Characterization and magnetic properties of Fe–Co(C) nanocapsules were investigated systematically by means of x-ray diffraction, Mössbauer spectroscopy, x-ray photoelectron spectroscopy, transmission electron microscopy, energy dispersive spectroscopy analysis, chemical analysis, oxygen determination, and magnetization measurement. The effects of elemental carbon, decomposed from a methane atmosphere in carbon arc process, on the phase structures, magnetic states and surface characterization were studied. Carbon atoms favor forming a new core/shell type structure, consisting of a carbon coating and a core containing a carbon solution. The mechanism of formation of the nanocapsules as well as origin of ferromagnetism and paramagnetism are discussed.

The structural and magnetic characteristics of iron nanoparticles synthesized by a chemical vapor condensation (CVC) process were investigated systematically by an x-ray diffraction method, high-resolution transmission electron microscopy, Mössbauer spectroscopy, magnetometry and thermogravimetric analysis. Typical particle sizes were found to be in the range of 5–13 nm with uniform dispersion. The resulting microstructure of the nanoparticles correlated with parameters of the CVC process. In particular, a CVC technique was derived to fabricate Fe nanoparticles with different magnetic states, e.g., superparamagnetic, ferromagnetic, or a mixture of these two states.

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Iron nanoparticles were synthesized by chemical vapor condensation (CVC) without the aid of LN 2 chiller. The powder synthesized at 400 °C was a mixture of amorphous and crystalline α-Fe. Fully crystallized iron particles were then obtained at and above 600 °C. When the reactor temperature was 1000 °C, however, nonmagnetic γ-Fe was stabilized together with α-Fe. The synthesized particles, mostly possessing the core-shell type structure, were all nearly spherical, but the average particle size rapidly increased as the temperature increased. The surface layer that enclosed the iron core and became thicker in smaller particles was Fe 3 O 4 or Fe 3 O 4 -related amorphous. Except for the one synthesized at 1000 °C, the iron nanoparticles were not fully saturated. The iron nanoparticles (~20 nm) synthesized at 600 °C exhibited i H c ~ 1.0 kOe and M s ~ 170 emu/g.

New manufacturing processes, such as thermochemical, mechanochemical and chemical vapor condensation processes, have been developed to obtain nanostructured materials. Nanoscale size tungsten (W) base composite powders of less than 60 nm particle size such as WC/Co and W/Cu systems can be synthesized by thermochemical and mechanochemical processes using metallic salt precursors as starting materials. Nanostructured W base composite materials showed better sinterability, microstructural uniformity with ultrafme microstructures and mechanical properties than did commercial W base composite materials. Non-agglomerated nanoscale size TiO2 powder can be synthesized by the Combustion Flame Chemical Vapor Condensation (CF-CVC) process using metallorganic precursors as a starting material. In this paper, scientific and technical issues on the synthesis of nanostructured materials by the new chemical processes are considered.