Tungsten(VI) oxide, also known as tungsten trioxide or tungstic anhydride, WO₃, is a chemical compound containing oxygen and the transition metal tungsten. It is obtained as an intermediate in the recovery of tungsten from its minerals. Tungsten ores are treated with alkalis to produce WO₃. Further reaction with carbon or hydrogen gas reduces tungsten trioxide to the pure metal.

 

Tungsten trioxide has excellent performance in electrochromic, catalysis, gas sensing and other aspects, its composite oxides, tungsten bronze, generally refers to the metal oxide with deep metallic luster color, and usually metal conductors or metal-semiconductors, the formula of tungsten bronze is A_xWO₃, but with different types of cations and the number of moles ( different A, x value), the structure and color shades of the compounds will vary. Currently potassium cesium tungsten bronze and tungsten bronzes cesium are relatively common, cesium tungsten bronze is widely used in the preparation of the conductive thin film and insulating agent in glass transparent insulation paint because of its low resistance and excellent transmittance of visible and near-infrared shielding properties.

 

Some scholars have proposed a solid-phase synthesis method of cesium tungsten bronze powder by vacuum sintering without external passing gas protection. This method belongs to the metal oxide powder preparation technology. The synthesis steps are as following. (1) tungsten compound and cesium salt are weighed as the W / Cs molar ratio (2~3.5), milled until mix evenly; (2) The milled material should be put into the hermetic container in Hourumafu furnace, the reaction temperature is 750~800 °C, the reaction time is 1 ~2h; (3) the blue-black cesium tungsten bronze powder with complete crystals will be obtained after reaction.

 

This method takes the first place to use solid materials and directly react in a sealed vessel to prepare cesium tungsten oxide, without passing inert gas or reducing gas, which uses the gas generated from their own reaction of NH₃, CO₂ or water vapor as the protective gas, to make the color of the resulting powder is blue-black. This method saves gas supply, reduces costs, and the synthesis process is simple,the reaction period is short, which is suitable for industrial production.