While the cost efficient synthesis of metal nanoparticles is still limited, many magnetic separation technologies rely on larger particles of metal oxide compositions. We therefore modified a flame process, known for the large-scale manufacture of silica, for the successful synthesis of metallic cobalt nanoparticles.

We show the continuous preparation of air stable cobalt nanoparticles at a production rate of 30 g / hour by a modified flame synthesis method under highly reducing conditions. 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 magnetization (>124 emu/g) together with a low (<100 Oe) coercivity. With optional functionalization of the particle surface the material has promising applications as metallic magnetic nano-beads.

References: R.N. Grass and W.J. Stark, J. Mater. Chem, 2006, DOI: 10.1039/b601013j;