During tungsten oxide reduction process the size of tungsten powder particle is usually varies. At present, there are two main theories to explain tungsten powder particle size changing at the reduction process change.

First is growth mechanism by chemical vapor migration. Tungsten oxide in contact with steam, will generate produce a volatile hydrated tungsten oxide (WO2 (OH) 2), and evaporated to gaseous phase react with H2 occurring homogeneous gas reduction reaction. The reduction product is deposited on the nucleation of tungsten grain, so that tungsten powder particles grow. This process reaction rate is quick, and the reduction product forms will change significantly compared to the raw materials.

Second is solid-phase local chemical reaction mechanism. The solid tungsten oxide contacts with H2 gas causing gas- solid reaction. With oxygen atom removing the lattice will rearrangement. This process is slow reaction rate, and reduced product shape does not change.

In tungsten powder reduction process, the above two mechanisms exist simultaneously, what kind of mechanism play a role part depending on the temperature and moisture content of the atmosphere. 

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When blue tungsten oxide has same quality, the reduction process plays an important role at tungsten powder particle size. In producing fine tungsten powder must be strictly controlled reduction of temperature, hydrogen flow rate, hydrogen gas humidity, the thickness of the material layer, through hydrogen speed and direction, as they will influence fine tungsten powder producing.

Firstly, hydrogen-way requirements, generally speaking, there are two ways through hydrogen: cis hydrogen and inverse hydrogen. When the hydrogen reduction reaction at low temperatures and low humidity conditions, following hydrogen flow direction to push the boat along will obtain fine tungsten powder which is better than using inverse hydrogen way produce tungsten powder.

For another requirement is the reduction temperature, the higher reducing temperature the faster response, the more intense vapor transport, resulting in crystalline powder. And tungsten powder will agglomerate and coarse. Therefore, during the reaction the temperature should use low starting point, warmed gently heating system. Because the reduction temperature is low, heating will not so fast, so the water for the reaction is not too much which is in favor of the producing fine tungsten powder.

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Hydrogen reduction – carbonization method produces tungsten powder having a simple operation, coating reasonable, stable and reliable advantages. the process of hydrogen reduction is: tungsten oxide →hydrogen reduction →sieving → blending → tungsten powder.

With the improvement of tungsten powder manufacturing level, has made great progress in the selection of tungsten oxide raw materials. Starting with tungstate (H2WO4) and yellow tungsten oxide (WO3) and now widely used blue tungsten oxide (referred to WO2.90) and purple tungsten oxide (referred to WO2.72 ) as a raw material. Structure, components and their physical and chemical properties of raw materials have great impact on tungsten powder particle size and uniformity. During the restore process, by regulating the various process parameters can control the particle size of the tungsten powder, such as the temperature of reduction, material thickness, hydrogen flow, ventilation direction.

The method for producing tungsten carbide powder is using tungsten oxide producing tungsten power then tungsten powder mix with carbon back making tungsten carbide powder. At the first using  method mixed tungsten powder and carbon black at 1400~1600℃high temperature carbonization and get WC powder. Since the method can not make tungsten powder and carbon full contact, easily lead to incomplete carbonation. Then switch to using hydrogen reduction, firstly hydrogen will react with black carbon and producing hydrocarbon. And then carbon-containing gas will carbonize tungsten powder to tungsten carbide powder.

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Tungsten target is also called tungsten sputtering target，which is made from raw ground tungsten powder. Tungsten target owns high melting point, elasticity, low coefficient of thermal expansion, resistivity and fine heat stability and other properties.
Pure tungsten and tungsten alloy targets have been widely applied in electrical industries, chemical equipment (X-Ray tube, thin-film material, semi-conductor integrated circuit), medical equipment, smelting equipment, rare earth smelting, aerospace and many other fields. For example, Mo alloys and   tungsten X-ray targets which can withstand extreme thermal stress and temperatures over 2,000℃, are used for the general medical diagnostic and amigo- cardiograph. All tungsten targets have superior quality and durable, guaranteeing longer life.
Tungsten target become one of the main source for X-ray targets because of the electronic structure of tungsten. The production process of tungsten target is that pressing the tungsten powder into form and sintering, then hot isostatic pressing, bloomed, cold rolling, annealing, cutting, machining and bonding with a copper backing plate. 

 

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