Effect of Al2O3 and Cr2O3 on Liquidus Temperatures in the Cristobalite and Tridymite Primary Phase Fields of the MgO-"FeO"-SiO2 System in Equilibrium with Metallic Iron

Abstract

The effects of alumina and chromite impurities on the liquidus temperatures in the cristobalite/tridymite (SiO 2 ) primary phase fields in the MgO-"FeO"-SiO 2 system in equilibrium with metallic iron have been investigated experimentally. Using high temperature equilibration and quenching followed by electron probe X-ray microanalysis (EPMA), liquidus isotherms have been determined in the temperatures range 1 673 to 1 898 K. The results are presented in the form of pseudo-ternary sections of the MgO-"FeO"-SiO 2 system at 2, 3 and 5 wt% Al 2 O 3 , 2 wt% Cr 2 O 3 , and 2 wt% Cr 2 O 3 ϩ2 wt% Al 2 O 3 . The study enables the liquidus to be described for a range of SiO 2 /MgO and MgO/FeO ratios. It was found that liquidus temperatures in the cristobalite and tridymite primary phase fields, decrease significantly with the addition of Al 2 O 3 and Cr 2 O 3 .KEY WORDS: slag; liquidus; phase equilibria; MgO-"FeO"-SiO 2 -Al 2 O 3 -Cr 2 O 3 system. ExperimentalThe experimental procedure used in the present investigation is one that has been developed specifically to provide accurate liquidus data in complex slag systems.7-9) The details of the procedure as adopted specifically for slags in the system under investigation are given in previous publication by the present authors.1) The procedure essentially involves the preparation of the synthetic slag compositions from high purity oxide and metallic iron powders; high temperature equilibration in Mo or Fe foil with metallic iron excess in a neutral gas atmosphere (temperature is within Ϯ2 K); rapid quenching of the samples enabling the phases present at temperature to be retained at room temperature; and determination of the compositions of the phases present of the samples using electron probe X-ray microanalysis (EPMA). Standards supplied by Charles M Taylor Co. Stanford, CA were used in EPMA measurement. The phase analyses have been shown to be accurate within Ϯ1 wt%.Only metal cation contents were measured by EPMA; the oxygen content was added according to the assumed oxidation sate. All iron was calculated as FeO in the present work. However, it should be kept in mind that small amounts of Fe 3ϩ are always present in the sample, even in contact with metallic iron. Results and DiscussionTo consider the effects of Al 2 O 3 and Cr 2 O 3 on liquidus ISIJ International, Vol. 45 (2005) The experiments were carried out in the cristobalite and tridymite primary phase fields in the MgO-"FeO"-SiO 2 -Al 2 O 3 system in equilibrium with metallic iron. EPMA measurements of the phase compositions obtained in the present study are reported in Tables 1, 2 and 3. The data obtained have been used to construct liquidus isotherms in the MgO-"FeO"-SiO 2 -Al 2 O 3 system with 2, 3, and 5 wt% Al 2 O 3 (Figs. 1(a), 1(b), and 1(c)) at temperatures in the range 1 723 to 1 873 K. The liquidus surfaces on the limiting ternary systems of MgO-Al 2 O 3 -SiO 2 and "FeO"-Al 2 O 3 -SiO 2 were taken from Osborn and Muan.10,11) The general shape of the cristobalite/tridymite liquidus surfaces for the s...

Effects of Al2O3 on Phase Equilibria in the Olivine Primary Phase Field of the MgO-"FeO"-SiO2-Al2O3 System in Equilibrium with Metallic Iron

“…As described in a previous publication, 2) there are several ways in which the influence of alumina addition and replacement on the liquidus can be viewed and represented. The change in liquidus temperature depends on which directions in the compositional space changes are made.…”

“…Two compositions in the MgO-"FeO"-SiO 2 system were selected to compare the effects. Point A1 has bulk composition 49.1SiO 2 , 32.4MgO and 18.6FeO in wt%, and point A2 has 51.3SiO 2 Figs. 3(a) and 3(b).…”

“…This system describes a number of industrially important metallurgical slags. Previous studies [1][2][3] have shown that the presence of alumina can have significant effect on the liquidus temperatures of the slags. Data on the MgO-"FeO"-SiO 2 , 1) MgO-Al 2 O 3 -SiO 2 4) and "FeO"-Al 2 O 3 -SiO 2 5) subsystems have been described in detail.…”

“…The pseudobinary system 2MgO · 2Al 2 O 3 · 5SiO 2 -2FeO · 2Al 2 O 3 · 5SiO 2 , part of the MgO-"FeO"-SiO 2 -Al 2 O 3 system, was investigated by Miyashiro 6) using optical microscopy and X-ray diffraction. The study presents information on the conditions of formation of cordierites ((Mg, Fe) 2 7) investigated the MgO-"FeO"-SiO 2 -Al 2 O 3 system with SiO 2 (quartz saturation) at 1073 K and 3 kbar. Subsolidus equilibria and tie lines were determined in their studies using X-ray diffraction and the petrographic microscope.…”

Phase Equilibria in the Olivine Primary Phase Field in the MgO-"FeO"-SiO2 System in Equilibrium with Metallic Iron

“…Previous papers 1,2) have reported phase equilibria in the silica and pyroxene primary phase fields. The focus of the present paper is determination of phase equilibria in the olivine primary phase field in the MgO-"FeO"-SiO 2 system.…”