A wet‐chemical preparation of a Fe 3 O 4 ‐CuO composite powder in core‐shell structure

Abstract

We developed a process for coating CuO powder with magnetite film from an aqueous solution. Reaction solution contained 0.12 M of FeCl2 and 0.03 M of CuCl2. The Cu2+ ions promoted the oxidation of Fe(OH)2 to form Fe3O4. The solution was maintained at pH ∼6 using CH3COONH4 of 0.2 M as a buffer to prevent the formation of hematite. The CuO grains of a spherical shape and ∼50 μm in size were mechanically suspended in the solution, on which magnetite particles were directly deposited. The mole ratio of Cu2+ / Fe2+ strongly influenced the coverage of the magnetite film as well as the morphology of the constituent grains. When the Fe2+ / Cu2+ mole ratio was 1: 0.5, the spherical magnetite particles of ∼60 nm in diameter coated well each CuO grain with the thickness of ∼3 μm. The prepared powder exhibited that the saturation magnetization and the coercivity reached to ∼5.4 emu/g and ∼575 Oe, respectively. On heating up to 450 °C, the powder experienced two oxidations below 400 °C, indicating the formation of γ-Fe2O3. The magnetic composite powder appeared to be stable up to 400 °C. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)