Structural and magnetic properties of cobalt nanoparticles encased in siliceous shells

详细信息    查看全文

• 作者：Michael A. Zalich ; Michael L. Vadala ; Judy S. Riffle ; Martin Saunders ; Timothy G. St. Pierre
• 刊名：Chemistry of Materials
• 出版年：2007
• 出版时间：December 25, 2007
• 年：2007
• 卷：19
• 期：26
• 页码：6597 - 6604
• 全文大小：951K
• 年卷期：v.19,no.26(December 25, 2007)
• ISSN：1520-5002

文摘

Stable colloidal dispersions of cobalt nanoparticles were prepared by refluxing toluene solutions of dicobalt octacarbonyl in the presence of poly(dimethylsiloxane-b-(methylvinylsiloxane-co-methyl(2-trimethoxysilethyl)siloxane)) (PDMS-b-(PMVS-co-PMTMS)) dispersion stabilizers. The nanoparticles coated with the polysiloxane copolymer were subsequently heated at 600 or 700 °C with the goal of forming siliceous shells on the cobalt surfaces to protect them from oxidation. The thermolysis processes at 600 and 700 °C produced increases in the cobalt specific saturation magnetizations (σ_s) from 48 to 141 and 146 emu g⁻¹ of cobalt respectively. The siliceous coatings provided oxidative protection under ambient conditions for long periods. However, mechanically grinding the thermally treated nanoparticles led to decreases in σ_s upon aging in air. Particle size analyses indicated an increase in average particle size in the materials heated at 600 °C, but the materials that were heated at 700 °C retained their small nanoparticle sizes. Electron diffraction and X-ray diffraction confirmed that the heat-treated cobalt nanoparticles were predominantly in the face-centered cubic phase, while the materials that had not been heated at the elevated temperatures were only weakly crystalline. Hence, the increases in σ_s from the preheat-treated to the heat-treated materials were attributed to an improvement in particle crystallinity, combined with less oxidation due to partial protection by a siliceous shell.