Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O. Its shape is like sheet or needle.

Ammonium paratungstate being calcined in the air can produce tungsten trioxide. During the drying process, water was removed under about 100 degree Celsius. When temperature is above 240 degree Celsius, it turns into ammonium metatungstate. Under 300-350 degree Celsius, it becomes ammonium tungsten bronze. When temperature reaches 400 degree Celsius, hexagonal crystal tungsten trioxide comes into being. Finally triclinic crystal tungsten trioxide forms under 500 degree Celsius.

Calcination temperature and speed also affect the property of tungsten trioxide. The higher the temperature is, the larger the grain size of tungsten trioxide. The heating speed will cause the different superficial area of tungsten trioxide particle. Tungsten trioxide can be used to made tungsten product and shielding matirials which is widely used in industry.



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Ammonium metatungstate spray dryer existing problems are listed as below:

1.Wall sticking phenomenon. Wet powder sticks in the drying chamber. The main reasons are: feeding amount exceed standard so it can not fully evaporate; before starting the drying process, the temperature of drying chamber is insufficient; after starting spraying, the feed speed is too fast.

2.Moisture content of product is too high. Low ventilating out temperature is the main reason that would affect the moisture content. Ventilating out temperature can be adjusted via feeding amount. So reduce the feeding amount will raise ventilating out temperature.

3.Finished product is of low purity. It is mainly because the air filtration is inefficient; incomplete cleaning of drying machine causes residual powder mixes up with finished product.

4.Grain size of finished product is too fine. This will affect ammonium metatungstate solubility and flow ability. It is mainly caused by the low solid content of liquid material.  



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The new process of calcination for ammonium paratungstate to tungsten trioxide by microwave was investigated.

The results of experiment show that the maximum decomposing rate of ammonium paratungstate is 96 .67 % after 4 min by microwave heating. In the new calcining process, the primary influnce factor is ammonium paratungstate' s weight, the secondary factors are time and microwave power. In this experiment range, the optimum conditions are that the microwave power is 650 W, the calcining time is 4 min, and the ammonium paratungstate′s weight is 10g.

Compared to the traditional method which will take two hours, the producing efficiency improves a lot. It is 1/30 of the original time. It embodies the advantages of microwave calcination. The finished product is of high purity, flow ability and good quality. Tungsten trioxide can be used to made tungsten product and shielding matirials which is widely used in industry.

 

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Aqueous sols of tungsten oxide dihydrate (WO₃·2H₂O) were prepared from Na₂WO₄ by an ion-exchange method. An aqueous solution of Na₂WO₄ was let to flow through a glass column packed with protonated cation-exchange resin. The effluent, initially transparent, turned into an opaque viscous fluid (pale yellow) in a few hours, before yellow precipitate deposited to completion in three days. The precipitate was a mixture of a crystalline phase of WO₃·2H₂O and an amorphous phase, and the crystalline part could be separated from another by washing with deionized water and centrifuging. The gel of WO₃·2H₂O thus obtained consisted of platelike crystallite 25 nm thick and 42 nm wide as evaluated from the X-ray diffractometer (XRD) peaks, and could be dispersed well into deionized water to form a stable suspension of colloidal particles with a mean diameter of about 30 nm. The mean particle size as well as the crystallite size tended to increase gradually with the repetition of dispersion in water under ultrasonic wave agitation and gelling by centrifuging. On heating, the gel (WO₃·2H₂O) changed to the monohydrate (WO₃·H₂O) at 100 °C, which in turn changed to the anhydride (WO₃) at 240 °C. Remarkably XRD patterns showed conspicuous preferred orientation of WO₃·2H₂O crystallites in (0 1 0) plane after the sol was centrifuged for a long time (10 h) and, upon dehydration, it was inherited by the dehydrated phases, resulting in the conspicuous orientation of WO₃ crystallites in (0 0 1).


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Due to its high density, excellent absorption behaviour against radiation and environmental friendly characteristics, tungsten alloy can be widely used to produce Technetium 99( Tc99) tungsten radiation shielding. Tc99 tungsten radiation shielding usually be used in nuclear medicine, which as the radiation shielding and container for Technetium 99m.

One of the commonly used radioactive materials in nuclear medicine is technetium 99 (Tc99). This is produced in a tungsten Tc99 generator, which contains a radioactive core, loaded with molybdenum 99 which decays to produce Tc99. This is mixed with sodium chloride and other chemicals before being injected into patients. The tungsten provides protection to the clinical staff handling tungsten Tc99generator.

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Radiation is an effective tool within medicine for both diagnostics and treatment of patients. Techniques such as SPECT and PET utilize radioactive materials injected into the patient, which are then monitored by gamma cameras (SPECT) or scanners (PET) to detect the presence of tum ours in the body. Due to its high density, excellent absorption behaviour against radiation and environmental friendly characteristics, tungsten alloy can be widely used in SPECT and PET utilize radioactive materials injected as tungsten alloy syringe shield.

2 mm solid tungsten flange helps syringe shield the hand when withdrawing liquid from a vial. Flange is easily removed to allow transition from drawing dose to patient injection. 9 mm thick glass-5.2g/cc gives the greatest protection of any glass in any syringe shield and syringe shield is easily replaced. twist-turn and the syringe is held firmly.

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Packing: in iron drum with double inner plastic bag of 50kgs or 200kgs net  each.

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Installation method of tungsten points in automotive relay is shown as follows:
To fully play the properties of the automotive relay, the installing direction should be in accordance with the impact resistance direction of the automotive relay. That is to say, impact direction should be perpendicular to the direction of movement of the armature and tungsten points to effectively improve the anti-shock and impact resistance performance of the normally closed tungsten points in the non-energized state,.

In order to improve contacting reliability and to avoid the patter of tungsten points, tungsten carbide falling on the surface of tungsten points, the axial of tungsten points of automotive relay should be parallel to the ground when it is installed.

You should put the small load tungsten points on the top of the large load tungsten points when installing multiple sets of automotive relay.
You can choose housing installing method for preventing the damage of mounting feet in shock and vibration condition when install large volume of relays.

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i) Synthesis of 5-substituted 1-H-tetrazoles

The [2+3] cycloaddition reaction between nitriles and sodium azide, catalyzed by several tungstates, produced the corresponding 5-substituted 1-H-tetrazoles. Sodium tungstate dihydrate was used only for benzonitrile and 36% yield was obtained.


 

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