Applications of porous materials

There are many applications of porous materials. Their ability to fill space with a minimum weight leads to their use in packaging. Life jackets and rafts use porous materials because of their low density. Examples of their use as thermal insulators range from Styrofoam cups to heat shields for space craft. Aluminum baseball bats are filled with foam to dampen vibrations. The low elastic moduli and high elastic strains of foams lead to use as cushions and mattresses. Filters are made from porous materials.

Stiff lightweight structures such as aircraft wings are made from sandwiches of continuous sheets filled with foams or honeycombs. Open porous structures can form frameworks for infiltration by other materials leading to application of biocompatible implants. Open pore structures are used as supports for catalysts.

Fabrication of porous foams

Natural cellular materials include sponges and wood. Foams of polymers, metals, and ceramics can be made by numerous methods. Foams are often produced by entrapping evolved gas. Inert gasses such as CO2 and N2 may be dissolved under high pressure and released by decreasing the pressure. Gas bubbles may also be formed by chemical decomposition or chemical reaction. Mechanical beating will produce foams. Foamed structures may be formed by bonding previously expanded spheres as in the case of polystyrene. Incomplete sintering of pressed powders creates materials with continuous internal passages that find use as filters and oilless bearings.