Development of Hexagonal Closed-Packed Cobalt Nanoparticles Stable at High Temperature

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• 作者：Vctor A. de la Pea O′ ; Shea ; Pilar Ramrez de la Piscina ; Narcis Homs ; Guillem Arom ; Jos L. G. Fierro
• 刊名：Chemistry of Materials
• 出版年：2009
• 出版时间：December 8, 2009
• 年：2009
• 卷：21
• 期：23
• 页码：5637-5643
• 全文大小：925K
• 年卷期：v.21,no.23(December 8, 2009)
• ISSN：1520-5002

文摘

Cobalt metal particles have several stable phases depending on their size and the temperature employed in the preparation. The face-centred cubic (fcc) structure is thermodynamically stable above 450 °C, whereas the hexagonal-closed packed (hcp) phase is stable at lower temperatures. Cobalt oxide reduction carried out under H₂ atmosphere leads to fcc-Co phase. This study shows that the reduction of cobalt oxide under CO or H₂+CO mixtures giver rise to the formation of a hcp-Co phase, which still remains stable at high temperatures (up to 700°C). This circumstance is due to the encapsulation of hexagonal cobalt nanoparticles by carbon nanofibers that minimizes the surface energy of these cobalt structures. Moreover, this encapsulation effect prevents the sintering and oxidation reactions of hcp-Co metallic phase even at a high temperature (up to 700°C) Thus, the reduction atmosphere plays a key role in the formation and stabilization of these cobalt phases.