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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Samples of tungsten-modified borated zirconia were prepared to be used as catalyst in 2-phenoxyethanol acetylation. The borated zirconias were obtained by impregnation of two zirconias (S2 and S4) obtained by the micellar method using different zirconium precursor concentrations with boric acid solution containing 0.3 moles B/dm³. These solids and the parent zirconias were impregnated with two concentration levels of ammonium metatungstate solutions (0.11 and 0.22 moles W/dm³). The solids containing boron mainly have amorphous characteristics and strong acidity, while those that contain only tungsten showed stronger acidity and evidence of the presence of a crystalline phase.

The specific surface area and the pore volume slightly decreased in the solids obtained by adding tungsten to borated zirconia, and more markedly in those that contain only tungsten, and the mean pore size increased with respect to the parent support. It was observed that in the 2-phenoxyethanol acetylation using acetic acid as acylating agent and tungsten-modified borated zirconia as catalyst, the yield to acetylated product was high and it is correlated with the acid strength of the catalysts. In turn, the solids that contain only tungsten have a correlation with the acidity, but lead to low yield values due to a poorer dispersion of the tungsten species. The best yield was obtained with the catalyst prepared with the borated S4 zirconia containing 15% g B₂O₃/100 g support and 12.5% g W/100 g support. Using this catalyst and the same reaction conditions, the acetylation of different alcohols and phenols was studied, the reactivity order being as follows: primary alcohols > secondary alcohols > phenols.


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At present both ammonium paratungstate (APT) and AMT are being used as tungsten sources in the catalyst industry. Since APT has a limited solubility in water (about 2 to 3 percent at room temperature), the user converts APT to a more soluble peroxytungstate form by means of reaction with hydrogen peroxide in order to prepare the catalyst. While AMT is highly water soluble, and thus need not be converted, it is in general more expensive than APT, due to the complexity and/or low yields of processes for producing it.

A process for producing ammonium metatungstate (AMT) from ammonium tungstate (AT) solution is described which involves the addition of about 3.6 percent by weight of silica to an AT solution, digestion for at least about 4 hours at a temperature of at least about 98°C, followed by filtration to remove the silica from the AMT solution. Typically about 0.4 percent by weight of silica remains after filtering. The resulting AMT solution may be further processed to recover solid AMT, such as by evaporation or spray drying.


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A particular advantage of the invention is that the silica used in digestion and subsequently filtered from the digested solution of ammonium metatungstate may be reused repeatedly, that is, its capacity to promote formation of AMT is not diminished with use. While the exact mechanism is not well understood at this time, the role of silica is to prevent the precipitation of insoluble APT and therefore to allow lowering of the pH to the AMT forming region, about 4 to 4.5.

After digestion is completed, the silica is removed, such as by filtering, and the solid AMT may be recovered in the conventional manner, such as by evaporation or spray drying.

The silica used in the invention may be any commercially available silica, provided that its impurities, both in kind and amount, are consistent with the final envisioned application for the AMT. For example, both sodium and phosphorus may be considered objectionable impurities for certain catalyst applications. Residual silica which cannot be removed from the digested AMT solution by filtering is generally below 1 percent by weight, and typically from 0.3 to 0.6 weight percent WO₃basis, and is compatible with many catalyst applications.


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