Perovskite membranes by aqueous combustion synthesis: synthesis and properties

The objective of this work is to identify optimum synthesis, compacting and sintering conditions in order to achieve a pure phase fully densified La0. 8Sr0.2CrO3 (LSC) perovskite membrane. The aqueous combustion synthesis of L SC powders was investigated over a wide range of synthesis conditions by us ing the metal nitrates (oxidizer)-glycine (fuel) system. The powders were p ressed and sintered to create dense materials, which were characterized. It was shown that depending on fuel/oxidizer ratio, phi, the reaction can pro ceed in three different modes: Smoldering Combustion Synthesis (SCS), phi < 0.7, with maximum temperature, T-m < 600 degreesC; Volume Combustion Synth esis (VCS), 0.7 < phi < 1.2, 1150 degreesC < T-m < 1350 degreesC; Self-prop agating High-temperature Synthesis (SHS), 1.2 < phi < 1.6, 800 degreesC < T -m < 1100 degreesC. In turn, the characteristics of synthesized powders dep end on the combustion mode. The crystalline structure of as-synthesized pow ders becomes more defined as phi increases (amorphous for SCS; crystalline for VCS and SHS), The specific surface area decreases slightly when mode ch anges from SCS (similar to 25 m(2) g(-1)) to VCS (similar to 20 m(2) g(-1)) , however, it increases substantially under SHS conditions (up to 45 m(2) g (-1)). It was also shown that calcination is beneficial only for SCS powder s, while VCS and SHS powders may be sintered directly as synthesized, thus bypassing the time and energy consuming calcination step. The, measured oxy gen permeation values for the membranes are comparable with the best candid ate materials reported in the literature. (C) 2001 Elsevier Science B.V. Al l rights reserved.