Matters needing attention of silver tungsten contacts prepared by infiltration are the following:

1. Tungsten powder’s thickness. If tungsten powder is too thin, then, the closed pores inside tungsten porous skeleton will increase, affecting silver (liquid metal) to enter.

2. The structure of tungsten skeleton. Only when the porous tungsten skeleton has interconnected and firm network structure, the prepared silver tungsten contacts can get the best electrical contact performance. Besides, only the tungsten powder having a certain particle size and particle size composition, it will be able to form the desired porous tungsten skeleton structure. It is a network of interconnected and solid particles consisting of tungsten particle and has open pores with smooth surface.

3. Temperature. Temperature will affect the quality of silver tungsten contacts. If the temperature is too high, the viscosity of the liquid will be reduced in favor of infiltration, however, because the surface tension of the liquid is also reduced, so that is detrimental to the infiltration. If the temperature is too low, and after sintering, the porous tungsten skeleton strength decreases, you need to extend the sintering time and is not conducive to economic production.



 

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Measurements of the luminescence decay time have been made for a number of single crystals of calcium tungstate for excitation by cathode rays, α and γ radiation. The values obtained for cathode-ray excitation were, in general, 20–30% higher for all crystals, while for α excitation, several crystals showed no change in decay time, while others showed a decay time 20% faster. Measurements of the temperature dependence of the decay time and thermoluminescence experiments indicate that these differences in behavior can be attributed to differences in the density of energy traps and nonradiative centers in the crystal and to a rise in temperature in the excited channel. μ Measurements of the luminescence decay time have been made for a number of single crystals of calcium tungstate for excitation by cathode rays, α and γ radiation. The value of the decay time was found to depend both on the crystal used and on the nature of the excitation. For γ-ray excitation, the decay time was in the range 6.1 to 6.8.

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Scheelite mineral (CaWO₄) is the main raw material used in tungsten production. In this study the dissolution of synthetically prepared CaWO₄ in oxalic acid (H₂C₂O₄) solutions was studied. The effect of following parameters on the dissolution of reaction was investigated: stirring speed, temperature, H₂C₂O₄ concentration and particle size. The amounts of tungsten leached were followed by using Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES) instrument. X-ray Powder Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analytical techniques were used to characterize the leach residues. The results obtained show that the dissolution reaction takes place in two steps: first, the intermediate calcium aqua oxalato tungstate (Ca[WO₃(C₂O₄)H₂O]) chelate compound was obtained. Second, this compound reacted with H₂C₂O₄ to form water soluble hydrogen aqua oxalato tungstate (H₂[WO₃(C₂O₄)H₂O]) and solid CaC₂O₄H₂O. CaC₂O₄H₂O formed covered the surfaces of unreacted CaWO₄particles as a protective layer and the dissolution reaction was interrupted after a certain conversion at high temperatures and H₂C₂O₄ concentrations.

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An evaluation of calcium tungsten oxide (CaWO4) nanoparticles’ properties was conducted using the powders generated from an all-alkoxide solvothermal (SOLVO) route. The reaction involved a toluene/pyridine mixture of tungsten(V) ethoxide ([W(OEt)5]) with calcium bis(trimethyl silyl) amide ([Ca(N(Si(CH3)3)2]) modified in situ by a series of alcohols (H-OR) including neo-pentanol (H-OCH2C(CH3)3 or H-ONep) or sterically varied aryl alcohols (H-OC6H3R2-2,6 where R = CH3 (H-DMP), CH(CH3)2 (H-DIP), C(CH3)3 (DBP))]. Attempts to identify the intermediates generated from this series of reactions led to the crystallographic identification of [(OEt)4W(μ-OEt)2Ca(DBP)2] (1). Each different SOLVO generated “initial” powder was found by transmission electron microscopy (TEM) and powder X-ray diffraction (PXRD) to be nanomaterials roughly assigned as the scheelite phase (PDF 00-041-1431); however, these initial powders displayed no luminescent behavior as determined by photoluminescence (PL) measurements. Thermal processing of these powders at 450, 650, and 750 °C yielded progressively larger and more crystalline scheelite nanoparticles. Both PL and cathodoluminescent (CL) emission (422–425 and 429 nm, respectively) were observed for the nanomaterials processed at 750 °C. Ion beam induced luminescence (IBIL, 478 nm) appeared to be in agreement with these PL and CL measurements. Further processing of the materials at 1000 °C, led to a coalescence of the particles and significant improvement in the observed PL (445 nm) and CL measurements; however, the IBIL spectrum of this material was significantly altered upon exposure. These data suggest that the smaller nanoparticles were more stable to radiation effects possibly due to the lack of energy deposits based on the short track length; whereas the larger particles appear to suffer from radiation induced structural defects.

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Calcium tungstate phosphors activated by the Ln³⁺ ions (Ln=Pr, Nd, Tb, Yb) were synthesized by a traditional high-temperature solid-state method. The crystal structures and morphologies of the products were characterized by scanning electron microscopy (SEM), X-ray powders diffraction (XRD) and infrared spectra (FT-IR). The samples were found to show luminescence properties (down-conversion, DC, at excitation wavelength 254 nm and up-conversion, UC, at excitation wavelength 980 nm). CaWO4 doped with Tb³⁺/Yb³⁺showed green DC and UC luminescence characteristic of Tb(III) ion in the range of 470-660 nm, cor-responding to the ⁵D₄→⁷F_6,5,4,3,2 electronic transition. CaWO₄ doped with Pr³⁺/Yb³⁺showed week blue, green and red (DC and UC) luminescence of Pr(III) ion, in the wavelength region of 450-700 nm. Emission peaks were ascribed to the ³P₁→³H_4,5,6, ³P₀→³H_4,5,6, ³P₁→³F₂ and ³P₀→³F₂ transitions, respectively. CaWO₄ doped with Nd³⁺/Yb³⁺phosphor emitted orange UC luminescence at 450-690 nm (²P_3/2→⁴I_15/2, ⁴G_7/2→⁴I_{9/2,11/2,13/2}) and strong near-infrared UC luminescence at 720-900 nm (⁴F_7/2+⁴S_3/2→⁴I_9/2, ⁴F_5/2+²H_3/2→⁴I_9/2, ⁴F_3/2→⁴I_9/2) which is the characteristic of Nd(III) ion.

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Due to tungsten alloy has high density, excellent radiation attenuation properties, and environmental friendly, it is widely used in medical imaging technology. Medical imaging technology has tended to become more integrated over the past decade. While combined Positron Emission Tomography and Magnetic Resonance Imaging (PET/MRI) is rapidly gaining popularity, no commercial systems for combining the complementary functional imaging techniques of Single Photon Emission Computed Tomography (SPECT) and MRI have been developed. This is mainly due to the physical space constraint, magnetic incompatibility of collimators and the required rotation mechanism inside the MRI bore. Some approaches investigated this integration but no one focused on the development of preclinical SPECT systems and their integration with pre-clinical MRI without compromising image quality and taking into account the MR-compatibility of the collimator material. This study investigates eddy currents in the collimator due to the magnetic field gradients, for different resistivities of tungsten, for small animal SPECT/MRI. Collimator resistivity can be tuned nowadays through tungsten additive.

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Beam collimators, which are usually made of tungsten alloy shielding, including linear accelerators and tungsten multi-leaf collimators and so on. Beam collimators are 'beam direction' devices used in the X-ray tube housing, along with an arrangement of mirrors and lights, in such a way that the light and X-ray fields match each other. They are made of lead shutters which completely absorb the photons, and thus reduce patient dose as well as focus the radiation accordingly to the area of interest. They allow different projections of X-ray fields.
 
In linear accelerators (linac), the primary collimator may be constructed of depleted uranium (DU) as this material is approximately 1.6 times more dense than lead. The secondary motorised collimators which greater define the beam shape are constructed of tungsten. Multi-leaf collimators (MLCs) which are now in widespread use in medical linacs consist of two collimator banks of thin tungsten 'leaves' with each bank consisting of 40 to 80 leaves (so a total of 80 to 160 leaves). This allows each tungsten leaf to move independently under computer control. MLCs allow even more diverse field shapes to be created which can shield organs at risk whilst allowing the complex shape of the tumour bed to be irradiated to allow maximum cell kill.

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Tungsten polymer Shielding’s density approaching twice that of high density Lead Blankets of similar thickness. Highly flexible and can be molded/formed into any shape. Often competitively priced to lead alternatives.

The advantages of tungsten polymer shielding system:

• Provides approx. 75% Attenuation as compared to solid lead
• Attenuation of 175% compared to a high density lead blanket
• Priced competitively to lead for many applications
• Available as a blanket, ribbon wrap or molded shapes; flexible or rigid
• Cut materials to fit without needing to seal edges - no residue
• Included fasteners, grommets, locking devices, etc., as required
• Improved fit-up --- molded applications typically will yield much higher reduction factors - less weight with same impact
• Tested to 550°F/288°C

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There are three ways for producing tungsten disulfide which are the following:
The first method: tungsten disulfide produces by firing decomposition method. Firstly, stirring tungsten acid and ammonia water with at 57 ~ 60 ℃ to react for three hours, heat prevention  more than 16 hours of natural sedimentation. After reaction get the sodium tungstate then to react with hydrogen sulfide gas, to generate tetrathiotungstate acid. Finally after calcination, the tetrathiotungstate acid will decompose to tungsten disulfide. During the reaction, heating should at 100 ~ 200 ℃ / hr temperature gradient from room temperature to of 700 ~ 1200 ℃. Then after  heat preservation for 24 to 48 hours, then at 30 ~ 110 ℃ / hour temperature gradient descending to room temperature, and finally crushing the material. Related chemical reaction of the reaction equation is as follows:
H2WO4 + 2NH3 • H2O → (NH4) 2WO4 + 2H2O
(NH4) 2WO4 + 4H2S → (NH4) 2WS4 + 4H2O
2 (NH4) 2WS4 + 3O2 → 2WS2 + 4NH3 + 2S + 2SO2 + H2O
The second method: putting sulfur vapor through the red-hot tungsten can form tungsten disulfide
The third method: mixing tungsten with stoichiometric sulfur  at 800 ℃ for 24 hours in a nitrogen atmosphere can be formed WS2. If changing the reaction conditions, namely in 6MPa reacted with 1800 ℃, can be formed orthorhombic WS2.

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Sulphur is a nonmetallic chemical element, and elemental sulfur is usually kind of yellow crystals, also known as sulfur. There are many elemental sulfur allotropes, such as rhombic sulfur, monoclinic sulfur and sulfur elasticity. Sulfur is an important element in the human body protein for human life is important. Sulfur is mainly used in fertilizers, gunpowder, lubricants, pesticides and anti-fungal agent production.
Tungsten trisulfide is a reddish brown powder and its chemical formula is WS3, molecular weight 280.11, CAS registry number 1215-19-8. Tungsten trisulfide slightly soluble in water, soluble in hot water, alkali metal carbonates and alkali metal hydroxides, in addition it can generate colloidal solution in hot water.
Producing tungsten trisulfide can use thermal decomposition method of ammonium tungstate (a kind of hydrogen sulphide saturated ammonium tungstate). Or making hydrogen chloride to react with ammonium tetrathiotungstate obtains tungsten trisulfide.

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