Nano tungsten disulfide due to its good performance and broad application prospects is widespread concern, there are many experts and scholars prepared a lot of research on it. However, tungsten disulfide natural mineral is relatively rare, general produce by chemical method to extraction, chemical synthesis method can produce high purity, low impurities and fine granular sulfide oxide. On the other hand it can produce different functional requirements sulfide oxide, therefore chemical synthesis method for produce nano tungsten disulfide has been widespread concern. But it also makes production costs high tungsten disulfide nano particles.
Currently, There are many methods for produce tungsten disulfide, such as ammonium tetrathiotungstate thermal decomposition method, hydrogen sulfide reduction method, high-energy ball milling method, carbon nanotubes space limitations method, hydrothermal synthesis method, hydrogen sulfide or sulfur vapor reduction method, high energy physics and chemistry combine method and so on. So that producing methods of nano tungsten disulfide general can be divided into two types, namely, direct reaction of tungsten and sulfide to form tungsten disulfide or making them react to form reaction precursor and then by ecomposition or reduction with appropriate to generate tungsten disulfide nanoparticles.

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Ammonium tetrathiotungstate, also known as ammonium thiotungstate and ammonium tetrathiot, it is a bright orange crystals with a metallic luster. The physical properties of ammonium tetrathiotungstate as follows: chemical formula: H8N2S4W, molecular weight: 348.18, density 2.71. Related System Number as follows: CAS registry number: 13862-78-7, MDL registry number: MFCD00061410, PubChem registry number: 24860418. Ammonium tetrathiotungstate has some harm to the environment, so during the operation can not be discharged it directly into lakes and rivers or sewer.
Making ammonium tungstate and tungstate to react to generate ammonium tetrathiotungstate and the producing process are as follows:
1. The ammonium tungstate by ammonia dissolved.
2.And then reaction with ammonium sulfide solution, the molar ratio S / W = 4-6：1, the reaction temperature: room temperature to 90 ℃, reaction time: 0.5 to 3 hours, static crystallization time: 8to24 hours.
3. Finally, the crystals were filtered, washed with water and washed with percutaneous ethanol, and finally dried to obtain ammonium tetrathiotungstate.

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301
Number of Players: Any number of players may play, but normally two individuals or two teams play.
Numbers in Play: All the numbers are in play, but some receive greater use than others. The 19 and 20, for instance are used extensively for scoring points since they are the highest numbers on the tungsten dartboard. All the numbers may be used to throw the necessary doubles in the game.
This game is generally played by two people but can be played by teams. Each player starts with 301 points. The goal for each player is to reach zero, exactly, by subtracting the amount they score in a turn from the amount they had left from the previous turn. The player cannot start subtracting until they double in (hits one of the 21 doubles on the tungsten dartboard including the double bull). Once the double is hit, then all scores will count. To end the game, the player must also double out (ie. If they have 32 left, then they will need use tungsten dart to hit a double 16 to win. If they then hit a single sixteen, leaving 16, their next target would be a double 8. If they should hit more points than they have left, then they have busted. Their turn is over and they will resume with the same score they started with on that throw the next time it is their turn to throw.). If they hit the double leaving them zero points, then they have won the game.

501
Number of Players: Any number of players may play, but normally two individuals or two teams play.
Numbers in Play: All the numbers are in play, but some receive greater use than others. The 19 and 20, for instance are used extensively for scoring points since they are the highest number on the tungsten dartboard. All the numbers may be used to throw the necessary doubles in the game.
This game is generally played as a team event, though we also play it in our single events. All players/teams start with 501 points. Unlike 301, you do not have to double-in, but can start on any number. Each player/team subtracts the amount they score from the amount they have left. To win, like 301 above, the player/team will need to double-out to reach zero.

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Spherical calcium tungstate microcrystals were prepared with heat treatment at 100 ℃ and using a calcium tungstate muddy solution by precipitation with natrium tungstate and calcium nitrate as starting materials, and with cetyltrimethyl ammonium bromide as a surfactant. The spherical calcium tungstate microcrystals were characterized by X-ray diffraction and transmission elec-tron microscopy. The results indicate that the crystallites of the calcium tungstate samples are excellent, and the diameters of the calcium tungstate microcrystals with outstanding spherical morphology are 2.1-3.2 μm, and the particles are well dispersed and not aggregated. Cetyltrimethyl ammonium bromide plays an important role in the formation of spherical calcium tungstate microcrystals. When excited at 265 nm, the luminescence of calcium tungstate microcrystals exhibits a luminous peak in the blue band. The luminescent intensity of spherical calcium tungstate microcrystals is about two times greater than that of the aggregate particles.

 

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Calcium tungstate nanocrystalline was successfully synthesised via a microwave irradiation method using Ca(NO₃)₂ and Na₂WO₄ in ethylene glycol, without the requirement of any calcination. The product was analysed by X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and photoluminescence spectrometry. XRD, SAED and TEM revealed that the product was body-centred tetragonal CaWO₄ with an average particle size of 12 nm. Different oscillation modes were detected by Raman spectroscopy and FTIR. They showed the strong W–O stretching in [WO₄]²⁻ tetrahedrons at 711–933 cm⁻¹. Photoluminescence (PL) of CaWO₄ nanocrystalline showed the maximum emission peak at 422 nm.

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There is a facile microemulsion-mediated hydrothermal procedure to synthesize the precursor of Eu³⁺-doped CaWO₄ nanoparticles.SEM shows that the nanoparticles are similar to sphere.The Eu³⁺-doped CaWO₄ phosphor was characterized by powder X-ray diffractometer.According to our measurements with XRD,the products belong to tetragonal structure.The effects of sintering temperature and time on the luminescence of the samples were investigated.The luminescence data indicate the optimum condition for heat-treatment of the precursor was at 600℃ for 2h.The effects of different content of Eu³⁺ on the luminescence of CaWO₄∶Eu³⁺ nanoparticles were also investigated,and the results display that luminescence intensity is enhanced with the slightly increasing of Eu³⁺ content,the optimum of Eu³⁺-doped concentration is 0.1 %(mole fraction).

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The role of defects formed owing to the deviations from stoichiometry is analyzed for CaWO₄ single crystals grown by the Czochralski method. It is shown that the defects leading to the light scattering in CaWO₄ crystals affect the spectra of X-ray luminescence and the luminescence kinetics only slightly, but give rise to an additional peak in the thermoluminescence spectrum. Addition of WO₃ to the melt eliminates the light scattering and the additional thermoluminescence peak.

 

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The seven independent adiabatic elastic constants of CaWO₄ are calculated using Born's longwave method and the rigid ion model of Steinman et al. (1972). Good agreement exists between the calculated elastic constants and those measured by Gluyas et al. (1973). The sign of C₁₆ is consistent with the observation of Farley et al. (1972). Further the dynamical equilibrium conditions are also found to be satisfied for this model.

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The e.p.r. spectrum of (ReO₄)O^2- in CaWO₄ has been measured in the temperature 4-120 K as a function of orientation. The spectrum including many forbidden lines may be fitted to the spin Hamiltonian H = μ _BB\cdot g\cdot S\cdot +I\cdot tilde{A}\cdot S\cdot +I\cdot tilde{P}\cdot I\cdot in tetragonal form with S = 1/2 and I=5/2. At 4.2 K, endor measurements for the magnetic field oriented parallel to the unique axis, taken in conjunction with the e.p.r. spectrum, yield spin Hamiltonian parameters g_\| = 1.8549 ± 0.0002, g_perp = 1.7164 ± 0.0002, A_perp = (±)(42± 2)× 10^-4 cm ^-1, A_perp = (±)(324± 2)× 10^-4 cm ^-1 and P_\| = (mp)(5± 3)× 10^-4 cm ^-1, with g_N = (±) 1.27 for the ¹⁸⁷Re nuclide. These parameters are consistent with the single electron occupying the |3z² - r²> orbital of a 5d¹ ion. The e.p.r. linewidth, which is strongly sensitive to both orientation and temperature, has been examined in detail. Preliminary studies of the relaxation properties of the centre are discussed in qualitative terms.

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The energy levels of the 4I ground term of Er³⁺ in single crystals of CaWO₄ were established by absorption and fluorescence spectra measurements. The measurements were made using crystals at temperatures of 2, 20, and 85°K. The energy level scheme allows an interpretation of the 1.612‐μ four‐level CaWO₄:Er³⁺ laser transition and shows the terminal energy level of this transition to be 318 cm⁻¹ above the ground state rather than 375 cm⁻¹ as reported by Kiss and Duncan. An effective Hamiltonian of the form suggested by Karayianis was diagonalized in a basis of Russell–Saunders wavefunctions to obtain the calculated energy levels and wavefunctions for the entire ground term of Er³⁺. The calculation takes into account the complete J mixing of the states within the ground term and is equivalent to determining the effects of the spin–orbit interaction to better than second order. An rms deviation of 18 cm⁻¹was found as the best agreement between the calculated and experimental energy levels using the Hamiltonian: H = λ1(L⋅S) + λ2(L⋅S)2 + λ3(L⋅S)3 + ΣlmB†lmClm. The empirically determined parameters are (in cm⁻¹) λ1 = − 613, λ2 = − 19.3, λ3 = − 0.499, B20 = 404, B40 = − 685, B60 = 12.4, B44 = 728,ReB64 = 452, and ImB64 = 164. Using wavefunctions determined with these parameters, the g factors were calculated for the states of the ground term. The calculated and measured g factors for the two lower energy states are in good agreement where the calculated values are g‖(ground state) = 1.265, g⊥(ground state) = 8.487, g‖* (first excited state) = 3.22, and g⊥* (first excited state) = 7.06, and the measured values in the same order are g‖ = 1.247, g⊥ = 8.400, g‖* = 3.42, and g⊥* = 6.98. A Γ5,6ground statewavefunction is compatible with the results obtained here, whereas a Γ7,8ground statewavefunction is not. Previous studies had not established the ground statewavefunction uniquely.

 

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