Preparation of Blue Tungsten Oxide - APT Mild Hydric Reduction Method

Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. Compared with yellow tungsten oxide, blue tungsten oxide with its high activity, large surface area, easy doping, original crystalline shape is seen as an upgraded version of the Yellow tungsten oxide.

Blue tungsten oxide is one of the most important raw materials for the manufacture of tungsten powder. In China, there are three main methods for preparation of the blue tungsten oxide: APT closed calcination method, APT mild hydric reduction method and intrinsic reduction method. And the APT mild hydric reduction method is the most used method.

multi-tube furnace image

The whole preparation process reacts in a multi-tube furnace of which the heating zone is divided into three parts. In the furnace tube, the heated APT•5H2O installed on the heat resistant boat is decomposed. Feeding a small amount of hydrogen into the furnace tube can keep the reducing atmosphere. Decomposed gas product and waste gas are discharged out of the furnace and then fired. The phase composition of hydrogen blue tungsten oxide can be controlled by the flow rate of hydrogen, reduction temperature and speed regulation.

Heating temperature in multiple tube furnace is controlled at the range of 400℃—500℃. In the heating process, a small amount of hydrogen play a catalytic role, increasing the degree of ammonium tungstate out of crystalline water and ammonia and the reduction degree of ammonium paratungstate. Blue tungsten oxide began to form when the temperature reached 450 ℃.

Compared with APT closed calcination method, mild hydrogen reduction method is more environmental friendly. In the process of APT closed calcination, ammonia gas, as a harmful factor to health and environment, is required. For comparison, APT hydrogen mild reduction method only needs a small amount of hydrogen, discharging the environmental pollution problems. And under appropriate parameters, APT hydrogen mild reduction method can prepare blue tungsten oxide with higher quality.

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