Synthesis of iron—cobalt ultrafine particles by decomposition of Fe(CO)5---Co(CO)3NO using a TEA CO2 laser

Ultrafine particles of iron—cobalt alloy were synthesized and isolated at room temperature in a maximum yield of 90% by the dielectric breakdown of a mixture of Fe(CO)₅ (5 Torr) and Co(CO)₃NO (0.5 Torr) on irradiation with a tightly-focused laser beam of a transversely-excited-atmospheric (TEA) CO₂ laser. CO and NO are also obtained as volatile products. Transmission electron micrographs of the iron-cobalt particles show the existence of fine and well-organized spherical particles. The distribution of the particle size is relatively uniform in the range 6–9 nm with a mean particle size of 8 nm. In X-ray diffractometry, the ultrafine particles are found to be mainly f.c.c. γ-iron—cobalt alloy which is normally stable in the range 1183–1234 K to 1673–1773 K. The b.c.c. -iron—cobalt, iron oxides and cobalt oxides are observed as minor products (γ-iron—cobalt to iron---cobalt OXIDES=8:1:1). The ratio of iron and cobalt atoms in the particles can be changed by changing the mixture of Fe(CO)₅ and Co(CO)₃NO. The ratio of γ-iron—cobalt to -iron—cobalt to iron—cobalt oxide also depends on the ratio of iron and cobalt atoms in the particles.