Preparation of Blue Tungsten Oxide - APT Closed Calcination
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 and used.
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 closed calcination method is the most used method.
In APT closed calcinations, ammonia escaping by thermal decomposition or a small amount of introduced ammonia gas is used as reducing agent. Characteristics of this method: thermal decomposition temperature fluctuates between 550℃-700℃, high yield and stable quality. Phase composition of blue tungsten oxide is 70% W20O58 and 30%WO3.
APT closed calcination method always keeps the furnace system with positive pressure in the heating process, preventing the air from entering the furnace. By this way, ammonia from APT pyrolysis splits into hydrogen and nitrogen. And in the weak reductive atmosphere, the blue tungsten oxide is produced.
In the process of sealed calcination, ammonium paratungstate(APT) transmutes into BTO by four stages.
1, 220℃, generation of enerateg amorphous APT or amorphous bronze
2, 300℃, generation of ammonium tungsten bronze
3, 420℃, generation of yellow tungsten oxide
4, 480℃-600℃, generation of blue tungsten.
In APT closed calcinations, ammonia escaping by thermal decomposition or a small amount of introduced ammonia gas is used as reducing agent. Characteristics of this method: thermal decomposition temperature fluctuates between 550℃-700℃, high yield and stable quality. Phase composition of blue tungsten oxide is 70% W20O58 and 30%WO3.
APT closed calcination method always keeps the furnace system with positive pressure in the heating process, preventing the air from entering the furnace. By this way, ammonia from APT pyrolysis splits into hydrogen and nitrogen. And in the weak reductive atmosphere, the blue tungsten oxide is produced.
In the process of sealed calcination, ammonium paratungstate(APT) transmutes into BTO by four stages.
1, 220℃, generation of enerateg amorphous APT or amorphous bronze
2, 300℃, generation of ammonium tungsten bronze
3, 420℃, generation of yellow tungsten oxide
4, 480℃-600℃, generation of blue tungsten.
The main equipment of APT closed calcination method is rotary calciner. Rotary calciner’s size is decided by production requirements. Generally, the furnace is 6-8 m in long, 300-450 mm in diameter and made of stainless steel.
Temperature, time and specific area are influencing factors which will affect the quality of blue tungsten oxide during calcining process. And temperature is the most important factor.
Temperature, time and specific area are influencing factors which will affect the quality of blue tungsten oxide during calcining process. And temperature is the most important factor.
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