THERMALLY ACTIVATED CRYSTALLINE PHASE RESTORATION IN DISORDERED BARIUM FERRITE POWDER PREPARED BY BALL-MILLING

Depending on milling conditions (air or vacuum) for the same milling t ime, a different level of decomposition and structure disorder in BaFe 12O19 ferrite powders can be obtained by ball milling. Air-milled mate rial has a tendency to form a gas-saturated disordered structure (supe roxide) and to transform into simple oxides (reduction process through oxygen-saturated disordered phase) as opposed to the vacuum-milled po wder where a highly disordered phase occurs. Both powders have a diffe rent morphology (particle size and distribution). Annealing processes produce crystalline barium ferrite phase with interesting magnetic pro perties, but in the present paper only structural transformations are analysed. Scanning electron microscopy, X-ray diffraction and thermal analysis techniques were applied to study the effects of heat treatmen t (10 h at 773 or 1273 K) in disordered BaFe12O19 ferrite powders prep ared by 1000 h ball milling in air and vacuum.