During the preparation of tungsten tube in CVD(Chemical Vapor Deposition) process, in order to improve the strength and toughness of CVD tungsten tube, one or several layers of very fine tungsten wire can be wound on deposition matrix to obtain CVD tungsten tube wound by tungsten wire (the tungsten wire-CVD tungsten composite materials). CVD tungsten tube wound by tungsten wire allows the tungsten tube to change the direction of growth, and the crystal grains will also be refined, so the strength and toughness of CVD tungsten tube is improved.

Because of the presence of tungsten wire, the density and purity of CVD tungsten tube wound by tungsten wire will decline slightly. But it still owns more than 99% of purity; and still has higher density than 19g / cm3

Therefore, CVD tungsten tube wound by tungsten wire owns a high purity and density, a significant increase in crush strength, and fracture morphology of significantly change.


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Controlling the deposition matrix removal process is one way of suppressing the generation of tungsten tube surface transverse cracks.

If adopting vacuum melting method to remove the deposition matrix, the temperature rising rate should be slow, especially when the temperature is over the deposition temperature to the melting point of copper. This method is preferred options, because this method can make the removal of the matrix and the deposited tungsten tube’s stress annealing process going on simultaneously. In one hand, the transverse cracks of tungsten tube surface can be suppressed; on the other hand, the deposited matrix material can be recycled directly.

Using nitric acid, then the concentration of nitric acid should be less than 35%. Because, if the corrosion rate of deposition matrix is excessive, then stress release rate of tungsten tube will be too fast, furthermore, it will also makes the corrosion deposit matrix uneven, resulting in t tungsten tube will generate cracks in deposit matrix removal process.

 

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Suppression method of tungsten tube surface transverse cracks:

Rate of temperature increase of annealing treatment should be carried out slowly instead of too fast; especially the temperature ranges below tungsten’s brittle transition temperature, in order to release deposition tungsten tube’s internal stress slowly.

Underspeed the cooling rate after the end of the deposition, especially the temperature ranges above tungsten’s brittle transition temperature. This is an important thing, particularly for the deposition preparation of products which has big size, thick wall, and complex shape and is easy to produce concentrated stress.

In the condition of meeting the strength requirements and processing conditions of the deposition matrix, the matrix thickness should be uniform and as thin as possible to reduce the deformation stress during cooling process.

Selecting the matrix material whose expansion coefficient is close to the base material, by this way, the residual stress within deposited products can be significantly reduced.

 

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Ammonium paratungstate (or APT) is a white crystalline salt of ammonium and tungsten, with the chemical formula (NH₄)₁₀(H₂W₁₂O₄₂)·4H₂O.

Ammonium paratungstate is produced separating tungsten from its ore. Once the ammonium paratungstate is prepared, it is heated to its decomposition temperature, 600 °C. Left over is WO₃, tungsten(VI) oxide. From there, the oxide is heated in an atmosphere of hydrogen, reducing the tungsten to elemental powder, leaving behind water vapor. From there, the tungsten powder can be fused into any number of things, from wire to bars to other shapes.

When concentrating an ammoniacal solution of tungstic acid (i.e. hydrous WO₃), the product obtained is ammonium paratungstate. Below 50 °C, the hexahydrate is formed, whereas when the temperature of the solution is above 50 °C, the pentahydrate or heptahydrate is formed. The former crystallizes as triclinic plates or prisms, whereas the latter as pseudorhombic needles.


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Ammonium metatungstate, also known as AMT, is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃, aqueous fairly stable. It is white or slightly yellow crystals which has no harmful components and slightly acidic.

Component of ammonium metatungstate is listed as below:

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Ammonium metatungstate is a source of high purity, water soluble tungsten which is essentially free of alkali and other metallic impurities. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate.

It is also used as a raw material for the production of tungsten catalysts for a variety of reactions including oxidation, hydroxylation, hydrogenation, and polymerization. Suitable carriers can be impregnated with alkali-free solutions of tungsten and processed to remove the water and ammonia. Such catalysts are used by the petrochemical industry.

Other applications include: reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).



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Ammonium paratungstate is a white, finely divided, crystalline material. It is produced by evaporation of purified ammonium tungstate solution to obtain pure paratungstate crystals. Controls of time, temperature, concentration and PH, determine the quality and physical characteristics of the ammonium paratungstate crystals.

Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also tungsten powder including tungsten trioxide, tungsten blue oxide. Those powders are then used to make numerous products including wire, cutting tools, billets, welding electrodes, mining tools and many others. There are alloy series too, such as tungsten carbide alloy blade, alloy drill, alloy molds, etc.; and other wear, pressure, temperature and other machinery and equipment components. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry. Other applications are in the fields of absorbent gels, coloring agent in the porcelain industry and the catalyst industry. 


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Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also tungsten powder including tungsten trioxide, tungsten blue oxide. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate. It can also be used as reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).


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Tungsten element is more effective shielding and good machinable so that it is widely used in medical as collimator.Compare to lead ,tungsten is much more environmentally friendly and higher density which means smaller parts for the same weight.in neutron,X-ray and gamma ray optics,the collimator is a device that filters a stream of rays so that only those traveling parallel to a specified direction are allowed through.according to the use of lenses it is not yet possible to focus radiation with such short wavelengths into an image as is routine with electromagnetic radiation at optical or near optical wavelengths however tungsten collimator could be used in neutron ,X-ray and gamma-ray.

Tungsten shielding can be used the following medical areas:
Multileaf collimators
Radio guided surgery
Gamma probe
Medical isotope transport and containment
Radiotherapy machines
Computerized tomography scanners
Single-photon emission tomography
Positron emission tomography
Computerized tomography and X-Ray security machines
Oncology treatment systems
Oncology instruments
Radioactive syringe protection

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The energy dispersive X-ray detector consists of a multi-element detector and two collimator slits. The detector is a cryogenically cooled high-purity Ge-detector with 23 crystals arranged in a semi-annular array, which is comprised by tungsten shielding.
 
The 23 detector crystals are equally spaced in steps of 8.2°, covering azimuthal angles from 0° to 180°. The detectors are in orthogonal pairs, allowing simultaneous measurement of 11 sets of orthogonal q-vector components. Tungsten shielding is hiding in detector to control the direction of energy dispersive. This design is intended to improve the determination of strain tensor components and permits the measurement of crystallographic texture with a single detector set-up. The multi-element arrangement is also an advantage when the average grain size in the sample is comparable with the beam dimension. In this case, reflections can vanish for certain azimuthal angles. Element 23 at 180° is symmetrical to element 1 at 0° and is used for detector alignment.

The photograph is showing the tungsten shielding is hided in the 23 detector crystals.  

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