Carbonation passivation layer of scandium loaded BSCF perovskite

Abstract

Abstract This work investigates the improved CO 2 stability of the partial substitution of scandium (Sc) in the B-site of perovskite ceramic materials thus forming a compound also containing barium (Ba), strontium (Sr), cobalt (Co) and iron (Fe) as Ba 0.5 Sr 0.5 (Co 0.8 Fe 0.2 ) 1−x Sc x O 3-δ . The concentration of Sc in the B-site was varied between 0 and 40 mol%. It was found that perovskite cubic structure was maintained by the substitution with Sc. Further, the cubic cell lattice parameter increased as a function of Sc. However, XRD parameters showed that not all Sc was fully incorporated into the crystal structure of the perovskite, as Sc 2 O 3 phase was also detected. Exposure of as-prepared powders to CO 2 gases resulted in the carbonation reactions occurring at temperatures about 100 °C below those observed for unstable pure BSCF (i.e. no Sc) perovskite. This was attributed to the catalytic effect of Sc, which promoted the carbonation reaction of BSCF-Sc. Subsequently, discs were prepared and exposed to CO 2 gases at 800 °C. The analysis of the discs’ surface showed that the perovskite cubic structure retained 96% of its original values upon CO 2 exposure for the samples loaded with 40 mol% Sc, which then reduced to 32% to samples containing 5 mol% Sc. These results proved to be counterintuitive, as Sc promoted the carbonation reaction at lower temperatures for powders, though enhanced the stability of disc exposed to CO 2 atmosphere. Further analyses of the discs by scanning electron microscopy revealed images containing a rich carbon layer, as a passivation carbonation layer, which protected the remainder of the bulk perovskite structure in the disc.