Porous ceramics mimicking nature—preparation and properties of microstructures with unidirectionally oriented pores

Abstract

Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures.

Magnetic Biomorphic BaFe12-xCrxO19 Ceramics with Multilayer Wall Structure Made from Spruce Templates

“…Many other ceramics such as TiO2 ceramics (Qian et al 2015), Al2O3 ceramics (Liu et al 2006), and Sr3Co2Fe24O41 ceramics (Pullar et al 2015) have been made since then. These materials feature excellent strength at a low density and high stiffness and elasticity (Okada et al 2011). The morphology of such bio-organic material consists of a hierarchical system, ranging in size from millimeters (growth ring patterns in wood) to microns (cellulose fibres, wood cells).…”

Ice templating of ZrB2–SiC systems

“…Ice templating is a versatile and environmentally friendly forming technique that enables the achievement of complex anisotropic porous microstructures [7][8][9][10]. It has been widely used for many porous ceramics such as alumina [7,8], zirconia or alumina-zirconia [11,12], titanium dioxide [13], silica [14] and hydroxyapatite [15].…”

“…Conventional sintering is then adopted to consolidate the walls of the porous ceramic structure [7,8]. The final microstructure and the properties are determined by the ice crystal growth direction during freezing [7][8][9][10]. Unidirectional channel-like (lamellar) porosity is obtained in the case of unidirectional freezing.…”

Study of thermal properties of mullite porous materials

“…The properties and applications of porous ceramics depend on the nature of the materials, pore shape, porosity, and pore size. Furthermore, some properties of porous ceramics, such as mechanical strength, are closely related to the pore morphology and skeleton structure, which are determined mainly by the processing technique applied [1][2][3][4].…”