Preparation of plastic ferromagnetic composite materials for magnetic encoders

Monodispersed spheres of ferromagnetic metals like iron, cobalt and nickel, can be synthesized on a micrometric and sub-micrometric scale by simply reducing their salts with boiling polyols. These magnetic particles embedded into a polymeric matrix can be exploited for a number of technological applications (e.g., barcodes for magnetic encoders, magnetic storage media, electromagnetic shielding, etc.). The spherical shape of particles allows to prepare composites with high-filling factors and very uniform filler distribution. In addition, since ferromagnetic particles show size-dependent magnetic properties (e.g., coercivity), the possibility to control the particle size is of primary importance. Here, we have found that monodispersed cobalt spheres of different sizes can be obtained by reduction of cobalt hydroxide with diethylene glycol in presence of oleic acid. This organic compound absorbs on the metal surface, increasing compatibility with polymer in the resulting composite. The average particle size was related to the precursor amount and it was widely varied by simply controlling this parameter. Disproportion in ethylene glycol medium of in situ generated iron hydroxide (at 140 °C) has been used to produce monodispersed iron nanoparticles. © 2006.