Down-Sizing of Iron Powders via Evaporation in an Atmospheric Microwave Plasma Flame.

Iron nanopowders (Fe-NPs) were extracted and downsized by evaporating the iron powders in an atmospheric microwave plasma flame. The microwave plasma, which was generated by a mixture of nitrogen and argon swirl gases, evaporated the iron powders, immediately downsizing them to Fe-NPs. Subsequently, the Fe-NPs samples were collected by using bar magnets inside the collecting chamber. The Fe-NPs were analyzed by X-ray diffraction, Raman spectroscopy, optical emission spectroscopy, and a scanning electron microscopy. The Fe-NPs consisted of only iron phase and no Fe2O3 or Fe3O4 phases were formed during synthesis. The average sizes of the raw iron powders and the Fe-NPs were approximately $20~\mu \text{m}$ and 20 nm, respectively. The proposed method is simple and easily scalable. Thus, it is suitable for the mass production of Fe-NPs, overcoming the limitations of other catalyst-based synthesis methods. This paper provides a potential method for large-scale production of metal nanopowders which have potential applications in various fields owing to their unique properties at the nanoscale. [ABSTRACT FROM AUTHOR]