Carbonation passivation layer of scandium loaded BSCF perovskite

This work investigates the improved CO2 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 Ba0.5Sr0.5(Co0.8Fe0.2)(1-x)ScxO3-delta. 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 Sc2O3 phase was also detected. Exposure of as-prepared powders to CO2 gases resulted in the carbonation reactions occurring at temperatures about 100 degrees 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 CO2 gases at 800 degrees C. The analysis of the discs surface showed that the perovskite cubic structure retained 96% of its original values upon CO2 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 CO2 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