Potassium tungstate is white or colorless crystalline powder and is a monoclinic structure. Its physical properties are as follows: chemical formula: K2O4W, molecular weight: 326.0342, density: 3.12g/ml, melting point: 921 ℃, Solubility: soluble in water, insoluble in alcohol. K2O4W should be sealed in the storage vessel, and it is placed in a cool, dry place. Besides avoids contact with tungsten oxide, moisture or humidity. In addition, it is harm for the water, if there is no relevant government departments permission shouldn’t released to the surrounding.
Potassium tungstate is mainly used in analytical reagents, alkaloids precipitant, but also for the fine tungsten and bronze manufacture.
Potassium tungstate producing processes are as follows:
1.Mixed potassium dichromate (K2Cr2O7) with tungsten powder, after reaction to obtain potassium tungstate and chromium oxide.
2.W react with KOH to produce potassium tungstate.
W reacts with KOH solution, if no oxygen participate there is a slight reaction. But the reaction has oxidizing agent (such as KNO3, KNO2, KClO3, PbO2, etc.) will cause violet reaction.

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1. Tungsten alloy multi-blade grating with the thickness of 2.0 to 3.8mm and the plate flatness of 0.05mm.
2. Tungsten alloy protective tank for medical radiation shielding walls, shielded syringe for the shielding of medical radioactive liquor, and tungsten alloy memory for containers such as pots and tanks used for storing radioactive substances
3. Collimator for medical linear accelerators and cyclotrons
4. Shielding device for the shielding of rays of 60Co therapy apparatus.

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The tungsten alloy counterweight is formed by adding elements such as Fe, Ni, Cu, Co, Mo and Cr into tungsten serving as the matrix (the content of W is 85 to 99 percent). Tungsten alloy called high density alloy because its density is up to 16.5 to 19.0g/cm3. It also has the characteristics of high specific gravity, high strength, strong ray absorption capability, high thermal conductivity, small thermal expansion coefficient, good electrical conductivity, and good weldability and machinability, wherein the specific gravity is usually 16.5 to 18.75g/cm3; the tensile strength is 700 to 1,000Mpa; the ray absorption capability is 30 to 40 percent higher than that of lead; the thermal conductivity is 5 times that of mould steel; and the thermal expansion coefficient is only one second to one third of that of Fe or steel. In view of its excellent functions, the high density alloy is widely applied to the industries of aerospace, aviation, war, oil drilling, electrical appliances and meters, medicine and so on.

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According to USGS, world tungsten mine production was estimated to be 71,000 tonnes in 2013. China was the largest producer in 2013, followed by Russia and Canada. The top three countries accounted for 91% of the total production in 2013. Other major producing countries include Bolivia, Austria and Portugal.

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The content of tungsten in the Earth's crust is 0.007%. According to the data released by USGS in 2014, global tungsten reserves are around 3.5 million tonnes. About two-thirds of the world's tungsten resources are in the form of scheelite, and one-third are in wolframite-group minerals. The tungsten ore resources country distribution in the world is as follows:

According to the data released by USGS in 2014, world tungsten reserves are round 3.5 million tonnes. Tungsten resources are concentrated in China (1,900,000 metric tonnes), Canada (290,000 metric tonnes), Russia (250,000 metric tonnes), United States (140,000 metric tonnes), Bolivia (53,000 tonnes), Austria (10,000 metric tonnes) and Portugal (4,200 metric tonnes).

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About 20 species of tungsten minerals are known, of which wolframite [(Fe, Mn) WO₃] and scheelite (CaWO₄) have industrial value.Tungsten ore grade mined in 70s, more between 0.2 ~ 0.5% WO₃, can get containing tungsten trioxide 60 to 70 percent or higher grade tungsten concentrates after dressing. China's tungsten ore reserves account for more than half the world's total reserves, mainly in Hunan, Jiangxi, Guangdong and Fujian provinces. In 1979, the world's major tungsten producing countries (except China) of tungsten ore reserves and production in the following table: 



 

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Tungsten copper points, which can be applied to control the current of the switch, and mainly play a role in relays, contact switch, breakers, magnetic motors and other parts, also namely tungsten copper electrical points. Points properties will directly have an effect on the work of the entire electrical system, particularly communication system, modern automatic control system and other large power system, the system will work in a mess or even can’t run if one or more points in them, whose properties derogate, so, the work properties of tungsten copper points should be improved.

Properties requirements of tungsten copper points can be seen as below:
1. Require the points owning good electrical conductivity and nice thermal conductivity to reduce heat loss and the tungsten oxide on the surface of points;
2.Require points material having high boiling point, high melting points, high melting heat and evaporation heat  to reduce contact wear and the occurrence of welding of the points under the arc / spark action;
3. Require the point having stable chemical properties, stable contact resistance, and small change of contact resistance when it being polluted by the environment;
4. Require the points possessing appropriate elasticity and hardness, the contact area would be small when the hardness is too large,  due to bounce between the points, the wear will increase when the flexibility is greater;
5. Own the properties of easy machining and welding;
6. The price is lower.



 

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There are many factors on tungsten copper contacts, among which the main factors are structure size of the contacts, the manufacturing process, the particle size of tungsten powder, applications occasions, current properties and the breaking speed of contact and early pressure and so on. " Factors on Tungsten Copper Contacts - Structure Size and Manufacturing Process" which focuses on the factors of structure size and manufacturing process, and this article will introduce the factors of tungsten powder particle size, applications occasions, current properties and the breaking speed of contact and early pressure:

3. The tungsten powder particle size. Studies have shown that, whether it is with a thicker tungsten powder or thinner tungsten powder to prepare a contact material, their anti-arc erosion performance is not very good, but if prepare the contact by mixing the coarse powder and fine powder at a certain percentage, then the performance of tungsten copper contacts are relatively better. Note items: if the components of the contact material are different, then their mixing proportions are also different.

4. Applications occasions. The experimental results show that for different applications occasions, different components of the contact have its corresponding optimal application occasions. For example, in air or a vacuum switch, tungsten (90) / copper (10) its performance against arc erosion is the best.
5. Current properties. Studies have shown that if the properties of the current are different, and then its on-off process will produce different transient properties, however, after selecting the contact, its value is constant.

6. The breaking speed of contact and early pressure. Arcing time is determined by breaking speed especially early opening rate; arcing time can be shortened by increasing the early speed to achieve it, so that the possibility of contact ablation reduced. If the early pressure is increased, the mechanical vibration of the contact can be reduced, so that the arc erosion and mechanical wear is reduced.

 

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Factors on tungsten copper contacts can be seen from the following main points:

1. The structure size. In theory, if the structure size of tungsten copper contacts is larger, then its anti-arc ablation performance will be stronger, because its use of energy more dispersed. In actual use, because the limit size of electrical switch structure, its size can not do much. In recent years, someone has developed plug-in contacts, hollow contacts, not only accelerates the speed of heat dissipation of contact materials, but contacts can still maintain good contact state after the ablation.

2. The manufacturing processes. Now manufactures in China are commonly applying infiltration method (mixing powder, pressing, sintering) to prepare tungsten copper contacts. What is different is that whether there is the use of sintering tungsten skeleton infiltration process. Compared with the performance of tungsten copper contacts, the ones used the process for the preparation is more ideal than the other ones without using it. In recent years, foreign countries have adopted more advanced preparation technology to improve the life of the contacts, such as, arc melting, sintering rolling process, fiber-reinforced method and so on, but China for the use of these new processes are still in the laboratory stage.

 

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