Preparation of Submicron Tungsten Trioxide Ultrafine Powder 1/2

Due to various excellent properties of fine-grain carbide, submicron powder (average particle 1m) demand was a rapid upward trend in recent years. Today, industrial production has been able to ultrafine tungsten powder (average particle size 0.5m). Production of ultra-fine tungsten oxide powder material made increasing demands, especially in the purity and uniformity of raw materials.

The method of preparation of ultrafine tungsten trioxide powder there are many, the following method is used in many redox. Experimental procedure:
(1) APT was calcined in air at a temperature 500 ℃.
(2) Calcining the resulting reduction in hydrogen tungsten trioxide, temperature 850 ℃, insulation 25min.
(3) Oxidation in air after the first reduction resulting tungsten powder, temperature 500 ℃, insulation 20min.
(4)Reduction in hydrogen tungsten trioxide first after oxidation, temperature 850 ℃, insulation 25min.
(5) In the air oxidation of the second reduction resulting tungsten powder, temperature 500 ℃, insulation 20min.
(6) After the second oxidation resulting tungsten trioxide and second reduction resulting tungsten powder dispersed in distilled water, made after laser particle size analysis.
(7) Analytically pure alcohol dispersion of tungsten oxide and tungsten powder made after the electron probe scanning.
 
The particle size distribution of the resulting product test each step of FIG.

Analysis of results:
ATP obtained after calcined tungsten trioxide, most were pine needles together. When reduced under a hydrogen atmosphere, the surface of the tungsten trioxide aggregate is first restored, so that the surface density becomes smaller, because the tungsten trioxide powder since the tungsten is generated when deoxidation is reduced significantly smaller volume. That is, the reunion surface becomes fluffy. This reunion internal tungsten trioxide reduction will surface tungsten powder stays split, so a lot of surface microcracks reunion. Some also reunite a larger particle size; surface energy is small, cracks deeper, a direct result of reunion split, split into pieces smaller reunion. Thus, when generating the tungsten powder is oxidized, the surface of the tungsten powder agglomeration direct oxidation of tungsten trioxide. However, the reunion internal tungsten powder to be oxidized, oxygen atom necessary to reunite through the cracks into the interior surface combined with tungsten powder, which is sufficient to cause the crack to expand reunion split. Although this is a combination of an oxygen atom of tungsten powder, but the particle size or become smaller reasons. About produced tungsten trioxide have agglomeration of reasons, because of the oxidation reaction can be considered bound oxygen atoms, so that would have to rely on relatively close between tungsten powder filled with oxygen, thereby forming a reunion. After re-oxidation reduction of tungsten oxide, tungsten trioxide significantly smaller particle size, when the reason is still in deoxygenating reduction and tungsten
powder cracks.

 

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