Study of hematite-iron phase transformation during iron-carbon core-shell nanoparticles synthesis and investigation of their magnetic and microwave properties

The structural properties and microwave absorption capability of the iron nanoparticles and iron-carbon core-shell nanoparticles have been studied, in the present paper. The investigated nanoparticles were synthesized by hydrothermal route and by reduction of hematite nanoparticles during annealing in argon-hydrogen atmosphere. Hematite-iron phase transformation during the reduction process has been studied by X-ray diffraction (XRD). XRD patterns showed that in iron nanoparticles, hematite-iron phase transformation was completed after 30 min annealing whereas about iron-carbon nanoparticles, the phase transformation completion occurred after 65 min, and before 65 min annealing, wustite (FeO) phase was still present in XRD patterns. M-H loops and relative complex permittivity (ε) and permeability (µ) of the iron nanoparticles and iron-carbon nanocapsules were investigated too. According to the ε and µ spectra in 1-18 GHz, the carbon shell can affect microwave properties of the iron nanoparticles. Carbon shell can reduce microwave permeability and permittivity of the composites containing iron nanoparticles.