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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The silver tungsten points’ preparation methods: infiltration method and re-pressuring method.

1. Infiltration method. Infiltration method is a method of producing refractory metal and. low melting point metal prosthesis alloy Firs of all , to form a porous skeleton, you should press and pre-sinter the metal powder which possess high melting point, secondly, you should control the temperature until its initial temperature is higher than the metal that owns low melting point, then place the metal which has low melting point under/above the porous skeleton, and make the metal melt and immerge porous skeleton’s pores, to get the final product- silver tungsten points which own high density and other good properties.

2. Mechanical alloying. Mechanical alloying, as a new material preparation process, is gradually stepping into people's vision in recent years. And its concept was first put forward in the 1960's. Mechanical alloying has gradually been developed and is widely used nowadays. Mechanical alloying refers to: adopting high-energy ball milling, mixing two or more kinds of elements powder for a long time. Mixing powder will bear attrition force, impact, shear force, compression force and other forces and absorb mechanical energy in this process. In other words, under the role of milling media, after repeatedly pressing, welding, and crushing and fracture process and through solid state reaction or diffusion, the mixing powder will combined with each other to get the result-the product- silver tungsten points.



 

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Silver tungsten points to produce electric locomotives regulating switch:

Firstly, batching and mixing tungsten powder, silver powder and a small amount of nickel powder;
Secondly, to form porous skeleton, you should press the mixing powder;
Thirdly, you should stack the porous skeleton and the infiltration silver pieces, and place them in tungsten boat;
Finally, to make the molten silver infiltrated into porous skeleton pores completely, you should carry out infiltration sintering; and you can get the product-silver tungsten points after cooling. Sintering conditions: under the protection atmosphere, you should putt them in the furnace of molybdenum wire, and the infiltration sintering temperature is higher than the melting point of silver.

Using silver tungsten as raw material to produce electric locomotives regulating switch by infiltration processes:

Batching (tungsten powder (70%), silver powder, nickel powder) → Mixing powder(silver powder, tungsten powder(70%),nickelpowder) → Pressing → Semi-inspection,infiltration+hydrogen → sintering → Checking → Cleaning → Packing → Silver tungsten points



 

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The steps of silver tungsten points made by infiltration method:

First of all, pressing porous the skeleton with partial-induced silver or the silver blank and tungsten skeleton without silver; then, at the condition of high temperature, pre-sintering the porous skeleton; putting the two parts in a special melt sintering furnace after stacking up them together, and the next step is liquid sintering, the temperature should be controlled above the melting point of silver of 100℃. Under the molten state, silver will fill the pores of the porous skeleton through capillary action, ultimately silver tungsten points with high density is formed. The main steps of silver tungsten points as described bellow:

A small amount of silver, tungsten powder and adding other elements---mixing---preprocessing---skeleton molding + pure silver---pre-sintering (the temperature is over the melting point of silver) --- infiltrating---cooling 



 

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Different tungsten points material possess different properties, different ratio of the same kind of tungsten points material also have different properties, their density, hardness, specific resistance have a different scope.
Main performance index of silver tungsten contacts (with different ratio) as shown below:

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