Purple Tungsten Oxide Preparation
Purple tungsten oxide is a kind of tungsten oxide product developed in China in recent years. Its phase composition is WO2.72 or W18O49.
Because of its unique properties, purple tungsten oxide is the main raw material of ultrafine tungsten powder and nanometer tungsten powder.
The production of purple tungsten oxide is mainly made up of APT hydrogen reduction process. It is carried out in a multi tube furnace. There are two ways of flow direction of hydrogen in the furnace tube, one is that the direction of hydrogen flow is opposite to the direction in which the boat (material) is pushed in the furnace tube. This is the traditional method of hydrogen production by the medium and fine particle tungsten powder, which is called the reverse hydrogen reduction process. But later research found, such as changing the direction of hydrogen, the hydrogen flow direction and the boat forward in the same direction, can prevent spontaneous combustion of tungsten powder, refined products more conducive to the particle size of tungsten powder, this is the so-called hydrogen reduction process.
In the making process, when the particle size of tungsten powder less than 1 micron, which is pyrophoric, therefore, when the tungsten powder is treated in the cooling stage, it contacts the wet hydrogen, and when it leaves the reduction furnace, the surface of the fine tungsten powder has a protective oxide film on it. If reverse hydrogen reduction is used, the tungsten powder may be prevented from overheating by the addition of an inert atmosphere, such as nitrogen or hydrogen.
The process of reducing the hydrogen content of the purple tungsten oxide is based on the refining mechanism of the reduction of hydrogen. Compared with blue tungsten, purple tungsten has higher reduction activity. The advantages of producing ultrafine tungsten powder by industrial process are that there is no impurity pollution in the process of reduction (compared with the process of activation reduction of additives), and the chemical purity of the product is higher; Another significant advantage is that the process parameters in the reduction process can be precisely regulated and controlled so that ultrafine tungsten powders can be produced at different particle sizes.
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