Ferrimagnetic glass-ceramics are useful as thermoseeds for hyperthermal treatment of malignant tumors, especially those located in deep parts of the body, since hysteresis loss heating occurs locally at the cancer site when they are implanted around the tumor and subjected to an alternating magnetic field. In the present study, glass-ceramic powders containing a large amount of fine particles of zinc-iron ferrite (ZnxFe3-xO4) in a CaO-SiO2-based glassy matrix were prepared by the heat treatment of ZnO-Fe2O3-CaO-SiO2 glasses at various temperatures for 1 h in a 95CO2+5H2 atmosphere. The ZnxFe3-xO4 precipitated above 700°C, and its crystallite size and fraction increased with increasing heat-treatment temperature, reaching 130 nm and 37 mass% at 1150°C, respectively. The saturation magnetization of the specimen increased to 38.4 emu•g-1 with increasing heat-treatment temperature up to 1150°C. The coercive force of the specimen increased to 167.6 Oe at 1000°C, and then decreased with increasing heat-treatment temperature. When the heat-treatment period at 1150°C in a 95CO2+5H2 atmosphere was increased from 1 to 5 h, the content of ZnxFe3-xO4 was not changed, whereas the crystallite size of ZnxFe3-xO4 increased from 130 to 170 nm. The saturation magnetization and coercive force of the powders heat treated at 1150°C for 5 h in a 95CO2+5H2 atmosphere were 26.5 emu•g-1 and 150.5 Oe, respectively. The prepared glass-ceramic powders showed a large amount of heat generation of 12.4 W•g-1, under conditions of 300 Oe and 100 kHz.
2004 The Ceramic Society of Japan