International audiencePorous ceramics are commonly used in electrochemical, catalytic, biological, and filtration processes, but in many cases, improvements to their designed performance come at the expense of their mechanical properties. By controlling the pore morphology and orientation, it is possible to mitigate some mechanical losses while maintaining adequately porous microstructures. Hierarchically, porous ceramics with similar porosities but differing macropore arrangements were synthesized using both freeze casting and slip casting, and then tested in compression to study the effects of macropore morphology and orientation on mechanical behavior. The mechanical properties of the anisotropic structures were a strong function of the orientation of the macropores relative to the applied stress. The properties of the isotropic hierarchical porous structures were in between the two orthotropic directions of the anisotropic porous ceramics. For the freeze-cast samples, the compressive strength was a function of the macropore size. The experimental results are rationalized using detailed microstructural analysis

Aqueous dispersions of lanthanum strontium manganite (LSM) and yttria‐stabilized zirconia (YSZ) particles were controllably freeze‐cast and then partially sintered resulting in anisotropic, hierarchically porous ceramics for Solid Oxide Fuel Cell (SOFC) cathodes. The resulting microstructures have aligned pores with a characteristic spacing (λ) between pore centers. The effect of freezing rate, slurry viscosity, and solid loading on solidification velocity and resultant microstructures was explored. Varying these parameters resulted in samples with a range of independently controllable and reproducible microstructures. Homogenous dispersion of LSM and YSZ in the freeze‐cast structures was confirmed through elemental mapping. Freezing rate was found to have a significant effect on λ while solid loading affected overall porosity and ceramic wall‐ to‐pore size ratio but had only a small influence on λ. Viscosity was found to have a complex albeit small impact on λ but a significant effect on particle dispersion and colloid stability.

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Quasi-static discrete element method (DEM) simulations are used to model the elastic behavior of porous ceramic obtained by partial sintering. The porous ceramic is modeled as a set of particles bonded by solid necks. A new approach introducing bond interactions is proposed to allow, in particular, the correct prediction of Poisson's ratio. It leads to a simple formulation that takes into account the deformation of a particle subjected to multiple contact forces, without the complexity of a full finite element method (FEM) analysis. The advantage of this new formulation is demonstrated, first by a comparison with FEM calculations on a simple test case, and then by a comparison with experimental results and other models from the literature on random aggregates of partially sintered particles. The proposed model with bond interactions correctly predicts Poisson's ratio of porous ceramics and improves the accuracy of Young's modulus when compared with the DEM model without bond interactions.

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