Study On The Evolution Characteristics And Constitutive Model Of Graphite Lining In Rare Earth Electrolyzers

The damage of the rare earth electrolytic cell has severely restricted the sustainable development of the rare earth metal electrolysis industry in China.The graphite lining usually lose its effectiveness the earliest in a great number of electrolytic cell breakage accidents.Thus,it is self-evident that graphite lining is the weak link and key structural elements of electrolytic cell.Therefore,exploring the mechanism of the rupture of graphite lining corrosion,reveal the occurrence and development process,predict the process and deterioration of mechanical properties of the evolution of the graphite liner oxidation corrosion pore structure accurately,and thus take effective measures which was an important link in achieving optimal cell life design to prevent the corrosion and ensure the structural integrity and safety.In this paper,the multi-field coupling effect of the rare earth oxide-fluorinated salt molten salt electrolysis system graphite liner lining damage process was studied as the starting point,based on the porous media oxidation theory,the damage behavior of graphite lining was studied by varies of experiments,theoretical analysis and numerical analysis.The research was designed to construct a non damage identification technology of graphite lining in rare earth electrolysis environment by using micro CT,to analyse the evolution of micro structure of graphite lining and its response to the diffusivity,to establish the model of oxidation diffusion and pore structure evolution of graphite lining,and to deeply study the degradation of mechanical properties under oxidation corrosion.Based on this,a creep constitutive model of graphite lining under oxidative corrosion damage state and a coupled constitutive model of oxidative stress and stress coupling are established,and the damage evolution process of graphite lining was analyzed,which was used to predict the temporal and spatial evolution law of internal corrosion,stress and damage.The main work and research results of this paper are summarized as follows:? Based on CT image of graphite lining,we build graphic model and measure pore throat geometry parameters.Fractal dimension was used to characterize the fractal characteristics and porosity of pore structure of graphite lining.Pore and throat parameters were used to analyze the flow of air and electrolyte in graphite lining.Fractal dimension D was used to describe the irregular degree and corrosion degree of pore structure of graphite lining.? Based on the Fick law and the law of mass conservation,the coupling effect between oxidation reaction,gas diffusion and pore structure evolution in graphite lining was considered.A mathematical model for oxidation diffusion and pore structure evolution of graphite lined samples under the condition of rare earth molten salt electrolysis was established to study the diffusion and pore structure evolution process of graphite lining.? Through the analysis of the experimental results in different oxidation time under creep corrosion properties of graphite lined cylindrical specimens,considering the influence of oxidation corrosion effect on graphite lining damage and deterioration of creep parameters,this paper had analyzed the creep parameters of graphite lining deterioration,and obtained the damage evolution equation of its oxidation and corrosion.Through which we establish the creep constitutive model of oxidation corrosion deterioration effect consider the study ofcreep properties of oxidation corrosion under special graphite lining.? The Weibull distribution function was used to characterize the graphite liner element strength distribution on the mechanical damage and deterioration of the graphite liner;change of porosity of graphite lining corrosion under the action based on the introduction of graphite lined chemical damage variable,makes research on the graphite liner oxidation corrosion damage;Based on the porosity change under the oxidation corrosion of graphite lining,the chemical damage variable of graphite lining was introduced,and the oxidation corrosion damage of graphite lining was studied.Based on the generalized Lemaitre strain equivalence principle and considering the effect of oxidative stress damage coupling,a coupled constitutive model of oxidation stress and stress damage in graphite lining was established to explore the evolution process of graphite lining damage.