Synthesis and characterization of air-stable iron nanocrystalline particles based on a single-step swelling process of uniform polystyrene template microspheres

Polystyrene template microspheres of narrow size distribution were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. These template particles dispersed in aqueous solution have been used for entrapping Fe(CO)₅, by a single-step swelling process of methylene chloride emulsion droplets containing Fe(CO)₅, within these particles. The influence of different swelling parameters, such as the volume ratio [CH₂Cl₂/[Fe(CO)₅], on the size and size distribution of the swollen template particles was elucidated. Air-stable Fe/Fe₃C nanocrystalline particles have been prepared by thermal decomposition of the Fe(CO)₅ swollen template particles at 600°C in an inert atmosphere. Characterization of these air-stable Fe/Fe₃C nanocrystalline particles has been accomplished by light microscopy, TEM, XRD, TGA, XPS, elemental analysis, and magnetic susceptibility measurements. These nanocrystalline particles have a core - shell structure where a coating of Fe₃C and carbon protects the core body-centered cubic Fe from oxidation.