A thermodynamic model for evaluation of mass action concentrations of La2O3-Al2O3-CaF2-CaO-MgO slags for electroslag remelting based on the ion and molecule coexistence theory

Abstract

According to the ion and molecule coexistence theory (IMCT) for molten slags and corresponding phase diagrams, a thermodynamic model for the evaluation of mass action concentrations (designated by Ni for structure unit i) for La2O3-Al2O3, La 2O3-Al2O3-CaF2, La 2O3-Al2O3-CaF2-CaO, La2O3-Al2O3-CaF2-MgO and La2O3-Al2O3-CaF2-CaO-MgO slag systems for electroslag remelting (ESR) has been formulated. The influencing factors for the mass action concentration of La2O 3, such as mass fraction of Al2O3, CaF 2, CaO and MgO and temperature, were investigated. The results show that when the mole fraction of La2O3 is at 0.495, the mass action concentration of La2O3 · Al 2O3 achieves its maximum value 0.946 in the La 2O3-Al2O3 binary slag. In a composition area of La2O3: 10wt% ∼ 45wt%, Al 2O3: 0wt% ∼ 50wt% and CaF2: 20wt% ∼ 70wt% of the La2O3-Al2O3-CaF 2 ternary slag at 1873 K, the results show that the calculated values of NLa2O3 are in good agreement with the reported measured values of aLa2O3. The iso-curves of NLa 2O3 is also drawn from the calculated results, which reveals that the mass action concentration of La2O3 decreases with the increasing of the Al2O3 and CaF 2 content, and Al2O3 is stronger than CaF 2 in decreasing the mass action concentration of La2O 3. However, in La2O3-Al2O 3-CaF2-CaO, La2O3-Al 2O3-CaF2-MgO and La2O 3-Al2O3-CaF2-CaO-MgO slag systems, the mass action concentration of La2O3 increases with the increasing of the MgO and CaO content, and CaO is stronger than MgO in increasing the mass action concentration of La2O3. In addition, the mass action concentration of La2O3 increases with the increasing temperature at the composition of 30wt%La2O 3, 10wt%Al2O3, 40wt%CaF2, 10wt%MgO and 10wt%CaO. © [2013] by Walter de Gruyter Berlin Boston 2013.