Experimental Phase Equilibria Studies in the FeO-Fe2O3-CaO-SiO2 System in Air: Results for the Iron-Rich Region

Exploring the Composition and Structure of Triclinic SFCA-I

“…The likely lower limit of Al 2 O 3 concentration in SFCA-I (i.e., 1.4-2.7 mass%), and the low level of SiO 2 solubility (~0.15 mass%), is worthy of discussion in the context of the in-situ XRD analysis of Scarlett et al 22,23) There, in an alumina-free mixture designated AL0 by the authors and designed to form the Al 2 O 3 -free form of triclinic SFCA, SFC, SFCA-I was identified as forming, along with SFC, above ~1 400 K and through reaction of Fe 2 O 3 with calcium ferrite (i.e., CaO.Fe 2 O 3 , or CF). The compositional limits of SFC were probed by Pownceby and Patrick 24) and more recently by Cheng et al, 25) and the crystal structure by Ding and Guo. 26) Upon annealing of this SFCA-I at 1 488 K for more than 15 min it had completely converted to SFC.…”

<i>In-Situ</i> X-ray Diffraction Analysis of Phase Formation during Heating of Silico-Ferrite of Calcium (SFC) Compositions

“…This composition -82.36 mass% Fe 2 O 3 , 14.08 mass% CaO and 3.56 mass% SiO 2 -was designated AL0 and was within the SFC domain. 2,3) There, SFCA-I and SFC were observed to form above ~1 400 K through the solid-state reaction of Fe 2 O 3 and CF. Whilst this work provided important information regarding the phase changes occurring in the initial stages of sintering of an Al 2 O 3 -free mixture, the application to industrial sinter systems was limited by experiments being conducted at temperatures below 1 503 K and before melting of SFC.…”

“…1) The review was focused on a high-Fe, low-Si form called SFCA-I (general formula M 20 O 28 , e.g., Ca 3.2 Fe 2+ 0.8 Fe 3+ 14.7 Al 1.3 O 28 , triclinic crystal structure), and a low-Fe form called SFCA (M 14 O 20 , e.g., Ca 2.3 Mg 0.8 Si 1.1 Al 1.5 Fe 8.3 O 20 , also triclinic). The review also briefly referenced the Al 2 O 3 -free form of SFCA, SFC, the compositional and thermal domains of which have been probed by Pownceby and Patrick and more recently by Cheng et al 2,3) The formation mechanisms of SFCA and SFCA-I, as well as the effect of various parameters (e.g., Al 2 O 3 concentration and source, basicity, MgO and TiO 2 impurities, and oxygen partial pressure) on their formation during heating, have been extensively studied using in-situ X-ray diffraction (XRD). [4][5][6][7][8][9][10][11] In the first of these studies, Scarlett et al characterised the formation of SFCA and intermediate phases during heating under partial vacuum of sinter mixtures with compositions designed to form SFCA.…”

Iron Ore Sinter Macro- and Micro-Structures, and Their Relationships to Breakage Characteristics

“…Previous studies have shown that iron ore sinter properties depend on the bulk chemical composition of the sinters [11][12][13][14], the phases present and the volume fractions of these phases [11,15,16]. Fundamental research has established the influence of bulk composition, temperature and oxygen partial pressure on the phases formed under equilibrium [17][18][19][20] and non-equilibrium conditions [21][22][23][24][25][26]. Pownceby et al [17,18] investigated the phase equilibria in the Fe-rich region of the FeO-Fe 2 O 3 -CaO-SiO 2 system in air and in oxygen partial pressure pO 2 = 5 × 10 −3 atm from 1240 to 1300 • C. Chen et al [19] and Cheng et al [20] subsequently expanded the phase equilibria study in air to investigate the full extent of the primary phase field of SFC (silico-ferrite of calcium solid solution) which is believed to be a critical phase that enhances sinter quality [14].…”

“…Fundamental research has established the influence of bulk composition, temperature and oxygen partial pressure on the phases formed under equilibrium [17][18][19][20] and non-equilibrium conditions [21][22][23][24][25][26]. Pownceby et al [17,18] investigated the phase equilibria in the Fe-rich region of the FeO-Fe 2 O 3 -CaO-SiO 2 system in air and in oxygen partial pressure pO 2 = 5 × 10 −3 atm from 1240 to 1300 • C. Chen et al [19] and Cheng et al [20] subsequently expanded the phase equilibria study in air to investigate the full extent of the primary phase field of SFC (silico-ferrite of calcium solid solution) which is believed to be a critical phase that enhances sinter quality [14]. Nicol et al [21][22][23][24][25] investigated the non-equilibrium cooling behaviour of the melt in the FeO-Fe 2 O 3 -CaO-SiO 2 system in air as an effect of bulk compositions and cooling rates.…”