Preparation Of New Ceramic Oxygen Permeable Membranes And Research On Its Oxygen Permeability

Since the ceramic separation membrane can efficiently separate pure oxygen from the oxygen-containing atmosphere,it has broad application prospects in the fields of pure oxygen preparation,oxygen-enriched air production,and partial oxidation of methane.In practical applications,dense ceramic oxygen permeable membrane materials must meet two important factors:one is to have a sufficient oxygen permeation rate,and the other is to maintain high structure and chemical stability in the state of oxygen permeable separation.The thesis carried out research on the oxygen permeability and stability of the new ceramic oxygen permeable membrane materials,and developed two new oxygen permeable membrane materials.In the synthesis of conventional BaFeO_3-dmaterials,the radius of barium ions is large,while the radius of iron ions is small,and the tolerance factor deviates far from 1,which makes it difficult to form cubic perovskite oxygen permeable membrane materials.This thesis is based on the Ba-Fe-O₃ hexagonal composite oxide material with excellent chemical stability as the matrix.According to defect chemistry and crystallographic theories,the cobalt metal ions are doped into the B site of the BaFeO₃ material.Small radius cobalt ions induce the transformation of hexagonal BaFeO₃into cubic perovskite structure,and the Ba Co_xFe_1-xO_3-dmaterial can stably maintain the cubic perovskite structure from high temperature to room temperature in this specific doping interval,Ba Co_xFe_1-xO_3-dThe formation of cubic perovskite structure significantly increases its oxygen permeability.The results show that when the doping amount of cobalt ions is 5%,the structure of the membrane material starts to transform from hexagonal crystal type to cubic perovskite type.When the doping amount of cobalt ions at the B site ranges from 10 to 50%,the unit cell parameters It tends to become smaller,and the membrane material structure remains a cubic perovskite crystal phase structure,but when the doping amount is higher than 50%,the membrane material structure is no longer a pure cubic perovskite type.Studies have shown that at 950°C,the oxygen permeability of BaFeO₃material is only 0.154 ml.cm^-2.min^-1,while the oxygen permeability of the cubic perovskite oxygen permeable membrane obtained with 50%cobalt doping is 1.526 ml.cm^-2.min^-1,because of its structural phase change during the cooling process,it is not our first choice.We chose a relatively stable and high oxygen permeability membrane with a 40%cobalt content,and its oxygen permeability is 1.489 ml.cm^-2.min^-1,compared with BaFeO₃ material,the oxygen permeability increased by nearly 9.7 times.The thesis realized the effective control of the crystal structure parameters of the Ba-Fe-O₃material through the doping and modulation of cobalt ions,improved the oxygen transmission performance of the material,and achieved the purpose of increasing the oxygen permeability.At the same time,the thesis systematically explored the effects of the nature and concentration of doping elements on the crystal structure parameters,oxygen vacancy concentration,oxygen surface exchange and bulk diffusion coefficient,chemical stability,oxygen permeability and long-term stability of Ba-Fe-O₃ materials,and analyzed The mechanism of the influence of doping elements on the formation and migration of oxygen vacancies is discussed,and the understanding of the oxygen transport process of the new oxygen-permeable membrane material Ba-Fe-O₃ material is deepened.Based on the high stability of the dual-phase composite oxygen permeable membrane material composed of oxygen ion conductive phase and electronic conductive phase material,this paper developed copper ion doped Ce_0.8Sm_0.2O_2-d（SDC）-Sm_0.6Sr_0.4Fe_1-xCu_xO_3-d（SSFC）two-phase oxygen permeable membrane material.In this thesis,SSFC with high electronic conductivity was selected as the conductive phase and SDC with high stability as the oxygen ion conductive phase to prepare the SDC-SSFC dual-phase oxygen permeable membrane material.For the first time,this thesis systematically studied the effect of copper metal ion doping on the oxygen permeability and stability of the SDC-SSFC dual-phase oxygen permeable membrane.The research results show that the oxygen permeability of the SDC-SSF dual-phase oxygen permeable membrane without copper ions is 0.293 ml.cm^-2.min^-1 at 950℃,and when the copper ion doping is increased to 10%,The oxygen permeability of the SDC-SSFC dual-phase oxygen permeable membrane increased to 0.613 ml.cm^-2.min^-1.Compared with the SDC-SSF dual-phase oxygen permeable membrane,the oxygen permeability increased by nearly 2.1 times,and the During the oxygen process,the SDC-SSFC dual-phase membrane has a stable structure and no structural phase change occurs.Therefore,the SDC-SSFC dual-phase oxygen permeable membrane is a dual-phase oxygen permeable membrane material with excellent performance.The paper deeply studied the influence of copper ion doping on the crystal structure,microscopic morphology,oxygen permeability and chemical stability of the SDC-SSFC dual-phase perovskite oxygen-permeable membrane,and concluded the optimal doping amount of copper ions.Lays a good research foundation for the development of copper ion-based dual-phase oxygen permeable membranes.