“Continuous Cooling Transformation (CCT)” Concept for Iron Ore Sintering Using In Situ Quick X-ray Diffraction and Confocal Laser Microscope

Abstract

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., "quick X-ray diffraction (Q-XRD)," and an in situ laser microscope. In the new Q-XRD, a specimen was heated up to 1 773 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 ferrite 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.

<i>In Situ</i> Temperature Measurement of Sinter Beds at High Spatial and Time Resolution

“…CF appear at temperatures higher than 1 100°C. [4][5][6]14) It binds the raw materials in the sinter bed to form sinter. Important chemical reactions proceed as a result of the heat produced by the combustion of coke particles.…”

“…12,13) In situ X-ray diffraction (XRD) results showed that compound oxides drastically transform as the temperature increases from room temperature. [4][5][6]14) In situ XRD studies showed that CaO and Fe 2 O 3 start reacting to form mono-calcium ferrite (CF) at around 1 000°C.…”

“…Due to the difficulty in in situ observations at the high heating rate, there are still many debates on the formation mechanism of SFCA-I and other forms of calcium ferrites. [4][5][6][7][14][15][16][17] As shown above, the temperature in the sinter bed has a strong impact on the quality and yields of the sinter.…”

Influence of P₂O₅ on Dissolution Behavior of Lime in Molten Slag

“…The dissolution behavior of lime in the molten slag comprising CaO-SiO 2 -FeO or CaO-SiO 2 -FeO-P 2 O 5 was observed via a confocal laser-scanning microscope, which has been widely used to observe various phenomena in high-temperature processes; 11,12) moreover, the chemical composition of the observed specimens was analyzed using a scanning electron microscope/energy dispersive spectroscopy (SEM/EDS). On the basis of obtained results, the effect of P 2 O 5 on the dissolution behavior of lime is discussed.…”

In-Situ Study of Gaseous Reduction of Magnetite Doped with Alumina Using High-Temperature XRD Analysis

“…HT-XRD was used to study the lattice constant of the Fe-C system [14][15][16] and ferrite-austenite phase transformation. [17][18][19] In works, [20][21][22][23] it was applied to investigate the phase development in the sintering process. [20][21][22][23] HT-XRD was also used to study iron oxide reduction process.…”