**3. Methods and techniques for fabrication of porous ceramics**

In recent years, with the development of new needs and technologies, there was an increasing request for porous ceramic. Hence their fabrication methods are being widely studied and the subject of inclusive research. Partial sintering of ceramic powder compacts is one of the methods used to fabricate porous ceramic bodies, but this method mostly yields low porosities (less than 50%) and few options to significantly alter the pore size distribution [12]. Honeycombs also with well-defined unidirectional channels can be paste extruded from a variety of ceramic powders and more complex three-dimensional porous ceramics can be made by rapid prototyping techniques, such as 3D printing. Apart from these methods, it is possible to distinguish many different types of fabrication routes (**Figure 2**) for producing

Closed pores can contain a composition of gases that is independent of the environment [8]. When porosity is determined for any ceramic body, porosity can be distinguished for several types such as open (accessible from the outside) porosity (**Figure 1**) and closed porosity. Where open porosity can be further categorized into open dead-end pores and open pore channels. The presence of porosity depends on the specific application, so a more open porosity may be needed to be permeable such as a closed porosity or filters/membrane such as thermal insulator may be wanted. The sum of the open and closed porosity is mentioned to as the total porosity [9]. If the fractional porosity of a material is relatively low, then the closed porosity will dominate; at the fractional porosity increases, the open porosity level increases. The porous ceramics have been classified on the basis of nature of porosity, volume fraction and size of these pores [10]. The nature of porosity in natural ceramics depend on their genesis while in synthetic ceramics, it depends on their manufacturing and generally, it can be controlled. The pore size of these materials can be classified into three grades depending on the pore diameter: microporous (less than 2 nm), mesoporous (between 2 and 50 nm) and macroporous (more than 50 nm). The pore size distributions are usually measured by mercury intrusion porosimetry technique. The pore size distribution of the closed porosity is not determinable using this technique, but may occur, for example, by optical and electronic examination of a polished cross section. The pore size distribution represents the pore volume

**Figure 1.** Magnification of a single open pore in the alumina ceramic body.

2 Recent Advances in Porous Ceramics

in function of pore size and commonly is given as percentage or a derivative [11].

In recent years, with the development of new needs and technologies, there was an increasing request for porous ceramic. Hence their fabrication methods are being widely studied and the subject of inclusive research. Partial sintering of ceramic powder compacts is one of the methods used to fabricate porous ceramic bodies, but this method mostly yields low porosities (less than 50%) and few options to significantly alter the pore size distribution [12].

**3. Methods and techniques for fabrication of porous ceramics**

**Figure 2.** Schematic of porous ceramic processing methods: (a) partial sintering, (b) sacrificial fugitives, (c) replica templates, and (d) direct foaming [1].

porous ceramics such as the replica method, the sacrificial phase technique, direct foaming methods, paste extrusion and most recently developed rapid prototyping technique [13].

the growth of the neck touching particles by surface and volume diffusion can significantly increase the mechanical properties with minimal increase in density. The microstructure in porous ceramics can be controlled not only by adjusting the particle size and shape of the

Introductory Chapter: A Brief Introduction to Porous Ceramic

http://dx.doi.org/10.5772/intechopen.74747

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Classification of pores is one of the basic requirements of inclusive characterization of porous ceramics (**Figure 3**). There are different classes of pores described porous ceramic in the literature,

initial raw powders, but also through the process of sintering.

**6. Classification of porous ceramic**

**Figure 3.** Schematic of classification of porous ceramic [1].

The fields of application and specific forms of porous ceramics are wide and varied according to their manufacturing processes [14]. Some of its useful applications are in the manufacture of filter. As these porous structures are used to filter high-pressure gas at high temperature and are used as an aid to remove the contaminants. In the field of petroleum treatment, porous ceramics are used as a substrate for catalysts in the process of filtration. They are also used in recovering hydrogen from the crude oil. Other applications are thermal insulators in filter membrane to separate metal impurities from molten metals such as steel, iron and aluminum. Today, porous ceramic structures prepared from different materials based on their application are used widely in biomedical field. For example, porous calcium phosphate materials can be used to replicate bone architecture and allow the growth of osseous tissue on an artificial substrate, thereby forming an artificial living bone structure. There porous hydroxyapatite can be used to replace bone and also as a drug delivery system [15].
