Effect of SiO2 on the Mechanical Property and Reduction of Calcium Ferrite

SiO2-Fe2O3-CaO (SFC) is believed to be the transition phase during the SiO2-Fe2O3-CaO-Al2O3 (SFCA) formation process. The effect of SiO2 on the mechanical property and reduction of the CaO-Fe2O3-SiO2 system was inspected in this study. Experiments were carried out under air at 1200 °C with different amounts of SiO2 mixed with Fe2O3 and CaO. The mechanical properties and reduction of samples were studied. Results indicate that the hardness of samples gradually increases with the increase of SFC content. That may be caused by SiO2 solid solution in calcium ferrite. The larger the amount and smaller size of acicular calcium ferrites in samples, the greater the fracture toughness. The solid solution of SiO2 in calcium ferrite is beneficial to decrease the initial reduction temperature. The apparent activation energy values of the samples with the different content of SiO2 from 0% to 5% are 167.23, 84.36, 87.90, 96.02, 92.44 and 107.83 kJ·mol−1, respectively. The microstructure of lump samples after reduction consists of four phases, i.e., CF (CaFe2O4), SFC, calcio-wüstite (CW) and Fe. It was not difficult to find the Fe in the samples reduced from CW. Scanning electron micrograph images have revealed that the acicular-like calcium ferrites are more easily reduced than the platy-like ones.