A Thermodynamic Model for Evaluation of Mass Action Concentrations of La ₂O ₃-Al ₂O ₃-CaF ₂-CaO-MgO Slags for Electroslag Remelting Based on the Ion and Molecule Coexistence Theory

摘要

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 N_( i )for structure unit i) for La_(2)O_(3)-Al_(2)O_(3), La_(2)O_(3)-Al_(2)O_(3)-CaF_(2), La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)-CaO, La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)-MgO and La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)-CaO-MgO slag systems for electroslag remelting (ESR) has been formulated. The influencing factors for the mass action concentration of La_(2)O_(3), such as mass fraction of Al_(2)O_(3), CaF_(2), CaO and MgO and temperature, were investigated. The results show that when the mole fraction of La_(2)O_(3)is at 0.495, the mass action concentration of La_(2)O_(3)?·?Al_(2)O_(3)achieves its maximum value 0.946 in the La_(2)O_(3)-Al_(2)O_(3)binary slag. In a composition area of La_(2)O_(3): 10wt%?～?45wt%, Al_(2)O_(3): 0wt%?～?50wt% and CaF_(2): 20wt%?～?70wt% of the La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)ternary slag at 1873?K, the results show that the calculated values of N _(La_(2)O_(3))are in good agreement with the reported measured values of a _(La_(2)O_(3)). The iso-curves of N _(La_(2)O_(3))is also drawn from the calculated results, which reveals that the mass action concentration of La_(2)O_(3)decreases with the increasing of the Al_(2)O_(3)and CaF_(2)content, and Al_(2)O_(3)is stronger than CaF_(2)in decreasing the mass action concentration of La_(2)O_(3). However, in La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)-CaO, La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)-MgO and La_(2)O_(3)-Al_(2)O_(3)-CaF_(2)-CaO-MgO slag systems, the mass action concentration of La_(2)O_(3)increases with the increasing of the MgO and CaO content, and CaO is stronger than MgO in increasing the mass action concentration of La_(2)O_(3). In addition, the mass action concentration of La_(2)O_(3)increases with the increasing temperature at the composition of 30wt%La_(2)O_(3), 10wt%Al_(2)O_(3), 40wt%CaF_(2), 10wt%MgO and 10wt%CaO.