Abstract
Abstract Herein, the evolution of reduction process of ultrafine tungsten powder in industrial conditions was investigated. The transition process of morphology and composition was examined via SEM, XRD, and calcination experiments. The results show that the reduction sequence of WO2.9 was WO2.9 → WO2.72 → WO2 → W on the surface, but WO2.9 → WO2 → W inside the oxide particles. With the aid of chemical vapor transport of WO x (OH) y , surface morphology transformed into rod-like, star-shaped cracking, floret, irregularly fibrous structure, and finally, spherical tungsten particles.
Highlights
Tungsten is widely used in products across the high density alloy [1,2], shielding material [3,4], photocatalyst [5], and cemented carbides [6].WC-Co-cemented carbides with ultrafine or nanocrystalline grains are widely employed in the precision machining field [7,8,9]
The crystallization is inhibited by low temperature, low height powder layer, and low dew point of hydrogen, all of which are essential conditions to produce ultrafine/nanocrystalline tungsten powder
Pseudomorphology, coarse agglomerates, and irregular crystallization of tungsten powder are obtained from reduction of ammonium paratungstate (APT) or tungsten oxide [13]
Summary
Tungsten is widely used in products across the high density alloy [1,2], shielding material [3,4], photocatalyst [5], and cemented carbides [6].WC-Co-cemented carbides with ultrafine or nanocrystalline grains are widely employed in the precision machining field [7,8,9]. The reduction step from tungsten oxide to pure tungsten powder is critical to determine the final grain size. Several factors can affect the particle size of tungsten powder, such as temperature, raw material [10], height of powder layer [11], doping [12], dew point of hydrogen [12], etc. In addition to the particle size of tungsten powder, the morphology and agglomeration state of powder are crucial properties [10,13]. The crystallization is inhibited by low temperature, low height powder layer, and low dew point of hydrogen, all of which are essential conditions to produce ultrafine/nanocrystalline tungsten powder. The whole evolution process of morphology is still not clear due to various reduction conditions. The aim of this paper is to investigate the evolution of powder in reduction process
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