Nanocrystalline ferromagnetic metals (such as Fe, Co and Ni) have many applications in magnetic data storage, magnetic toners in xerography, magnetic inks and ferrofluids. However, nanocrystalline metals are very sensitive to rapid environmental degradation. This attribute significantly limits the scope of their potential industrial applications. Encapsulation of nanocrystals with graphitic layers is a way to protect metal crystals from negative environmental influence. Also, carbon coatings can endow these particles with biocompatibility and make carbon-encapsulated particles useful in bio-engineering applications, such as drug delivery, biosensors, magnetic hyperthermia and magnetic contrast agents for magnetic resonance imaging.

Carbon-coated cobalt nanoparticles were successfully synthesized by catalytic ethylene decomposition. Nanocrystalline cobalt was prepared by cobalt hydroxide precipitation, followed by calcination and reduction. A small amount of structural promoters was added. The process of cobalt oxide reduction and cobalt carburisation was carried out in a thermobalance. The carburisation process was performed under pure ethylene flow in the temperature range 340 - 400°C. After carburisation process the samples were cooled under helium flow or reduced under hydrogen flow in the temperature range 500 - 560°C. The phase composition of the samples was determined using XRD technique. The phases in carbon-coated nanocapsules turned out to be fcc-Co and hcp-Co. The HRTEM method was used to study the morphology of the samples after carburisation. Both carbon-coated cobalt nanocapsules and carbon nanotubes were found in the samples.

The financial support of the Scientific Network "Nanomaterials as Catalysts for New, Environmentally Friendly Processes" for the participation of the corresponding author in the EMRS Fall Meeting'06 is gratefully acknowledged.

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