Tunable dye laser spectroscopy has been used to study energy transfer processes in CaWO₃:Sm³⁺ crystals. Fluorescence and excitation transitions for samarium ions in different crystal-field sites have been identified and their changes in width and position with temperature studied. This information is used to characterize energy migration among samarium ions as a function of temperature, samarium concentration, time after the laser pulse, and pressure. The interaction mechanism causing energy migration is identified as electric quadrupole-quadrupole. At low temperatures it was found that only single-step transfer between nearby ions takes place, while at high temperatures multi-step diffusion of energy occurs. These results are interpreted in terms of the Anderson (1958) localization concepts for systems with inhomogeneously broadened transitions, and quantitative estimates of the transfer rates and diffusion parameters are obtained.

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If the gap of tungsten contacts of distributor is reduced, then: the closing time of tungsten contacts will be prolonged; ignition coil ignition energy will store more; before the tungsten contacts opening, current formed in the primary coil will be relatively large; when the tungsten contacts are opened, the maximum secondary voltage is relatively high.

If the gap of tungsten contacts of distributor is increased, then: the closing time of tungsten contacts will be shortened, which resulting in ignition energy reduction and the maximum secondary voltage drop. And because the opening time of tungsten contacts open ahead, it will cause that ignition advance angle increases.

However, the gap of tungsten contacts of distributor is not too small. If the gap is too small, when tungsten contacts are closed, it will form a strong contact spark and lost the primary ignition energy, resulting in tungsten contact ablation. And because the cutoff of primary current circuit is not complete, so the maximum secondary voltage will be reduced.




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The normal value of tungsten contacts gap of the distributor is generally around 0.35mm-0.45mm. If the gap is large than normal value of 0.1mm, the engine will use more petrol than 3% of fuel; if small  than 0.1mm, then 5％of fuel.

Ignition energy, ignition advance angle and the maximum secondary voltage will affect the automotive ignition system performance. If the ignition energy is insufficient, it will cause the mixture gases do not ignite properly. If the ignition advance angle is too small or too large, so the mixture gases will not normally burn after ignition. If the maximum secondary voltage is low, then the spark plugs do not flash over normally. These factors will make the power of engine decline, fuel consumption rise and dysfunction and so on. So, appropriate tungsten contacts gap of the distributor can mitigate the impact of car ignition energy, ignition advance angle and the maximum secondary voltage to car ignition system.




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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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