Government regulations on lead and other hazardous substances in various electronic and electrical equipment are forcing medical device OEMs and others to find suitable substitutes for parts that have been manufactured from lead and other restricted materials, with plastics coming to the rescue.

A material has been found, that alternative to those being restricted by government regulations: poly-tungsten thermoplastic. This material can be machined and fabricated in a variety of configurations, and has the density of traditional metals without the safety issues associated with lead. Poly-tungsten is more durable than other lead substitutes and offers equal or better radiation-shielding capabilities in electronic and electrical products. Because it is malleable, poly-tungsten offers increased design flexibility and the opportunity to create molded parts in lieu of multi-part assemblies.

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Names

IUPAC name   dihydroxy-dioxotungsten

Other names   Orthotungstic acid

CAS Registry Number   7783-03-1

Properties

Chemical formula   H2WO4

Molar mass    249.853 g/mol

Appearance    yellow powder

Density   5.59 g/cm3

Melting point        100 °C (212 °F; 373 K) (decomposes)

Boiling point 1,473 °C (2,683 °F; 1,746 K)

Solubility in water        insoluble

Solubility      soluble in HF, ammonia

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

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Tungstic acid refers to hydrated forms of tungsten trioxide, WO₃. The simplest form, the monohydrate, is WO₃·H₂O, the dihydrate WO₃·2H₂O is also known. The solid state structure of WO3•H2O consists of layers of octahedrally coordinated WO₅(H₂O) units where 4 vertices are shared. The dihydrate has the same layer structure with the extra H₂O molecule intercalated between the layers. The monohydrate is a yellow solid and insoluble in water. The classical name for this acid is 'acid of wolfram'.

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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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