Study of microstructure modification on La0.7Sr0.3Co0.2Fe0.8O3-δ (LSCF 7328) asymmetric flat membrane

Abstract

The LSCF 7328 (La_0.7Sr_0.3Co_0.2Fe_0.8O_3-δ) asymmetric flat membranes were successfully prepared via a phase-inversion method followed by sintering at 1200 °C. In this study, a variety of poly(ethylene glycol) (PEGs) as the pore-forming agent, with  3 wt% composition and a wide ranges of molecular weight (Mw) (200 to 8000 Da) were used to tests its’ effect to the properties of LSCF  membranes. The results show that the PEGs, as additives, were able to modify the pore morphology and mechanical properties of the LSCF 7328 membrane. The morphological evidence from SEM images showed that the LSCF membranes have an asymmetric configuration, comprised of sponge-like and finger-like pores which are integrated with a dense layer. The variation in average pore size is clearly seen, starting from 13.00 to 135.33 μm, following the increase in PEGs molecular weight. The LSCF membranes which were prepared using PEG additive have higher hardness (1.2 – 13.6 Hv) than the membrane with no PEG  (0.2 Hv). In contrast, the porosity and pore volume of the membranes decrease with the increase of PEGs molecular weight. The decrease might be due to the formation of various closed macro-voids as the molecular weight of PEGs increases. Furthermore, the thermal expansion coefficient of the membrane with different PEGs molecular weight (ie. 400, 600, 4000 and 6000) Da posses no significant different, i.e. around 16 x 10^-6 °C^-1, although the membrane showed different morphology and mechanical properties.