Cobalt doped ammonium paratungstate (Co-doped APT) precursors for the fabrication of cemented carbides were synthesized by co-precipitation, where W and Co are mixed on the atomic scale. The effect of cobalt content on the reduction of W–Co precursor was studied. W–Co precursors with different ratios of tungsten to cobalt were prepared and calcined at 220 °C for 5 h in air, followed by a reduction in hydrogen gas at 600 and 650 °C for different times. The resulting powders were characterized with respect to phase constituent, specific surface area, particle size, density, and morphology of the reduced powders.

It has been found that the addition of cobalt results in a higher reduction rate toward the metallic phases. However, the particle size of the reduced powders increases with increasing cobalt content, while its relative density decreases. The specific surface area of reduced powders at 650 °C increases for short reduction times, due to reduction of oxides to metal powder, and decreases for long reduction time due to agglomeration of metal powder. Cobalt plays the role as a catalyst during the reduction processing. On the other hand, it promotes the agglomeration of small particles. However, the completely reduced powders were well nanostructured with an average particle size between 20–50 nm.




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In order to improve the quality of tungsten products and the export need of tungsten wire, the method for producing high purity ammonium paratungstate is under research. In order to reduce producing cost, improve producing efficiency of tungsten, ammonium paratungstate prepared by tungsten concentrate is studied.

Tungsten concentrate preparing ammonium paratungstate mainly uses soda lye under alkaline leaching tungsten concentrate. During the processing procedure, the alkaline using amount is 2-3.5 times more than the theoretically amount. The first step is evaporation and crystalline of sodium tungstate. Firstly evaporate sodium tungstate in the reaction tower, coarse sodium tungstate crystal is produced. Then add water and hydrochloric acid into it and then acid decomposition happens. After acid decomposition, tungstic acid is produced and was mixed up with ammonium. It is then being processed under 80-95 degree Celsius for 4-6 hours, evaporation amount is between 60-70. The final process is crystalline, filtering, washing and dry. Then the finished ammonium paratungstate is made. 




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Non-isothermal kinetic (k, A and ΔE) and thermodynamic (ΔH, C_p and ΔS) parameters of ammonium paratungstate decomposition to the onset of formation of WO₃, were determined by analysing thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC) curves recorded at various heating rates (1–30°C min⁻¹). Thermal events encountered throughout the decomposition course were due to three endothermic (at 120 ° C (I), 195 ° C (II) and 359 ° C (IV)) and two exothermic (at 265 ° C (III) and 386 °C (V)) processes. The events I–IV were accompanied by weight losses resulting from the elimination of volatile components [(NH₄)₂O, NH₃ and H₂O] leading to the formation of intermediate solid products (metatungstate and polytungstate), whereas event V was due to the crystallization of WO₃ in the immediate vicinity of its formation (at 370 ° C).


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Due to tungsten alloy has high density, excellent radiation attenuation properties, and environmetal frendly, it is widely used to produce into tungsten syringe shield. Tungsten syringe shields, also called injection shields, are designed to reduce hand exposure to radioactive injections. With a great ability of radiation shielding, the barrel of the tungsten syringe shield can reach 0.06''-0.08''. And it is able to reduce radiation exposure from Tc-99m by more than 99%.
            
Detials of Tungsten Syringe Shield:

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The cyber-knife is a frameless robotic radiosurgery system used for treating benign tumors, malignant tumors and other medical conditions. The cyber-knife technology was invented to treat all stages of cancer patients and this treatment has remained successful till now. Due to tungsten alloy has high density, excellent radiation attenuation properties, and environmetal frendly, it is widely used in cyber-knife technology as tungsten collimator. Tungsten collimators are used as a main manufacturing component of this machine. One of the features of this cyber-knife is robotic mounting. In it, the tungsten collimators are fixed and used because they can produce circular radiation fields and collimate the radiations easily.

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Infiltration process for the preparation of silver tungsten points:
Firstly, pressing tungsten skeleton and silver blanks;
Secondly, pre-sintering tungsten skeleton at high temperature;
Thirdly, carrying out liquid phase sintering, that is, stack silver blanks and tungsten skeleton together into sintering furnace, the temperature is higher than the melting point of silver. Silver in the molten state will fill the tungsten skeleton pore by capillary action, and silver tungsten contacts are prepared.

The principle of capillary action of silver tungsten points prepared by infiltration process, its equation expressed as follows:

H = 2α * cosθ / g * ρ * γ

As can be seen from the above equation, if θ is smaller, silver (liquid metal) is easier into the tungsten porous skeleton gaps, that is to say, it is more easily to get desired silver tungsten contacts with high density.
the variable of H = 2α * cosθ /ρ * g * γ are shown as follows:
H: height of the liquid infiltrate into the capillary (mm)
α: surface tension (N / m²) between the liquid and gas phases
θ: wetting angle
ρ: liquid density (kg / m³)
g: acceleration of gravity
γ: capillary radius (mm)



 

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Tungsten articulatable hand-held probe is the smart answer to the question of whether a straight or an angled probe is more suitable for the localization of sentinel lymph nodes in breast cancer, melanoma, prostate cancer or other cancers.


Spatial resolution, angular resolution and sensitivity of tungsten articulatable hand-held probe depend strongly on the actual measurement conditions and from the selected tungsten collimator geometry.

The spatial resolution and sensitivity of different tungsten collimators were determined in a water phantom.

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Mechanical alloying processes for the preparation of silver tungsten point (W - 35 Ag):

Preparing materials procedure:
Pure silver powder, purity is more than 99%, and its diameter is between 1μm and 2μm;
Pure tungsten powder, its purity is over 99.3%, and its diameter is between 1μm and 5μm;
Mixing procedure: mixing silver powder and tungsten powder, between which, the content of silver is around 35%;
Milling procedure: milling grinding materials whose diameter is 6.35mm of WC small ball under the condition of air, time is controlled between 0h to15h in the milling machine; and motor speed is around 250r / min.
Pressing procedure: using one-way press to press mixing powder under 300Pa conditions to make compact.
Sintering procedure: sintering for 2h to get the maximum sintering density under hydrogen conditions, and the sintering temperature is around 870 ℃.
Cooling procedure: After sintering procedure, waiting for the sintering furnace cooled to room temperature.
Hot pressing procedure: heating 1h under 600Pa conditions, and the temperature is around 850 ℃, then hot-pressing the sintering compact.



 

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Tungsten articulatable hand-held probe is the smart answer to the question of whether a straight or an angled probe is more suitable for the localization of sentinel lymph nodes in breast cancer, melanoma, prostate cancer or other cancers.

The angular resolution of tungsten articulatable hand-held probe with a standard collimator (40°) is determined in the near field (distance: 3 cm) and in the far field (distance: 10 cm).

The spatial resolution of tungsten articulatable hand-held probe with a standard collimator (40°) is determined in the near field (distance: 1 cm). The probe has an excellent spatial resolution < 17 mm.

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The main causes of tungsten points’ gap misalignment of distributor as described bellow:

1. The gap of tungsten points will become smaller because the top block of movable arm of contact is abrasive.
2. Tungsten points’ gap after the surface oxide shedding will increase because tungsten points are ablative.
3. The distributor’s shaft and bushing wear on each other, it will make the tungsten contacts’ gap volatile, become small or big suddenly, and will result in the emergence of the distributor shaft swing phenomenon.

4. Drivers adjust improperly. Drivers would usually tend to use visual methods and their experience to adjust the gap of tungsten points, instead of check and adjustments. It can result in the size misalignment of the tungsten contact gap.

So, you should adjust the gap of tungsten contact of distributor correctly to improve the engine's power for reducing the consumption amount of fuel and maintaining the operation of the engine normal.



 

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