**4. Porous ceramic structure and properties**

Porous ceramics possess a number of suitable properties, which combine the features of ceramics, and porous materials such as low density, lightweight, low thermal conductivity, low dielectric constant, thermal stability, high specific surface area, high specific strength, high permeability, high resistance to chemical attack and high wear resistance [13]. Either porous ceramics are reticulate (interconnected voids surrounded by a connection of ceramic) or foam (closed voids within a continuous ceramic matrix). Reticulated porous ceramics are usually used for molten metal, industrial hot-gas filters, catalyst supports, and diesel engine exhaust filters.

Pore size and porosity percentage are controlled by the particle size distribution of starting ceramic powders, fabrication techniques, types of binder used, concentration of binder and sintering conditions respectively [1]. Generally, the particle size of raw ceramic powder should be geometrically in the range between two to five times larger than that of pores in order to provide the desired pore size. The Porosity percentage reductions with increased making conditions such as pressure, sintering temperature and time. Furthermore, the fabrication influences such as the amount and type of additives, green densities, and sintering conditions (temperature, pressure atmosphere, etc.) significantly affect for the porous ceramics microstructures.
