Structure and Relative Thermal Stability of Mesoporous ( La, Sr) MnO3 Powders Prepared Using Evaporation-Induced Self-Assembly Methods.

LaMnO₃ and ( La, Sr) MnO₃ were prepared as mesoporous powders using sol-gel methods that incorporated evaporation-induced self-assembly of surfactants as structure-directing agents. The precursor and surfactant concentrations, surfactant character (mainly molecular weight), aging humidity, and annealing temperature were all found to influence the specific surface area of the powders, which were maximized at 50 and 46 m²/g for LaMnO₃ and ( La, Sr) MnO₃, respectively. Increased metal nitrate contents in the initial sol composition and increased relative humidity during aging led to products having increased specific surface areas owing to increased mesoporosity. The lower molecular weight surfactant CTAB was found to generate higher specific surface area powders than those generated using the larger molecular weight nonionic surfactants P-123 and F-127. On the other hand, the relative thermal stability of the mesoporous powders, annealed at 750°C for 100 h, increased with the molecular weight of surfactant. Mesoporous powders having promising thermal stability and surface areas in the 20-25 m²/g range were easily obtainable using P-123 and F-127, indicating that high surface area electrocatalysts with mesoporous microstructures can be prepared for high temperature applications. [ABSTRACT FROM AUTHOR]