The reason why tungsten oxide has different colors is mainly due to the combination of the following factors:
- Oxygen content and chemical structure
Oxygen content
The color of tungsten oxide is closely related to its oxygen content. Depending on the oxygen content, tungsten oxide can form a variety of compounds, such as WO3 (yellow tungsten oxide), WO2.9 (blue tungsten oxide), WO2.72 (purple tungsten oxide) and WO2 (brown tungsten oxide). These compounds have different electronic and energy band structures due to the different number and arrangement of oxygen atoms, which in turn affects their light absorption and reflection properties, resulting in different colors.
Chemical structure
In addition to the oxygen content, the chemical structure of tungsten oxide is also an important factor in determining its color. For example, the w18o49 phase in tungsten oxide has a special color-changing function. Under high temperature and vacuum conditions, the w18o49 phase will undergo a structural transformation, leading to a change in its electronic structure, which in turn causes a change in color.
Second, the production process and conditions
Production process parameters
The color of tungsten oxide is also affected by the production process parameters. These parameters include calcination time, reduction time, reduction gas concentration and so on. By adjusting these parameters, the crystal structure and surface state of tungsten oxide can be changed, thus affecting its color.
Oxidizing and roasting conditions
For blue tungsten oxide, its roasting process directly determines its color. Lower temperature and short time roasting is conducive to the formation of blue center, producing dark blue; while high temperature and long time roasting may destroy the blue center, making the color lighter.
Other factors
Particle size
The particle size of tungsten oxide nanoparticles also has a significant effect on its color. As the particle size decreases, the surface effect and quantum size effect of tungsten oxide nanoparticles gradually appear, leading to changes in light absorption and scattering characteristics, and then change the color.
Environmental conditions
Environmental conditions such as light and humidity also have a certain effect on the color of tungsten oxide. Light may lead to photochromic phenomenon, while humidity may affect the interaction between tungsten oxide and the surrounding environment.
The different colors of tungsten oxide are due to its oxygen content, chemical structure, production process and conditions, and a combination of other factors. These factors affect the electronic structure, energy band structure and surface state of tungsten oxide, which in turn determine its light absorption and reflection properties, thus showing a rich variety of colors.
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