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The effect of yttrium on the reaction of tungsten oxide with CO was studied for the preparing various morphologies and size of tungsten carbide. The reaction rate, phase composition, particles size and morphology, surface area of samples were studied by TG (thermogravimetry), XRD (X-ray diffraction), SEM (scanning electron microscopy) and BET (Brunauer–Emmett–Teller), respectively. It was found that the reaction route was following WO3 → W18O49 → WO2 → WC at lower temperature, while at higher temperature, an intermediate phase W was formed and then carbonized to WC. During the reaction of pure WO3 or mixtures (1 wt.% Y(NO3)3 + WO3) with CO at lower temperature, the final products almost maintained the large irregular block shape. With the increase of temperature, the large WC particles were degraded and the obtained sub-particles became much more dispersed. After the addition of yttrium nitrate, the rod-like sub-particles were transformed into more stable polyhedral-shaped sub-particles with a smaller size. Furthermore, the mechanism of effect of yttrium on prepared tungsten carbides were analyzed in detail.

In this investigation, the Li2CO3-assisted hydrogen reduction method was proposed to produce different morphologies and size of metallic tungsten particles. The effects of temperature and content of Li2CO3 additive were both considered. The experimental results showed that both the temperature and additive had great effects on the morphology and size of produced tungsten particles. As the increases of temperature and fraction of Li2CO3, the morphology of tungsten particles was changed from spherical to polyhedral; while the size of these particles was increased; and the obtained products became more and more dispersed. The addition of Li2CO3 also affected the reduction rate dramatically. It was found that the Li2CO3 additive retarded the initial reduction reaction, but it could obviously improve the later reduction (WO2 to W) at a high temperature, furthermore, the higher fraction of Li2CO3 made this promotion more remarkable. Based on above results, the reduction mechanism was proposed: without additive, the reduction entirely obeys pseudomorphic transformation mechanism at low temperature, and obeys CVT mechanism at high temperature; with additive, the reduction follows a mechanism of mixture of nucleation, pseudomorphic transformation and CVT at low temperature, while at high temperature, the sublimation of WO3, nucleation and CVT mechanisms all play important roles. Keywords: Li2CO3, Nucleation, Reduction, Morphology and size, Tungsten