Freeze casting of porous materials: review of critical factors in microstructure evolution

Abstract

Freeze casting is a promising technique to fabricate porous materials with complex pore shapes and component geometries. This review is aimed to elaborate the fundamental principles of the porous microstructure evolution and critical factors that influence the fundamental physics involved in freeze casting of particulate suspensions. The discussion separately analyses homogeneous and directional freeze casting for both aqueous and non-aqueous systems. The effects of additives, freezing conditions, suspension solids loading and particle size on pore shape, size and morphology evolution are discussed. Special techniques based on modified freeze casting, such as freeze tape casting, double sided freeze casting and field directed freeze casting, are also included.

Biomimetic superelastic graphene-based cellular monoliths

“…We explored a versatile, readily accessible and inexpensive solutionphase materials shaping technique, namely freeze casting, to explore the possibility of assembling graphene sheets into corklike monoliths. Previous studies have demonstrated that when an aqueous suspension of nanoparticles is frozen, phase separation can result in the rejection of solid nanoparticles from the forming ice, which are then accumulated between the growing ice crystals 28,29 . If the fraction of nanoparticles is higher than the percolation threshold, the entrapped particles can form a continuous 3D network.…”

“…Freeze casting has been successfully adopted to synthesize a variety of porous ceramic, metallic, polymeric and composite materials, including carbon nanotubes or graphene-based polymer composites 18,[30][31][32][33] . Although previous research on freeze casting has been centred on polymers and spherical particles 28,29 , we were particularly interested in studying how 2D graphene sheets interact with anisotropic ice crystal growth without the interference of other polymer or surfactant additives. In this work, GO, which can be readily produced from graphite in large quantities 2 , was chosen as a precursor to synthesize graphene-based monoliths.…”

“…1d, upon freezing, the partially reduced GO sheets are rejected from the forming ice and entrapped between neighbouring ice crystals to form a continuous network whose structure is determined by ice crystal template. As the growth rate of ice crystals is highly anisotropic (varied by 2-3 orders of magnitude along different growing directions 28,29 ), the 2D pr-GO sheets are forced to align along the moving solidification front, while they are concentrated and then squeezed at the crystal boundaries, yielding a highly ordered layered assembly. Furthermore, because the p-p attraction between pr-GO sheets is enhanced as a result of partial reduction, the as-formed network was found to be quite stable and could maintain its structural integrity upon thawing.…”

Biomimetic Materials by Freeze Casting

“…Freeze casting is a relatively simple, inexpensive, and adaptable technique to fabricate bulk porous scaffolds and hybrid composites. Deville,14 Gutierrez et al, 15 Qian and Zhang, 16 and Li et al 17 provide excellent reviews of general freeze casting topics, including the processing principles, materials, structures, properties, and applications. This article focuses on freeze casting as it relates to different biomimetic materials and processing modifications inspired by nature.…”

“…[14][15][16][17] Figure 1 shows the basic processing steps involved in freeze casting porous ceramic scaffolds and hybrid ceramic-polymer composites-the main focus of this article. First, a liquid slurry containing ceramic powders and a freezing vehicle (e.g., water) is mixed with a dispersant (e.g., surfactant) and binder (e.g., long-chain polymer), which aid in colloid dispersion and green body integrity, respectively (Fig.…”