Calcium ferrite is very important for improving the properties of strength and reducibility of sinter. But the formation mechanism of binary calcium ferrite under the stable condition of CaO·2Fe
2O
3 was not studied sufficiently. Therefore, as fundamental study of calcium ferrite formation, the mechanism of calcium ferrite formation in solid state reactions between CaO and Fe
2O
3 at 1190°C in air was investigated by using the diffusion-couple method. The results are summarized as follows.
(1) The reaction between CaO and Fe
2O
3 starts at the CaO/Fe
2O
3 interface to form CaO·Fe
2O
3. After a short initial period, three kinds of calcium ferrites, 2CaO·Fe
2O
3 (C
2F), CaO·Fe
2O
3 (CF), and CaO·2Fe
2O
3 (CF
2) grow in that order from CaO layer toward Fe
2O
3 layer.
(2) The formation rates of C
2F, CF and CF
2 are controlled by the diffusion of Ca
2+ and Fe
3+ in each layer.
(3) The C
2F forms at the interfaces of CaO/C
2F and C
2F/CF, but the formation rate at the CaO/C
2F interface islarger than that at the C
2F/CF interface. The CF forms at the CF/CF
2 interface, and grows toward CF
2 phase except for the beginning of the reaction. The CF
2 forms at the CF
2/Fe
2O
3 interface, and grows toward Fe
2O
3 phase. The thickness of each layer of calcium ferrites increaces with the progress of reaction time.
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