A wet-chemical preparation of a Fe_3O_4-CuO composite powder in core-shell structure

摘要

We developed a process for coating CuO powder with magnetite film from an aqueous solution. Reaction solution contained 0.12 M of FeCl_2 and 0.03 M of CuCl_2. The Cu~(2+) ions promoted the oxidation of Fe(OH)_2 to form Fe_3O_4. The solution was maintained at pH ～ 6 using CH_3COONH_4 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 Cu~(2+)/ Fe~(2+) strongly influenced the coverage of the magnetite film as well as the morphology of the constituent grains. When the Fe~(2+)/ Cu~(2+) 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 ℃, the powder experienced two oxidations below 400℃, indicating the formation of γ-Fe_2O_3. The magnetic composite powder appeared to be stable up to 400℃.