NICKEL-IRON ALLOY MAGNETITE COMPOSITES - SYNTHESIS AND MICROSTRUCTURE/

We describe the procedure to obtain composites made of a nickel-iron a hoy and magnetite. A KOH concentration of 14 mol/liter is required, Me tal diffraction lines are broad, due to heterogeneous composition and bad crystallization, Balls Of metal 0.1-0.2 mu m wide stuck to magneti te octahedra are easily observed by SEM and TEM. Nickel hydroxide crys tallizes for a nickel to iron ratio >0.33 int addition to metal and sp inel, HRTEM shows metal and spinel grains covered by a thin layer of N iO crystals of 20 nm recovered by an amorphous phase 2-3 nm wide, This latter crystallizes in NiO under the electron beam, Crystallographica l relationships occur between NiO and the spinel phase, Well-crystalli zed and hydroxide-free nickel-iron alloy/magnetite composites are obta ined in all cases after annealing at 800 degrees C in an argon atmosph ere, (C) 1998 Academic Press.