Coherent emission at 1.047 μ from trivalent praseodymium in calcium tungstate was observed. This emission coincides with strong infrared fluorescence at the same wavelength and was found to be stimulated mostly by absorption of blue light by the ³P₀, ³P₁, and ³P₂ bands. The emission corresponds to a ¹G₄↠³H₄ transition with the terminal level 377 cm−1 from the ground state. The oscillation threshold was the same at 4.2°, 20°, and 78°K. No stimulated emission was observed at room temperature. The lifetime of the metastable state ¹G₄ is 50×10−3 sec. A new technique used to measure the lifetime is described. 

 

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Average grain size and distribution of particle of ammonium paratungstate is affected by the PH value of solution. Nucleary speed and crystalline speed is affected by PH value apparently. After crystallization, the PH value is controlled between 8.0-7.8, it will reduce the nucleary amount and forming speed, the small amount of crystal nucleus can turn into large grain size steadily, also the limited PH value will make the coarse ammonium paratungstate which is distributed evenly.

Adding 10%-20% dilute hydrochloride acid into solution to the PH value 6.5-7.5, the apparent density of crystal decreases, the crystal shape is regular which makes it more convenient to prepare fine ammonium paratungstate particle. By adjusting crystallization mother liquor to the ideal PH value 6.0-8.0 and heat to above 50 degree Celsius will obtain high purity ammonium paratungstate crystal.




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Tungsten diselenide (WSe2) conductivity is ten parts per million than the best conductivity which is diamond, it is the world's lowest conductivity material. In general, poor conductivity material (or insulator) is a porous material, but also one of the most insulation materials. Tungsten diselenide has low thermal conductivity, which is the system heat loss is not easy, so the system's energy conversion efficiency will be higher. If can full to use its insulation properties, will likely significantly increase the efficiency of energy use.
And because the main structure is composed of the upper and lower layer which is the selenium atom and the intermediate layer are tungsten atoms. This structure of WSe2 material like graphene can absorb light and the light absorption can be used to produce electricity. With further study, the researchers according to this feature of tungsten diselenide developed diodes which produce by tungsten diselenide, and this material can be applied to thin flexible solar cells.

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Tungsten diselenide is a gray inorganic compound, the main structure is composed of the upper and lower layer which is the selenium atom and the intermediate layer is tungsten atoms. Besides, every layer combined with van der Waals force, so tungsten diselenide in sixth metal dichalcogenides are very stable semiconductors. Its physical properties are as follows: the chemical formula: WSe2, molar mass: 341.76 • mol-1, density 9.32, CAS number: 12067-46-8.
Tungsten diselenide is often used in solar cells photovoltaic devices, while WSe2 photoelectrode in very stable under acidic and alkaline, and therefore it can be used in photovoltaic chemical barrier. Also WSe2 monolayer which is mechanical exfoliation can be used in the production of transparent photovoltaic equipment and ultra-thin LED.
Producing tungsten diselenide can put tungsten sheet in selenium vapor at high pressure and high temperature (over 800K) heating, then using sputtering deposition techniques to form hexagonal crystal on the sheet with right element proportion.

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Tungsten diboride is a black powder, its physical properties are as follows: chemical formula: BW2, molecular weight 378.49, density 1.6 g/ml, melting point: 2670℃, having metallic conductivity, dissolved in aqua regia. Tungsten diboride should be stored in airtight, cool and dry environment. If compliance the rules will no decomposition. BW2 commonly used in the wear-resistant coating and semiconductor thin film.
Tungsten diboride synthesis methods are as follows:
1. Tungsten and boron as raw material, making two of them to full mix and grind , above 1400 ℃ heating reacted WB. And then continued reaction to obtain W2B, after cooled, pulverized to obtain the product.
2. Mixing tungsten and stoichiometric boron powder in molar ratio W:B = 2:1, sintering in a vacuum or an argon atmosphere at 1200 ~ 1300 ℃, can be obtained tungsten diboride.
3. Using solid-phase method to produce tungsten boride, where stoichiometric metal tungsten and boron as raw martial after mixed, milled, shaped, heated at above 1400 ℃ to obtain WB. To continue reaction to produce W2B, after cooled, pulverized to obtain the product.

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Tungsten boride is a black or gray hexagonal crystalline powder, its physical properties are as follows: chemical formula: WB, molecular weight: 194.65, density: 15.2g / cm3, melting point: 2660 ℃, the lattice constants a=3115nm, c=1.693nm, microhardness 3700kg / mm2, is a poorly soluble substance and having a metallic conductivity. It is often used as a wear-resistant coating and a semiconductor thin film wear parts.

The registry number of tungsten boride is as follows: CAS number: 12007-09-9, EINECS number: 234-498-8, MDL number: MFCD00049708, PubChem number: 24846684.

Producing tungsten boride can use electric furnace heated tungsten and boron to react directly then to obtain tungsten boride.
Tungsten boride synthesis method is as follows:
1. Tungsten and boron as raw material, making two of them to full mix and grind , above 1400 ℃ heating reacted WB.
2. Take 1mol tungsten and 1mol boron powder in a vacuum or in an argon atmosphere set in 1200 ~ 1300 ℃ sintering, available WB.
3. Using solid-phase method to produce tungsten boride, where stoichiometric metal tungsten and boron as raw martial after mixed, milled, shaped, heated at above 1400 ℃ to obtain WB.

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Scheelite is a calcium tungstate mineral with the chemical formula CaWO4. It is an important ore of tungsten. Well-formed crystals are sought by collectors and are occasionally fashioned into gemstones when suitably free of flaws. 

Etch pits on (001) surfaces of calcium tungstate crystals, formed on treatment with hot dilute solutions of hydrochloric acid, were identified to be dislocationetch pits. The technique is able to follow the motion of dislocations during annealing by the formation of new sharp‐bottomed pits adjacent to flat‐bottomed pits at the initial dislocation positions. Inclusions, both solid and gaseous, are an important source of dislocations in crystals of calcium tungstate grown from the melt.

 

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An etch-pitting technique is described for revealing the points of intersection of dislocations with the (100) and (001) surfaces of calcium tungstate single crystals; each etch pit represents one dislocation. The dislocation configuration that is responsible for the residual strain in as-grown ``a'' axis crystals and the mechanism of its growth from the melt are discussed. Preliminary results concerning the distribution of impurities in doped calcium tungstate crystals and the effect of doping on dislocation density and distribution are described. The solution behavior of calcium tungstate in various solvents and a chemical polishing procedure for calcium tungstate are presented.

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Tungsten copper points’ material is made of tungsten which possesses high melting point, high hardness and other excellent performance and copper which own thermal capacity, high electrical conductivity and excellent performance, which owning good arc-erosion resistance, high strength and anti-welding properties. Tungsten copper points are mainly applied in switching circuit and oil circuit breakers and SF6 high voltage circuit breakers due to their not easily oxidization and less wear and tear. Breaking capacity of tungsten copper points has been greatly improved with improved contact structure recently.

Now, it is reported that the arc-erosion resistance can be improved by adding a certain amount of nickel in copper tungsten points; and the ablative performance of copper tungsten points can be increased if tungsten powder’s particles diameter is down to 5μm around, wherein the burning rate of the copper tungsten points will decrease to a minimum if the content of tungsten is increased to 80% -90%.



 

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Tungsten copper contacts material is an alloy made of tungsten (with high hardness, high melting point and other excellent performance) and copper (with high electrical conductivity, thermal capacity and excellent performance), possessing high strength, good arc erosion resistance performance and anti-welding properties. Because tungsten copper contacts is not easily oxidized, thus they have less wear and tear, so it is mainly used for switching circuit breakers, oil circuit breakers and SF6 high voltage circuit breakers. In recent years, breaking capacity of tungsten copper contacts has been greatly improved with improved contact structure.

Now, it has been reported, adding an appropriate amount of nickel in copper tungsten contacts, their arc erosion resistance performance are improved; if the diameter of tungsten powder particles is down to 5μm or so, you can increase the copper tungsten contacts’ ablative performance, wherein if the content of tungsten is increased to 80% -90%, the burning rate of the copper tungsten contacts will down to a minimum.



 

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