious, indicating that its structure Sequence poor, probably due to the content of tungsten is too high, the silicon oxide outside the tunnel crystallization

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Tungsten Oxide Electrochromic Thin Film


Electrochromic film materials include various organic and inorganic compounds, of which the most studied is tungsten oxide, the main methods of preparation include vacuum thermal evaporation, electron beam evaporation, sputtering, vapor deposition, electrodeposition and sol - gel method. Electrochromic film a certain temperature heat treatment can improve their adhesion and cycle life, but the high temperature heat treatment tends to affect the magnitude of the response time and color film. General physical preparation methods require high temperature heat treatment, such as electron beam evaporation method needs a heat treatment 500e, 350e thermal evaporation requiredRF sputtering need 200 ~ 300e. These methods are often due to expensive equipment, technical complexity and demanding process conditions and subject to certain restrictions; the chemical preparation of the sol - gel method is a simple equipment, low temperature deposition uniformity and easy preparation method for preparing a large area, but usually 100e need more heat. Alkoxide method as required 250e of heat treatment, ion exchange need 150e, halogenated oxidation need 120e. 

80e heat treatment method has been reported, and in a soft deformable polyethylene terephthalate (PET) Preparation of the electrochromic thin film on the substrate so as to cover any irregularities in the surface shape of the object, but the film thus prepared The cycle life of only dozens of times, can not meet the actual needs. Sodium tungstate as raw material, ion exchange acid solution, ethanol, and polyvinyl alcohol (PVA) as an additive, by sol - gel prepared by the superior performance of the tungsten oxide electrochromic films. This film just 75e of the heat treatment temperature, the driving voltage of -1 ~ + 1V, fully colored and fade time of only a few seconds, coloring in aqueous solution - fading cycles up to 600 times, the color can be kept after coloring number of days.
The resulting film is colorless and transparent, colored blue after uniform color. At 300 ~ 900nm wavelength, variation in the film of the colored state and the faded state transmittance. When fading state, the transmittance in the visible and near-infrared region are more than 93%, but in the near-ultraviolet region due to the absorption of the matrix glass, so that a decrease in transmittance. When the colored state, in the region of 600nm or more has a good absorption, transmittance of 21% or less, which is displayed with its appearance coincides blue. Transmittance in the colored state of 600nm or less significantly increased, but the colored state and the faded state at 500nm transmittance difference also more than 50%. Test results show that the film color changed significantly, having good light controllability.