Nanostructured α/β-tungsten by reduction of WO3 under microwave plasma

The formation of tungsten by microwave plasma induced reduction of coarse grade, crystalline (monoclinic and hexagonal blend) WO3 was investigated. It was observed that nanostructured α-W (cubic; space group: Im-3m) as well as β-W (cubic, space group: Pm-3n) are present in the final product. The fraction of β-W was higher (56 (± 3) wt.%) when compared to α-W (41 (± 4) wt.%). The high resolution scanning electron microscopy revealed narrow size distribution of the as synthesized tungsten with average particle size of about 10–25 nm. The estimated crystallite sizes from the log-normal size distribution obtained from the Warren-Averbach's Fourier treatment of the XRD profile were about 12 (± 3) and 15 (± 2) nm for α and β-W, respectively. The observed particle/crystallite sizes were significantly finer when compared to conventional plasma synthesized tungsten due to lower processing temperature in microwave plasma synthesis technique.