Carbon Coating, Carburization, and High-Temperature Stability Improvement of Cobalt Nanorods

• Published in: Journal of physical chemistry. C Vol. 117; no. 30; pp. 15808 - 15816
• Main Authors: Ibrahim, Mona, Marcelot-Garcia, Cécile, Aït Atmane, Kahina, Berrichi, Ekrame, Lacroix, Lise-Marie, Zwick, Antoine, Warot-Fonrose, Bénédicte, Lachaize, Sébastien, Decorse, Philippe, Piquemal, Jean-Yves, Viau, Guillaume
• Format: Journal Article
• Language: English
• Published: Columbus, OH American Chemical Society 01.08.2013
• Subjects: Chemical Sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Fullerenes and related materials; Fullerenes and related materials; diamonds, graphite; Infrared and raman spectra and scattering; Material chemistry; Materials science; Nanocrystalline materials; Nanoscale materials and structures: fabrication and characterization; Nanotubes; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Physics; Specific materials; Raman spectra; Crystal orientation; Surface treatments; XRD; High temperature; Coatings; Cobalt; Thermal stability; Crystallites; Size effect; HCP lattices; Nanorod; Crystal structure; Cobalt oxide; Scanning electron microscopy; Organic solvents; Raman spectroscopy; Carbon; Faceting; Thickness; Transmission electron microscopy; Anisotropy; Fullerenes; Structure modification; Nanostructured materials; X-ray photoelectron spectra
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/jp3125457

The reactivity of highly crystalline hcp cobalt nanorods (NRs) with organic solvents at high temperature was studied. Cobalt NRs with a mean diameter of 15 nm were first synthesized by the polyol process and then heated to 300 °C in octadecene (ODE), oleylamine (OA), or mixtures of these two solvents. The surface and structural modifications of the Co NRs were characterized by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and scanning and transmission electron microscopy (SEM and TEM). A disordered carbon shell was formed at the cobalt rod surface, the thickness of which can be tuned from 5 to 25 nm by increasing the amount of oleylamine in the solvent mixture. This carbon shell partially reduced the native cobalt oxide observed at the surface of the NRs and drastically improved their temperature stability as inferred from in situ XRD study and TEM. The shape anisotropy and the crystallite anisotropy of the hcp phase are both preserved up to 400 °C for the carbon-coated cobalt rods, whereas the uncoated NRs lose their anisotropy at 225 °C. Treatments at 300 °C in ODE/OA mixtures for different durations allowed the progressive carburization of Co to Co2C. The crystallographic orientation of the Co2C grains within the cobalt NRs combined with the different carbon-shell thickness on the {101̅0} and (0001) facets of the rods suggested a preferential carburization from the lateral facets of the hcp cobalt rods.