CaWO₄ phosphor activated by the Tm³⁺/Yb³⁺,Er³⁺/Yb³⁺ and Ho³⁺/Yb³⁺ ions were synthesized by a traditional high-temperature solid-state method.The crystal structures and morphologies of the products were characterized by X-ray powders diffraction method (XRD),infrared spectra (FT-IR) and scanning electron microscopy (SEM).The samples were found to show up-conversion luminescence properties.CaWO₄ doped with Tm³⁺/Yb³⁺ showed blue luminescence characteristic of Tm(Ⅲ) ion in the range of 460-485 nm,corresponding to the 1G4→3H6 electronic transition.CaWO₄ doped with Er³⁺/Yb³⁺ showed strong green luminescence at 510-565 nm (2H11/2,4S3/2→4I15/2) and weak red luminescence at 640-685 nm (4F9/2→4I15/2) of Er(Ⅲ) ion.CaWO₄ doped with Ho³⁺/Yb³⁺ phosphor emitted green luminescence at 525-560 nm (5S2,5F4→5I8) and red luminescence at 630-670 um (5F5→5I8) and at 730-770 nm (5S2,5F4→5I7),which is the characteristic of Ho(Ⅲ) ion.

 

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Ammonium paratungstate (APT) is crystalline material with white powder. The production method of obtaining pure paratungstate crystal is by evaporation of purified ammonium tungstate solution. Factors influencing the quality and physical properties of APT are controlling time, temperature, concentration and pH. The Chinese national standard of manufacturing this product is GB/T 10116-2007, which is a revision of GB/T 10116-1988. Its CAS no is 11120-25-5; 14311-52-5, EINECS 234-364-9, formula of H8N2O4W and molecular weight of 283.9145. It is the raw material of manufacturing ammonium metatungstate, and also widely used for producing tungsten metal products.

The SEM micrograph of ammonium paratungstate is multiplying the product under scanning electron microscope, which can be 10 to 100,000 multiplied. The scanning micrograph of APT is really different from AMT. The shape showing from SEM of APT is with cubic shape, but round for AMT.




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Ammonium metatungstate is also named AMT, which is a kind of white crystal powder. AMT is the raw material for making tungsten product, and also widely used in alloyed steel, fireproof industries. Further more, it is a good tungsten based flux in oil chemical and ceramic industries. The manufacturing standard of AMT in China is GB/T 23368, which is also used for measuring the content of ammonium metatungstate. Based on different manufacturing degree, the products manufactured out by factories have performed different chemical contents. Standard used manufacturing ammonium metatunstate, AMT is GB/T 23368. The content of WO3 is 90.00% in most Chinese manufacturers, but 91.4~91.5% for Chinatungsten Online. For the different crystalized conditions, AMT can be analyzed as (NH4)6H2W12OnH2O, (NH4)6H2W12O40.XH2O and (NH4)6H2W12O40.

Scanning Electron Microscope (SEM) is a kind of scanning equipment using for micrograph by multiplying objects, which can be metal, powder, vegetables etc. Ammonium metatungstate is one of can-be scanned products. After scanning, the powder of AMT is showing ball shape with inner empty. All the balls are gathered together when the multiply value is low, but with gap when the value large enough, which means that the molecule of AMT are separate actually.




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Ammonium Paratungstate (NH₄)[H₂W₁₂O₄₂].4H₂O is the most important precursor for the majority of tungsten products. Exceptions are only products of melting metallurgy and Menstrum WC produced directly from ore concentrates.

All other intermediates such as tungsten trioxide, tungsten blue oxide, tungstic acid and ammonium metatungstate can be derived from APT, either by thermal decomposition or chemical conversion. 

APT is a white crystallized powder having average crystal size between 30 and 100 µm. Especially crucial for the quality is the purity. Typical levels of today’s commercial APT are (upper limits in µg/g):  Al 1-7, As 5-10, Bi 0.5-1, Ca 1-10, Co 1-10, Cr 1-10, Cu 1-3, Fe 3-10, K 2-10, Mg 1-7, Mn 1-10, Mo 5-30, Na 5-10, Ni 1-7, P 5-7, Pb 1-5, S 5-7, Si 1-10, Sn 1-10, Ti 3-10, and U 3-10. APT is packaged in polyethylene-lined drums or woven bags up to 1 ton.




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At the present time, crystalline AMT is being produced from APT. Although this process overcomes some of the disadvantages of the-prior art, in practice it is somewhat difficult to control for maximum conversion. As a consequence, on crystallization of AMT from solution, the residual APT must be removed in order to produce completely water-soluble AMT products. Another disadvantage of this process is its intermittent batch nature, requiring baking, digesting, filtering and concentrating of solutions before crystallization. On a production scale, such stepwise operations tend to be time consuming and costly.

As an improvement over the above process, a method for producing AMT directly from ammonium tungstate (AT) solution is came up with. AT solution is contacted with a liquid extraction system consisting of Di-Z-ethyhexyl phosphoric acid (D-2-EHPA)-tri-n-butyl phosphate (TBP)- kerosene, which extracts ammonium ion and rapidly lowers the pH to the AMT-forming region. The solution is then digested to allow formation of AMT.

While this method substantially avoids the formation of APT and is amenable to continuous processing, it has not found widespread use due to a tendency toward instability of the organic system, and resultant formation of insoluble phospho-tungstates in amounts up to percent or more of the total solid product, depending upon the conditions of formation.


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Ammonium paratungstate is a relatively insoluble salt which dissolves only to the extent of 4.5 parts in 100 parts of water at 22℃. and has limited solubility in hot water. On the other hand, ammonium metatungstate dissolves to the extent of 120 parts per 100 parts of water at 15℃. and is very soluble in hot water.

It is frequently desirable to obtain a relatively high concentration of tungsten in solution, Le. 30% W0 or more at ambient temperature. This is done most readily by dissolving ammonium metatungstate. On the other hand, ammonium paratungstate is a more common product which can be obtained by several methods during the recovery of tungsten from its ores. Heretofore, the market price of ammonium metatungstate has been much higher, compared to ammonium paratungstate, because of the difficulty entailed in manufacturing the former.




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There are many benefits belonging to tungsten copper electrodes.

High Wear Resistance
Due to the high melting point of tungsten (3 420 °C), WCu electrodes have a considerably longer service life than copper or graphite electrodes, in particular in the case of small electrodes which have undergone complex machining. Because the production costs of complex electrodes often far exceed the pure material costs.

Extremely Sharp Contours
The low wear levels of tungsten copper electrodes make it possible to focus the arc precisely and achieve greater geometrical accuracy in the workpiece.

High Surface Quality
The use of tungsten copper electrodes result in outstanding surface quality and, in particular, eliminates the need for circular electrode movements.

Good Machinability
The considerably greater modulus of elasticity and increased hardness offered by tungsten copper electrodes lead to exceptionally good machinability.

Improved Environmental and Working Conditions
The machining of graphite requires the use of special extraction systems to remove dust, prevent graphite-smeared floors and keep the air clean. In contrast, the machining of tungsten copper electrodes does not require any additional equipment.

 

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Electron spin resonance linewidths of Nd3+ in CaWO4 at 35 GHz and 4.2 K are examined experimentally and theoretically for a range of Nd concentration. The derivative peak-to-peak linewidths, as determined experimentally, increase from 1.1 mT at 0.034% Nd to 4.1 mT at 0.816% Nd in vacancy-compensated single crystals at a polar angle of 90°. The homogeneous broadening is found to be owing almost exclusively to the Nd-Nd dipolar interaction, while the predominant inhomogeneous mechanism is due to a crystalline axis misorientation of 57 min of arc. Both the spin-lattice relaxation time and the linewidth show an anomaly at a polar angle of about 30°, indicating the presence of cross-relaxation to an impurity, probably cerium.

 

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It is generally known that tungsten dart barrel is the main part of dart. Nowadays, tungsten became the standard material and widely used in dart barrel, for it has proportion of 19.3(when temperature is 20 degrees).That means put a high-density material into a small dimension. By the way, it is extraordinary durable, and could be processed.
Because of the special character of tungsten, it can be so difficult to produce with 100% tungsten. In fact, on the market, so called 100% tungsten dart is made of tungsten alloy. With the same weight, tungsten dart is thinner than brass dart. For all this special characters, as a result, tungsten has taken the place of brass and become the most popular material. tungsten dart billet through knurling and carving and finally became the stunning tungsten dart barrel ,and the weight is changing by size and tungsten content.

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