Shape Influence on CsxWO3 Nanocrystals Surface Plasmon Resonance
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- Category: Tungsten Information
- Published on Tuesday, 05 April 2016 17:59
- Written by xinyi
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Surface plasmons (SPs) are coherent delocalized electron oscillations that exist at the interface between any two materials where the real part of the dielectric function changes sign across the interface (e.g. a metal-dielectric interface, such as a metal sheet in air). SPs have lower energy than bulk (or volume) plasmons which quantise the longitudinal electron oscillations about positive ion cores within the bulk of an electron gas (or plasma). The charge motion in a surface plasmon always creates electromagnetic fields outside (as well as inside) the metal. The total excitation, including both the charge motion and associated electromagnetic field, is called either a surface plasmon polariton at a planar interface, or a localized surface plasmon for the closed surface of a small particle. The existence of surface plasmons was first predicted in 1957 by Rufus Ritchie. In the following two decades, surface plasmons were extensively studied by many scientists, the foremost of whom were T. Turbadar in the 1950s and 1960s, and Heinz Raether, E. Kretschmann, and A. Otto in the 1960s and 1970s. Information transfer in nanoscale structures, similar to photonics, by means of surface plasmons, is referred to as plasmonics.
Localized surface plasmon resonance phenomena have recently been investigated in unconventional plasmonic materials such as metal oxide and chalcogenide semiconductors doped with high concentrations of free carriers. Synthesize colloidal nanocrystals of CsxWO3, a tungsten bronze in which electronic charge carriers are introduced by interstitial doping. By using varying ratios of oleylamine to oleic acid, synthesize three distinct shapes of these nanocrystals—hexagonal prisms, truncated cubes, and pseudospheres—which exhibit strongly shape-dependent absorption features in the near-infrared region. It's rationalized these differences by noting that lower symmetry shapes correlate with sharper plasmon resonance features and more distinct resonance peaks. The plasmon peak positions also shift systematically with size and with the dielectric constant of the surrounding media, reminiscent of typical properties of plasmonic metal nanoparticles.
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CsxWO3 Hydrothermal Synthesis and Near-Infrared Shielding Properties
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- Category: Tungsten Information
- Published on Tuesday, 05 April 2016 17:50
- Written by xinyi
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Cesium tungsten bronze (CsxWO3, x=-0.1、0.2、0.3) powders were synthesized with different cesium content by the low temperature hydrothermal method in citric acid solution. Citric acid is a weak organic tribasic acid. It occurs naturally in citrus fruits. In biochemistry, it is an intermediate in the citric acid cycle, which occurs in the metabolism of all aerobic organisms. More than a million tons of citric acid are manufactured every year. It is used widely as an acidifier, as a flavoring, and as a chelating agent. A citrate is a derivative of citric acid; that is, the salts, esters, and the polyatomic anion found in solution. An example of the former, a salt is trisodium citrate; an ester is triethyl citrate. When part of a salt, the formula of the citrate ion is written as C6H5O73− or C3H5O(COO)33−.
Hydrothermal synthesis includes the various techniques of crystallizing substances from high-temperature aqueous solutions at high vapor pressures; also termed "hydrothermal method". Temperature-difference method is the most extensively used method in hydrothermal synthesis and crystal growing. Supersaturation is achieved by reducing the temperature in the crystal growth zone. The nutrient is placed in the lower part of the autoclave filled with a specific amount of solvent. The autoclave is heated in order to create two temperature zones. The nutrient dissolves in the hotter zone and the saturated aqueous solution in the lower part is transported to the upper part by convective motion of the solution. The cooler and denser solution in the upper part of the autoclave descends while the counterflow of solution ascends. The solution becomes supersaturated in the upper part as the result of the reduction in temperature and crystallization sets in.
The CsxWO3 film was prepared with PVA as film forming agent by roller coating method. The near-infrared shielding and heat insulation performance of the glass coated with CsxWO3 film with different cesium content were mainly investigated. The results indicate that the near-infrared shielding and insulation of the glass coated with CsxWO3 film is improved with the increasing of the cesium content. By comparison with the blank glass, the glass coated with Cs0.3WO3 film has best near-infrared shielding and heat insulation, and the temperature difference of heat insulation can attain to 13.5℃.
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Cerium-Tungsten Trioxide SCR Denitration Catalyst 1/2
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- Category: Tungsten Information
- Published on Friday, 01 April 2016 18:32
- Written by chunyan
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From the precious metal catalyst to today widely used SCR denitration catalyst which is using titanium dioxide as the main catalyst carrier, vanadium pentoxide, tungsten trioxide as main active ingredient, the SCR denitration catalyst has experienced a variety of important technological changes and condensed years of hard work from academics and numbers of plant personnel.
However, since the vanadium itself is highly toxic, it’s easy to cause body bronchitis, impaired vision and kidney damage. If the waste catalysts are not recovered, they will do a huge damage to environmental and body, therefore, in the great situation of environmental protection, the user must spend an expensive special costs in the recycling of waste SCR denitration catalyst. Faced with this situation, promoting a new non-toxic catalyst product has become the focus supporting and developing projects for government.
Many scholars and manufacturers have made great efforts in this area, also there is a new type of highly efficient, inexpensive SCR denitration catalyst product has been successfully developed. This non-toxic SCR denitration catalyst takes modified rare earth functional ceramics as a carrier, and takes cerium dioxide, tungsten trioxide as the main active ingredients; also it is mixed with a certain amount of zirconium dioxide, glass fibers, and other trace components.
Cerium, a silver-gray active metal, its powder is easily spontaneous combustion in the air, can soluble in acid, the highest abundance of rare earth elements. Cerium is easily oxidized at room temperature; therefore, when exposed in the air, it is easy to lose its luster and can even burn by using a knife to rasp in the air. Cerium is mainly as a reducing agent in the catalyst; it can be used as additives in manufacturing cerium salts for manufacturing medicine, leather, special glass, textile and other industries; at the same time, cerium alloy can be used to manufacture jet propulsion components because of its heat-resistant.
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Cerium-Tungsten Trioxide SCR Denitration Catalyst 2/2
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- Category: Tungsten Information
- Published on Friday, 01 April 2016 18:35
- Written by chunyan
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Rare earth element - tungsten trioxide SCR denitration catalyst can be applied to coal-fired power, glass, cement, steel mills plants, heating boiler room and other coal, oil, SCR flue gas denitration process. At the same time, because of this tungsten trioxide SCR catalyst belongs to rare earth system, which has many excellent properties, such as non-toxic, no need to recover, no fear for water, can be regenerated for several times, also it can be made into honeycomb, plate and corrugated and other types. This type of SCR denitration catalyst maybe possible fully replaces the imported VW-Ti system SCR catalyst technology in the near future.
Compares to ordinary V-W-Ti system catalyst, this cerium rare earth element tungsten trioxide denitration catalyst has many advantages:
1. None toxic effects, do not cause harm to humans and the environment;
2. Efficiency with long life
Experiments show that the catalytic ability of rare earth elements is higher than vanadium (V) element, thus brings the titanium dioxide, tungsten trioxide and other components reduced, so that the production costs reduced at the same time. Meanwhile, the increasing content of alumina also bring catalyst stiffness and hardness markedly improved, thus make the catalyst has longer life and better suit for glass furnace, cement, coal boiler other severer operating conditions with high ash content in flue gas;
3.Temperature window broaden, the minimum working temperature of this rare earth cerium-tungsten trioxide SCR denitration catalyst is as low as 260℃, which is 50℃ lower than the average 310℃, making the use scope expanded;
4. Can be regeneration more times, this kind of rare earth element catalyst is able to withstand repeated washing without damaged which means higher regeneration ability, it also greatly reducing the cost and realizing the goal of economic interests.
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Composite Carrier Tungsten Trioxide SCR Denitration Catalyst
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- Category: Tungsten Information
- Published on Friday, 01 April 2016 18:30
- Written by chunyan
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Denitration practices and researched have shown that the nature of carrier has a great impact on the catalyst’s activity and life. As an important part of the denitration catalyst, the developing carrier is also a problem which is eager to be solved. The catalyst most commonly used in the market today is generally takes titanium dioxide as a carrier, tungsten trioxide, vanadium pentoxide as the main active substance. Some scholars have provided a method that uses modified cordierite powder and titanium dioxide to prepare tungsten trioxide SCR denitration catalyst, thus to improving carrier performance and reducing cost, to get the high thermal stability and wear resistance flue gas denitration catalyst which is meeting the requirements.
Steps as follows:
1. Produce modified cordierite powder: immersing the cordierite powder in sulfuric acid with the temperature of 25~110 °C for 12 hours, and then drying it for 5~12 hours to obtain the modified cordierite powder;
2. Prepare catalyst active solution: dissolve the right amount of oxalic acid in deionized water for mix well, then add ammonium metavanadate, heated to 85 °C and keep the temperature for about 20 minutes;
3. Weigh the modified cordierite powder, titanium tungsten powder into a mixer, stir until uniformly mixed after glass fiber and polyvinyl alcohol added, then add catalyst activity and deionized water which are prepared;
4. Cool and adjust the solution after stirred uniformly, and decayed for 24 hours;
5. Form to honeycomb catalyst as required, and dry for 3.5~5 hours at 85~105 °C;
6. Calcining for 4~8 hours, and then continually calcining at 600 °C for 4~8 hours, to give the desired composite carrier tungsten trioxide SCR denitration catalyst products.
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