CONTINUOUS SYNTHESIS OF ULTRAFINE IRON PARTICLES BY CHEMICAL VAPOR-DEPOSITION OF FE(CO)

There is great difficulty in operating a continuous process for CVD of Fe(CO)5 by external heating, because iron particles are deposited on the reactor wall, and this clogs the reactor. We developed a novel CVD process for Fe(CO)5 with internal heating by which continuous preparation of iron particles is possible without deposition and clogging. Fe(CO)5 is charged into a reactor from a feed nozzle located at the center of the reactor bottom. High-temperature diluent N2 is introduced conically from the circumference of the nozzle with an incident angle of 30 degrees. Fe(CO)5 is mixed with the hot diluent N2 and heated up in a moment; the Fe(CO)5 is thermally decomposed in a magnetic field to produce ultrafine iron particles in necklacelike chains. Shielding N2 is supplied between the Fe(CO)5 feed nozzle and the hot diluent N2 mixing cone to prevent particle deposition on top of the nozzle and inner surface of the Fe(CO)5 feed nozzle. The reaction time is shortened by pre-decomposition of Fe(CO)5 because the first CO dissociation from Fe(CO)5 is the rate-determining step. A tangential N2 jet flow at the reactor outlet is effective in preventing Brownian deposition of particles due to the temperature difference between the reactor wall and the particles.