Combustion Synthesis Of La_0.2Sr_0.8Cr_0.2Fe_0.8O₃—x

Abstract

The cubic perovskile Lao_0.2Sro_0.8Cr_0.2Fe_0.8O₃—x, a candidate material for oxygen separating membranes, was synthesized from a mixture of La₂O₃-SrO₂-Cr-Fe-NaClCO₄ by Self-propagating High-temperature Synthesis (SHS). SrFeO_3-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^°C for 5 hours produced very homogeneous Lao_0.2Sro_0.8Cr_0.2Fe_0.8O₃—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°C had a maximum electrical conductivity of 8.8 S.cm^-1 at 560^°C in a pure oxygen environment, and its oxygen permeability was 3.35 × 10^-9 mols^-1cm^-2 at 980^°C in an oxygen partial pressure gradient from ~4 × 10^-5 atm. to 0,2atm.

Keywords:

• Lao_0.2Sro_0.8Cr_0.2Fe_0.8O₃—x
• SHS; perovskite; reaction mechanism; microstructure
• electrical conductivity
• oxygen permeability

Additional information

Notes on contributors

D. LUSS

Corresponding author, e-mail: [email protected]