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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The preparation of silver tungsten points is adopting infiltration method, the calculation should be accurate to ensure that the content of silver in silver tungsten points is qualified and you should not waste silver. The equation between the infiltrating silver’s content and actual density of tungsten skeleton can be seen as follows:

       R1 = Q * R2 / V * R3 * S

In the above equation,
R1 is referring to actual density of tungsten skeleton (g / cm³);
Q is referring to Requirements of infiltrating silver (g);
R2 is referring to theoretical density of tungsten skeleton (g / cm³);
V is referring to Skeleton volume (cm³);
R3 is referring to theoretical density of silver (g / cm³);
S is referring to correction value, and its range is between 0.8 and 0.9.



 

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Infiltration process for the preparation of silver tungsten contacts: First of all, you should press tungsten skeleton and silver blanks, then pre-sintering tungsten skeleton at high temperature, and then stack tungsten skeleton and silver blanks together into sintering furnace for liquid phase sintering, the temperature should be controlled above the melting point of silver, silver in the molten state will fill the tungsten skeleton pore by capillary action, and ultimately form silver tungsten contacts.

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

    H = 2α * cosθ / g * ρ * γ

Among them,
H: height of the liquid infiltrate into the capillary (mm)
α: surface tension (N / m²) between the liquid and gas phases
θ: wetting angle
g: acceleration of gravity
ρ: liquid density (kg / m³)
γ: capillary radius (mm)

As can be drawn 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.



 

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

Prepare materials:
Industrial pure tungsten powder, purity> 99.3%, Φ: 1μm - 5μm;
Pure silver powder, purity> 99%, Φ: 1μm - 2μm;
Mixing powder: Batch mixing tungsten powder and silver powder, silver content is of 35%;
Milling: in the air, milling in the milling machine for 0 to15h, the diameter of grinding media is 6.35mm of WC small ball, motor speed is controlled at 250r / min or so.
Pressing: under 300Pa conditions, with one-way presses pressing mixed powder, so that it becomes compact.
Sintering: under hydrogen conditions, the temperature is controlled at 870 ℃ sintering 2h for getting the maximum sintered density.
Cooling: After the completion of sintering, waiting the sintering furnace to be cooled to room temperature.
Hot pressing: Under 600Pa conditions, the temperature is controlled at 850 ℃, heating 1h, then hot-pressing the sintering compact.



 

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