| The effect of the basicity on the formation behaviour of calcium ferrites was investigated in the sintering process of Fe_2O_3-CaO-Al_2O_3-SiO_2 system. In the system of Fe_2O_3-CaO-Al_2O_3, the mineral structure consists of iron oxide particles and matrix phase, which is likely to be CF(calcium ferrite). When SiO_2 is added into Fe_2O_3-CaO-Al_2O_3 system, the area fraction of CF decreases sharply. When the basicity(CaO/SiO_2) decreases below the unity, CF does not form, and the mineral structure is composed of iron oxide particles and the silicate slag. The iron oxide particles are mainly magnetite in the temperature range higher than 1300℃, while they consist of both magnetite and hematite at the temperatures below 1250℃. When SiO_2 is added into Fe_2O_3-CaO-Al_2O_3 system, the formation of hematite is promoted in the lower temperature range. The increase of SiO_2 content tends to change the composition of CF from hemi-CF to mono-CF. The solubility of solutes such as CaO, Al_2O_3 and SiO_2 in CF increase with the increase of SiO_2 content in the system. |
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