Structural characterization and microwave properties of chemically functionalized iron particles obtained by high-energy ball milling in paraffin-containing organic environment

• Fe particles for magnetodielectrics were obtained by co-milling of Fe and paraffin.
• Structural parameters (bulk/surface) and microwave properties were studied.
• As-milled particles are characterized by nanograins and chemically modified surface.
• Microwave properties are governed by addition of solvent/surfactant into milling media.
• Plate-like particles covered with long-chain molecular residues have improved properties.

Magnetodielectric composites comprising dispersed metal particles as magnetic filler and organic dielectrics as a host matrix are of great importance because of both technological and fundamental interests. Surfactant-assisted high-energy ball milling in organic media is successfully used for the dispersion and surface modification of metal particles. In this paper, we have carried out structural and chemical characterization of iron particles (bulk/surface) prepared in paraffin-containing environment. The study was performed with high-resolution X-ray spectroscopic techniques using synchrotron radiation from BESSY II/HZB Berlin and DORIS/DESY Hamburg. It has been shown that high-energy ball milling leads to nanofragmentation of iron grains and formation of bare metal surface which is very active in dehydrogenation of organic molecules. The paraffin molecules are destructed with the accumulation of polycondensed aromatic structures containing covalently-bound paraffin residues on the iron surface. Under dry milling (without solvent), the organic environment molecules decompose almost completely, while under wet milling, the destruction of paraffin and perfluorononanoic acid molecules slows down significantly. An addition of perfluorononanoic acid along with n-heptane into the milling liquid results in sharp change in microwave characteristics, which may be attributed to formation of platelet-shaped particles with the surface covered with long-chain residues of paraffin and surfactant molecules.

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