Cobalt particles wrapped in graphitic carbon prepared by an arc discharge method

Abstract

Fine particles of cobalt and cobalt carbide nesting in multilayered graphitic sheets, which were synthesized by an electric arc discharge of carbon rods containing cobalt oxide (CoO), were studied by transmission electron microscopy, including microdiffraction and energy dispersive x-ray analysis. The size of the wrapped particles was typically in a range from 50 to 200 nm. Three phases of nested materials, hcp(α)-Co, fcc(β)-Co, and Co3C, were identified.

Magnetic stability of Al2O3-coated fcc-Co nanocapsules

“…It can be seen that, the XRD patterns of the as-prepared nanocapsules and those annealed at 400 and 500 K match only the fcc-Co structure and show no peaks for hcp-Co, which are well coincident with the SAED results. These results are different from the previous reports that fcc-Co and hcp-Co coexisted in nanoparticles [16,18,[20][21][22]. It has been well known that hcp-Co could exist stably at low temperatures, but ␤-Co with fcc structure is a high-temperature phase being stable above 417 • C. The reasons for the existence of the high-temperature phase (i.e., fcccobalt) in the fcc-Co/Al 2 O 3 nanocapsules at room temperature can be attributed to the lower surface energy of nanoscale particles and rapid cooling during the arc-discharge [16].…”

“…These results are different from the previous reports that fcc-Co and hcp-Co coexisted in nanoparticles [16,18,[20][21][22]. It has been well known that hcp-Co could exist stably at low temperatures, but ␤-Co with fcc structure is a high-temperature phase being stable above 417 • C. The reasons for the existence of the high-temperature phase (i.e., fcccobalt) in the fcc-Co/Al 2 O 3 nanocapsules at room temperature can be attributed to the lower surface energy of nanoscale particles and rapid cooling during the arc-discharge [16]. Also, there are no Co-oxide peaks detectable in the XRD patterns of the as-prepared nanocapsules and those annealed at 400 and 500 K. This indicates that the nanocapsules in the range of 300-500 K may be free from surface oxidation, due to the protective Al 2 O 3 shell.…”

“…The irregular shapes and the coarse surfaces of the nanocapsules are ascribed to the rapid quenching during the arc-discharge process [13]. Compared with previous reports [16][17][18][19], the as-prepared nanocapsules show higher dispersivity with different annealing temperatures. It can be concluded that the shell plays an important role in reducing the interaction of the nanocapsules and preventing the growth of fcc-Co nanoparticles.…”

Size dependent interface energy and its applications

“…It is interesting that as D decreases, the metastable high-pressure phases and some denser parking phases, which have not been found in bulk state, are easily formed at ambient pressure. This phenomenon has been found in CdSe [167,261,262], HgS [263], ZnO [264], ZnS [265], GaAs [266] Fe [267], Co [268], Cr [269], and In [270]. The essential reason is that there exists size-dependent P in for an isotropic spherical or quasispherical nanoparticle by f through Laplace-Young equation, namely Eq.…”

Sharp Carbon‐Nanotube Tips and Carbon‐Nanotube Soldering Irons

“…[5] Along with the well known electrical, mechanical, and thermal properties of the CNTs, the presence of a metal filling inside their core has been suggested to enhance their applicability in magnetic recording media and new electronic devices, and to reinforce the material durability. [7,8] Here we report two interesting phenomena of nano-electron beam assisted machining of iron-filled MWCNTs: the fabrication of atomically sharp Fe-based tips and the direct interconnection of two large diameter MWCNTs. Previous attempts to solder CNTs had been performed through metal [5] and amorphous carbon [2] deposition at the tips, but the results showed little or questionable success.…”