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

Abstract

Liquidus temperatures and phase equilibria have been determined in the olivine primary phase field of the MgO-"FeO"-SiO 2 -Al 2 O 3 system. Liquidus isotherms have been determined in the temperature range from 1748 to 1873K. The results are presented in the form of pseudo-ternary sections of the MgO-"FeO"-SiO 2 with 2 and 3 wt% Al 2 O 3 in the liquid. The study enables the liquidus to be described for a range of SiO 2 /MgO ratios. It was found that liquidus temperatures in the olivine primary phase field decrease with the addition of Al 2 O 3 .KEY WORDS: slag; liquidus; phase equilibria; olivine; MgO-"FeO"-SiO 2 -Al 2 O 3 .ing phase analysis measurements within Ϯ0.5 wt% are presented in this investigation. Results and Discussion LiquidusTo consider the effect of Al 2 O 3 on liquidus temperatures in the region, the experimental results are represented in the form of pseudo-ternary sections MgO-"FeO"-SiO 2 at fixed weight percentages of Al 2 O 3 in the liquid phase.The experiments were carried out in the olivine primary phase field in the MgO-"FeO"-SiO 2 -Al 2 O 3 system in equilibrium with metallic iron. The data obtained have been used to construct the liquidus isotherms in the MgO-"FeO"-SiO 2 -Al 2 O 3 system with 2 and 3 wt% Al 2 O 3 (Figs. 1 and 2) at temperatures in the range 1748 to 1873 K. EPMA measurements are presented in Tables 2 and 3.The general shapes of the olivine liquidus surfaces for the MgO-"FeO"-SiO 2 -Al 2 O 3 slags containing 2 and 3 wt% Al 2 O 3 are similar to that in the ternary system MgO-"FeO"-SiO 2 .3) It can be seen from Figs. 1 and 2 that, compared with the MgO-"FeO"-SiO 2 system, there is a decrease in the liquidus temperatures in the olivine primary phase field with the presence of alumina.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. This point is illustrated for a selected compositional range using three different methods of comparison. 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 , 29.0MgO and 19.7FeO in wt%, liquidus temperatures for these compositions are 1873 K and 1823 K respectively ( Table 4) Conjugate LinesInspection of the EPMA measurements in Table 2 shows that there is no solubility of Al 2 O 3 in the olivine phase. Tie lines at temperatures of 1773 and 1823 K between olivines and liquid phase compositions in the MgO-"FeO"-SiO 2 -Al 2 O 3 system with 2 wt% Al 2 O 3 are projected on the plane of the MgO-"FeO"-SiO 2 system as shown in Figs. 5(a) and 5(b) respectively. The solubility of 2FeO · SiO 2 in 2MgO · SiO 2 increases with decreasing temperature. For a given temperature the composition of the solid phase is enriched with MgO relative to the equilibrium liquid phase.

Phase Equilibria in the System “FeO”–CaO–SiO₂–Al₂O₃–MgO with CaO/SiO₂ 1.3

“…The experimental procedure in the present study has been well developed at the University of Queensland, [14][15][16][17][18][19] which has been proven to be able to provide accurate phase equilibria data for complex slag systems. It includes high temperature equilibration, quenching and electron probe X-ray microanalysis (EPMA).…”