Preparation Blue Tungsten Oxide by Self-Reduction Method from Ammonium Paratungstate

Because of the shortcomings like cost control and environmental protection in preparation of blue tungsten oxide by traditional reduction method, in order to overcome these problems, domestic and foreign scholars, manufacturers and so on, are trying to develop new methods. Some studies have pointed out that Self-reduction method, use ammonium paratungstate (APT) as raw materials, heating APT in a sealing container to produce blue tungsten oxide. Self-reduction method, just as its name implies, is a method that reactant set under certain conditions in the environment of good airtight, the reaction itself producing some reductive substances which will has a reduction of the oxide to get target product.

Specific steps:
1. Send APT into sealed container, heated to 400℃ to 600℃, APT will decomposition into tungsten trioxide (WO₃), ammonia (NH₃) and water vapor (H₂O);
2. Using tungsten oxide WO_X as the good property catalytic for NH₃ in a closed container, ammonia is further decomposed into N₂ and hydrogen;
3. Control of furnace temperature at 550 to 800℃, set the pressure at 0 to 2 mbar (0~200Pa), restore WO₃ to WO_2.9 by using hydrogen.

The advantages of using Self-reduction method:
1. Using the ammonia generated from ammonium paratungstate to restore tungsten trioxide, and no need to inlet other reducing gas, thus to reduce the production cost and improve the economic benefit;
2. Eliminate harmful gases such as ammonia and other harmful gas emissions at the same time, reduce air pollution and improve social benefits.

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