Microstructure of Carbon Encapsulated Superparamagnetic Co Nanoparticles
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Microstructure of carbon Encapsulated Superparamagnetic Co Nanoparticles Xiang-Cheng Sun*, 1, J. Reyes-Gasga2 and X. L. Dong3 1
Prog. Molecular Engineer, Instituto Mexicano del Petroleo (IMP), Lazaro Cardenas 152, 07730, D. F. Mexico *Fax: +525-333-6239, *E-mail:[email protected] 2 Institute of Physics, National University of Mexico, D.F. Mexico 3 Shenyang Polytechnic University, Shenyang, P. R. China ABSTRACT Carbon encapsulated magnetic Co nanoparticles have been synthesized by modified arc-discharge method. Both high-resolution transmission electron microscopy (HREM) and powder x-ray diffraction (XRD) profiles reveal the presence of 8-15nm diameter crystallites coated with 1-3 carbon layers. Specially, HREM images indicate that the intimate and contiguous carbon fringe around those Co nanoparticles is good evidence for complete encapsulation by carbon shell layers. The encapsulated phases are identified as hcp (α)-Co, fcc (β)-Co and cobalt carbide (Co3C) nanocrystals by using x-ray diffraction, electron diffraction and energy dispersive x-ray analysis. However, some fcc (β)-Co particles with a significant fraction of stacking faults are observed by HREM and confirmed by means of numerical Fourier transform (FFT) of HREM lattice images. In particular, the carbon encapsulation formation and growth mechanism are also reviewed. INTRODUCTION Since the discovery of a simple method for generating of fullerene (C60) in macroscopic quantities by Kratschmer and Huffman [1], many attempts had been carried out to prepare various types of their derivatives [2-4]. The report of the presence of LaC2 and YC2 encapsulated in carbon shell layers that had been found in a carbonaceous deposit grown on a cathode surface of carbon arc [5, 6], had ever drawn particularly great interest. Because encapsulating materials into the hollow core of carbon nanostructures (nanopolyhedra or nanotubes etc) had changed their physical properties of the carbon nanomaterials drastically [7]. In other words, encapsulations of second phases inside carbon shell/nanotubes have attracted much attention in the materials science community. Because it not only offered an opportunity to investigate dimensionally confined systems, but also the encapsulated materials were likely to be immune to environmental effects or degradation due to the protective carbon sheets around them. Several modified carbon-arc methods had been adapted for the production of carbon-coated nanocrystalline of ferromagnetic transition metals (Fe, Co, Ni) and their carbide compounds of uniform size [8, 9]. The concentric carbon shells around the core magnetic materials are airtight and protect the encaged materials and carbides from the ambient atmosphere. Such carboncoated magnetic nanoparticles have potential for a variety of industrial applications [10]. In this work, we herein report a novel procedure for preparation of superparamagnetic cobalt (Co) and cobalt carbide (cementite, Co3C) nanocrystals W6.26.1
encapsulated in thin carbon layers. Moreover the detailed encapsulati
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