PREPARATION AND CONTROL OF DIAMETER OF UL TRAFINE IRON PARTICLES BY CHEMICAL-VAPOR-DEPOSITION OF FE(CO)5

The mechanism of particle formation by pyrolysis of Fe(CO)5 and a tech nique for changing primary particle diameter were studied. The size di stributions of the primary particles are almost log-normal and their g eometric standard deviations are 1.2-1.4. The mechanism of particle gr owth by this method consists of two steps: the first is nucleation and condensation in the inlet part of the reactor, and the second is coag ulation and coalesence in the following part of the reactor. The prima ry particle diameter is affected by feed concentration, residence time , pre-decomposition ratio of Fe(CO)5 and temperature of hot diluent ni trogen and reactor wall, in which the first, second and third factors are the most effective in controlling the diameter. The magnetic flux in the axial direction of the reactor does not affect the size of the primary particle, although it results in a necklace-like chain of the particles.