2014 Volume 100 Issue 2 Pages 170-179
In this study, the formation of calcium ferrites during heating and cooling was investigated by in situ and real-time observation using a newly developed system, i.e., in situ "quick X-ray diffraction (Q-XRD)," and an in situ laser microscope. In the new Q-XRD, a specimen was heated up to 1773 K, and X-ray diffraction patterns were measured using a pixel-array area detector with an interval as short as a few seconds. In situ observation both of crystal structure and microstructure successfully revealed the effects of heating and cooling rates on the sintering reaction in the CaO-Fe2O3 system with special attention to overheating and overcooling phenomena. The first continuous cooling transformation (CCT) concept for iron ore sintering was proposed to understand overcooling phenomena when the molten oxide cooled down to room temperature and magnetite (Fe3O4), hematite (Fe2O3), and various types of calcium ferrites were formed. The CCT diagram for sintering provides crucial and fundamental information on the sintering accompanying solidification, precipitation, and formation of calcium ferrites from the molten oxide, and can be used as a guideline for controlling sintering processes.
