This paper demonstrates fine size-controlled synthesis of superparamagnetic carbonencapsulated iron nanoparticles, by a supersonic plasma jet assisted rapid, bulk-production process, by manipulation of the pressure in the sample collection chamber. Transmission electron microscopy and small angle x-ray scattering measurements confirmed the formation of single-crystals with a narrow size distribution, having core average size of 5.0 nanometer and encapsulated by an ultrathin carbon coating, for sub-mbar pressure. VSM and Mossbauer characterization established the nanocrystallites to be superparamagnetic in nature, with saturation magnetization 67 emu/g and coercive field 7.4 Oe. Controlled plasma heating during synthesis led to the burning down of extra carbon that resulted in further enhancement of the magnetization of the product. Graphitization of the encapsulating layers also enhanced, which could successfully protect the metallic core from oxidation, as well as improved its cyto-compatibility. This purified sample could be ideal for targeted drugs delivery and water treatment applications. Another sample was processed through controlled reaction with oxygen, the as-synthesized sample having magnetic properties approaching that of the first sample, which may be more attractive especially for water treatment processes because of the simpler single-step processing of the material.

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Fine size-controlled synthesis of superparamagnetic iron-oxide and its nanocomposites are reported by a supersonic thermal-plasma assisted process. The effects of oxygen flow rates, gas injection position, and carrier gas types were studied, and the phase composition of the product material was estimated by Rietveld refinement technique. The smallest iron-oxide nanoparticle sample with 10 nm average size was synthesized at 19 liters per minute flow of oxygen, which also had the largest contribution from the magnetite/maghemite phases at 88%. The saturation magnetization and the magnetic coercivity of this superparamagnetic sample were measured as 28 emu g −1 and 6 Oe, respectively, the latter one is the smallest value reported in the literature produced by a plasma method. The sample demonstrated satisfactory biocompatibility behavior, which should be suitable for advanced bio-medical and environmental applications. A superparamagnetic nanocomposite material containing ironoxide, carbon-encapsulated iron nanoparticles, along with single-walled carbon nanotubes was also produced while injecting oxygen into the vacuum chamber and using hydrogen as the carrier gas. The average particle size was 5.1 nm, which had saturation magnetization of 52 emu g −1 and coercivity 10 Oe. The sample was found to be slightly more toxic, assumed due to the presence of the single walled carbon nanotubes. The high rate of production and single step processing were the other important advantages of this synthesis technique for the nanocomposite material.