Preparation And Multi-scale Simulation Of MgO-BaO-CaO-Al₂O₃-B₂O₃-SiO₂ System Sealing Materials For ITSOFC

The sealing material is one of the key materials of intermediate temperature solid oxide fuel cell（ITSOFC）.The stability of the material structure and the stability of the performance seriously affect the service life of ITSOFC.Therefore,it is of great significance to study the ideal sealing material for the development of SOFC.As a suitable sealing material,glass-ceramic has the advantages of low cost,good sealing performance and adjustable performance.BCABS（Ba O-Ca O-Al₂O₃-B₂O₃-Si O₂）glass-ceramic has good sealing performance.However,when used at high temperature,the structure of the material will change over time,resulting in a decrease in the coefficient of thermal expansion and a mismatch with other components.In order to improve the thermal stability of BCABS,the MBCABS（Mg O-Ba O-Ca O-Al₂O₃-B₂O₃-Si O₂）system was designed by adding Mg O to the original system formula to improve the sealing performance by adjusting the material structure.The main contents of this paper are as follows:（1）The relationship between MBCABS composition and glass structure was studied by Materials Studio software combined with molecular dynamics simulation.The results show that with the increase of Mg O content,the coordination geometry of boron ions changes from[BO₃]to[BO₄],and coexists with the ligand of silicon ions[Si O₄],which can improve the stability of the glass network..At the same time,the proportion of bridging oxygen in the glass network decreased from 53.9%to 29.5%,and the proportion of Qⁿ units changed from units containing more bridging oxygen to units containing more non-bridging oxygen,indicating that Mg O as an external network destroyed the network structure of the glass,reduced the degree of network polymerization,and made the glass easy to crystallize.（2）The quenched glass was prepared by melt quenching process,and the network structure of the quenched glass was analyzed by FTIR and Raman.The test results can be consistent with the variation of the glass network structure obtained by molecular dynamics simulation.The green body of sealing material was prepared by tape casting process,and the glass-ceramic sealing material was obtained after solid phase sintering.The addition of7.5 wt%Mg O can inhibit the precipitation of Ba Al₂Si₂O₈.Through long-term thermal stability analysis,it was found that the crystalline phase of all formulations was basically stable after 100 h,and the corresponding performance also tended to be stable.The CTE of all samples at 1 h is 11～12.5×10^-6 K^-1,which is within the acceptable range.With the increase of heating time,the CTE of M0～M2 is lower than 11×10^-6 K^-1,which is no longer applicable to other components.（3）The finite element method of COMSOL Multiphysics software was used to study the stress distribution of all MBCABS sealing materials under temperature difference after different formulations and different heat treatment time.The sealing model is established based on the planar SOFC with a plane size of 10mm×10mm,and the symmetrical boundary is used to simplify the calculation.The properties of materials used in different components were simulated with Ni-YSZ as anode material,MBCABS as sealing material and Crofer22APU as interconnect material.The results show that when the CTE difference between the components is small,the stress is small.The simulation results well reflect the relationship between material properties and performance.In this paper,the influence of components on the material structure is studied by molecular dynamics and experiments.The reasons for the change of measurement performance are analyzed from the material structure.The material properties are applied to the sealing stress analysis by finite element simulation.Multi-scale research can play a guiding role in the selection and development of SOFC stack.