Experimental and theoretical study of Fe

This study investigates the compositions of (Fe2+, Mg)(Al, Fe3+)2O4 spinels equilibrated with a 1 M (Fe2+, Mg)Cl2 aqueous solution at 800°C and 4 kbars. The objective is to derive exchange isotherms between the chloride solution and (Mg, Fe2+)Al2O4 spinels and to establish activity-composition relationships within the binary join FeAl2O4-MgAl2O4, which displays a significant positive deviation from ideal behavior. The methodology involves both experimental measures and a Gibbs free energy formulation to model the spinel solid solution, allowing a calculation of Gibbs free energy changes for specific reactions, notably AG = 2.9 kcal at 800°C and 4 kbars. The analysis results in a characterization of tie-lines between coexisting aluminous and ferric spinels, as well as insights into the non-ideal behavior of the spinels and the resulting miscibility gaps. The findings emphasize the role of defect end-members in the spinels' compositions, leading to an estimated vacancy content. This study contributes to the understanding of spinel systems and their equilibrium behaviors under diverse conditions.