The thermal decomposition of ammonium paratungstate by preparing ammonium metatungstate: ammonium paratungstate and a small amount of citric acid catalyst after mixing into the far infrared, rotary furnace, controlled thermal decomposition temperature 200 ～ 280 ℃, decomposition of about 1 h. The removal of ammonia and water, ammonium paratungstate weightlessness rate was 5% ~ 6%.

The thermal decomposition products immediately after the slurry, adding proper amount of ammonia, Ph value is adjusted in the 3 to 4 range, at 90 ℃ digestion slurry. After evaporation to ammonium metatungstate content of 50% can be used as a liquid product to sell, crystallization, when the evaporation to the original volume of 20% filtering and separating, granulating product. Also can be evaporated and concentrated liquid product is prepared by spray drying. As of 45% ~ 50% ammonium metatungstate by high-speed centrifugal rotary spray dryer, imports of hot air temperature 250 ～ 300 ℃, outlet temperature 90 ～ 95 ℃, the obtained product is a spherical crystal, particle size is 200 mesh accounted for 95%, free water <1.5%.



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Tungsten pentachloride is dark green crystal flash, break down easily when exposed to air. There are two methods for its producing: one is in the hydrogen to restore tungsten pentachloride, and the other produce by six tungsten chloride and tetrachlorethylene reaction.
Using hydrogen reduction to producing tungsten pentachloride and the chemical reaction equation is: 2WCl6 + H2 → 2WCl5 + 2HCl. First, heating tungsten hexachloride at 410 ~ 425 ℃ in quartz tube will be at the same time introducing hydrogen to restore. During the reaction, there generating WClO and cheap WCl4, WCl2 and others, so it needs to sublimation purification in a stream of nitrogen, and then stored in a sealed tube.
By tungsten hexachloride and tetrachlorethylene reaction to obtain tungsten pentachloride the  chemical reaction equation is: 2WCl6 + C2Cl4 → 2WCl5 + C2Cl6. This reaction equipment is same with tungsten tetrachloride’s. Firstly making reaction equipment in vacuum state, and ready for 4 ~ 7g of tungsten hexachloride and tetrachlorethylene 25ml, and irradiation of 100W bulb at 100 ℃ the reaction is carried out in an oil bath for 24 hours.

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Tungsten pentachloride is kind of flash dark green crystal, its physical characteristics as follows: formula: WCI5, molecular weight: 361.2, the relative density: 3.875, melting point: 243 ℃, boiling point: 275.6 ℃, soluble in acetonitrile, benzene, chloroform, carbon disulfide and other organic solvents. Tungsten pentachloride CAS No. is 13470-14-9.
Tungsten pentachloride are sensitive to moisture and water, if placed in the air, which generates green surface film. Hydrolyzed in water will produce blue oxide (W20O58), but in the air can produce oxychloride (WOCl4) by heating. Besides tungsten pentachloride can reacted with amine will easy to generate amino compound. In most polar solvents can decompose, and slightly soluble in carbon disulfide and other non-polar solvents. To produce tungsten pentachloride can use hydrogen reduction tungsten hexachloride at 250 ~ 280 ℃ or use red phosphorus reduction tungsten hexachloride at 380 ~ 400 ℃. Or it can obtain by tungsten tetrachloride disproportionation reaction.

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After hydrolysis VOSO4 and NaSO4 and calcination obtain tungsten-doped vanadium dioxide powder, and then can use vanadium dioxide and tungsten-doped vanadium dioxide powder to producing thermochromism coating. Producing process as follows:
1. First putting VO2 powder, xylene, oil dispersants and ceramic milling beads in a planetary ball mill, 650r/min grinding 20 ~ 30min to obtained VO2 suspension.
2. The suspension was mixed with resin to produce coating with solid content 40% which help VO2 can maintain long-term stable storage.
3. Using a wire bar to make rein form a film and then dried at room temperature. The film thickness is 60 to 70 um.
During the producing process the longer grinding time, grinding grain trend has grown, easy aggregates and VO2 phase transition performance will continue to decline. Comprehensive experimental data found grinding time is about 20 ~ 30min can get the smallest average particle size of 275nm. Prepared coatings below TC without significant spectrum absorption or transmission peaks， at TC above, the coating in near-infrared band (1000 ~ 2500nm) exhibit low permeability, 400 ~ 1000nm band transmission slight increase, this is because when the VO2 powder metal-semiconductor phase transition the band gap change cause transmittance change.

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Due to vanadium dioxide has unique properties, so it is suitable for produce thermochromism coating and be wildly used. To make thermochromism coating is by hydrolysis VOSO4 and NaSO4 with calcination to obtain tungsten-doped vanadium dioxide powder, then mixed acrylic resin with vanadium dioxide powder to obtain it. Before making thermochromism coating should to produce vanadium dioxide and tungsten-doped vanadium dioxide powder. And the producing process as follow:  
(1) Putting 0.1molVOSO4 • xH2O into 0.2molNH4HCO3 solution by constant current mercury for 1.5h. Filtered the precipitate, and then washed with deionized water and ethanol, after vacuum drying to give a vanadium hydroxide powder.
(2) The powder was placed in a ceramic boat charged with an inner diameter of 35mm quartz tube, in the front the pipe keep 40cm for preheating. Besides for protecting the reaction should pass into the nitrogen flow rate 200 ~ 1500ml / min.  And then calcinate in 573 ~ 1073K for 3 ~ 40h and the heating rate is determined by the tube furnace itself power, about 20 ℃ / min. Finally to obtain VO2 powder this is undoped.
(3) The tungsten-doped vanadium dioxide powder producing steps is similar to vanadium dioxide producing. But at the first should mixed 0.5mol / L Na2WO4 solution in proportion into VOSO4 solution.

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Vanadium dioxide (VO2) is a metal-semiconductor and phase transition product, was metallic, when the temperature is below 34K, VO2 is monoclinic structure, was semiconductor, while the electrical conductivity, transmittance, magnetic susceptibility mutations. Due to this characteristic, so it is widely use in many different industries, such as buildings tone film, thermistor material, photoelectric switch material and infrared light imaging. VO2 powder can form a film in a complex surface or surface which can’t stand high temperatures by dispersed and spreading process. Besides by doping the other materials with VO2 can help it to reduce phase transition temperature (TC) to room temperature, so it is particularly suitable for thermochromism windows producing and other purposes. And now there has many methods for producing thermochromism window such as thermal decomposition method, spray pyrolysis and hydrothermal synthesis method.
After many studies found by hydrolysis VOSO4 and NaWO4 with calcination can obtain tungsten-doped vanadium dioxide powder. Then making tungsten-doped vanadium dioxide powder mix with acrylic resin can obtain coating which has thermochromic functional and the temperature is near the room temperature. What’s more the amount of tungsten-doped and TC can be precisely adjusted by Na2WO4 solubility.

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In tungsten electron multileaf collimator (EMCL) are standard equipment for modern Linacs. The tungsten leaves are close to the beam source and need to be of high density material and thin in order to get good beam shaping properties in ISO center. Multileaf collimators are a basic requirement for IMRT.

In electron therapy still applicators are used to shape the beam, which needs to be done close to the patient.Tungsten electron multileaf collimator was designed as a substitute for all electron applicators, and as it made similar to photon-MLC design, remote controlled beam collimation and isocentric dose delivery can be done, similar to photon RT.

Tungsten electron multileaf collimator is mounted to the Gantry by means of an adapter, and the 30 tungsten leaves made of brass shaper the field up to the field size of 21.4 cm x 21.4 cm in 100 cm ISO center distance. The tungsten leaves are located 16 cm above the ISO center.

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Radiotherapy tungsten multi-leaf collimators can accurately focus beams of radiation to target cancerous cells. In internal methods such as branchy therapy radioactive seeds can be implanted directly into a tumour. Prior to delivery, the seeds are held in tungsten shielding safe to protect medical staffs from the radiation.

There is a need to carefully control the emission of radiation; to protect those working with potentially harmful isotopes and to ensure that treatments effectively kill off cancerous cells, without harming healthy tissue. This is where tungsten shielding plays a vital role.

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Spray drying is a wide applied process in liquid process shaping and drying industry. It can be used to transform solution, emulsion, suspension and paste liquid into powder and granular solids. When the finished particle size distribution, residual moisture content, density and particle shape must meet with precise standards, spray drying becomes an ideal method.

The types and reasons for wall sticking during spray drying were analyzed. There are three types of wall sticking: half wet materials, materials with low melting point, dry powder. The wall sticking of half wet materials is concerned to the structure, fixing and operation of spray drying tower and sprayer, the motion of hot air in tower. The melting sticking occurred when the melting point of materials is lower than the drying temperature. The wall sticking of dry powder is concerned to geometric figure of cyclone chamber, roughness of wall, velocity of air and static charge. 



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4.Proper operation process. For the pheumatic spray drying tower, the process parameter often refers to drying temperature, feeding velocity and pressure of nozzle. Drying temperature includes inlet air temperature and outlet air temperature. Increase inlet air temperature can promote liquid evaporation, which will solidify the liquid before it contacts the wall which will reduce the wall sticking waste rate and increase yield of product. Besides that, temperature also affects the diameter of grains. When the temperature is low, the grain size is bigger which will prolong the drying process. When the inlet air temperature stay the same, raise the outlet air temperature can reduce the temperature differences to fasten drying efficiency.

5.The movement of hot air in the dry tower. The movement of hot air in the dry tower affects wall sticking directly. When the total amount of inlet air stay the same, the proportion of the air for protection atmosphere and air for drying will affects the drying result. If the air is insufficient for drying, liquid will stick on the wall before getting dried.



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