Abstract
The preparation of Mn-Zn ferrites and Ni-Zn ferrites composed of fine grains has been carried out by hot pressing under various conditions. The results obtained are summarized as follows. α-Fe2O3 was more liable to form in the Mn-Zn ferrrites specimen prepared by the hot pressing than that prepared by the conventional sintering under ordinary pressure due to the remaining O2 in the specimen. Therefore, it was confirmed that the hot pressing process in vacuum was more suitable than in 1%O2 or N2. Mn-Zn ferrites whose grain size is about 2μm was obtained by the process where the specimen was heated to 1248K at the heating rate of 0.028K/s, and isothermal holding under OMPa for 1.8ks and hot pressing under 40MPa in the vacuum of 1.33 × 10-2Pa for the subsequent 1.8ks at the same temperature of 1248K, using coprecipitated Mn-Zn ferritcs powders. Extremely fine grains of about 10-20nm were obtained in both of Mn-Zn ferrites powders and Ni-Zn ferrites powders by MG process, and it was confirmed that using these powders, both specimens of Mn-Zn ferrites and Ni-Zn ferrites prepared by the above-mentioned hot pressing process consist of finer grains than 1μm.
