Abstract
Precursors with hexaferrite composition were prepared from Ba(OH)2 8H2O and α-Fe2O3 or amorphous Fe2O3 powders by a planetary mill-treatment in acetone. Extracted water from Ba(OH)2·8H2O brought about hydration and resulted in amorphization of α-Fe2O3. The mill-treatment promoted agglomeration between hydrated amorphous Fe2O3 and Ba(OH)2 in acetone which had poor polarity. The precursors derived from α-Fe2O3 and Ba(OH)2·8H2O formed BaFe12O19 at 800°C through the intermediate formation of BaFe2O4 at 600-700°C. This hexaferrite powder showed poor sinterablity. In contrast, using the amorphous Fe2O3 as a constituent, BaFe12O19 formed directly at 700°C. From this powder, dense sintered materials consisting of fine plate-like particles of about 1μm can be obtained at temperatures lower than 1250°C. Above 1250°C, the size of plate-like particles increased to 10μm without intragranular pore defects.
