Because of tungsten powder and tungsten carbide powder chemical purity and physical properties has high requirement so producing tungsten powder and tungsten carbide powder process is very complex and the cost is higher too. But tungsten powder composition when not strictly required in most cases where there are a lot of impurities so using industrial pure carbon reduction tungsten powder is an economical and easy way. In a vacuum furnace use carbon reducing tungsten trioxide making high purity tungsten powder and tungsten carbide powder provided by melting and casting.
According to current science and technology, using industrial pure carbon or tungsten carbide powder as a casting material is fully meet the requirements. Using carbon restore tungsten trioxide is similar with using hydrogen restore tungsten trioxide. At atmospheric pressure, at a temperature condition of 750 ℃ heating tungsten trioxide so it will mix with carbon black or graphite powder occurring reduction. The reaction chemical equation is: WO3 + 3C = W + 3CO, WO3 + 4C = WC + 3CO. The temperature under 1000 ℃, mainly using CO participate in a reaction and chemical equation is: WO3 + 3CO = W + 3CO2, CO2 + C = 2CO. The main process includes milling mixing, compression molding, dried at 200 ℃ temperature, then vacuum carburizing, and then filtered through milling.
Fine and uniformity tungsten powder are key point for producing carbide, and micron and submicron tungsten carbide powder is useful to producing carbide. According to the relevant academic report found that single tungsten oxide can produce submicron or micron tungsten powder. Using violet tungsten oxide (VTO) producing fine tungsten oxide not only the process of it is simple as well as process parameters are easy to control and also equipment are not complex etc. Producing process as follows:
1. VTO were first reduction in hydrogen, along a first temperature of 640 ℃, the second temperature of 760 ℃, third temperature of 860 ℃, when the temperature reaches 860 ℃ heat preservation for 20min.
2. in the air at 500 ℃ making tungsten powder to oxidation with slowly heated for the first time, then heat preservation for 10min.
3. Replace the first step and second to continuous cycle reduction reaction.
4. Using alcohol on the analytical results above steps were dispersed pattern, then using BT-9600 laser particle size analyzer and JXA-840A electron probe scanner to analysis particle size and morphology of samples.
Tungsten trioxide film is a new type of functional material, which has a wide range of applications in smart windows, a large area flat-panel displays, gas sensor, and so on the field. But because WO3 Films still have some shortcomings, such as discoloration and sensitivity is not high, it will cause a lot of restrictions in the application. In order to improve its performance so that it can be widely used, the optimization can generally divided into three kinds: one is preparing a novel surface topography WO3 film.
The second is the preparation of nanometer WO3 composite film, third film doped WO3 modified. With further research to expand, need to find new chemicals, new fetters, explore preparation skills and preparation parameters appropriate to improve the surface appearance of the film become a hot topic. Currently, for performance optimization WO3 film discoloration research focused on electrochromic and temperament discoloration. And to improve its photochromic,less heat to research color and other properties. Future research in this area can be expanded.
Violet tungsten oxide using the APT as raw materials,which is during at the closed furnace in the industry. Under certain conditions, adding NH3 during calcination, and the NH3 will decompose H2 and N2, it will form a wet hydrogen atmosphere furnace in the stove, so that APT under mild reducing atmosphere, gradually decompose, generating purple oxide reduction.
There are many factors in the process of preparing violet tungsten, one by the hydrogen reduction of tungsten oxide mechanisms apparent hydrogen greater humidity, the temperature required to obtain the higher tungsten purple, so choose the calcination temperature should be 770 ~ 815 ℃, Second, in the calcination process feed speed, tube speed, NH3 traffic and others factors affect the production of tungsten purple in varying degrees. In the preparation of tungsten purple we should to coordinate various relationships in order to produce a single phase purple tungsten. Its chemical equations are: 3 [5 (NH4) 2O · 12WO3 · 5H2O] = 2w18O49 + 40H2O + 35H2 + 15N2. Comprehensive variety of experimental results can be obtained tungsten production violet optimum parameters are as follows:
Furnace tube rotational speed（r.min-1）
NH3 Rate of Flow/(m3.h-1)