Ce-la-o System Phase Diagram Studies

An understanding of thermqdynamics and phase diagrams is fundamental and essential to the study of materials science.Experimentation and computation can be used to confirm phase diagrams.Limited of the experiment condition,one could not measured all data to make a phase diagram of a system.From 1970s,by the development of computer,phase diagram calculation has improved quickly,in which the Thermo-calc software is a general and flexible software for all kinds of thermodynamics and phase diagram calculations,which is based upon a powerful Gibbs Energy Minimizer.Cerium and Lanthanum,and also with their oxides,are widely used as catalyzer, electrode in solid fuel cell,thermo barrier coating,et al.The Ce-La-O is a typical solid solution system.Research into the phase diagrams of the system and its subsystems,the phase structures and the state of the Ce-La alloy's oxidation can be found.In this paper,the Thermo-calc software was used to study the phase diagrams of the subsystems in the Ce-La-O ternary system,combined with data from literature and information from our experimentation.Raman spectra,scanning electron microscope and atomic force microscope were adopted to study the oxidation process of Ce-La alloy in air.The solid solution of oxides was found in the surface of the alloy,which can be Ce₂O₃-La₂O₃ or CeO₂-La₂O₃ as posed in the oxygen.The band of Raman spectra at 456cm^-1 was assigned to the first-order Raman spectrum of CeO₂,while the 837cm^-1 one was due to O₂^2- which was relative to Ce³⁺.The change of the ration between the intensities of the two bands revealed the two-step process of the surface oxidation of the alloy.The series of CeO₂-La₂O₃ solid solutions were prepared with the Sol-Gel method. X-ray diffraction figures of the solid solutions indicate that the CeO₂-La₂O₃ system was composed by the solid solutions based upon the structure of CeO₂ and La₂O₃ respectively.La₂Ce₂O₇ has a solid solution of a fluorite structure which is same to CeO₂,not a compound like Pyrochlore.The experimental information and data from literature were evaluated.Ideal solid solution model and Two-sublattice solution model were selected to describe different phase.Three subsystems(Ce-La,Ce-O,La-O) and two pseudo systems (CeO₂-La₂O₃,Ce₂O₃-La₂O₃) were calculated.Compared with the diagrams obtained from experimentation in literature,the results from calculation are not bad.