Effect of Macropore Anisotropy on the Mechanical Response of Hierarchically Porous Ceramics

Abstract

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

Gas permeability of ice-templated, unidirectional porous ceramics

“…As extensively reported [20–24], porous ceramics processed by ice-templating usually exhibited a bimodal pore distribution. In both samples, larger pore size corresponds to the open unidirectional porosity created by the sublimation of the ice crystals and, thus mainly controlled by the solids loading.…”

“…This behavior might be caused by the larger connectivity among the walls that prevents the structure from buckling and shearing stresses. [24] Unfortunately, this pore structure also exhibits the lowest permeability. On the other hand, ice-templated samples frozen at slow cooling rate, either lamellar or honeycomb morphology, exhibited both a higher compressive strength and permeability than the samples prepared by pore formers.…”

Synthesis, structure and mechanical properties of ice-templated tungsten foams

“…4) and by the interaction of neighboring colonies of varying orientations in the radial plane. 48 Additionally, wall fracture is a likely deformation mechanism, especially at ambient temperature below the BDTT of tungsten.…”

The effect of gelation on statically and dynamically freeze‐cast structures

“…A too large magnification results in very few channels per image, while a too small magnification results in closed pores. The lamellar channels of freeze‐cast structures have previously been shown to be arranged in domains of varying orientations and angles relative to the freezing direction, as is also evident from the perpendicular cross sections in Figure , resulting in what appears to be closed pores in the parallel cross‐sectional images.…”

“…The approach of implementing static and dynamic freezing profiles and gelation prior to freeze‐casting is carried out on La 0.66 Ca 0.33−x Sr x Mn 1.05 O 3 (LCSM) ceramic powders. Ceramic processing—and thus freeze‐casting—of LCSM powders is similar to that of LSM powders used by Lichtner et al, and has previously been reported by the authors of this paper . In addition, LCSM is magnetocaloric, meaning that the temperature of the material will change if a magnetic field is applied .…”