Ce The Experimental And Theoretical Studies Of The Oxygen Reaction

Ce,the second element in lanthanides,the 4f electron of which lie on the critical station between localized and non-localized,has many similar properties with Plutonium whose 5f electron lie on the similar station with 4f electron of Ce.Investigation on reaction of Ce-O system will be a guide for research on Pu-O system.Systemic studies were carried out by TG,DSC,SEM,RAMAN,XRD,XPS and self-made reaction container combining the first-principle.Firstly,based on the SEM, RAMAN and XRD study of macroscopical model of Ce-O reaction,an appropriate simulation model was confirmed,and then numerical model and numerical simulated method were built.Then,infection of temperature and pressure of oxygen were studied by theory simulation combining with TG and DSC.Transform dynamics of Ce oxides were forecasted by simulation and validated by experiments.Finally,aiming at the special condition of Ce(Pu),conventional X-ray intensity method to measure oxidation dynamic was improved.The results of SEM,RAMAM,XRD and XPS show that under room temperature and atmosphere,Ce₂O₃,Ce₇O₁₂ and CeO₂ form orderly during oxidation process of Ce.Ce₂O₃ is firstly formed upon Ce and then it was rapidly oxidated to Ce₇O₁₂,finally Ce₇O₁₂ is oxidated to CeO₂.It is a break transformation from Ce₇O₁₂ to CeO₂.CeO₂ is formed abruptly until the oxidation layer reached about 12um after 96h oxidation under room temperature and atmosphere,before that CeO₂ almost can not be observed.Combining with the first principle simulation on critical structure,density and energy,we discuss the formation mechanism of three oxides and reasons of abrupt formation of CeO₂.Simulation results show that abrupt transformation from Ce₇O₁₂ to CeO₂ is relational to station changes of 4f electron from localized to non-localized and this also is supported by XPS and SEM study.All the research show that Ce,Ce₂O₃,Ce₇O₁₂ system is more appropriate than other metals as a simulation system of Pu,Pu₂O₃,PuO₂.Infection of temperature on Ce-O reaction dynamic under high and low oxygen pressure is studied by TG.Parabola oxidation velocity of Ce₇O₁₂ and Ce₂O₃ in dry air and adsorption coefficient are got by experimental measurement.Deoxidization dynamic from Ce₇O₁₂ to Ce₂O₃ under scarcity oxygen condition,oxidation dynamic from Ce₂O₃ to Ce₇O₁₂ and critical oxygen pressure from Ce₇O₁₂ to Ce₂O₃ under certain conditions are forecasted and measured by numerical model and experiments.The calculated results agree well with experiments.Statistical diffusion theory and mass quality function law are applied to study the affection of oxygen pressure on Ce-O reaction dynamic. Simulation results show that reaction velocity firstly increases and then decreases with decrease of Oxygen pressure.Affection of Oxygen pressure on reaction dynamic is studied by TG.and simulation.The calculated results agree well with experiments.Experiment study under low oxygen pressure has not been carried out for the sake of lack of experiment equipments.By adding oxidation rate equation,traditional X-ray intensity method was modified.Combining with numerical fitting method,oxidation of Cerium in air was studied using modified X-ray intensity method.Results show that parabolic rate constants of Ce oxidation in air can be deduced by this modified method without knowing initial thickness of oxides.