Ultrafine cobalt and cobalt alloy particles have been prepared by spontaneous autocatalytic reduction.
The influence of parameters such as protein structure, magnetic field applied for reduction and reduction reagent on particle growth was investigated. Ultrafine cobalt particles with the size ranging from 60 to 700Å can be easily obtained by using various kinds of proteins and thier particle sizes markedly depend on the structure of proteins used. The suggested explanation of protein effect is that the nuclei of cobalt particle are formed on each functional polypeptide group of the macromolecular protein. The strength of magnetic field, which is applied for reduction, should be more than twice as large coercive force of cobalt and cobalt alloy partticles. X-ray diffraction studies were carried out on the samples obtained by the reduction of hydrazine and hypophosphite. Cobalt particles obtained by the hydrazine reduction have almost fee crystal structure, and not in those containing phosphorous. However, in the case of hypophosphite reduction, the particles are crytalline hcp. This behavior may be explained by the increase of Co-P components.