Abstract
As W-type hexagonal ferrite permanent magnets with the formula SrO⋅2FeO⋅8Fe2O3 contain both ferrous and ferric oxides, a complicated atmosphere control during the sintering process is necessary in manufacturing, which is impractical for industrial production. Thus, a simple manufacturing method which is characterized by employing a combination of the addition of carbon and the adoption of nitrogen atmosphere in sintering was investigated, so that high performance permanent magnets were successfully prepared. It was found that the additional amount of carbon and the heating temperature for drying green body are closely associated with oxidation and reduction in the sintering process. The unfitted conditions for synthesis are apt to produce extra phase, such as hematite and magnetite which influence magnetic properties. Especially, small amounts of magnetite which are produced by a reduction phenomenon during the sintering process decrease coercivity remarkably. A pure W-phase was formed by addition of 0.2wt% carbon and drying green body at 200°C for 3h. The highest magnetic properties obtained by the present work are remanence of 0.48T (4.8kG), coercivity of 200kA/m (2.5kOe) and the maximum energy product of 42kJ/m3 (5.3MGOe).
