Use sodium tungstate solution as raw material, preparing ammonium metatungstate solution by solvent extraction or ion exchange. Solvent extraction and ion exchange which is basically the same process and the preparation of ammonium paratungstate. The difference is in the back-extraction (or desorption) operation, stripping agent (or desorbent) and amount of different concentrations in the solution was maintained at pH 3 to 4 cases, back-extracted (or desorption) obtained metatungstate ammonium solution. This method in general APT production process, unnecessary use of stripping agent (or desorbent) can be produced under conditions of AMT solution, so it is a simple method.

Ammonium tungstate solution as a raw material by solvent extraction or ion exchange, then the cationic extractant (or a cation exchange resin) and extracted (or adsorbed) ammonium tungstate solution [NH4] + ion, and then with a suitable stabilizer and can output under the condition of pH AMT solution, which is both simple and economical method. Ammonium metatungstate solution solvent extraction or ion exchange method was the same concentrated crystals or spray drying to take ammonium metatungstate products.



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The crystal properties of ammonium paratungstate like crystal morphology, average particle size, particle size distribution, apparent density and flow ability affect the properties of tungsten powder, tungsten wire and tungsten alloy. Single crystal ammonium paratungstate due to its eminent physical properties has become ideal raw materials for preparing tungsten products.

Based on crystallization theory of single crystal ammonium paratungstate, the influences of crystallization device, stirring speed, temperature on crystallization agglomeration of ammonium paratungstate were studies. The results show that the optimal stirring speed is determined as 30, 50, 70r/min, respectively in different developmental stages of crystallization. Under optimal conditions, single crystal rate arrives to optimal value. Suitably reducing pre-crystallization temperature, single ammonium paratungstate crystal rate has more space for enhance. When crystallization temperature is 80 degree Celsius, crystal rate was 96% to achieve the best value. The fluid layer flow control technology and devices for single ammonium paratungstate crystal preparation can effectively reduce collisions between grains, so that the ammonium paratungstate powder single crystal rate can arrive at more than 90%.



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Vanadium dioxide film is a new type of heat-sensitive functional materials. It is with increasing temperature at about 68 ℃ will change from semiconductor monoclinic rutile structure to metallic state tetragonal rutile structure. Besides the resistivity and infrared light transmittance and other physical properties are also mutated, based on this characteristic, it is widely used in optical data storage, optical switches and smart windows and other fields. However, due to the phase transition temperature of vanadium dioxide is too high to be widely used. After the studies found that the incorporation a small amount of tungsten ions in vanadium dioxide film can effectively reduce the phase transition point of the film, which is conducive to tungsten vanadium dioxide film be applied in more areas.
Vanadium dioxide doping tungsten cause phase transition temperature lower there are two interpretations, the first one is because when the metal - semiconductor phase transition the vanadium atoms of lattice center off center octahedral voids, then tungsten which has larger atomic radius replace vanadium atoms, however, vanadium octahedral body no extra space for tungsten atoms from the center so as to stabilize the vanadium dioxide metal phase. The second explanation is tungsten has more than two d electrons into V3d vanadium, making the band gap of the semiconductor phase decreases.

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The physicochemical basis of the heterogeneous reaction between the components of the system (sodium oxalate)-(sodium nitrate)-(tungsten(VI) oxide) has been studied. The reaction of WO3 with sodium oxalate-nitrate mixtures occurs at a lower temperature and at a higher rate than the reaction with pure sodium carbonate. A high-yield process for the synthesis of high-purity sodium tungstate has been developed on the basis of this study.

 

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Single crystal ammonium paratungstate is the ideal raw material for high performance tungsten material due to its high physical properties. Single crystal ammonium paratungstate powder has good flow ability. Tungsten powder calcined by single crystal ammonium paratungstate which is pressed and drew into tungsten wire, the rate of finished products can reacn 90%. On the contrary rate of finished products made by polycrystal ammonium paratungstate is 70%. Thus single crystal ammonium paratungstate has become the required raw material for high quality tungsten wire.

Besides that, single crystal ammonium paratungstate has high apparent density, gaps between the grain is even and small, it has low mechanical defects, high compaction density, and has become the raw materials for tungsten wire and tungsten alloy products. For example, the service life of hammer made by single crystal ammonium paratungstate is 2-3 times longer than polycrystal APT. Single crystal ammonium paratungstate has become the perfect raw materials for ammo, high density alloy and other tungsten products.



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Before beginning the process to convert APT to AMT, a conventional pH, probe was calibrated using standard solutions at pH 4 and 7. 3000 mL of double distilled water was heated to 90-95° C. Approximately 250 g of APT powder was added to the hot water, and the mixture was stirred using a stir bar. Cation exchange resin was added incrementally in portions of approximately 10 g until the pH of the liquid portion of the APT/water mixture was between 3 and 4. The total volume of resin necessary to reach a pH between 3 and 4 was approximately 675 mL resin/Kg APT. As the APT dissolved in the acidified water, it reacted to form AMT, thereby allowing more APT to dissolve in the solution and drive the conversion of the APT toward completion.

The dissolution and reaction of the APT initially occurred relatively quickly. As the reaction proceeded the reaction mixture changed from an opaque white slurry to a clear, slightly yellow or amber solution. When the solution appeared clear, indicating that substantially all of the APT had been converted, additional APT was added in two 250 g increments until the solution contained 750 g APT (250 g/L). The 750 g of APT reacted in the process (250 g initially+500 g added) was dissolved and converted to AMT in approximately 90 minutes. 



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Collimators are fabricated using the above tungsten alloy and 304 stainless steel material as cladding. The tungsten alloy shield for the tungsten directional collimator is designed to provide a 50 degree radiation beam and is encased with stainless steel and totally sealed by argon arc welding.

When an exposure is taken with tungsten directional collimator attached to the exposure head of the guide tube of gamma camera, the radiation beam coming out will have a 50 degree solid angle in the forward direction. The primary radiation beam intensity in all other area except the front side will be reduced to 5% with the collimator.

At a source to film distance (SFD) of 50 cm, the beam will cover an area of a circle with 24 cm radius which is sufficient to cover a film size of 37 cm x 30 cm. Overall size : 44 mm dia x 82 mm long. Weight : 1.15kg.

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Tungsten powders were prepared by Self-propagating High-temperature Synthesis (SHS) method directly from hitherto unreported system: sodium tungstate (Na₂WO₄) and magnesium (Mg). The adiabatic temperatures of self-propagating combustion reactions with different amount of Mg in Na₂WO₄ + Mg system were calculated. The influences of different starting conditions (molar ratios of Mg/Na₂WO₄ and relative densities of samples) on the compositions and microstructure of reaction products were investigated. It shown that, the complete reduction of WO₃ required a 60% excess of magnesium over the stoichiometric molar ratio Mg/Na₂WO₄ of 3. The amount of the impurities is minimal at appropriate relative density. At last, tungsten powders can be obtained after the acid enrichment and distilled water washing.

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The tungsten collimator kit is a main component of medical X-ray detector. This detector system was designed to simultaneously measure the X-Ray tube peak potential (kVp), and to characterize the mammographic X-Ray tube spectrum.

The components of tungsten collimator kit:

Stainless steel collimator housing

1. Tripod and mounting plate
2. Laser pointer
3. Brass Spacer
4. 7 Tungsten (W) Collimator disks:

• 1 mm thick with 25 µm hole
• 1 mm thick with 50 µm hole
• 2 mm thick with 100 µm hole
• 2 mm thick with 200 µm hole
• 2 mm thick with 400 µm hole
• 2 mm thick with 1000 µm hole
• 2 mm thick with 2000 µm hole

All Tungsten disks are made of alloy HD17 (90% W, 6% Ni, 4% Cu). All Tungsten disks and spacers have a diameter of 0.625 inches. This Tungsten (W) Spacer /Collimator is 36 mm thick with a 300 µm hole. It is designed to stop and collimate x-rays greater than 100 keV produced from high energy tubes.
 

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Both radiotherapy and most effective chemotherapeutic agents induce different types of DNA damage. Here we show that tungstate modulates cell response to DNA damaging agents. Cells treated with tungstate were more sensitive to etoposide, phleomycin and ionizing radiation (IR), all of which induce DNA double-strand breaks (DSBs). Tungstate also modulated the activation of the central DSB signalling kinase, ATM, in response to these agents. These effects required the functionality of the Mre11-Nbs1-Rad50 (MRN) complex and were mimicked by the inhibition of PP2A phosphatase. Therefore, tungstate may have adjuvant activity when combined with DNA-damaging agents in the treatment of several malignancies.

 

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