2. Adding seed crystal and （NH₄）₂WO₄ solution.
During the first nucleary, adding seed crystal will obtain ammonium paratungstate which has largest Fsss grain size and apparent density. Adding complete seed crystal will obtain ideal even ammonium paratungstate. After the nucleary of ammonium paratungstate, adding （NH₄）₂WO₄ solution increase Fsss grain size and apparent density of ammonium paratungstate without changing distrubition of grain size. If the adding speed increases, micro ammonium paratungstate will be formed.

3.Mixture.
Increase the mixture speed, crystal formation rate is controlled by surface reaction instead of distribution. Ammonium paratungstate grain size varies in different mixture speed.

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Grain size of ammonium paratungstate affects the grain size of tungsten powder. Macro grain ammonium paratungstate has large apparent density and flow ability which promote the property and quality of tungsten powder. Marketing demand for macron ammonium paratungstate enlarges year by year. Macro grain ammonium paratungstate formation conditions include the influence of temperature, adding seed crystal and （NH₄）₂WO_4, the influence of mixture.

1.Temperature. Rapid heating up and reduce the degree of super saturation before boiling up. It will not only improve producing efficiency, also reduce the production rate of metatungstate radical A （HW₆O₂₁^5-）and the conversion rate of metatungstate radical A to metatungstate radical B（H₂W₁₂O₄₂^10-）.

Medium temperature nucleary. Reduce the formation of crystal nucleus. During nucleary of ammonium paratungstate, raise temperature in a certain degree will make the crystal grain size smaller.

Formation under high temperature. Reduce the rate of second nucleary. After the first nucleary, the distribution of ammonium paratungstate grain size depends on the second nucleary. After the first nucleary, heating up rapidly, reduce mixing time, thus reduce the second nucleary and crystal broken degree.


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Tungsten borides are compounds of tungsten and boron, and their most remarkable preoperty is high hardness. The Vickers hardness of tungsten borides or tungsten diboride is about 20GPa, and that of WB4 is about 30 GPa for loads exceeding 3 N. δ-WB and WB2 crystals have metallic resistivities of 0.1 and 0.3 mΩ·cm, respectively. The oxidation of W2B, WB and WB2 is significant at temperatures above 600 °C. The final oxidation products contain WO3 and probably amorphous B2O3 or H3BO3. The melting temnperatures of W2B, WB and WB2 are 2670, 2655 and 2365 °C, respectively.
WB2 has the same hexagonal structure as most diborides such as AlB2, MgB2 and it has several forms, α (tetragobal), β (orthorombic) and δ (tetragonal).
There are the ways for synthesis the tungsten borides.  Single crystals of WB2−x, x=0.07–0.17 (about 1 cm diameter, 6 cm length) were produced by the floating zone method, and WB4 crystals can be grown by arc-melting a mixture of elemental tungsten and boron.

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On one hand, tungsten silicide is used in microelectronics as a contact material, with resistively 60-80μΩcm and it is often used as a shunt over polysilicom lines to increase their conductivity and increase signal speed. On the other hand, tungsten silicide also finds use in microelectromechanical systems and for oxidation-resistant coatings. Besides, tungsten silicide layer can replace tungsten films which are made by chemical vapor deposition. What’s more tungsten silicide is also used as a barrier layer between silicon and other metals such as tungsten.
Tungsten silicide layers can be prepared by chemical vapor deposition, besides films of tungsten silicade can be plasma-etched using for example nitrogen trifluoride. There is producing process as follow:
1.Using monosilane or dichlorosilane with tungsten hexafluoride as source gases.
2.The deposited film is non-stoichiometric and require annealing to convert to more conductive stoichiometric form.

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Tungsten disilicide also known as tungsten silicide, and it is an inorganic compound, a silicide of tungsten. It is an electrically conductive ceramic material. The physical properties of tungsten disilicide are as following: chemical formula：WSi2, molar mass:240.011g/mol, density:9.3g/cm3,melting point:2160℃, which is insoluble in water, but soluble in fluorine aqua regia, what’s more, it has good anti-oxidation. Besides, there are tungsten disilicaide chermistry which is it can react violently with substances such as strong acids, fluorine, oxidizers and interhalogens.
On one hand it is used in microelectronics as a contact material, with resistively 60-80μΩcm. On the other hand it is often used as a shunt over polysilicom lines to increase their conductivity and increase signal speed.

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Tungsten and silicon at 1900 ℃ sintered in an argon gas to form tungsten disilicide and  tungsten trisilicide.
Tungsten trisilicide was known as W5Si3, is in a tetragonal crystal, its physical properties are as follows: chemical formula: W5Si3, molecular weight: 1003.77, melting point: 2320 ℃, decomposition at about 1450 ℃, in air at 500 ~ 700 ℃ will oxidized, dissolved in HNO3 + HF mixed acid.
There are some system numbers about tungsten trisilicide which are as follows: CAS registry number: 12039-95-1, EINECS System number: 234-912-7.
Tungsten trisilicide can produce by tungsten and silicon reaction, the chemical equation of  producing process is 5W + 3Si → W5Si3, which the producing process is as follows:
1. In accordance the molar ratio of the tungsten and silicon is 5:3 and then mixing them with evenly.
2. pass over argon to reactor, and then at the 1400 ℃ to sintered tungsten trisilicide in an argon atmosphere.

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Producing tungsten silicide there has two ways: one is through the reaction of tungsten powder and silicon powder in an argon gas into the vacuum extraction, and the other is making tungsten and silica powder to sintered at 1200 ℃ in an argon atmosphere by calcinate.
There are introduce using tungsten powder and silicon powder in a vacuum process to produce tungsten the producing processes which are as follows:
1. The tungsten powder and silicon powder ingredient at a molar ratio of 1: 2, titanium powder and graphite powder ingredient at a molar ratio of 1: 1, and then were mixed evenly by separately.
2. The silicon powder and tungsten powder mixed powder packed in crucibles middle, the titanium powder and graphite powder packed in crucibles middle where the tungsten-silicon mixed powder be. Finally, put titanium-ink mixed powder on top of all the mixed powder at the middle of crucibles. In the middle of crucibles where has mixed powder of tungsten-silicon and titanium-ink mixed powder and the weight ratio of (0.8 to 1.2): 1.
3. Replace the crucible into sealed reactor, evacuated, then filled with argon, and then stare the reaction of mixture powered.
4. After the material is cooled removal the materials, and then apart the titanium carbide and tungsten disilicide separated, respectively, to obtain crushed tungsten disilicide and titanium carbide powder.

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Tungsten silicide is a black and gray (blue gray) tetragonal crystals are stable at room temperature and atmospheric pressure, its physical properties are as follows: chemical formula: WSi2, molecular weight: 240.01, melting point:> 900 ℃, tungsten silicide insoluble in water and aqua regia, can be dissolved in a mixture of nitric acid and hydrofluoric acid. Tungsten silicide is usually used for making anti-oxidation coating layer and the resistance wire poultice. It has a certain irritation, if you do not accidentally come into contact the tungsten silicide may cause inflammation of skin and eyes, although it is usually not hazardous to water, but the absence of relevant government departments licensing, the material can not be discharged into the surrounding environment. For storage of silicon oxide, it should be sealed and placed in a room temperature, cool and dry place.
Tungsten silicide related system numbering: CAS registry number: 12039-88-2, MDL number: MFCD00049704, EINECS number: 234-909-0, PubChem ID: 24864814.

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In 1950s, tungsten powder is often prepared by tungsten acid and yellow tungsten oxide. In 1960-1970s, America, France, Netherlands and Britain used blue tungsten oxide to produce tungsten powder instead of tungsten acid and yellow tungsten oxide. China started to do the research on blue tungsten oxide in 1970-80s. Tungsten powder property is being affected by a lot of factors including producing method and raw material. When producing super fine tungsten powder, the oxide content of tungsten oxide should be low. When producing fine tungsten powder, oxide content of tungsten oxide should be higher. Thus the producing method of blue tungsten oxide which is of low cost, high property and environmental friendly is under investigation.

Use ammonium paratungstate as raw material, under specific preparing technology and certain temperature, ammonia cracked into hydrogen, ammonium paratungstate is under micro reduction and then blue tungsten oxide is prepared.




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Ammonium paratungstate preparing blue tungsten oxide affecting factors are listed as below:

1.Temperature. As the temperature going up, grain size of blue tungsten oxide changes a little and irregularly. It turns out the effect of temperature is not obvious. Oxide content and ammonia content fall down.

2.Feeding speed. Feeding speed mainly controls the reduction time. The faster the feeding speed is, the shorter the reduction time. As the prolong of reduction time, oxide and ammonia content reduces. But the temperature has larger influence than reduction time. Ammonium paratungstate cracks into crystal water and ammonia under high temperature and turns into yellow tungsten oxide. Yellow tungsten oxide which is under hydrogen reduction and turns into blue tungsten oxide.

3.Speed of rotary furnace. As the speed of rotary furnace goes up, blue tungsten oxide grain size will be more even. It is because material gets more contact with furnace and the heating surface is bigger. It increase the uniformity and distribution of grain size of blue tungsten oxide.




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