Processing and characterisation of porous lanthanum strontium manganite--role of porosity on electrical conductivity and morphology

摘要

Lanthanum strontium manganite (La_(0.84)Sr_(0.16)MnO_3 - LSM) powder was prepared by combustion of the gel formed by oven drying the aqueous metal nitrates solution and citric acid on a laboratory heater. The chemical and phase purity of the as formed precursor were confirmed by thermogravimetry-differential thermal analysis (TG-DTA) and X-ray diffraction. The morphological feature and crystallinity of the as formed and calcined powders have been studied by TEM. The powder calcined at 1300 deg C was used, and the temperature of onset of sintering in compacts was evaluated. Compacts sintered at 1400 deg C exhibited only 7 percent open porosity. Bodies with porosity in the range of 10 to 45 percent were prepared by incorporation of varying amounts (3 to 21 percent) of petroleum coke as pore former in the compact. The heat treatment schedule to remove petroleum coke from the green bodies was fixed from TGA of the petroleum coke. Porous specimens with 45 percent open porosity formed by using 21 wt- percent petroleum coke at a sintering temperature of 1400 deg C. The thermal expansion coefficient, electrical conductivity and SEM microstructure of these sintered porous specimens were evaluated and these properties correlated.