The survey results of longitudinal interface of tungsten tube with different processing rate by SEM (Scanning Electron Microscope) show that:

There is no big change between spinning tungsten tube and sintered tungsten compact tissue when processing rate is 12%, that is to say, completely non-deformed tissue still exist in tungsten tube, and its crystal grains show equiaxed grains and sintering hole is circular.

All parts of the spinning tungsten tube are already deformed when processing rate reach 26 %, the grain will somewhat elongated, and sintering hole is oval-shaped.

When processing rate up to 45-68%, spinning tungsten tube is not completely broken, in which can still see the original grain boundaries, and the crystal grain further elongated, the sintering hole is also further stretched.

When the processing rate of spinning tungsten tube rising to 76%, fibrous tissue occurs, the original crystal grains are broken, the original crystal grain boundaries no longer been sawn, sintering holes disappear.

 

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Tungsten contact features:
Wear resistance;
Arc erosion resistance;
Good melt resistance;
Size deviation: dh ± 0.05mm;
High purity of more than 99.95%;
Hardness is between 71 and 74HRA;
High capability of breaking current;
Density range is 19.1g / cm3 ~ 19.3 g / cm3;
Weld strength can withstand greater than 83MPa;

The number of crystal grains is more than 10,000PCS / mm2;

The carbon content of nail seat base is less than or equal to 0.10% of the low-carbon steel;

The evaporation of the metal surface and less transfer consumption due to electro-thermal effect;

Welding purity of tungsten copper alloy is not less than 99.95%. (product is available according to customer's drawings and size)

 

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Tungsten contact, a component which is made of pure tungsten, is used for turning on or breaking the circuit in the switch.

Characteristics of tungsten products: tungsten products have wear resistance; arc erosion resistance; high capability of breaking current; good melt resistance; the evaporation of the metal surface and less transfer consumption due to electro-thermal effect and other characteristics.

Tungsten contact application: tungsten contact is widely used in agriculture, industry, science and technology and defense fields, such as relays, communications machine, Magneto, sirens, cars and motorcycles.

Technological requirements of tungsten contact: With the development of industry, people have also been strict with the process requirements of the tungsten contact. They require tungsten contact rods without cracks, and with smooth surface; good flatness, concentricity and roundness; crystal grains in section is fine and uniform, and its fibers is short.

 

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Currently in four common refractory metals for tungsten tube process, tungsten, molybdenum, tantalum, niobium, in which tungsten tube is the one whose processing is with maximum difficulty, because it has a higher brittle transition temperature, larger deformation tension, greater difficulty of machining and so on.

Powder metallurgy for seamless tungsten tube by spinning process as follows:

Loading powder → isostatic pressing (pressure is controlled at about 196MPa) → finishing the outer surface of tungsten tube→ hydrogen sintering (temperature is controlled at 2350-2400 ℃ around, heat preservation time for the 5-6h) → spinning --- general tungsten tube → grinding ---tungsten tube with thin wall and high precision.

Spinning: In the heat roller wheel spinning machines, heating tungsten tube using the flame mixed with hydrogen and compressed air and spinning, temperature is 1000 ℃ around.

Avoiding the tungsten tube will crack in spinning process, usually annealing is adopted (through hydrogen; temperature controlling: 1000-1100 ℃; insulation 1h), to increase the plasticity of tungsten tube.

 

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Learn blue tungsten oxide (blue tungsten) phase component is good for producing good performance tungsten powder preparation, according to investigate the phase composition, selecting the raw materials and control of the production process can be more clear which can be producing good performance tungsten powder. Blue tungsten oxide during the restore reaction the main phase component of it is mainly β- tungsten oxide (WO_2.9), γ- tungsten oxide (WO_2.72), tungsten dioxide (WO₂) and tungsten powder.

First discussing the reduction process there are from blue tungsten oxide to γ- tungsten oxide. According to research data shows that the main phase components of β- tungsten oxide are rough and surface has cracks. As the development of reaction the oxygen atoms decrease and vacancy increase, the β-tungsten oxide restore to γ- tungsten oxide. And γ-tungsten oxide surface roughness is further increased, further increases cracks, particle morphology is needle-like and short rod, its irregular, but these structures favor the reduction reaction. γ- tungsten oxide particle morphology depends on reduction temperature, heating rate, material thickness and other factors.

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By using SEM to observer the particle size and bulk specific gravity of blue tungsten oxide discover that baking temperature between 400 ~ 500 ℃ blue tungsten oxide particles more uniformly. When baking temperature at 400 ~ 500 ℃ can obtain fsss particle average of 11.9 ~ 12.0um, bulk specific gravity of blue tungsten oxide 2.49 ~ 2.50 g / cm². When baking temperature at 400 ℃, blue tungsten oxide average fsss particle size is 12.0um and bulk specific gravity is 2.50g / cm². when the baking temperature is 450 ℃, the fsss particle size is 11.9um, bulk specific gravity is 2.50 g / cm². The solution temperature baking at 500 ℃, Fei particle size of 12.0um, bulk specific gravity of 2.49 g / cm².
analyzing the above data can be found, baking temperature between 400 ~ 500 ℃ the particle size distribution curve is quite the same and the particle are uniformity. Within each temperature range, the particle size distribution fluctuates within a region, each particle size distribution mainly between 10 ~ 40um and the bulk specific gravity fluctuation is not great. At the same time at different temperatures, the average diameter of blue tungsten oxide particle size also has a corresponding effect. The higher the temperature the blue tungsten particle size will be increased, but the impact is not obvious.

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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. Its shape is like sheet or needle.  It is insoluble in water and alcohol. 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 has different molecular formula under different crystallization condition:
(1)3(NH4)2O - 7WO3 - 6H2O

(2)5(NH4)2 - 12WO3 - 5H2O

(3)5(NH4)2O - 12WO3 - 5H2O

(4)5(NH4)2O - 12WO3 - 11H2O


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The main cause of CVD tungsten tube longitudinal cracks lies that: the deposition way of the inner wall of tungsten tube and the deposition process is not well controlled. The fundamental reason is that the tensile stress due to tungsten tube’s wall contraction (its cooling speed is too fast, and the amount of reaction gas is too much in unit time). Because the stress is concentrated at the growing crystal grain boundaries, so these positions are easy to crack. Growth of columnar crystals of tungsten tube is growing along the radial direction, leading to rapid expansion of the crack into the grain boundaries.

The depositing of tungsten tube inner wall is by heating the outer wall of the deposited matrix to the deposition temperature.

In the cooling process of the deposition, the inner wall of deposition tungsten tube will cooling rapidly due to continuous passing-through of hydrogen, while the outer wall of the cooling rate will be relatively slow.

 

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Ammonium metatungstate is also called AMT, it is inorganic chemical product. Its molecular formula is H8N2O4W and molecular weight is 283.9145. CAS number is 11120-25-5;14311-52-5. It is white or slightly yellow crystals which has no harmful components and slightly acidic. The solubility in water is 303.99/loogH:O when 20℃, aqueous fairly stable. It is insoluble in alcohol.

Ammonium metatungstate 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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Oxygen index have certain impact on the performance and morphology of blue tungsten oxide, researcher determination of oxygen index of blue tungsten oxide by weight method. After experimental data analysis found that the baking temperature has great impact on oxygen content and the color of blue tungsten oxide. When baking temperature at 350 ~ 500 ℃, the oxygen index between 2.96-2.90. Changing the baking temperature, the color and oxygen content of blue tungsten oxide also will change and surface gloss index has varying degrees of change.
At 350 ℃, blue tungsten oxide’s color is yellow-blue and has high oxygen index, matte. As the temperature increases, blue tungsten oxide gradually be reduced, when the baking temperature reaches at 450 ℃blue tungsten oxide’s color translated into blue-black and surface of it has metal light, oxygen index of 2.94. When baking temperature reached 500 ℃, oxygen index of 2.90, blue tungsten oxide color is blue-black. As the temperature continues to rise in parts of blue tungsten oxide restore into WO2.72 , then the blue color of blue tungsten oxide become more deepen and oxygen index further reducing. When baking temperature reaches 550 ℃, it began to appear purple WO2.72, but most retain the blue color which to form a heterogeneous mixture.

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