Synthesis and Characterization of Carbon-Coated Magnetite for Functionalized Ferrofluids

Carbon-coated magnetite nanoparticles (NPs) were synthetized by the mechanochemical method in a high-energy ball mill using hematite and amorphous carbon as precursors. The milling was performed at 700 r/min, with a ball/powder mass ratio of 35 in stainless steel vials with WC balls and Ar atmosphere. The precursor powders were milled from 1 to 18 hours and they were annealed for 2 h in Ar at 500 °C. Structural and magnetic properties of the NPs were investigated by X-ray diffraction (XRD), vibrating sample magnetometry and high resolution transmission electron microscopy (HRTEM). XRD patterns, refined with the Rietveld method, show that magnetite is present in samples milled from 6 hours onward and that after milling for 18 hours and annealing, the sample contains a single crystalline phase. Magnetization curves for samples with different milling times show saturation magnetizations ranging from 34.1 emu/g after 1 h to 78.0 emu/g after 18 h. Coercive fields are about 500 Oe for all samples. HRTEM studies reveal that the samples are made of amorphous carbon clusters with magnetite NPs less than or equal to 20 nm. This system seems appropriate for biomedical applications.