Fabrication Of Nanosized Magnetic Metal/Cenosphere Shell-Core Comoposite Microspheres

The precursors of metal coated cenosphere composite microspheres were synthesized by the aqueous heterogeneous precipitation using metal salts, ammonium bicarbonate and cenosphere as main raw materials. Subsequently, the metal(Fe, Co, Ni and alloys)-coated cenosphere composite microspheres and multilayer Al₂O₃/Fe/cenosphere were successfully obtained by reduction of the precursor composite microspheres in an H₂/N₂ atmosphere. The morphology, composition, phases of the precursor composite microspheres and the resultant metal coated cenosphere composite microspheres were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD). The thermal decomposition process of the precursors was investigated by thermogravimetry-differential scanning calorimetry (TG/DSC). The magnetic properties of the nano metal coated cenosphere composite microspheres were studied by vibrating sample magnetometer (VSM). The aqueous heterogeneous precipitation process were mainly influenced by the content of coated particles, concentration and adding rate of solutions, pH value and surface active reagent, et al. On the basis of tests, optimized processing parameters for fabrication of nanosized metal coated cenosphere composite microspheres were determined: 10～15 g/L of cenosphere powders, 0.15～0.3 mol/L of solution, 2～4 ml/min of feeding rate, 900～1200 r/min of agitation speed, at 6.0～8.0 of pH and 4～6 ml/L of PEG400. The decomposition and reduction procedure was work out according to the investigated of thermal reduction process for precursors. The experiment results indicate that metal-coated cenosphere composite microspheres with grain size of about 50nm and these shell-core structural spherical powders have a good coherent combination between the coatings and metal coatings with nanometer grains are uniform and dense. The nanosized metal-coated cenospheres exhibits a much higher magnetic coercivity than pure metal powders, and the coercivity of the multilayered Al₂O₃-Fe-coated cenospheres almost increases two times than that of the monolayered nanosized metal-coated cenospheres.