The Sintering Characteristics of Mixing SiO₂ with Calcium Ferrite at 1473 K (1200 °C)

The liquid-generating capability in high basicity sinter was investigated by adding SiO₂ to CaO·Fe₂O₃ (CF) at 1473 K (1200 °C) in air for 4 hours. X-ray diffraction, electron-probe microanalysis, and optical microscopy combining with etching test were used to characterize the phase change of sintered samples. The results show that the minor SiO₂ additions from 0.14 wt pct to 6.49 wt pct to CF depressed the melting temperature of CF. New phases of formation included from SFC (silico-ferrite of calcium), SFC + Hem (Fe₂O₃) + CS (CaO·SiO₂) to Hem + CS in samples with SiO₂ additions from 0.05 wt pct to 21.74 wt pct. With the maximum SFC produced in sample, the amount of SiO₂ addition was 10.64 wt pct. To understand the depressing mechanism of CF melting temperature, the experiments of differential scanning calorimetry for samples of CF, SFC, CF-SiO₂ (3.0 wt pct), and CF-SFC (50.0 wt pct) had been carried out. The result shows that mixing of SiO₂ or SFC with CF decreased the melting temperature of CF by 35 K and 34 K (35 °C and 34 °C), respectively, resulted in melting temperature approaching the eutectic temperature between CF and SFC. The phase relations between CF and SFC, as well as the intermediate products in depressing the melting temperature, will be an important guide to improve the sintering characteristics of iron ores.