Fabrication of Al2O3@BaFe12O19 core-shell powder by a modified heterogeneous precipitation method

Core-shell structural composites are promising to quench the desire for low-cost, lightweight and multifunctional magnetic materials, but the fabrication of highly pure shell nanoparticles with a desired morphology on a heterogeneous nuclear is still a big challenge. This study gives a successful illustration by in-situ synthesizing BaFe12O19 nanoparticles as a shell on Al2O3 core powders using BaCl2 and FeCl3 as precursors, instead of commonly used Ba(NO3)(2) and Fe(NO3)(3), by a modified heterogeneous precipitation process followed by calcination for crystallization. After calcination of the precipitants from the raw precursor mixture of BaCl2:FeCl3 for 1:10 at 800 degrees C, and for 1:8.5 at 900 degrees C, respectively, pure BaFe12O19 formed on pristine Al2O3, mostly with a hexagonal plane, about 100-200 nm in basal diameter and 20-100 nm in thickness. The highest saturation magnetization and coercivity of the coated Al2O3 @ BaFe12O19 powders was 23.3 emu/g and 5149 Oe, quite higher than that of the direct-mixed Al2O3-BaFe12O19 composite powder, and BaFe12O19-containing composites reported in literature, which could be atributed to the hexagonal shape of BaFe12O19 and uniform shell dispersion on Al2O3 core. The formation mechanism for the Al2O3@BaFe12O19 powders was discussed in detail.