Combustion synthesis of La0.2Sr0.8Cr0.2Fe0.8O3-x

The cubic perovskite La0.2Sr0.8Cr0.2Fe0.8O3-x, a candidate material for oxygen separating membranes, was synthesized from a mixture of La2O3-SrO2-Cr- Fe-NaClO4 by Self-propagating High-temperature Synthesis (SHS). SrFeO3-x and LaCrO3 were the main intermediates and the final composition and morphology was formed by interaction between them. The final structure was a solid solution of Fe and Sr rich oxides and La and Cr rich oxides. Decreasing the reactant particle size increased the homogeneity of the SHS product and increased the velocity of the propagating combustion front. Calcination of the SHS product at 1400 degrees C for 5 hours produced very homogeneous La0.2Sr0.8Cr0.2Fe0.8O3-x. The sinterability of powders made by SHS was better than those prepared by either GNP (glycine-nitrate process) or freeze-drying. A disc prepared from the SHS product by 10 hours calcination at 1400 degrees C had a maximum electrical conductivity of 8.8 S.cm(-1) at 560 degrees C in a pure oxygen environment, and its oxygen permeability was 3.35 x 10(-9) mol.s(-1).cm(-2) at 980 degrees C in an oxygen partial pressure gradient from similar to 4 x 10(-5) atm. to 0.2 atm.