Tungsten carbide powder (WC) is kind of dark gray powder, which using proportional tungsten powder and carbon black mixture as raw material to produce tungsten carbide powder. And in tungsten carbide powder the carbon atoms embedded tungsten metal lattice gap and did not destroy the original metal lattice, but to form interstitial solid solution, also known as interstitial compound. It is mainly used in produce tungsten carbide alloy.
The production of tungsten carbide powder is mainly through mix metal tungsten powder and carbon black as raw materials which according to a certain proportion of formulated. And then putting mixture into the graphite boat and placed in the carbon tube furnace or a sense of high-frequency electric furnace with a certain temperature to carbonization, and then by ball milling, screening to obtain tungsten carbide powder.
Tungsten carbide powder should be stored in dry, ventilation and acid-free atmosphere, to prevent oxidation, in which the storage period should not exceed six months. The external package of tungsten carbide should be drum and the internal packaging should be polyethylene bags, tightly sealed. According to fsss's size, tungsten carbide powder can be divided into 12 grades, as shown below.

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Tungsten carbide powder (WC) as a black hexagonal crystal with a metallic luster, a dark gray powder, the hardness close to diamond, is the main raw material for the produce tungsten carbide. Its physical characteristics are as follows: chemical formula: WC, melting point: 2870 ℃, boiling point: 6000 ℃, the relative density of 15.63 (18 ℃), it does not dissolve in water, hydrochloric acid and sulfuric acid, easily dissolved in mixture acid of nitric acid and hydrofluoric acid which is a good conductor of electricity and heat. Tungsten carbide is fragile, if adding a small amount of infiltration of titanium such as cobalt, titanium and other metals can reduce brittleness, but also make the tungsten carbide used in more areas. Using tungsten carbide as steel cutting tools used often adding titanium carbide, tantalum or they mixtures in order to improve the anti-knock capacity.
Tungsten carbide powder may be dissolved in a variety of carbide, especially in titanium carbide forming solid solution TIC-WV. Another compound of tungsten and carbon is tungsten dioxide carbide, the formula W2C, a melting point of 2860 ℃, boiling point of 6000 ℃, the relative density of 17.15, while its properties, preparation method, use of tungsten carbide powder and similar.

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Tungsten hexafluoride (WF6) is only stable varieties in tungsten fluoride which can produce by industrial. It is mainly used in the chemical vapor deposition of tungsten, the chemical equation for this reaction is: WF6 + 3H2 → W + 6HF. The reduction of tungsten hexafluoride can be restore to metallic tungsten and HF by hydrogen or other reducing gas (such as GeH4, SiH2F2 and diethylsilane etc.) at high temperatures. Tungsten hexafluoride as a raw material widely used in the electronics industry as base of tungsten metal chemical vapor deposition (CVD) process technology, such as using WSi2 as wiring materials of LSI which is made by WF6. Besides, using CVD technology of mixing metal to produce tungsten and the rhenium complex coating may be used to manufacture X-rays emitter electrode of a solar absorber. What’s more WF6 in the electronics industry still mainly used as a semiconductor electrode and the conductive paste and other raw materials.
In addition to applications in the electronics industry, tungsten hexafluoride used in non-electronic aspect is also very broad. By CVD technology to generate hard tungsten carbide on the surface of the steel can improve the surface properties of the steel. Additionally, tungsten hexafluoride is also widely used in fluorinating agent, polymerization catalyst and feedstock of optical materials to manufacture low resistance and high melting point interconnect lines or some components, such as tungsten tube and crucibles.

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There are many synthetic methods tungsten hexafluoride. The following introduce chemical reactions which use tungsten, halogen and HF to react then to form tungsten hexafluoride. Tungsten hexafluoride formed by the react of tungsten, halogen and HF where the chemical reaction equation is as follows: W + 3X2 + 6HF - WF6 + 6HX. Wherein the X2 is a halogen, usually Cl2 or Br2, the reaction is carried out in an autoclave which make by monel alloy.
Using Cl2 as example, in order to ensure that the product has a good yield, generally make Cl2 and HF appropriate excess, in the theory chlorine and tungsten hexafluoride molar ratio of 3: 1, while in the experiment used 3~6: 1. Theory hydrogen fluoride and tungsten hexafluoride molar ratio of 6: 1, is used in the experiment used 6~10: 1, the reaction temperature is controlled at 150 ~ 450 ℃. While increasing the reaction temperature can make the reaction quickly but the temperature is too high will cause severe corrosion of equipment and WF6 partially decomposed.
By the way this method often has by-product, it is not a good way for produce tungsten hexafluoride not only by environmental protection or economic efficiency.

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Currently, there are there methods for synthesis tungsten hexafluoride which are common used. The first is by direct reaction of fluorine gas and tungsten to generate tungsten hexafluoride. The second is tungsten and nitrogen trifluoride (NF3) direct reaction to produce tungsten hexafluoride. The third method is to generate tungsten hexafluoride by react halogen, tungsten and HF. The following is introducing the reaction of using tungsten and nitrogen trifluoride to produce tungsten hexafluoride and in this reaction NF3 as fluorinating agent.
The reaction equations of tungsten and nitrogen trifluoride reaction is as follows: W + 2NF3 - WF6 + 3N2, the reaction conditions at temperatures greater than 400 ℃ decomposition of NF3 to produce F2. F2 reacts with the metal to generate tungsten hexafluoride. Besides the NF3 moisture content which used in reaction direct related to the purity of the product. That is need high-purity NF3 to produce tungsten hexafluoride. But the high-purity NF3 requires cryogenic condensation method to cool NF3 at -130℃~ -70℃, after water solidified to separate to make it. What’s more the reactor should make by nickel or monel. But this will lead to increased production costs, and a higher investment risk, which are not suitable for applied industrial production.

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Tungsten hexafluoride is a strong fluorinating agent, with the exception of nickel, monel and stainless steel, make many metal fluoride at room temperature. In the dry state it has low corrode for glass, but able to respond quickly in heavy moisture. Tungsten hexafluoride and ionic halide react can form complex compound at a high temperature to reduce tungsten by hydrogen.
There are three methods for synthesis of tungsten hexafluoride, is described below using fluorine gas as the fluorinating agent in the process to produce tungsten hexafluoride: making tungsten and fluorine gas (F2) direct reaction to synthesis tungsten hexafluoride, in order to prevent the erosion container wall of fluorine, the reaction vessel material should be monel, nickel or stainless steel. Chemical reaction equation is as follows: W + 3F2 - WF6.
This reaction is carried out under the conditions of 400 ℃, tungsten direct reacts with F2 to  produce tungsten hexafluoride, because the nature of F2 is too lively, in order to make the reaction proceed smoothly requires a certain proportion of nitrogen added. Generally the tungsten metal is added by tungsten powder to make the gas-solid phase contact area as large as possible, and then collect tungsten hexafluoride into another low temperature container by liquid form.

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Produce tungsten powder usually by reducing tungsten oxide which restored ammonium paratungstate or tungsten trioxide by hydrogen. And the reaction is usually carried out in electric tube furnace or rotary furnace. Using hydrogen reaction method to produce tungsten powder there are two important processes, the first is at a temperature of 500℃-700℃ restore tungsten trioxide to tungsten dioxide. And the second is at 700℃-900℃ temperature, tungsten dioxide is reduced to tungsten powder. What’s more tungsten powder good properties (such as purity, particle size, size distribution, etc.) depends on the reduction process, such as the reduction temperature, boat load of tungsten oxide, boat speed, flow rate of hydrogen and hydrogen water content. In addition, using aluminum, calcium, zinc and others to restore tungsten powder also caused a big concern.
Except using hydrogen reaction method to produce tungsten powder, in the early time also using tungsten oxide carbon reduction method to restore tungsten powder which is at the temperature above 1050 ℃. But this method will produce low-purity tungsten powder, so there is less use in industry.

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Tungsten powder restores by hydrogen in four tube muffle furnace where the tungsten oxide as raw material. The particle size of tungsten powder mainly 0.6-3.0um which can be divided into coarse, medium and fine several granularities. Tungsten powder is used to process powder metallurgy of tungsten products and as raw material of tungsten alloy. Tungsten powder can be made into wire, rods, tubes, plates and other processing materials and shaped products. Besides, tungsten powder mixing with other metal powders can be made into a variety of tungsten alloys, such as tungsten and molybdenum alloys, tungsten-rhenium alloy, copper alloy of tungsten and tungsten heavy alloy. And there is another important application of tungsten powder which is used tungsten carbide powder and then uses it to produce carbide tools, such as turning tool, milling cutter, drill and mould.
After many experiments found that the performance of tungsten powder will directly affect the quality of tungsten materials and tungsten powder metallurgy products. Particularly the purity and particle size of tungsten powder affecting products evidently. During the restore reaction, reduction process and raw materials is the main reason for the performance of tungsten powder. Therefore, to produce a good performance of tungsten powder not only to control the reduction process has to choose the good performance of the tungsten oxide raw material.

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Ammonium paratungstate tetrahydrate, APT·4H2O dissolves rather slowly in aqueous ammonia at room temperature. Dissolution at higher temperatures increases the rate of dissolution, but the amount of dissolved tungsten decreases due to the lower solubility of ammonia at higher temperatures which results in a lower PH of the solution. The rate of dissolution was found to be independent of the crystal size. It is therefore concluded that the rate-controlling step occurs in the solution.

Calcination of APT·4H2O in air, nitrogen and hydrogen/nitrogen mixtures, into an X-ray amorphous product, is shown to be one way to improve the dissolution rate and to increase the dissolved amount of APT·4H2O. The highest solubilities can be obtained by calcining APT·4H2O in air or nitrogen at temperatures ranging from 250 to 310°C for approximately 2 h. When the temperature is too low or the residence time is too short some crystalline APT·4H2O will still exist; WO3 is formed when the temperature is too high or the residence time too long.


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Ammonium paratungstate calcined in air change course: T ≥ 240 ℃, and transferred as ammonium metatungstate (AMT).

When the temperature is between 300 ~ 350 ℃, it turns into ammonium tungsten bronze ATB. When the temperature is under 400 ℃, it turns into the hexagonal WO3. When the temperature reaches to 500 ℃, it becomes triclinic crystalline tungsten trioxide.

Ammonium paratungstate purity and crystalline are hereditary. Calcination temperature, speed has a significant impact on the physical and chemical properties of the product.

The higher the calcining temperature, the more coarse particle size of the obtained WO3. Rapid heated will cause the larger specific surface area. Slowly heated which results in the perfect crystalline and smaller specific surface area.


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