The effects of sintering time and temperature on the dimensional change and magnetic properties have been observed in barium ferrite permanent magnet. The starting material was a commercial calcined barium ferrite powder containing small amounts of $SiO_2$ and PbO.
The specimens of cylindrical shape were sintered in air at 1100℃, 1150℃, 1200℃, 1250℃, and 1300℃ for 30 minutes, 1 hour, 2 hours, and 4 hours. The axial and radial dimensional changes under these sintering conditions were accurately measured. Density was observed to increase with progress of sintering, but at 1300℃ it decreases with increasing sintering time.
As sintering progressed, remanence, coercive force, and(BH) max. initially increased with sintering temperature and time. But above 1250℃ these properties drop sharply with increasing sintering time and temperature. This effect is attributed to the formation of new phases that could not be clearly identified by X-ray diffraction.
