THE EFFECT OF SILICA CHARACTERIZATION ON THE MICROSTRUCTURE OF BAFE12O19 FERRITES

The anisotropically formed BaFe12O19 ferrites were prepared from the hot-rolled mill scale and silica was added to the ferrite during fine milling in the range 0.15 to 0.50 wt%. These ferrites were sintered at 1220° C for 2 h. The grain growth of the ferrites is dominantly influenced by the sizes of the silica added. Coarse-grain (≈ 1 μm) silica tends to promote discontinuous grain growth, which increases drastically with slightly increasing amounts of silica added, while fine-grain (≈ 0.013 μm) silica tends to retain fine grain microstructures with the same increasing amount of silica. The average grain size of the ferrite without silica addition was 8 to 10 μm. The size was increased to as large as 30 μm on addition of 0.15% coarse-grain silica and the microstructure was full of extremely large grains on the addition of 0.50% coarse-grain silica. © 1990 Chapman and Hall Ltd.