The preparation of silver tungsten contacts can be powder metallurgy or infiltration method.

Silver material characteristics:
Low melting point, low hardness, volatile, low wear resistance, good thermal conductivity characteristics;
When the load is large, the silver contacts material is easier to form an arc and welding;
Because silver has low hardness and volatile characteristics, so under the effect of DC, silver film will form electrical erosion and spikes;
At high temperature and humid environment, silver will form silver sulfide film in the surface of sulfur or sulfur compounds.

Tungsten content of silver tungsten contacts material is usually around 20% -80%, silver tungsten contacts advantages: they own good oxidation resistance, good electrical and thermal conductivity, arc erosion resistance, excellent electrical wear resistance ability and good anti-welding capability. Silver tungsten contact shortcoming: contact resistance is unstable. When the silver tungsten contacts frequently running because the contact surface of silver and tungsten will produce a mixed oxide, the splash degree of contact resistance of the film surface will increase.

Silver tungsten contacts application: it is widely used in thermostats, circuit breakers, micro-switches, etc., and can also be used for electrical contacts, high current heavy equipment.




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For trivalent praseodymium (Pr³⁺) and quadrivalent praseodymium (Pr⁴⁺) codoped CaMO₄ (M = W, Mo) powders, the luminescence propriety of matrix is obviously influenced by carrier concentration. The light emission intensity of CaWO₄ matrix decreases exponentially with increasing of Pr concentration because oxygen-deficient obtains an electron supplied by Pr³⁺ (5d). However, the light emission intensity of CaMoO₄ is enhanced by Pr codoping because the quasi-free electrons increase the probability of radiative combination. The difference of photoluminescence properties in the two materials are attributed to the bonding character of M and O in the CaMO₄ structure.

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Tungsten contacts, also known as tungsten points or tungsten electrical contacts, which are used to act as a contact part, used in instruments, equipment and switching equipment, etc. Their roles are: turn on and interrupt the current. Therefore, tungsten contacts will directly affect the performance of the switching devices that is running state. About a hundred years ago, people started using contact materials, which began with pure gold, pure silver and pure platinum and other contact materials, until about the 1940s, people began using alloy materials, such as, silver copper, gold silver and platinum indium materials. After the 1960s, people gradually found more composite materials of precious metal. Tungsten was found in 1781, since then, people gradually shift their attention to tungsten materials.

Tungsten contact materials have wear-resistance, high density (19.25g / cm3), high melting point (up to 3422 ° C), high purity, high hardness, corrosion resistance, low conductivity and other characteristics.

Characteristics of silver material: in all metals, silver has the best thermal conductivity, excellent processing performance and high antioxidant capacity and so on.




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In the studies on phonons in CaWO₄, Kanamori et al. investigated the phonon dispersion of translational modes alone, ignoring the finite moment of inertia of tungstate ions and Coulomb interactions. In our present investigations, based on external mode formalism (Venkataraman and Sahni), we consider the coupling of the translational and librational modes and include the long range interactions. The effective ionic charges of the Coulomb interactions and the effective ionic radii of Born–Mayer short range potential arc determined so that the dynamical equilibrium conditions are satisfied and lattice energy is of the right order in comparison with other complex ionic crystals (Rao et al.). The phonon dispersion relations in CaWO₄ along [001] and [110] directions arc calculated and found to be in reasonable agreement with available neutron data (Steinman et al.). The generalized LST relations (Venkataraman et al.) computed with our model agree with the IR data of Barker. In the long wavelength limit, the acoustic branches fit well with experimental data, indicating that this model can explain the acoustic properties as well. Zone centre phonons in CaMoO₄, SrWO₄, SrMoO₄, BaWO₄, BaMoO₄, PbWO₄, and PbMoO₄ are also investigated and compared with experimental data to study the influence of polarizability and a possible breakdown of external mode formalism.

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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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