Effect of Gas Atmosphere on the Phase Chemistry in the CaO–FeO–Fe₂O₃–SiO₂ System Related to Iron Ore Sinter-making

Abstract

Experimental phase equilibria studies have been carried out to investigate the phase chemistry in the CaO-"Fe 2 O 3 "-SiO 2 system related to the iron ore sinter making in 1 atm CO 2 at 1 200-1 230°C. The measurements have been performed using a modified experimental technique involving high temperature equilibration and rapid quenching followed by electron probe X-ray microanalysis (EPMA). In contrast to the equilibria in air, the experimental results show that no silico-ferrite of calcium (SFC solid solution) is formed in 1 atm CO 2 within the temperature range investigated; that is, the SFC phase is not stable at liquidus temperatures. The liquidus for the iron-rich corner of the CaO-"Fe 2 O 3 "-SiO 2 system in CO 2 atmosphere for the spinel (magnetite Fe 3 O 4) and dicalcium silicate (C 2 S = Ca 2 SiO 4) primary phase fields has been proposed.

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

“…14) More recent phase equilibria studies conducted by Chen et al to investigate the thermodynamic stability of SFC phase at equilibrium in 1 atm CO 2 also showed that no SFC phase was formed under pO 2 conditions more reducing than air. 15) Both previous reduced pO 2 investigations, however, were equilibrium studies and provided no information regarding the pre-cursor phases that develop during SFC formation. The elucidation of phase formation mechanisms, including observation of intermediate phases, in the SFC system would therefore be a novel contribution to the fundamental knowledge of iron ore sinter mineralogy.…”

Factors influencing the microstructures of iron ore sinters

“…The phases formed on cooling of the melt should form the majority of the phase assemblage in the product sinter. Recent studies undertaken on synthetic sinter materials (Patrick and Pownceby 2002;Chen et al 2019aChen et al , 2019b indicate that the phases and the product microstructures formed are largely determined by the phase equilibria and the solidification process. This being the case the focus of the present study then is to unambiguously demonstrate the effects of key process parameters, such as bulk composition, cooling rate and oxygen partial pressure on the phase assemblages and microstructures of synthetic iron sinter materials.…”

“…In Figure 1 (b) it can be seen that the matrix consists of Platy SFCA + Magnetite + Glass. The SFCA phase (silico-fer-rite of calcia and alumina) is an iron-rich complex solid solution containing aluminium, calcium, iron and silicon oxides (Pownceby et al 1998;Pownceby and Patrick 2000;Patrick and Pownceby 2002;Pownceby and Clout 2003;Chen et al 2019aChen et al , 2019b. The term platy is used here to indicate the high aspect ratio of the SFCA crystals, which appear to intersect with each other forming a three-dimensional network structure.…”

“…The difficulties associated with experimental studies of the iron oxide-rich system mean that the phase equilibria for the Al 2 O 3 -CaO-FeO-Fe 2 O 3 -MgO-SiO 2 system, which describes the principal chemical components in the sinters, have yet to be accurately established. Limited phase equilibrium data are available for the CaO-FeO-Fe 2 O 3 -SiO 2 (Pownceby et al 1998;Pownceby and Patrick 2000;Patrick and Pownceby 2002;Pownceby and Clout 2003;Chen et al 2019aChen et al , 2019b and Al 2 O 3 -CaO-FeO-Fe 2 O 3 -SiO 2 (Patrick and Pownceby 2002;Pownceby and Clout 2003) systems. Relatively few fundamental studies have been undertaken on the mechanisms of microstructure formation in sinters properties (Egundebi and Whiteman 1989;Hsieh and Whiteman 1989;Dawson 1993) and the results have not provided a clear framework for predicting the outcomes of the sintering process.…”

Effects of Basicity and Al2O3 Content on the Chemistry of Phases in Iron Ore Sinter Containing ZnO

“…Especially, calcium-ferrite-based materials are sensitive to several factors such as the composition, [29][30][31][32][33][34][35][36] thermal history, [37] and gas atmosphere. [18,38,39] Therefore, it is important to control the factors and analyze the samples exactly.…”