Blue Tungsten Oxide Preparation -- APT Closed Calcination Method
Blue Tungsten Oxide is one of the important raw materials for making tungsten powder.
Compared with yellow tungsten, blue tungsten oxide is considered to be an upgraded version of yellow tungsten oxide because of its good activity, large surface area, easy to dope and maintain original crystal shape. And it’s widely used.
There are three main methods for making blue tungsten, APT closed calcination method, APT hydrogen light reduction method, intrinsic reduction method. APT closed calcination is one of the most widely used methods.
APT closed calcination method is the most used to produce blue tungsten oxide production. The characteristics of APT closed calcination method is: use thermal decomposition of ammonia or a small amount of ammonia into the reducing agent, thermal decomposition temperature fluctuations in the range of 550 °C - 700 °C, high yield, stable quality, which is composed of 70%W20O58 blue tungsten oxide, 30WO3%.
APT closed calcination method its essence is in the heating process, always keep the furnace system with positive pressure, so that the air can not enter the furnace, APT produced by the decomposition of ammonia can be split into hydrogen and nitrogen, the furnace has weak reductive atmosphere, the final product is blue tungsten.
APT transformed into TBO by closed calcination has roughly four stages.
1. When 220 °C, generating amorphous or amorphous bronze APT.
2. When 300 °C, generating ammonium tungsten bronze.
3. When 420 °C, generating yellow tungsten.
4. When 480 °C - 600 °C, generating blue tungsten.
The main equipment of rotary calcination furnace APT closed calcination method, the size of the rotary kiln was decided according to production requirements, general furnace length 6 - 8 meters, 300 - 450 mm in diameter, made of stainless steel welded.
In calcination, the factors affecting the final quality of blue tungsten are temperature, time, specific surface area, etc. The most important factor would be temperature.
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