2016年11月28日星期一

Tungsten Oxide Used to Increase the Heat-input Amount of Near Infrared Radiation

The invention relates to the use of tungsten oxide or tungstate to increase the heat-input amount of near infrared radiation. It was found that these materials exhibit a distinct higher effect than other known Infrared Radiation(IR) absorbers although absorbing the same amount of energy. This is very surprising and cannot be explained so far. Tungsten bronzes incorporated in coatings led to a much higher temperature increase upon irradiation with IR than expected according to its spectral absorption capacity. The temperature increasing measured was distinctly higher than found with other known IR absorbers and reached almost the temperature observed with carbon black.

Tungsten Oxide Photo

Many technical processes (like laser welding and marking of plastics, Near Infrared Radiation(NIR) curing and drying of coatings, drying of printings, laser marking of paper, curing and drying of adhesives, fixing of ink toners to a substrate, heating of plastic pre-forms etc.) require an efficient, quick and focused local heat-input through IR radiation. The conversion of IR radiation into heat is realized by placing appropriate IR absorbers at the place where the heat is required. Carbon black is a well known efficient IR absorber for such processes. But carbon black has one big draw back: that's its strong black colour. Thus carbon black cannot be applied for coloured (other than black or grey), uncoloured, white or transparent systems. For such systems a "white or colourless carbon black" is a great technical need.

Very surprisingly the tungsten oxide material of the present invention comes quite near to this target profile, although it is slightly bluish to grayish. But due to its surprisingly high efficiency of conversion of IR radiation into heat, this tungsten oxide material can be applied at such a low concentrations that its own colour is acceptable for most applications. The same is true for transparency: the material (plastics, coatings) containing this tungsten oxide remains also highly transparent.

The NIR curing of coatings can be used for all type of coatings including both pigmented and unpigmented coating materials. Depending upon the nature of the organic binder, coatings may comprise solvent or may be solventless or water-free. They may also comprise fillers and other additives in addition to the pigments. Any kind of coating is suitable in the method according to the invention, for example, powder coatings, clearcoats, high-solids coatings, effect coatings, high-gloss coatings, silk-finish coatings, matt-finish coatings, spray coatings, dip-coatings, pour-coatings etc.


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Tungsten Oxide Metallic Smart Windows Could Function in the Future as Electronics

Tungsten oxide is one of the mostly studied cathodic coloring electrochromic material. Electrochromic property of WO3 has been made into different electrochromic device and is applied in real life. There are many advantages of electrochromic device, transmittance can change continuously in a wide range and can be adjusted manually.

A B.C. engineering lab has created metal-coated glass that transmits up to 10 per cent more light than conventional glass and opens the door to windows that function as electronics. The most immediate use of the technology is to create smart window that can be programmed to absorb or reflect heat, depending on the needs of a building’s occupants, said lead investigator Kenneth Chau, a professor at the University of British Columbia Okanagan. “What’s interesting about this discovery is that it’s counterintuitive, because we always think of metals as being opaque, so it runs against our expectations,” he said. “I think one of the most important implications of this research is the potential to integrate electronic capabilities into windows and make them smart.”

Tungsten Oxide Metallic Smart Window Photo

But weren’t we all expecting glass to get a lot smarter?
“That’s true. When you watch Iron Man movies, they have displays on glass, they do computations on glass. This is a tiny step in that direction,” he said. Films like Iron Man and Star Trek provide scientists with inspiration for scientific progress, he said. “There is a dream that we can make glass smarter. These films give us concepts to strive for; the hard work is uncovering the science to make it happen.”

Glass is a crystalline structure that is fairly transparent, but not completely, you can still see it. Thin layers of metal actually boost the amount of light that goes through. While conventional glass does not conduct electricity, the metal layer creates an object with very different properties and the possibility of adding a variety of advanced technologies to a brilliantly transparent surface. Adding electronic control to windows will allow you to change the amount of light and heat passing through to more effectively use the energy provided by the sun naturally.

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Tungsten Oxide Industry Analysis and Outlook 2016-2023

Tungsten Oxide Market: Emerging Applications and Drivers
Tungsten oxide has several everyday uses. It is used in the manufacture of tungstates for fireproofing fabrics, for x-ray screen phosphors, and in gas sensors. Tungsten trioxide is also used as a pigment in coatings, paints, and ceramics due to its rich yellow color. In addition, tungsten trioxide has also proven useful in the production of smart windows or electro chromic windows. Smart windows are essentially electrically switchable glass that can alter its light transmission properties when a certain voltage is applied. This allows the user to obtain the desired level of tint on their windows by deciding how much light they want passing through.

The growth in end user industries is expected to increase consumption of tungsten oxide. The growth in medical and firefighting industry is set to drive the tungsten oxide market. In addition, rising consumption of semi-conducting compounds in emerging economies of Asia Pacific and Latin America is expected to boost demand for tungsten oxide. However, availability of substitutes and fluctuating raw material prices could hamper the growth of the market.

Tungsten Oxide Photo

Tungsten Oxide Market: Regional Dynamics
Growth in tungsten oxide demand is expected to be led by the Asia Pacific market, particularly China which accounted for majority of consumption in 2013. Major manufacturers of tungsten compounds are relocating their production facilities to China due to availability of cheap labor, infrastructure and attractive government policies. Republic of Korea, India, Vietnam, Malaysia, Cambodia, Australia, New Zealand and Sri Lanka are other major consumers of tungsten oxide in Asia Pacific. North America and Europe are mature markets and expected to experience moderate growth.

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Tungsten Oxide As New Material Can Boost Waste Heat Harvesting

A new material that emits short-wavelength thermal radiation when heated could be used in systems that convert waste heat into electrical energy thus boost waste heat harvesting. Created by an international team co-led by researchers at Purdue University, the University of Alberta and Hamburg University of Technology, the material comprises alternating layers of 20 nm of tungsten oxide and 100 nm of hafnium oxide.

Tungsten oxide is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO3. It is insoluble in H2O and acids, but soluble in hot alkalis. It is n type semiconductor material, the special physical and chemical property make it used in various filed and become the important functional material in modern scientific research.

tungsten oxide photo

The structure was chosen so that the emission of long-wavelength infrared photons from the material is suppressed while the emission of shorter wavelength photons is enhanced. These shorter wavelength photons have enough energy to drive a photovoltaic cell, while the longer wavelength photons do not. The research team tested the material by heating it to 1000˚C and using it to power a photovoltaic cell. They found that the new material produced 90% more electrical energy than a conventional black-body infrared emitter. It could someday be used to generate electricity from the waste heat produced by industrial processes and even automobile engines.


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N-doped Nanoporous Tungsten Oxide Electrode

Doping is commonly used to improve visible light responsive of transition metal oxide. A lot of researches show that metal ion like rare earth can promote the photocatalytic property of semiconductor material, however, metal doping may cause thermal stability of catalyst decreasing, it will introduce photo electron and recombination center of valance to lower its photoelectric property. Doping N can greatly improve the visible light absorption rate of semiconductor material.
Preparing of nanoporous tungsten oxide electrode:

1) Treating method for tungsten foil: Firstly cut it into 10mm x 15mm pieces, using waterproof abrasive to polish it, then clean it with acetone, isopropanol, methyl alcohol and deionized water ultrasound cleaning for 15min, blow it with nitrogen gas.

2) Use tungsten foil as anode, Pt foil of 10 x 15mm as counter electrode, put them into electrobath, the distance between two electrodes is 25mm. Then put electrobath in water bath of constant temperature, adjust the bath temperature to control the reaction temperature. The reacting area is 0.88cm2. Adding a certain amount of ready-prepared 1mol/L(NH42SOsolution electrolyte with different concentration of NH4F.

Photoaction Spectra
(Photoaction spectra of nanoporous WO3 photoelectrodes annealed at different temperature)

N-doping method:
Put the prepared nanoporous WOin tube furnace, inject NH3/N2(1:2), heat to certain temperature by heat up rate 5℃/min, keep it for a while, then cool it down to room temperature. Purity of NH3 and N2 is 99.999%, flow rate is 120ml/min.


Schematic Diagram
(Schematic diagram of energy band for undoped and N-doped nanoporous WO3 photoelectrodes)

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Cesium Tungsten Oxide Ultra Fine Powder Preparing Method

Tungsten oxide has excellent performance in electrochromic, catalysis, gas and other aspects. The composite oxides - tungsten bronze metal oxides generally refer darker colored metallic luster, and usually a metal conductor or metal semiconductor. Currently, cesium tungsten oxide, due to its low resistance and excellent visible light transmittance and near-infrared shielding properties, is widely used in the preparation of the conductive film used in glass septum thermal insulation coating.

The traditional preparation method of cesium tungsten oxide uses tungsten, tungsten acid source, Cs/W molar ratio of 1: (2.857~100), at 180~200°C reaction conditions for 1~3 days. The preparation takes a long reaction period, is of low efficiency, which is not conducive to industrial production.

Cesium Tungstate Molecular Photo

A process for preparing cesium tungsten oxide ultrafine powder, comprising the steps of:
(1) In accordance with Cs / W molar ratio of 1: (1.5 to 2.8), weigh cesium salt and tungsten salt. A chelating agent and alcohol reagent are added and reacting under 170 °C condition for 3h. Then mix them up.
(2) The step (1) was charged into a pressure vessel bomb reaction under 260 ~ 270°C reaction condition for 5 ~ 8h;
(3) The Step (2) was obtained by reaction of an alcohol wash, centrifugation, at 80°C under conditions of complete crystallinity dried in vacuum to obtain cesium tungsten oxide powder.


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