Tungsten Crystal Growth during Hydrogen Reduction of Tungsten Oxide (II)

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Category: Tungsten Information
Published on Thursday, 05 February 2015 18:29
Written by cq
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In order to obtain coarser powder, the normal method is reducing and carburizing treatment of tungsten oxide in the presence of alkali metal compounds at high temperature. Thus, the obtained powder particle size can be above 50 µ m (Fsss). But its defects and micro-strain are relatively more than those of the powder without addition of dopant. Some researches show that the crystalline perfection of tungsten carbid e grain in the alloy can be impaired by tungsten starting material which undergoes the adulteration of alkali metal.
 
At high temperature, yellow tungsten oxide (WO3) is reduced to metal tungsten under hydrogen in the stepwise reduction sequence of WO3→WO2.9→W 18O 49→WO2→W. The overall reduction rate is limited mainly by the WO2→W transition. The nucleation and growth of
W grain occur in the WO2→W transition.  
 
The technical conditions of WO2→W transition greatly affect the grain size, uniformity and crystalline of W powder.
 
In order to obtain coarse-grain tungsten powder, the transition of WO2→W must proceed under relatively high pH2O/pH2 in hydrogen atmosphere throughout. 
 
 
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