Macro and Nano Porous Materials

Porous materials can be classified into two groups: macroporous and nanoporous materials. The first has pores larger than one meter in diameter, while the latter has pores as small as the nanometer. Furthermore, the materials can also be distinguished from the pore, isotropic and anisotropic form. The isotropic pores are spherical or polyhedral, while the anisotropic pores are elongated pores aligned unidirectionally or distributed in a random direction. Here, two types of examples on macroporous metals are shown in the next. Foamed metals can be manufactured using foaming phenomena; bubbling occurs when the hydride is added to the high viscosity melted aluminum and during the solidification process foaming takes place to produce expanded aluminum . The porosity is over 90%, which has an ultra-light weight. These are widely used for the sound of absorbing materials and shock absorber for cars . Another example is the lotustype metals with directional pores, which can be fabricated through unidirectional solidification using the solubility space of the hydrogen between solid and liquid. The specific force in the direction parallel to the directional pores is equivalent to the strength of non-porous materials. Therefore, the lotus-based materials have sufficient strength even in porous materials. Lotus copper and aluminum are expected to be used for heat sinks for electronic devices; the straight and penetrable pores look like a bundle of thin tubes. The refrigerant can flow through the pores under a slight pressure drop and effectively cool the Joule heated devices.