Study On Phase Equilibrium Relationship Of CaO-Al₂O₃-CeO₂-5%w（MgO） Slag System Under Air Atmosphere At 1500℃

A new type of aluminate slag system CaO-Al2O3-CeO2-MgO as refining slag and tundish covering agent has become the main research direction in the design and development of rare earth steel metallurgical slag system.However,in the process and theoretical research,it is found that the thermodynamic data of the slag system is lack,and the basic theoretical research is lack,which leads to the limited thermodynamic data for reference.This paper takes CaO-Al2O3-CeO2-MgO quaternary slag system as the research object.Under the theoretical guidance of metallurgical physical chemistry,conduct high-temperature equilibrium static method experiments,and use SEM-EDS and other detection and analysis methods to study and analyze the equilibrium phase of the CaO-Al2O3-CeO2-MgO slag system under 1500℃ air atmosphere conditions and within the set composition range type and phase balance relationship,and draw the corresponding isothermal phase diagram.Under the experimental conditions,the following conclusions are obtained:(1)Within the range of the experimental slag system,there are five different phase equilibrium relationships in the CaO-Al2O3-CeO2-MgO slag system under the air atmosphere of 1500℃.They are Liquid+CeO2+MgO·Al2O3+CaO·2Al2O3,Liquid,Liquid+CeO2,Liquid+CaO+CeO2+MgO and Liquid+CeO2+MgO·Al2O3,respectively.Ce in the equilibrium phase is stable in the form of+4 valence.(2)Within the scope of the slag system in this experiment,when w(CaO)/w(Al2O3)is in the range of 1.00～1.76,with the increase of the content of w(CeO2),the composition point of the slag sample moves from the two-phase coexistence zone of Liquid+CaO to the four-phase coexistence zone of Liquid+CaO+CeO2+MgO.The composition point is far away from the liquid phase at 1500℃,that is,the melting temperature increases.(3)Within the scope of the slag system in this experiment,when w(CaO)/w(Al2O3)is 0.59,as the content of w(CeO2)increases,the position of the composition point of the slag sample gradually moves away from the liquid phase region at 1500℃ and enters Liquid+CeO2+MgO·Al2O3 three-phase coexistence zone,that is,the melting temperature of the slag sample increases.(4)Within the scope of the slag system in this experiment,the content of w(CeO2)is 40.14%.With the decrease of w(CaO)/w(Al2O3),the position of the slag sample composition point first decreases and then increases from the 1500℃ liquid phase.That is,the melting temperature of the slag sample decreases first and then increases.The composition point of the slag sample enters the three-phase coexistence area of Liquid+CeO2+MgO·Al2O3 from the four-phase coexistence area of Liquid+CaO+CeO2+MgO,and then enters the four-phase coexistence area of Liquid+CeO2+MgO·Al2O3+CaO·2Al2O3.(5)Within the scope of the experimental slag system,the solid phase coexistence zone of CaO-CeO2-MgO and the solid phase coexistence zone of CeO2-MgO·Al2O3－CaO·2Al2O3 in the CaO-Al2O3-CeO2-MgO slag system were determined under the air atmosphere of 1500℃.(6)Within the scope of the experimental slag system,the isophase diagram of CaO-Al2O3-CeO2-MgO slag system at 1500℃ under air atmosphere was drawn,and the two-phase equilibrium coexistence zone of Liquid+CeO2 and three-phase equilibrium coexistence zone of Liquid+CeO2+MgO·Al2O3 in the phase diagram was determined.Liquid+CaO+CeO2+MgO,Liquid+CeO2+MgO·Al2O3+CaO·2Al2O3,and liquid phase region.