Tungsten Oxide

Tungsten oxide photochromic incluence factors are various. In addition to the structure and composition of itself, which the atmosphere the tungsten oxide exist will also impact on its chromogenic performance. Considered from the internal structure of tungsten oxide, there are different structures of tungsten oxide there. From relatively stable triclinic, monoclinic to cubic, tetragonal and very unstable hexagonal bronze, pyrochlore phase, but the most studied at the present is amorphous (a-WO 3 ) or polycrystalline (c-WO 3 ) film’s photochromic properties. After the study found that a-WO 3  compared with c-WO 3  has a good photochromic property, mainly because c-WO 3  has lattice defects or small surface area or others.  The internal factors which mentioned above is the main reasons of determine the material properties, and external also has great impact on tungsten oxide photochromic which can not be underestimated, especially on different atmosphere. From colored aspects

Nano tungsten oxide has strong organizational ability to grow and in a stable reaction conditions the interactions between molecular are fairly obvious. Molecular can epitaxial growth which is in accordance with lattice arrangement strictly and to form the formation ratio complete and single component structure. With the improvement of nano technology, now there have been some special forms tungsten oxide , including arborescent, clitheriform, nanorods, nanowires and other special forms.  There are many producing methods for special form nano tungsten oxide which can be divided into three types: high-temperature synthesis, hydrothermal synthesis method, and solution low temperature synthesis method. Although high-temperature synthesis method is most common, but it has high requirements in equipment so this method is difficult wildly be used. The hydrothermal synthesis method is acidification W (CO)  6  and ammonium tungstate, the reaction is from 2 to 100 hours at 160-200 ℃

Tungsten bronzes are a special class compounds which is non-stoichiometric and the chemical formula is MXWO3 (0 <X <1). The M of MXWO3 can be an alkali metal, calcium, strontium, barium, rare earth metals, copper, ammonium, hydrogen and so on. Such compounds are more exist in hexagonal, cubic and tetragonal, its structure is basis on WO6 octahedral structural, forming a layered having a six-membered, five- or four-membered ring channels through the apex of a rigid skeleton structure of tungsten oxide structure.  Tungsten oxide compounds in bronze phase  has special physical properties, which generally has a high electronic conductivity and faster ion transport properties, which conducts electricity can achieve 2.5 × 10 6 Ω -1 m -1 , is a low-temperature superconductors. Recently it was widely used in electrochromic displays, electrode and PH sensors and other area, so then it becomes a hot issue again. Many methods for preparing tungsten oxide bronze, common in three ways:

Using different power laser radiation study tungsten oxide nanowires found that with increasing laser power (0.72mw ~ 20mw), the Raman spectra of tungsten oxide nanowire has significant changes, when the laser power Raman spectra of tungsten oxide nanowire is low the Raman signal also not strong. Peak shape and peak data will not change much. As the power increases, the Raman signal also increases. When the laser power is increase to certain strength, then tungsten oxide will react with oxygen become tungsten trioxide. At this time the tungsten trioxide is monoclinic phase. When the laser powder drops to 3mw the Raman peaks has been unable to return to the peak, indicating that the oxidation process is irreversible. With the laser power is increased again, tungsten trioxide nanowire phase transition from monoclinic phase to β phase, has studying by the changing of laser power found the monoclinic phase of tungsten oxide change to the β phase so the this process is reversible

Blue tungsten oxide forms including composition, phase composition, surface area, particle size and oxygen index and so on. Blue tungsten oxide particle size has a significant impact at the tungsten powder reduction on tungsten powder particle size, which the coarse blue tungsten is good for producing fine tungsten powder, because coarse blue tungsten oxide particles in the process of reduction has good permeability can exclusion vapor water which have a greater advantage.  To a certain extent, blue tungsten oxide specific surface area also affect tungsten powder particle size having a large specific surface area of ​​blue tungsten oxide in favor of   producing fine tungsten powder. Because the more advanced blue tungsten oxide surface area, the greater its reaction interface, reducing activity, the better.  In the study also found the relative composition of blue tungsten oxide will effect tungsten powder particle size this is also can not be ignored. After comparing the

In addition to the blue tungsten oxide form affects tungsten powder particle size, the process parameters also affect the size of tungsten powder. Influence of process parameters on the tungsten powder particle size is mainly hydrogen mode, heating systems and hydrogen influence humidity. There are two kinds of hydrogen modes, one is cis hydrogen mode and the other is inverse hydrogen. The study found that cis hydrogen mode reduction of tungsten powder particle size is significantly thinner than the inverse hydrogen mode. ATB phase blue tungsten powder at low temperature with cis hydrogen mode can producing tungsten powder particle size thinner, narrow distribution, and the nature the better.  In heating system, the researchers found that heating from a low temperature and the heating process more gentle process are good for the producing fine tungsten powder. At the same time hydrogen humidity also impact on the tungsten powder particle size, at the same other process pa

After the study, we found that violet tungsten oxide particle affecting factors includes raw material (APT) particle size and production process conditions. Production process conditions include reducing temperature, heating rate, water vapor and hydrogen pressure ratio, material thickness and reaction time. Firstly, the influence factor is water vapor and hydrogen partial pressure ratio, which are water vapor and hydrogen partial pressure ratio increases and the size of products larger. This is mainly due to the formation of hydrogen gas to form a volatile humidity hydrous tungsten oxide, tungsten oxide which is easy to cover the finer particles, so that the particle size increases.  Secondly, the impact factor is heating rate, after experiment found that to produce fine particles the heating speed should not too fast. When the reduction in a tube furnace, the heating rate depends on the furnace temperature gradient and push the boat speed, hence reducing the furnace temperature

With the development of research, the ultra-fine particles as a new material have been widely used in modern industry and science. Violet tungsten oxide (VTO) has special properties and structure so get a lot of favor in producing ultrafine tungsten powder. During producing tungsten powder not only process conditions is important but the raw marital particle size is also an important factor. Therefore, to study violet tungsten oxide particle affecting factors is very important. Producing violet tungsten oxide is through boatload an amount of ammonium paratungstate and pushes it into the reduction furnace hot zone. At the same time add a certain proportion of hydrogen and steam mixture to heat at a certain temperature, after a period heat preserving then cooling to obtain. During the reaction, the factors that influence the violet tungsten oxide grain size are the raw material (APT) particle size and production process conditions. Production process conditions include redu