Thermodynamic studies in the MgO – FeO – Al2O3 system

Abstract

Prediction of the phase composition is one of the most important tasks in the development of new refractory materials and their operation in thermal units. The most complete information on phase interactions and thermodynamic stability of phase combinations is contained in the phase diagrams.
 The article presents thermodynamic studies of the three - component system MgO – FeO – Al2O3, which is of great interest for the production of refractory materials with high performance characteristics. Based on the analysis of binary systems of this system, it was found that, the stable phases are MgO, FeO, Al2O3 and MgAl2O4, FeAl2O4. The results analysis of calculating the Gibbs energy for the reaction (FeO + MgAl2O4 = MgO + FeAl2O4) indicates the thermodynamic stability of the phases combination of MgO, FeAl2O4 to a temperature of 1141 K. Above the temperature of 1141 K FeO and MgAl2O4 are stable phases. Thus, in the system MgO – FeO – Al2O3 up to the temperature of 1141 K, the phases MgO – FeAl2O4 and MgAl2O4 – FeAl2O4 coexist, above this temperature — FeO – MgAl2O4 and MgAl2O4 – FeAl2O4.
 The data obtained make it possible to predict thermally stimulated phase changes that give the effect of thermoplasticity and will be important for obtaining refractory materials with high performance characteristics based on the MgO — FeO — Al2O3 system.

Thermodynamics of Solid-Phase Exchange Reactions Limiting the Subsolidus Structure of the System MgO-Al₂O₃-FeO-TiO₂

“…Reaction ( 3) is reversible at a temperature of 1141 K (Table 2), and the combination of the MgO and In the Al2O3 -TiO2 -FeO subsystem, reaction (4) is the most thermodynamically probable and ensures the stability of the combination of the starting compounds Al2O3 and FeTiO3 (positive and maximum values of ΔG in modulus according to Table 2), according to reaction (5), the combination of compounds in the reaction products is more stable: FeAl2O4 and FeTiO3 (negative values of ΔG in the entire investigated temperature range (see Table 2):…”

“…We carried out a thermodynamic analysis of the subsolidus structure of the MgO -Al2O3 -FeO -TiO2 system by comparing the Gibbs free energy in the temperature range 800 -2076 K according to the method [4], using the thermodynamic data presented in table. 1, for model solid-phase exchange reactions [5,6]. The calculation of the change in the Gibbs free energy with temperature makes it possible to judge the direction of the solid-phase reactions and the preference for the formation of certain combinations of phases [7].…”