Effect of microstructure and thickness on oxygen permeation of La₂NiO_4+δ membranes

Lanthanum nickelate, La₂NiO₄ (LNO) powders were synthesized by a sol–gel method. These powders were compacted to obtain LNO membranes. The grain size effect on the permeation of LNO membranes was examined by variation of the sintering time of membranes from 5 to 48 h. The microstructure of membranes was analyzed using scanning electron microscopy (SEM) and the grain size was determined using a statistical approach. The grain size was observed to increase with the dwell time following a power law. The permeation of the membranes increased with increasing dwell time up to 15 h. For dwell time of 48 h, the permeability decreased sharply. The oxygen permeation of LNO membranes was also measured as a function of membrane thickness in the same temperature range. With the aim of looking at the effects of bulk diffusion and kinetics of surface-exchange, the membrane thickness was varied from 0.8 to 1.3 mm. The characteristic critical thickness (L_C) of the membrane, at which the surface exchange kinetics becomes dominant, was found to be 1.0 mm in the temperature range of 700–1000 °C.