A Wet-Chemical Preparation of a Fe3O4-CuO Composite Powder in Core-Shell Structure

초록

We developed a process for coating magnetite film on CuO powder from an aqueous solution for producing a microwave absorbing material using magnetic and conductive coupling effect. The CuO grains were spherical and their diameter is ~50 um. Reaction solution contained 0.12M of FeCl2 and Cu2+ ions. The Cu2+ ions promoted the oxidation of Fe(OH)2 to form Fe3O4. The solution was maintained at ~6 in pH using CH3COONH4 of 0.2M as a buffer to prevent the formation of hematite. The CuO grains were mechanically suspended in the solution, on which magnetite particles were directly precipitated and deposited. The mole ratio of Cu2+/Fe2+ strongly influences the coverage of the magnetite film as well as the morphology of the constituent grains. When the reaction was performed for one hour and at 65℃ and the Cu2+/Fe2+ mole ratio is 0.5, the spherical particles of ~90 nm in diameter coated well each CuO grain with the thickness of ~3um. The prepared powder exhibited that the saturation magnetization and the coercivity reached to ~6 emu/g and ~500 Oe, respectively. On heating up to 600℃, the powder experienced two oxidations. One existed around 100℃ ~ 250℃, while the other occurred around 400℃~ 500℃. It is unclear that the first one reflects the formation of γ-Fe2O3. However, at 500℃, the Fe3O4 was completely transformed to hematite. The magnetic composite appeared to be stable up to 400℃.