**10. Porous ceramics and catalyst carriers**

but they are difficult to give a consistent general classification of porous ceramics including catalyst carriers in various chemical processes, electrolyte carriers in fuel elements, adsorbents. As well as filtration of liquids, hot gases, melted metals and alloys, membranes for separation and purification of gas and liquids etc. The purpose of these classifications is to organize pores in classes by grouping them based on their common characteristics like structure, size, shape, accessibility etc. Therefore, porous ceramics can be classified according to the different characteristic attributes such as chemical composition of initial ceramic materials, porosity percentage, physical state of these products, refractoriness correlated to service temperatures, destination

Ceramic foams are porous brittle materials with closed, open-celled structures or partially interconnected porosity [17]. Ceramic foams are a special class of porous materials included of large voids with linear dimensions in the range between 10 and 5 mm. Foams are also called cellular ceramic materials because their structure can be represented by a lattice of a repeatable unit called "cell". They are fabricated from a broad kind of ceramic materials; specifically both oxide and non-oxide, which includes pure oxides, aluminosilicates and carbides that are being considered for the whole range of possible applications. These include filtration, catalysis, impact-absorbing structures, thermal insulation, performs for metal-ceramic composites, biomechanical implants, high specific strength materials and high efficiency combustion burners. The ceramic foams have been produced in a variety of materials with different shape sizes, densities and degree of interconnectivity. Foams or cellular are usually made with the density between 10 and 40% of theoretical and the pore sizes less than 1 mm. Ceramic foams can be made with a variety of microstructures with controlled properties through several versatile and simple methods, such as direct foaming, replica, sacrificial template techniques [5].

**8. Porous ceramics using additive manufacturing techniques**

because of the good thermal properties and relative strength of ceramic materials.

The manufacturing of complex porous ceramic parts with defined microstructure is a challenge today [18]. Concerning this issue, additive manufacturing technology is a promising alternative to conventional manufacturing procedures. Various additive manufacturing technologies like laminated object manufacturing (LOM), stereolithography (SLA), fused deposition modeling (FDM), selective laser sintering (SLS) and three-dimensional printing (3D printing) have already been used to fabricate different porous ceramic shapes [19]. One of the fastest and most efficient technologies is 3D printing. The introduction of 3D printing technology into the porous ceramic industry provides greater speed and flexibility, eliminates tool constraints, needs only low cost investment, and enables the sustainability of the additive manufacturing process. The 3D printing can be used in the making of porous ceramics in a different of applications. For example, it is widely used for catalysis chemical reactors, biomedical applications and filtration technologies. It can also be used to produce porous ceramic membranes, energy storage and heat exchangers,

and application area [1].

6 Recent Advances in Porous Ceramics

**7. Ceramic foams**

Porous ceramics have a good activity and high absorption materials. The reaction rate and conversion increase significantly for the reactive fluid that flows through the porous ceramic networks [22]. The ceramic catalyst carrier plays a major role in promoting the chemical reaction. Due to the chemical corrosion resistance and thermal shock of porous ceramics, they can be used in highly required service conditions, like the reactor in chemical engineering and the vehicles gas exhaust treatment. As well as the fine metal particles are usually supported on the heterogeneous catalyst carriers, which are generally ceramic. Catalysis becomes also progressively more important in environmental pollution control. The catalyst effectively reduced pollution from automotive and industries applications. The ceramic used must have connected porosity and the pore size can differ between 6 nm and 500 μm. Alumina, titania, zirconia silica and silicon carbide are the most popular choices for catalyst supports. These ceramic powders are formed into a variety of shapes such as cylinder bars or hollow beads or clover-leaf shaped sections. They are then sintered to their final density. Porous ceramics also can be used as carriers in the recycling of steam, oxidation of ammonia, recombination of methane, destruction of volatile organic compounds (VOCs) by incineration and decomposition of organics by photocatalysis.

## **11. Porous ceramics and membranes**

Porous ceramic membranes can be used to separate water, oil, liquids, solids, dust in gas, yeast or thallus and blood cells and to clarify alcohol in the food, chemical and medical industries. In addition, these membranes act as biological reactors in the recovery of fermented fluid. During the last few decades, the ceramic membrane applications have increased because of their excellent chemical, mechanical and thermal stability, and high separation efficiency [23]. High-permeability ceramic membranes can only be obtained in an asymmetric multilayer arrangement with microporus support, providing mechanical strength and reducing flow resistance. Commercially porous ceramic membranes of oxides such as alumina and zirconia are not suitable for large-scale application because these kind of oxide membranes are very expensive. Recently, the natural minerals such as zeolite, apatite, dolomite and clays have received increasing attention due to their cheap fabrication and multiple applications. The development of ceramic membranes made of natural minerals could lead to a new critical technological revolution that would add significant economic value to the natural minerals found all over the world.

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