Preparation of Textured Polycrystalline La2NiO4+ δ Membranes and Their Oxygen-Transporting Properties

Abstract

Due to its high chemical and thermal stability in CO2 atmosphere and its anisotropic crystal structure, the Ruddlesden-Popper phase La2NiO4+δ has attracted considerable attention in the research field of oxygen-transporting membranes. The anisotropic properties of La2NiO4+δ can be exploited in textured polycrystalline membranes to control the oxygen diffusion through this material. To fabricate textured La2NiO4+δ membranes, powder mixtures consisting of fine-grained equiaxial La2NiO4+δ matrix particles and large plate-like La2NiO4+δ template particles in different mass ratios were uniaxially pressed and then sintered in air. For this purpose, the anisotropic template particles were synthesized by molten-flux method using NaOH as flux [1]. In the powder mixture, the La2NiO4+δ template particles can be aligned perpendicular or parallel to the pressing direction, depending on the geometry of the pressing tool and the sample preparation. After the sintering process, textured La2NiO4+δ membranes were obtained, which was verified by measuring X-ray diffraction patterns and pole figures. Further X-ray diffraction measurements together with the calculation of the Lotgering orientation factor revealed that an increasing content of the template particles in the ceramic materials leads to a stronger texturing. Scanning electron microscopy micrographs show some individual plate-like La2NiO4+δ grains well embedded in the matrix. Homogeneous distribution of lanthanum, nickel and oxygen in the ceramics was confirmed by energy-dispersive X-ray spectroscopy. Finally, the influence of the template particle content in the La2NiO4+δ membranes on the oxygen permeation performance is discussed. [1] Escobar Cano, G.; Brinkmann, Y.; Zhao, Z.; Kißling, P.A.; Feldhoff, A. Sol–Gel-Process-Based Molten-Flux Synthesis of Plate-like La2NiO4+ δ Particles. Crystals 2022, 12, 1346. https://doi.org/10.3390/cryst12101346