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 0.15 to 0.50 wt % silica was added during fine milling. These ferrites were sintered at 1220 C for 2 h. Their grain growth is dominantly influenced by the sizes of the silica added. Coarse-grain (1 micron) silica tends to promote discontinuous grain growth, which increases drastically with slightly increasing amounts of silica added, while fine-grain (0.013 micron) 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 micron. The size was increased to as large as 30 micron 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. 5 refs.