Tungsten trioxide, also known as WO3, tungsten oxide or tungstic anhydride, is mainly applied to produce tungsten powder and tungsten carbide powder. And then the two kind of powder are used to produce all kinds of pure tungsten products (such as tungsten wires, tungsten electrodes and tungsten rods, etc.) and tungsten carbide products (such as tungsten carbide molds and tungsten carbide knives, etc.) respectively. 
WO3 can also be used as a kind of pigment (for yellow ceramics) or as a kind of coating and anti-corrosion paint (for ships), etc. It can also be used to manufacture tungstates for x-ray screen phosphors, fireproofing fabrics, and so on. WO3 has been employed in producing electrochromic windows or smart windows recently. These windows are electrically switchable glass that change light transmission properties with an applied voltage. This allows the user to tint their windows, changing the amount of heat or light passing through.
The nature of WO3 varies in accordance with preparation conditions (rate and temperature):
1. WO3 made under high temperature is insoluble in water.
2. WO3 made at low temperature is more active and soluble in water.
The crystal structure of WO3 depends on the temperature:
1. It is triclinic from -50 to 17 °C.
2. It is monoclinic from 17 to 330 °C.
3. It is orthorhombic from 330 to 740 °C.
4. It is tetragonal at temperatures above 740 °C.
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