Preparation And Characterization Of La_9.33Si₆O₂₆ Ceramic By Molten Salt Method For Solid Electrolyte Application

Recently, the Solid Oxide Fuel Cell has become the research focus because of environmental protection and efficient energy, but its high operating temperature is still a biggest problem for its practicability. Therefore, it's necessary to study the low-temperature electrolyte for SOFC. In this background, this paper carried out the research of apatite La_9.33Si₆O₂₆ electrolyte, which included the optimization of synthesis method, the analysis of conductive mechanism and the theory suggestion of doping or replacement.La_9.33Si₆O₂₆, which shows high conductivity in low temperature and has the stable oxygen ion migration number in a wider oxygen partial pressure, is the typical one of oxy-apatite materials for low-temperature SOFC application. In order to decrease the synthesis temperature and improve the performance of La_9.33Si₆O₂₆ precursor powder that is closely related to the later electrolyte, this paper first made an attempt to prepare the La_9.33Si₆O₂₆ powder by molten salt method. The experimental parameters contained the ratio of reactants and salt, the synthesis temperature and sintering temperature were all discussed respectively by the comparison with the product powders by solid state method. The results proved that this attempt was feasible without the traditional disadvantages. Meanwhile, the synthesis conditions of molten salt method had strict requirement which was related to the mass ratio and the synthesis temperature. Beside, the increase of sintering temperature could play a positive role in the character of later ceramic, for example, the density, the grain plumpness, the performance and so on.There were two kinds of oxygen ion carriers in La_9.33Si₆O₂₆ electrolyte, free oxygen O (4) and gaps oxygen O (5). The more gaps oxygen are, the better the electric conduction is. For further study, impedance response, vibration mode and activate energy were all analyzed through the impedance spectroscopy of La_9.33Si₆O₂₆ electrolyte. In addition, the micro-model and equivalent circuit of La_9.33Si₆O₂₆ electrolyte were founded based on the theory of Maxwell model, Beekmans -Heyne model, shortcut between two-phase ceramic model and effective media model.The ultimate aim of this study was to operate oxy-apatite electrolyte with better performance. So in the last part, the doping or replacement of La bits were analyzed theoretically, which provided new thoughts and theory suggestion in the improvement of material performance for the future study.From the micro to macro, from synthesis to performance, from experiment to theory, this article made a comprehensive analysis of La_9.33Si₆O₂₆ electrolyte, which achieved basically the expected goal of this experiment.