Investigation on Reaction Schemes of Iron Ore Sintering Process by High Temperature in-situ X-ray Diffraction and Micro-texture Observation - Technical Report No. 118 - March 2018

Oct 29, 2026

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Iron ore sintering is a high-temperature, non-equilibrium reaction in which Ca-Fe-O melt forms. To clarify liquid sintering mechanisms, iron oxide and calcium ferrite precipitation from liquid Ca-Fe-O was monitored using high-temperature in-situ X-ray diffraction alongside laser microscope observation. Based on measured cooling-rate dependence of phase-transition temperatures, a continuous cooling transformation (CCT) diagram for iron ore sintering was established.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages6

Reading Time15 min

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Introduction

Background of iron ore sintering

Phase transformations in CaO-Fe2O3 system

Motivation for in-situ high-temperature observation

Experimental

NIPPON STEEL & SUMITOMO METAL TECHNICAL REPORT No. 118 MARCH 2018 UDC 622 . 785 . 5 : 548 . 73 Investigation on Reaction Schemes of Iron Ore Sintering Process by High Temperature in-situ X-ray Diffraction and Micro-texture Observation Reiko MURAO* Masao KIMURA Abstract Iron ore sintering is a high-temperature, non-equilibrium reaction process that involves the formation of Ca-Fe-O melt. To clarify the mechanisms of liquid sintering, we observed the precipitation of iron oxide and calcium ferrite from liquid Ca-Fe-O by high-temperature in-situ X-ray diffraction and laser microscope observation. A continuous cooling transformation (CCT) diagram for iron ore sintering was devised based on the data on the cooling-rate dependence of the phase transition temperature obtained through the observation. 1. Introduction Fine iron ore is sintered into lumps 5 to 50 mm in size called sintered ore, which is an important iron source accounting for more than 70% of the blast furnace burden in the Asia-Pacific region. Sintered ore is produced by mixing fine iron ore with limestone (flux) and coke breeze (heating fuel), granulating the mixture into pseudo-particles, heating them by combustion of the fine coke to 1 450 to 1600 K, above the eutectic temperature according to the phase diagram for the CaO-Fe2O3 quasi-binary system (1 478 K) (see Fig. 1 (a)), 1) and then holding them at the temperature range for several minutes. Part (b) of Fig. 1,2) which was prepared based on general technical literature,3–6) schematically illustrates the microstructural changes of the material during the sintering process. The starting material, pseudo-particles, consists of fine iron ore, limestone and coke adhering to core particles of iron ore up to 10 mm in size. During the heating, oxides undergo phase transition and mutual diffusion at the interface between the adhering fines and nucleus grains, a molten liquid of an Fe-Ca-O system forms, and during the subsequent cooling, calcium ferrites precipitate, networks of pores form, and as a result, the structure of sintered ore is formed wherein Fe2O3 nucleus grains are fused together by calcium ferrites. The types, formation amounts and microstructures of the crystal phases of calcium ferrite, which change depending on process factors such as grain size, gangue content, temperature history, and oxygen partial pressure, affect the strength, reducibility, and other properties of sintered ore. 3–9) Many researchers have studied the crystal structure of the Fe-Ca-O system and its stability, and there have been many reports on these aspects. 1) Three different phases of calcium ferrite exist in the CaO-Fe2O3 quasi-binary system: Ca2Fe2O5(C2F) 10), CaFe2O4(CF) 11) and CaFe4O7(CF2) 12). (Henceforth C stands for CaO, F for Fe2O3, and W, which will appear soon, for FeO.) Of these three, CaFe2O4(CF) is a high-temperature phase, and is stable only in the temperature range of 1 428 to 1 499 K. On the other hand, depending on oxygen partial pressure, α-CFF,β-CFF, and γ-CFF phases, all containing Fe2+, form at 1323 K, 13) and that of Ca 2Fe 9O 13( C2W5F2) , C a 2Fe 7O 11( C2W3F2) , CaFe3O5(CWF), CaFe4O6(CW2F) and CaFe5O7(CW3F) phases format 1 393 K. 14, 15) The above verifies that the types of phases appearing and the ratios of coexisting phases change depending on slight changes in the heating condition and chemical composition even under near-equilibrium conditions. Also, when gangues such as SiO2 and Al2O3 are present, composite oxides of a continuous solid solution type containing Fe, Ca, Si, and Al form; such phases include SFCA (Ca2(Fe, Ca)6(Fe, Al, Si)6O20) and SFCA-I ((Ca, Fe)4(Fe, Al)16O28) . 16, 17) The process of iron ore sintering is a non-equilibrium process that takes place within a very short time, and to clarify its process mechanisms, an analytical approach combining a phase diagram of a multi-component system and in-situ observation of high-temperature reactions is effective. Howeve

FAQs

What reaction mechanism is investigated in the paper?

The paper investigates reaction schemes in iron ore sintering by tracking liquid-phase-related precipitation, especially iron oxide and calcium ferrite formation from Ca-Fe-O melt.

How are phase changes observed during sintering?

High-temperature in-situ X-ray diffraction is used to follow crystal-structure changes, and a laser microscope is used to observe micro-texture development during heating and cooling.

What outcome is produced to describe cooling behavior?

The study devises a continuous cooling transformation (CCT) diagram based on cooling-rate dependence of phase-transition temperatures obtained from the observations.

Oct 29, 2026

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