Preparation Of Carbon-encapsulated Metal Nanoparticles By DC Arc Plasma

Carbon-encapsulated metal nanoparticles(CEMNs)are a new kind of carbon/metal nanocomposite,carbon layers which form by amorphous carbon or graphite arrange around metal nanoparticles which located in the center to form core-shell structure.Owing to their novel structures not only prevent their oxidation and environment degradation,and effectively resist their agglomeration and resolve the problem of metal nanoparticles can not steadily conservation under atmospheric conditions.owing to their novel magnetic optical and chemical properties, they have wide potential applications in many fields such as high density magnetic recording apparatus,magnetic fluids,magnetic resonance imaging, catalyst,new energy and bio-medicinal.In this thesis,we first have an overview of Preparation of Carbon-encapsulated metal nanoparticles and applications of metal Carbon-encapsulated metal nanoparticles.Next we investigate the plasma preparation technology.As a heat source of high temperature,plasma processing technique has many special characteristics,such as high thermal efficiency,high temperature,concentrated energy, steady arc, active environment,easy to operation and extremely cooling rates,all these characteristics provide the perfect physical chemistry conditions applied for the production of metal nanopowders.Last we successfully preparated metal nanopowders by direct current arc plasma method under certain conditions. The shape,micrograph,crystalline structure,specific surface area and magnetism of the nanopowders were characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM) and the corresponding selected area electron diffraction (SAED)the specific surface area and pore analyzer(BET) and Vibration sample magnetometer (VSM).We ameliorated and optimized arc discharge experimental equipment,gaining direct current arc plasma experimental equipment.We successfully preparated carbon-encapsulated Fe nanoparticles by direct current arc plasma method under certain conditions.The shape,micrograph,particle size and its distribution,and degree of graphitization of carbon-shell crystalline structure of the Fe core were characterized via X-ray diffraction (XRD),high resolve transmission electron microscopy (HRTEM) and Raman Spectra.The chemistry composition, thermal properties,magnetism,antioxidant of carbon-encapsulated Fe nanoparticles were studied by using X-ray energy dispersive spectrometry (XEDS), thermo gravimetric analyzer(TGA)and differential scanning calorimeter (DSC)and vibration sample magnetometer (VSM) at room temperature respectively. We investigated the variation of the coercive force and the saturation magnetization with particle size. We found that average particles size is 27nm, have the characteristics of super paramagnetic.While those average particles size is 50nm are permanent magnetic. Carbon-encapsulated Fe nanoparticles have better oxidation resistance than the Fe nanopowders which surface have been passivated.Finally, we investigated the microcosmic factors of the processing parameters effect on the carbon-encapsulated Fe nanoparticles;we established reasonable formation mechanism model of carbon-encapsulated Fe nanoparticles prepared by DC arc plasma method to illuminate the formation of carbon-encapsulated Fe nanoparticles prepared.Using thermodynamics,dynamics and Fe-C phase diagram investigated the formation mechanism of carbon-encapsulated Fe nanoparticles.