Microstructural characteristics and elastic modulus of porous solids

Porous La0.6Sr0.4Co0.2Fe0.8O3−δ ceramic films with different porosities were fabricated by constrained sintering on dense substrates of Gd-doped ceria at 900-1200 °C. The actual digital three dimensional microstructures of the as-sintered films were reconstructed using focused ion beam/scanning electron microscope tomography and their elastic moduli were calculated using finite element modelling based on the reconstructed microstructures. The calculated moduli were found to be in good agreement with experimental results. Porosity was found to be the primary factor influencing the elastic modulus. In order to explore the influence of microstructural features other than porosity the real microstructures, and artificial microstructures based on spherical mono-size particles, were coarsened numerically at constant porosity using a cellular automaton method. The simulation results showed that in the initial stages of sintering, when interparticle necks are small, the modulus increases with the neck size. However, as the coarsening increases further, the modulus becomes insensitive to the details of the microstructure and only depends on porosity. The results also show that simulation gives inaccurate results if the ratio of characteristic length of the simulated volume to the characteristic length of the microstructure is too small (less than approximately a factor of 8).