Crystallization of (FeO, Fe2O3)-CaO-SiO2 Glasses and Magnetic Properties of Their Crystallized Products

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Abstract
The crystallization process of an Fe2O3 40, CaO⋅SiO2 60wt% glass was investigated as well as magnetic properties of the crystallized products, in order to reveal principles for obtaining ferrimgnetic and bioactive glass-ceramics useful as thermoseeds for hyperthermia of cancer. When the glass was heat-treated up to temperatures 700° to 950°C, magnetite particles were homogeneously precipitated in a CaO⋅SiO2-based glassy and/or crystalline matrix. The diameter and content of the magnetite increased from 6 to 30nm and 10 to 36wt%, respectively, with increasing temperature of the heat treatment from 700° to 950°C. Above 1000°C, a part of the magnetite was converted into hematite (α-Fe2O3). The glass showed maxima in saturation magnetization and coercive force, 32emu/g and 500 Oe, respectively, when heat-treated up to 950°C. The variation of the magnetization with heat treatment temperature could be well quantitatively interpreted in terms of the content of the magnetite, whereas that of the coercive forces could be explained only qualitatively in terms of the particle size of the magnetite. The coercive forces of the magnetite-containing glass-ceramics were much higher than those of the magnetite powders of the corresponding particle sizes which were prepared from aqueous solutions.

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