Mechanical properties and failure behavior of unidirectional porous ceramics

Abstract

We show that the honeycomb out-of-plane model derived by Gibson and Ashby can be applied to describe the compressive behavior of unidirectional porous materials. Ice-templating allowed us to process samples with accurate control over pore volume, size, and morphology. These samples allowed us to evaluate the effect of this microstructural variations on the compressive strength in a porosity range of 45–80%. The maximum strength of 286 MPa was achieved in the least porous ice-templated sample (P(%) = 49.9), with the smallest pore size (3 μm). We found that the out-of-plane model only holds when buckling is the dominant failure mode, as should be expected. Furthermore, we controlled total pore volume by adjusting solids loading and sintering temperature. This strategy allows us to independently control macroporosity and densification of walls, and the compressive strength of ice-templated materials is exclusively dependent on total pore volume.

Gradient-Hierarchic-Aligned Porosity SiOC Ceramics

“…These pores are probably resulting from small bubbles that were entrapped during the solidification of the ceramic suspension, and represent a unique feature, as they create an effective path for permeation and diffusion of fluids also in the radial direction. Compared to other aligned porosity ceramics, the average diameter of channels of SiOC samples (0.59–1.25 mm) are clearly higher than of those processed by ice-templating (2.9–19 μm)3132 and by inclusion of polymeric fibers as sacrificial fillers (9–43 μm)832. On the other hand, channel size distributions in samples L1–L3 were much more homogeneous than those observed in biomorphic SiC prepared from hardwood precursors, where the vascular transportation system in the tissue creates naturally a bimodal diameter distribution of large vessels surrounded by very small channels32333435.…”

Gamma-irradiation-induced micro-structural variations in flame-retardant polyurethane foam using synchrotron X-ray micro-tomography

“…For example, higher sphericity leads to improved toughness in the bio-ceramic (Veljović et al, 2011). Permeability has also been reported to have a dependence of pore shape and orientation (Seuba et al, 2016). Similarly, variation in sphericity of pores also affects piezoelectric and dielectric properties of materials (Zeng et al, 2007).…”

Fabrication of ice-templated tubes by rotational freezing: Microstructure, strength, and permeability

“…The system was left under rotational freezing for a minimum of 5 minutes. The next steps were similar to the regular ice-templating process and detailed elsewhere [17]: demoulding, freeze-drying (Free Zone 2.5 Plus, Labconco, Kansas City, Missouri, USA), and sintering. Tubular specimens were sintered in air at 1400 • C for 3 h with a heating and cooling rate of 5 • C/min.…”