PREPARATION OF FINE-GRAINED MN-ZN FERRITES BY HOT-PRESSING

The preparation of Mn-Zn ferrites composed of fine grains has been car ried out by hot pressing under various conditions. The results obtaine d are summarized as follows. (1) alpha-Fe2O3 was more liable to form i n the specimen prepared by hot pressing than in that prepared by the c onventional sintering under ordinary pressure due to the remaining O-2 in the specimen. Therefore, it was confirmed that the hot pressing pr ocess in vacuum was more suitable than in 1%O-2 or N-2. (2) Mn-Zn ferr ites whose grain size is about 2 mu m was obtained by the process wher e the specimen was heated to 1248 K at the heating rate of 0.028 K/s, and isothermally held under 0 MPa for 1.8 ks and hot pressing under 40 MPa in the vacuum of 1.33 x 10(-2) Pa for the subsequent 1.8 ks at th e same temperature of 1248 K, using coprecipitated Mn-Zn ferrites powd ers. (3) Mn-Zn ferrites powder whose grain size is extremely fine of a bout 10-20 nm was obtained by the MG process in Ar, and it was confirm ed that using these powders, Mn-Zn ferrites specimen whose grain size is finer than 1 mu m was prepared by the above mentioned hot pressing process.