Ammonium paratungstate is a relatively insoluble salt which dissolves only to the extent of 4.5 parts in 100 parts of water at 22℃. and has limited solubility in hot water. On the other hand, ammonium metatungstate dissolves to the extent of 120 parts per 100 parts of water at 15℃. and is very soluble in hot water.

It is frequently desirable to obtain a relatively high concentration of tungsten in solution, Le. 30% W0 or more at ambient temperature. This is done most readily by dissolving ammonium metatungstate. On the other hand, ammonium paratungstate is a more common product which can be obtained by several methods during the recovery of tungsten from its ores. Heretofore, the market price of ammonium metatungstate has been much higher, compared to ammonium paratungstate, because of the difficulty entailed in manufacturing the former.




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There are many benefits belonging to tungsten copper electrodes.

High Wear Resistance
Due to the high melting point of tungsten (3 420 °C), WCu electrodes have a considerably longer service life than copper or graphite electrodes, in particular in the case of small electrodes which have undergone complex machining. Because the production costs of complex electrodes often far exceed the pure material costs.

Extremely Sharp Contours
The low wear levels of tungsten copper electrodes make it possible to focus the arc precisely and achieve greater geometrical accuracy in the workpiece.

High Surface Quality
The use of tungsten copper electrodes result in outstanding surface quality and, in particular, eliminates the need for circular electrode movements.

Good Machinability
The considerably greater modulus of elasticity and increased hardness offered by tungsten copper electrodes lead to exceptionally good machinability.

Improved Environmental and Working Conditions
The machining of graphite requires the use of special extraction systems to remove dust, prevent graphite-smeared floors and keep the air clean. In contrast, the machining of tungsten copper electrodes does not require any additional equipment.

 

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Electron spin resonance linewidths of Nd3+ in CaWO4 at 35 GHz and 4.2 K are examined experimentally and theoretically for a range of Nd concentration. The derivative peak-to-peak linewidths, as determined experimentally, increase from 1.1 mT at 0.034% Nd to 4.1 mT at 0.816% Nd in vacancy-compensated single crystals at a polar angle of 90°. The homogeneous broadening is found to be owing almost exclusively to the Nd-Nd dipolar interaction, while the predominant inhomogeneous mechanism is due to a crystalline axis misorientation of 57 min of arc. Both the spin-lattice relaxation time and the linewidth show an anomaly at a polar angle of about 30°, indicating the presence of cross-relaxation to an impurity, probably cerium.

 

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It is generally known that tungsten dart barrel is the main part of dart. Nowadays, tungsten became the standard material and widely used in dart barrel, for it has proportion of 19.3(when temperature is 20 degrees).That means put a high-density material into a small dimension. By the way, it is extraordinary durable, and could be processed.
Because of the special character of tungsten, it can be so difficult to produce with 100% tungsten. In fact, on the market, so called 100% tungsten dart is made of tungsten alloy. With the same weight, tungsten dart is thinner than brass dart. For all this special characters, as a result, tungsten has taken the place of brass and become the most popular material. tungsten dart billet through knurling and carving and finally became the stunning tungsten dart barrel ,and the weight is changing by size and tungsten content.

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Electron spin resonance linewidths of Gd7/2 in single crystal calcium tungstate (CaWO4) were examined experimentally and theoretically for Gd concentrations up to 0.05%, at the range over which single site occupation by gadolinium was maintained. The linewidths expressed as widths between points of maximum slope on derivative spectra, lay between 0.3 and 1.5 mT over the angular ranges 0° < θ < 90° and 0 < φ < 90° explored. There is good agreement between the form of the angular variation of linewidth and calculation based on dipolar broadening theory. Quantitatively, however, the predicted values are about five time larger than the observed linewidths; this difference may be due to exchange narrowing.

 

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Nanocrystals of calcium tungstate (CaWO₄) of three different grain sizes were synthesized through chemical precipitation technique and the grain sizes and crystal structure were determined using the broadening of X-ray diffraction patterns and transmission electron microscopy. The microhardness of compacted pellets of nanocrystalline calcium tungstate (CaWO₄) with different grain sizes were measured using a Vickers microhardness tester for various applied loads ranging from 0.049 N to 1.96 N. The values of microhardness showed significant reverse indentation size effect at low indentation loads. The microhardness data obtained for samples of different grain sizes showed grain size dependent strengthening obeying normal Hall-Petch relation. The dependence of compacting pressure and annealing temperature on microhardness of the nanostructured sample with grain size of 13 nm were also studied. The samples showed significant increase in microhardness as the compacting pressure and annealing time were increased.

 

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Single photon emission computed tomography (SPECT, or less commonly, SPET) is a nuclear medicine tomographicimaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. Due to its high density, excellent absorption behaviour against radiation and environmental friendly characteristics, tungsten alloy can be widely used in single photon emission computed tomography (SPECT) utilize radioactive materials injected as tungsten syringe shield. 2 mm solid tungsten flange helps syringe shield the hand when withdrawing liquid from a vial. Flange is easily removed to allow transition from drawing dose to patient injection. 9 mm thick glass-5.2g/cc gives the greatest protection of any glass in any syringe shield and syringe shield is easily replaced. Twist-turn and the syringe is held firmly.

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Tungsten collimators are made up of ground breaking components of tungsten alloy X-ray targets. The advantages of using tungsten collimators:

• Due to tungsten alloy is environmental friendly, tungsten collimator is one of the safest devices to be used on a job site which definitely reduces extra radiations.
• The extra or the scattered radiation around the film is automatically reduced which increases the quality of radiography shots.
• Safer and more understandable operation for radiographers.
• Tungsten alloy itself is more efficient shielding material than lead; it is easy to handle and can be used even without a license.
• One of its properties which are also ideal for Industrial use is that it does not spark.

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High density tungsten alloy has become an essential material for a wide variety of applications. It has the highest melting point of any metal, and its high density is equaled only by gold, platinum, and a few other rare and expensive metals. Pure tungsten is quite brittle and difficult to be machined. The addition of elements such as nickel, copper, and iron, creates a family of materials with extremely useful properties. High density tungsten alloys are economically fabricated by powder metallurgy techniques and are routinely machined by conventional methods. Mechanical properties add tensile strength, ductility, hardness-compare favorably with common engineering materials such as steel. Twice as heavy as steel and more than 50% heavier than lead, high density tungsten alloys have found wide acceptance where a concentrated mass is required in a limited space for such applications as radiation shielding, and a large variety of other uses.

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Crystallization kinetics of calcium tungstate from unstirred supersaturated solutions in sodium tungstate melts was studied by continuous cooling from initial crystallization temperature TO=1000° to 800°C to room temperature at cooling rates RT=0.67° to 3.3°C min−1. Crystals were examined by optical microscopy and analyzed by various methods. The main crystal growth was diffusion-rate-controlled. The final crystal growth was rate-controlled by the development rate of excess solute concentration. Diffusion rate constant (kD) values were estimated. These values increased with cooling rate and initial crystallization temperatures but they are very much smaller than the rate constants for diffusion-controlled growth of calcium tungstate from lithium chloride melts.

 

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