The surface of silver tungsten points would reach a molten state in the opening and closing moment because there are Joule heat and arc high temperature action among tungsten silver points and which will be solidified in the cooling process and weld after that resulting that working contacts no longer disconnected. If machinery is designed poorly or prepared improperly, which can bring about the result of silver tungsten contact bounce and short arc, and its welding problem will be very prominent at the time.

Anti-welding properties of silver tungsten points lie on the welding force of silver tungsten points. Welding force is referring to the force needed to separate the two welded silver tungsten points, and its size is connected to the tensile strength of silver tungsten points. If the toughness of contact material is better, then the tensile strength of silver tungsten points will be stronger, and the welding force will be greater, and its anti-welding properties will be worse; on the contrary, if the tensile strength of silver tungsten points is weaker, and the welding force will be smaller, and its anti-welding properties will be better.



 

Tungsten Metals Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten.com.cn
 Tel.: 86 592 5129696; Fax: 86 592 5129797
 Email: sales@chinatungsten.com
 Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
 Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
 Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

Acousto-optic modulators are main component of communication fibre-optic systems. From the other side the studies of the absolute piezo-optic effect (POE) are one of the important steps to estimate the acousto-optic efficiency of optical materials.The investigation results of POE in calcium tungstate crystals (CaWO4) has been represented. It is also proved that this crystal is essentially better acousto-optic material in comparison with lithium niobate (LiNbO3) widely used in acousto-optic devices.

 

Tungsten Powder Manufacturer&Supplier:ChinatungstenOnline-www.tungsten-powder.com
Tel.:865925129696;Fax:865925129797
Email:sales@chinatungsten.com
Tungsten&MolybdenumInformationBank:http://i.chinatungsten.com
TungstenNews&TungstenPrices,3GVersion:http://3g.chinatungsten.com
MolybdenumNews&MolybdenumPrice:http://news.molybdenum.com.cn

Because there are Joule heat and arc high temperature function between tungsten silver contacts, so their surface will reach a molten state in the opening and closing moment, which will be solidified in the cooling process and weld after that, leading a working contact no longer disconnected. If machinery is poorly designed or prepared improperly, it can cause silver tungsten contact bounce and short arc, at this time, its welding problem will be very prominent.

Anti-welding properties of silver tungsten contacts depend on the welding force of silver tungsten contacts; welding force refers to the force needed to be applied to separate the two already welded silver tungsten contacts, its size is related to the tensile strength of silver tungsten contacts material. If the contact material’s toughness is better, the tensile strength of silver tungsten contacts will be stronger, and the welding force will be greater, and the worse of its anti-welding properties; on the contrary, if the tensile strength of silver tungsten contacts is smaller, and the welding force will be smaller, and the better of its anti-welding properties.



 

Tungsten Metals Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten.com.cn
 Tel.: 86 592 5129696; Fax: 86 592 5129797
 Email: sales@chinatungsten.com
 Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
 Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
 Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

Notes of silver tungsten points prepared by infiltration are shown as follows:

1. The thickness of the tungsten powder. The closed pores inside tungsten porous skeleton will increase and then influence silver (liquid metal)’s entry if tungsten powder is too thin.

2. The structure of tungsten skeleton. The silver tungsten points could get the best electrical contact performance as the porous tungsten skeleton has firm and interconnected network structure. Besides, it can form the desired porous tungsten skeleton structure when the tungsten powder possesses a certain particle size and particle size composition. It is a network of firm and interconnected tungsten particles and has open pores with smooth surface.

3. Infiltration temperature. Infiltration temperature will have an effect on the quality of silver tungsten points. The viscosity of the liquid will be reduced to benefit infiltration if the temperature is too high. However, it is detrimental to the infiltration because the surface tension of the liquid is also reduced. The porous tungsten skeleton strength after sintering will decrease if the temperature is too low. And you should prolong the sintering time to make it be conducive to economic production.



 

Tungsten Metals Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten.com.cn
 Tel.: 86 592 5129696; Fax: 86 592 5129797
 Email: sales@chinatungsten.com
 Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
 Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
 Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

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.



 

Tungsten Metals Manufacturer & Supplier: Chinatungsten Online - http://www.tungsten.com.cn
 Tel.: 86 592 5129696; Fax: 86 592 5129797
 Email: sales@chinatungsten.com
 Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
 Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
 Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn

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.

Tungsten Powder Manufacturer&Supplier:ChinatungstenOnline-www.tungsten-powder.com
Tel.:865925129696;Fax:865925129797
Email:sales@chinatungsten.com
Tungsten&MolybdenumInformationBank:http://i.chinatungsten.com
TungstenNews&TungstenPrices,3GVersion:http://3g.chinatungsten.com
MolybdenumNews&MolybdenumPrice:http://news.molybdenum.com.cn

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.

Tungsten Powder Manufacturer&Supplier:ChinatungstenOnline-www.tungsten-powder.com
Tel.:865925129696;Fax:865925129797
Email:sales@chinatungsten.com
Tungsten&MolybdenumInformationBank:http://i.chinatungsten.com
TungstenNews&TungstenPrices,3GVersion:http://3g.chinatungsten.com
MolybdenumNews&MolybdenumPrice:http://news.molybdenum.com.cn

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.

Tungsten Powder Manufacturer&Supplier:ChinatungstenOnline-www.tungsten-powder.com
Tel.:865925129696;Fax:865925129797
Email:sales@chinatungsten.com
Tungsten&MolybdenumInformationBank:http://i.chinatungsten.com
TungstenNews&TungstenPrices,3GVersion:http://3g.chinatungsten.com
MolybdenumNews&MolybdenumPrice:http://news.molybdenum.com.cn

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.

Tungsten Powder Manufacturer&Supplier:ChinatungstenOnline-www.tungsten-powder.com
Tel.:865925129696;Fax:865925129797
Email:sales@chinatungsten.com
Tungsten&MolybdenumInformationBank:http://i.chinatungsten.com
TungstenNews&TungstenPrices,3GVersion:http://3g.chinatungsten.com
MolybdenumNews&MolybdenumPrice:http://news.molybdenum.com.cn

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.

  Tungsten Alloy Manufacturer & Supplier: Chinatungsten Online- http://www.tungsten-alloy.com
  Tel.: 86 592 5129696; Fax: 86 592 5129797
  Email:  sales@chinatungsten.com
  Tungsten & Molybdenum Information Bank: http://i.chinatungsten.com
  Tungsten News & Tungsten Prices, 3G Version: http://3g.chinatungsten.com
  Molybdenum News & Molybdenum Price: http://news.molybdenum.com.cn