effect of heat-treatment temperatures on magnetite oxidation in20sio2.50feo.30cao glass ceramic prepared by the sol-gel method

The effect of different heat-treatment temperatures on the magnetic, crystallization, and structural properties of 20sio2.50feo.30cao (mol%) glass ceramics was studied. the initial glass was synthesized by the sol-gel method at 25℃  with a precursors to solvent ratio of 1/5. after aging the resulted gel for 24 h at room temperature, it was dried in an electric dryer at 110 ℃ . by heat treatment at different temperatures, different phases such as magnetite, maghemite, and hematite were crystallized in the glass. the maximum stability temperature of magnetite and maghemite were 360℃  and 440℃  respectively. by increasing the heat treatment temperature to higher than 440℃ , the oxidation of maghemite to hematite was occureds. the highest magnetization amount (1.9 emu/g) belonged to sample heat treated at 680℃ . by increasing the heat treatment temperature to 840℃ , the magnetization decreased to 0.8 emu/g, due to the oxidation of maghemite. by increasing the heat treatment temperature from 440℃  to 680℃ , crystalline size of maghemite was increased from 40 to 200 nm. by forther increment of temperature to 840℃ , the size of maghemite crystals decreased to 17nm, due to the oxidation of maghemite to hematite.abstractthe effect of different heat-treatment temperatures on the magnetic, crystallization, and structural properties of 20sio2.50feo.30cao (mol%) glass ceramics was studied. the initial glass was synthesized by the sol-gel method at 25℃  with a precursors to solvent ratio of 1/5. after aging the resulted gel for 24 h at room temperature, it was dried in an electric dryer at 110 ℃ . by heat treatment at different temperatures, different phases such as magnetite, maghemite, and hematite were crystallized in the glass. the maximum stability temperature of magnetite and maghemite were 360℃  and 440℃  respectively. by increasing the heat treatment temperature to higher than 440℃ , the oxidation of maghemite to hematite was occureds. the highest magnetization amount (1.9 emu/g) belonged to sample heat treated at 680℃ . by increasing the heat treatment temperature to 840℃ , the magnetization decreased to 0.8 emu/g, due to the oxidation of maghemite. by increasing the heat treatment temperature from 440℃  to 680℃ , crystalline size of maghemite was increased from 40 to 200 nm. by forther increment of temperature to 840℃ , the size of maghemite crystals decreased to 17nm, due to the oxidation of maghemite to hematite.