COMPOSITE-MATERIALS MADE OF SPINEL (COYFE3-YO4) AND COBALT-IRON (COXFE1-X) - PARAMETRIZATION OF THE SYNTHETIC ROUTE

We describe the synthetic procedures to obtain composite materials mad e up of cobalt-iron alloy (CoxFe1-x, x=-0.8) and cobalt iron spinel ox ide (CoyFe3-yO4, y=0-0.6). The procedure employed is a low temperature reaction in alkaline (KOH) solution which involves the disproportiona tion of Fe-II into Fe-o and Fe-III and a reduction of Co-II. Hydroxide -free composites were obtained in a narrow range of KOH concentrations (for instance 11.3-14.5 mol/l when [Co]/[Fe]=0.33). This range is shi fted to larger values when [Co]/[Fe] is decreased. Low KOH concentrati on results in the formation of hydroxides or amorphous phases, while f or high concentration, beta-Co(OH)(2) precipitates. The metallic phase s have the alpha-Fe (b.c.c. structure) or alpha-Mn structure and the l attice parameter of the spinel, which is a cobalt - containing magneti te, lies between 8.396(2)Angstrom and 8.405(2)Angstrom. Particle size and resistance to oxidation (up to 300 degrees C) are increased when [ KOH](i) and [Co](i)/[Fe](i) increases. Coercive fields are improved fo r the lowest particle sizes and the highest [Co](i)/[Fe](i).