Paper detail

Mechanical Properties of La0.6Sr0.4Co0.2Fe0.8O3-d Fuel Cell Electrodes

LSCF is a promising candidate for the cathode in SOFCs. Understanding the microstructural characteristics is crucial to its application because they predominately determine the performance and durability of the porous cathodes and hence of the SOFCs. To date little work has been reported on its mechanical properties and their correlation with the 3D microstructures. The main purpose of this research was to study the mechanical properties of both films and bulk samples, and to evaluate the effect of microstructural parameters, by means of both experimental and numerical methods. Room-temperature mechanical properties were investigated by nanoindentation. The elastic modulus of the bulk samples was found to increase from 33.8 to 174.3 GPa and hardness from 0.64 to 5.32 GPa as the porosity decreased from 0.45 to 0.05 after sintering at 900 to 1200C. It was shown that reliable measurements of the true properties of the films were obtained provided that the effects from both surface roughness and substrate were minimised to neglected levels within a certain range of indentation depth to film thickness ratio. The fracture toughnesses of bulk LSCF were determined to increase from 0.51 to 0.99 MPam0.5. The microstructures of films were characterised using FIB-SEM slice and view technique and the actual 3D microstructure models of the porous films were reconstructed based on the tomographic data obtained. Finite element modelling of the elastic modulus agreed well with the nanoindentation results. The 3D microstructures were numerically modified at constant porosity using cellular automaton method, so that the influence on elastic modulus of factors other than porosity could be evaluated. It was found that the heterogeneity of the pore structure has a significant influence on the elastic properties computed using mechanical simulation.