Microstructure and oxygen permeability of a La0.6Sr0.4Fe0.9Ga0.1O3−δ membrane containing magnesia as dispersed second phase particles

Dense mixed-conducting membranes of La0.6Sr0.4Fe0.9Ga0.1O3−δ (LSFG) with various contents of MgO as second phase particles were prepared to evaluate the influence of magnesia inclusions on LSFG stoechiometry, microstructure and oxygen permeation. XRD and EDS investigations on sintered pellets revealed that magnesia inclusions were quite inert with the LSFG matrix phase, the composition of which remained identical whatever the magnesia content. LSFG pure phase material was synthesized through a solid-state route and sintered between 1250 and 1350 °C. Sintering temperature strongly affected microstructure of the LSFG membrane since rapid grain growth and decreasing density were observed when temperature increased. Small amounts of fine particles of magnesia, from 2 to 10 vol%, were found to significantly reduce grain size of sintered samples and made it possible to obtain a high density on a large sintering temperature range. Average grain size experimental data of LSFG in function of the amount of second phase magnesia were also compared with numerical models from literature. Oxygen permeation rates of pure LSFG and composite LSFG/MgO dense membranes were measured in an air/argon gradient, in a temperature range from 825 to 975 °C and results were discussed to explain the flux improvement of composite membranes.