Thermodynamic assessment of the chemical stability of (La0.8Sr0.2)0.98CrxFe1 − xO3 ± δ under oxygen transport membrane fabrication and operation conditions

Abstract

A comprehensive thermodynamic study by applying the CALculation of Phase Diagram (CALPHAD) approach on (La0.8Sr0.2)0.98CrxFe1−xO3±δ (x=0.3, 0.5, 0.7) (LSCrF) has been carried out to investigate the effect of atmosphere, temperature, and B-site dopant concentration on phase stability, solid and liquid phase formation, and microstructural evolution in LSCrF. The simulation results for the chemical stability of LSCrF, exposed to oxygen partial pressure (PO2) from 0.21 to 10−10atm and temperature from 1000 to 1400°C, reveal the formation of solid corundum, spinel, La2SrFe2O7, and the liquid phase. The simulations also show the chemical reactions of solid secondary phases with the liquid and perovskites under both equilibrium cooling and fast cooling conditions. The phase stabilities of the LSCrF samples under oxygen transport membrane (OTM) sintering and operation conditions are predicted. The study provides guidance on the densification enhancement of the LSCrF bulk materials during the sintering process through the control of the liquid phase concentration and the perovskite phase separation. In addition, the concerns of the release of the genotoxic carcinogens, i.e. chromium hexavalent (Cr6+) gas species from LSCrF to the environment under the sintering and operation conditions are addressed for the first time.