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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Ammonium metatungstate spray dryer wall sticking solutions include improve the structure and texture of drying tower, use the proper atomizer, proper installation of atomizer, proper operation process, etc.

1.Improve the structure and texture of drying tower. If the design of diameter of dry tower is smaller than the atomizer cone, it will cause a mass amount of wall sticking. In order to prevent wall sticking, the diameter of dry tower should be larger, thus the liquid material will fall down directly without making contact with wall of tower. But the diameter can not be too large because it will increase cost of equipment and occupied area., also affect flow speed of hot air in the tower and drying quality.

2.Use the proper atomizer. Atomizer is also called nozzle, it is the key part of spray dryer. Its different structure affect the distribution of misty liquid, also diameter and property of micro grains.

3.Installation of atomizer. If there is only one atomizer in the dry tower, the axis of atomizer should be on the center line of tower. If there are more than one atomizers, then the nozzle of atomizers should not be face to face.


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2. Inappropriate control of tungsten blanks granular can affect the quality of tungsten contacts

Since the mixing ratio of particle size of tungsten powder is inappropriate or uneven, resulting in coarse grain, fine grain, boxes of different crystal polymorphs exist in the sintered tungsten bar, in which fine grain may be too burning, which will affect tungsten workability of the ultimately affect the performance of tungsten contacts.


 

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⁵⁷Fe Mössbauer spectra of xNa₂O · (99 − x)WO₃ · ⁵⁷Fe₂O₃ glasses (30 ≤ x ≤ 42) comprised of a doublet due to octahedral iron, Fe³⁺(O_h), and a weak doublet due to Fe²⁺(O_h); a large Debye temperature of 580 K was obtained at low temperatures. Fourier transform infrared spectra of the sodium tungstate glasses showed a gradual increase in the fraction of WO₄tetrahedra (T_d) when Na₂O content was increased. Mössbauer spectra of the tungstate glasses irradiated with ⁶⁰Co γ-rays showed an increase in the fraction of Fe²⁺, due to electron transfer (scattering) from WO and FeO bonds to Fe³⁺, as the electron spin resonance spectra of iron-free sodium tungstate glass indicated a simultaneous formation of W⁵⁺ and the ‘hole’ trapped on the oxygen atom. From the linear relationship between glass transition temperature, T_g, and quadrupole splitting, Δ, of Fe³⁺ (‘T_g − Δ rule’), the slope of the straight line was estimated to be 260°C/(mm s⁻¹). Mössbauer spectra of heat-treated tungstate glasses showed a gradual change from Fe³⁺(O_h) to Fe³⁺(T_d), along with the precipitation of the Na₂W₂O₇ phase composed of W⁶⁺(O_h) and W⁶⁺(T_d). These results indicate that  iron occupies W⁶⁺(O_h) sites in glasses, while it occupies W⁶⁺(T_d) sites in glass-ceramics.

 

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