Iron/iron carbides/carbon core-shell nanostructures synthesized by laser pyrolysis

摘要

Multiphase composite nanoparticles presenting core-shell structures have been investigated by performing a detailed correlation between their synthesis parameters and the structural and magnetic properties. Basically in all the experiments iron pentacarbonyl as iron precursor and ethylene as laser energy transfer agent and as a secondary carbon source have been used. The capability of the synthesis technique to form nanocomposite particles by varying laser power density, inlet geometry, pressure in reactor chamber and gas precursors' ratio was tested. The results proved that the laser pyrolysis can produce particles between 4 and 10 nm diameters. Their sizes may vary according to the reactor pressure and gas flows but their size distributions remain sharp as long as an optimized geometry of the reactor is used. As a second step, the structure and magnetic properties were studied by different techniques such as TEM, HREM, SAED, XRD, FT-IR and Raman spectroscopy. The investigations reveal that, depending on the input parameters, some samples exhibit a nanocomposite structure consisting of iron / iron carbides (Fe3C or Fe2C5) core wrapped in a shell of amorphous or turbostratic carbon. The different magnetic phase identification was performed using Mossbauer spectroscopy and thermo-magnetic analysis.