Cobalt Nanoparticles by Reducing Flame Synthesis

Robert N. Grass, ETH Zurich, Switzerland, Zurich, Switzerland and Wendelin J. Stark, Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Str. 10, ETH Hönggerberg, Zurich, 8093, Switzerland.

The synthesis of magnetic metal cobalt nanoparticles in a turbulent flame was studied. Operation of a flame spray reactor at high fuel to oxygen ratio in a reducing atmosphere allowed continuous production of cobalt at a rate of 30 g / hour.[1] Nanoparticles of 20 - 60 nm in diameter consisted of metallic face-centered-cubic cobalt. The metal particles were protected against oxidation by a surface layer of less than 1 nm of cobalt oxide. The material was highly magnetic exhibiting a high saturation magnetisation (>124 emu/g) together with a low (<100 Oe) coercivity and proposed applications in electronics. Experiments under varying fuel to oxygen ratio were combined with thermodynamic calculations to illustrate the necessity for highly reducing conditions and enhanced gas mixing to enable the formation of metallic cobalt nanoparticles in flames.

[1] R. N. Grass, W. J. Stark, J. Mater. Chem., 2006, DOI: 10.1039/b601013j.