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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When the car is working, result in that the main reasons of tungsten contacts gap misalignment of distributor are shown as below:

1. Tungsten contacts ablation, it will cause the increase of tungsten contacts gap after the surface oxide shedding.
2. The top block of movable arm of contact wears, so the gap of tungsten contacts becomes smaller.
3. The distributor between the shaft and bushing will wear on each other, not only result in the distributor shaft swing phenomenon occurs, but will make the tungsten contact gap volatile, suddenly become small or big.

4. Driver’s improper adjustment. Under normal circumstances, the driver would use visual methods and their experience to adjust the gap of tungsten contacts, rather than through plug inspections and adjustments. This can cause the size misalignment of the tungsten contact gap.

Therefore, in order to improve the engine's power to reduce the consumption amount of fuel and maintain the normal operation of the engine, you should correctly adjust the gap of tungsten contact of distributor.



 

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Adopting infiltrating way to prepare silver tungsten contacts, you should calculate accurately to ensure the content of silver is qualified and do not waste silver. The expression between the actual density of tungsten skeleton and content of infiltrating silver’s is as follows:

       R1 = Q * R2 / V * R3 * S

Among them,
Q refers to: Requirements of infiltrating silver (g)
V refers to: Skeleton volume (cm³)
S refers to: correction value, in the range of 0.8-0.9
R1 refers to: the actual density of tungsten skeleton (g / cm³)
R2 refers to: theoretical density of tungsten skeleton (g / cm³)
R3 refers to: theoretical density of silver (g / cm³)



 

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Tungsten disulfide also known as tungsten sulfide, is a gray hexagonal layered structure, easy dissociation, has lubricating properties similar to graphite, commonly used in lubricants such as aerosols. Its physical properties are as follows: chemical formula: S2W, molecular weight: 247.97, density: 7.6g • cm-3, slightly soluble in water, soluble in water, insoluble in hydrochloric acid and alkali, but dissolved in molten alkali. Tungsten disulfide has reducing properties which can react with hot concentrated sulfuric acid, nitric acid, aqua regia and other strong oxidizing agent. Heating in the air or oxygen may be converted into tungsten trioxide.
Tungsten disulfide packing generally has two tape 25 kg and 50 kg with double plastic bags and metal bucket.
Tungsten disulfide with a certain irritation, if accidentally touching will irritate the eyes, respiratory system and skin. So during the operation should wear protective gloves, glasses or masks.
There are some registry numbers of tungsten disulfide which is CAS registry number. 12138-09-9, EINECS number 235-243-3, MDL No. MFCD: 00011467, PubChem number 24854626.

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Silver-tin oxide is an electrical contact material which is silver-based containing tin oxide, Ag-8.7SNO2 and Ag-12SnO2 properties is good than Ag-CdO such as corrosion resistance, arc resistance and thermal stability. It can produce by oxidation or by sintering. Besides, silver-tin oxide has consistent performance and long life is mainly used in medium-load electrical contact materials, such as various contactors and protection switch.
Silver-SnO2-WO3 is a material which adding tin oxide and tungsten oxide in silver-based. Because tungsten oxide (or molybdenum oxide) can improve the wettability of tin oxide, reducing the electrical connection overheating, thus significantly improving the service life. By the way it can obtain by sintering. Silver-SnO2-WO3 is mainly used in all kinds of contactors, motor starters, circuit breakers and other low-power appliances. Ag-11.5SNO2-0.5WO3 and Ag-11.2SnO2-0.8MoO3 can replace the Ag-CdO in many areas.

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Tungsten and chlorine react in the air or react with oxygen can generate tungsten oxytetrachloride (WOCl4) and tungsten chloride (WO2Cl), which tungsten oxytetrachloride is a red orange needle-like crystals, tetragonal crystal structure.
The physical properties of tungsten oxytetrachloride are as follows: the chemical  formula: WOCl4, melting point: 209 ℃, boiling point: 232 ℃, and has good hygroscopicty, it can generate tungstic acid by hydrolysis. Besides, it can be dissolved in an organic solvent such as carbon disulfide, benzene and others and easy and easily react with alcohol, phenol and acid group to form the corresponding compounds. What’s more tungsten oxytetrachloride easy react with   ammonium, amine, ether and acetonitrile to form complexes.
Producing method of tungsten oxytetrachloride has three which are as following: The first is through the tungsten trioxide and sulfur oxychloride reaction to from it; the second is reacting between tungsten trioxide and carbon tetrachloride to from; third is reaction in tungsten trioxide and tungsten hexachloride which will generate tungsten oxytetrachloride.

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Eu3+-doped calcium tungstate powders were prepared by a precipitation method and their properties were characterized by X-ray diffraction(XRD),fourier transform infrared spectroscopy(FT-IR),field emission scanning electron microscopy(SEM),and fluorescence spectrometer(PL).The products are spherical in shape and disperse well.The Eu³⁺ in co-precipitation material has good luminescence properties and the best performance is obtained with the Eu³⁺ mole content of 5%.

 

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People all must be aware of radiotherapies which are used to destroy cancer cells or tumour by directly putting radiation beams on it. Surgeons must take a lot of care when treating patients with this radiotherapy because the surrounding tissues of the tumour must not face this radiation or those tissues will get badly damage. Multi-leaf tungsten alloy collimator is used to keep the focus of beams on the right place and reduce the extra damage to the health tissues. This material consists of two very thin but heavy tungsten alloy plates which are configured in such a way that it works on exactly the tumour area by measuring the accurate shape and size.

These tungsten alloy collimators are made up of groundbreaking components of tungsten alloy X-ray targets. According to the recent medical research, tungsten alloy collimators, with high shielding capability and high density, are more successful in different radiation therapies as compared to X-rays and gamma rays.

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