Freeze casting, also known as ice templating, is a versatile technique extensively used for

creating well-controlled porous materials from various substances like ceramics, metals,

polymers, and carbon nanomaterials [1]. This method involves preparation of slurry then

directionally freezing and sublimating an aqueous slurry to fabricate porous materials with

aligned microstructures [2]. By adjusting freezing conditions, the porosity and pore structure of

the resulting material can be controlled [3]. Freeze casting has been applied to create porous

ceramics with directional or homogeneous microstructures, such as dense, cellular, and lamellar

microstructures [4]. The technique allows for the fabrication of porous structures with

controllable porosity and pore geometries [5].

Figure 1: The four processing steps of freeze-casting: slurry preparation, solidification, sublimation and

sintering.

In the context of using freeze casting in bricks, the method can be adapted to tailor the

microstructure of the final product, offering the ability to control over multiple scale

architectures [6]. By adjusting processing parameters, freeze casting can produce porous silica

with controllable and tunable porosity, showcasing the adaptability of the technique [7].
Moreover, freeze casting has been considered a powerful tool for creating nacre-mimetic

composites, indicating its potential for producing complex structures [6]. In summary, freeze

casting is a cost-effective and scalable method for fabricating porous materials with tailored

microstructures. By leveraging this technique, it is feasible to create bricks with controlled

porosity and specific microstructural features, making it a promising approach for innovative

construction materials.

[1] , "Freeze casting: from low‐dimensional building blocks to aligned porous structures—a review of
novel materials, methods, and applications", advanced materials, vol. 32, no. 17, 2020.
https://doi.org/10.1002/adma.201907176

[2] , "Ice-templated porous alumina structures", acta materialia, vol. 55, no. 6, p. 1965-1974, 2007.
https://doi.org/10.1016/j.actamat.2006.11.003

[3] , "Freeze casting for assembling bioinspired structural materials", advanced materials, vol. 29, no. 45,
2017. https://doi.org/10.1002/adma.201703155

[4] , "Freeze‐casting of surface‐magnetized iron(ii,iii) oxide particles in a uniform static magnetic field
generated by a helmholtz coil", advanced engineering materials, vol. 21, no. 3, 2019.
https://doi.org/10.1002/adem.201801092

[5] , "Inorganic cryogels for energy saving and conversion", journal of electroceramics, vol. 23, no. 2-4,
p. 452-461, 2008. https://doi.org/10.1007/s10832-008-9488-0
[6] , "Creating biomimetic central-radial skeletons with efficient mass adsorption and transport", acs
applied materials & interfaces, vol. 15, no. 41, p. 48551-48563, 2023.
https://doi.org/10.1021/acsami.3c10938

[7] , "Radial-concentric freeze casting inspired by porcupine fish spines", ceramics, vol. 2, no. 1, p. 161-
179, 2019. https://doi.org/10.3390/ceramics2010015

[8] Figure 2-7 -Steps of freeze-casting: slurry preparation,. . . (n.d.). ResearchGate.

https://www.researchgate.net/figure/7-Steps-of-freeze-casting-slurry-preparation-

solidification-sublimation-and_fig8_332370459

Slurry Preparation:

In this step, a slurry is prepared by mixing a ceramic powder with a liquid solvent or dispersant. The
ceramic powder serves as the primary material for the final product, while the liquid solvent or
dispersant helps to create a homogeneous mixture and provides the fluid medium for subsequent
processing steps.

The composition of the slurry, including the type and size distribution of ceramic particles and the
concentration of the dispersant, is carefully controlled to achieve the desired properties in the final
product.

Solidification:

Once the slurry is prepared, it is subjected to a controlled cooling process to induce solidification. During
solidification, the liquid solvent or dispersant freezes, forming ice crystals within the slurry.

The formation of ice crystals results in the creation of a porous structure, with ceramic particles
distributed within the ice matrix. The arrangement and morphology of the pores are influenced by
factors such as cooling rate, slurry composition, and the presence of additives.

Sublimation:

After solidification, the frozen slurry undergoes a sublimation process to remove the ice phase and leave
behind a porous ceramic scaffold. Sublimation involves the direct conversion of ice from the solid phase
to the vapor phase, bypassing the liquid phase.

The frozen slurry is typically placed in a controlled environment with low pressure and elevated
temperature, which allows the ice to sublime while minimizing the risk of melting. As the ice sublimes, it
leaves behind interconnected pores that define the final microstructure of the porous material.
Sintering:

The final step in the freeze-casting process is sintering, which involves heating the porous ceramic
scaffold to high temperatures to densify the structure and enhance its mechanical properties.

During sintering, ceramic particles undergo a process of solid-state diffusion and grain boundary
migration, leading to the consolidation of the material and the elimination of residual porosity. The
specific sintering conditions, including temperature, time, and atmosphere, are optimized to achieve the
desired microstructure and properties in the final product.

Figure 2: (a) porous alumina using an hypoeutectic camphor/naphthalene as a solvent[2] (b)

porous alumina using water as a solvent[3] (c) porous silicon carbide using polycarbosilane as

a precursor and camphene as a solvent[4] (d) porous alumina using camphene as a solvent[5].

[2] Araki, K., & Halloran, J. W. (2004). Room‐Temperature Freeze Casting for Ceramics with

Nonaqueous Sublimable Vehicles in the Naphthalene–Camphor Eutectic System.

 Journal of the American Ceramic Society, 87(11), 2014–2019.

https://doi.org/10.1111/j.1151-2916.2004.tb06353.x

[3] Deville, S., Saiz, E., & Tomsia, A. P. (2007). Ice-templated porous alumina structures. Acta

Materialia, 55(6), 1965–1974. https://doi.org/10.1016/j.actamat.2006.11.003

[4] Byung-Ho Yoon GENOSS Hae-Hyoung Lee Dankook University, Cheonan, South Korea H.-

J. Kim Korea Institute of Science and Technology Young-Hag Koh. (2007). Highly

Aligned Porous Silicon Carbide Ceramics by Freezing Polycarbosilane/Camphene

Solution. Journal of the American Ceramic Society.

[5] Araki, K., & Halloran, J. W. (2005). Porous Ceramic Bodies with Interconnected Pore

Channels by a Novel Freeze Casting Technique. Journal of the American Ceramic

Society, 88(5), 1108–1114. https://doi.org/10.1111/j.1551-2916.2005.00176.x

[7] Figure 4: Solidified camphene dendrites, leading to the formation of a dendritic porous

structure.

[6]Sylvain Deville. (n.d.). Freeze-Casting of Porous Ceramics: A Review of Current

Achievements and Issues.
[7]Deville, S. (2008). Freeze‐Casting of Porous Ceramics: A review of current achievements and

issues. Advanced Engineering Materials (Print), 10(3), 155–169.

https://doi.org/10.1002/adem.200700270