Fe or Co-Fe alloy manganese ferrite composites

We describe the procedure to obtain composites made of iron or iron-cobalt alloys and manganese-containing magnetite. A KOH concentration of 14 mol l(-1) is required. Iron and manganese based composites are made of metallic iron and manganese-containing magnetite. For Mn/Fe ratios higher than 0.15, hydroxide is also present. When cobalt is involved, hydroxide is encountered for Mn/Fe ratios higher than 0.2. The metal is thus an iron-cobalt alloy which crystallizes in the b.c.c. structure or in the a-Mn structure. This latter disappears by heat treatment above 180 degrees C. At 400 degrees C, cobalt of f.c.c. structure crystallizes. Above 500 degrees C, the composite transforms into the wustite structure. HRTEM and EDSX analyses show that the metal is coated by ferrite grains. (C) 1998 Elsevier Science S.A. All rights reserved.