Mohammad Javad Nayyeri (Assistant Professor at Science and Research Branch, Islamic Azad University, Iran (http://www.smasm.ir/))
Nature discovered and evolved low density cellular materials soon after on earth life began. Thanks to their cellular design, natural materials such as wood, cork, bones, and honeycombs fulfill structural as well as functional demands. A cellular material is one made up of an interconnected network of solid struts or plates which form the edges and faces of cells. These ultra-light materials exhibit unique physical and mechanical properties such as high specific rigidity, greatly increased energy absorbing capabilities and stable deformation mode which makes them ideal candidates for use in the automotive and aerospace industries while due to the large surface to volume ratio they are excellent for catalyst usage and heat exchanger.
Metal foam is a cellular structure made up of a solid metal containing a large volume fraction of gas-filled pores. These pores can either be sealed (closed-cell foam), or they can be an interconnected network (open-cell foam). There are several techniques for making metal foams which can be classified into 3 distinct classes: electrodeposition from an aqueous solution, casting and powder metallurgy.
The main characterization methods for metallic foams are optical and scanning electron microscopy and X-ray tomography. Physical and mechanical properties of metal foams depend on properties of base material, relative density of the foam, state of being closed or open cell, shape and size of the cells. Therefore, the range of properties offered by these advanced materials due to the wide range of their structures. Based on this feature, metal foams have been finding an increasing range of applications. Closed cell foams are basically used as construction and energy absorption materials (Automotive, Aerospace, Transportation, crash absorbers, noise controller and sport equipment) while open cell metallic foams are used as catalyst, heat exchanger, biomaterials, filtration and separation, battery and electrochemical industry due to their high surface to volume ratio.