Fabrication of lotus-type porous silicon by unidirectional solidification in hydrogen

Fabrication of Lotus-Type Porous Al-Si Alloys Using the Continuous Casting Technique

“…[4,6,13] The hydrogen gas solubility in the liquid and the solid phase is proportional to the root of the partial pressure of hydrogen, according to Sieverts' law, at the melting temperature in a metal-hydrogen system. [4][5][6]13] Therefore, we started the discussion with the assumption that the porosity in Al-Si alloys also depends on the amount of hydrogen rejected from the solid during solidification.…”

“…Recently, lotus-type porous metals, one class of the porous metals, have been investigated by many researchers; [3][4][5][6][7][8][9] these materials possess long cylindrical gas pores aligned in one direction. Lotus-type porous metals have superior mechanical properties originating from unidirectional pores, compared with conventional porous metals, the pores of which are almost isotropic and spherical.…”

“…[4][5][6][7][8][9]11] Recently, our group successfully fabricated a long-sized lotus-type porous copper slab using the continuous casting technique, [9,12,13] and we reported that both the porosity and pore size can be easily controlled by the solidification velocity and the hydrogen pressure in the continuous casting technique.…”

Routes of Formation for Porous Silicon

“…All the etching techniques tend to create "open" porosity where pores are accessible from the external surfaces of the structure. Specific techniques to create "closed" porosity include melt gasification (Nakahata and Nakajima 2004) and milling/sintering (Jakubowicz et al 2007). …”

Influence of Ultrasonic Agitation on Pore Formation and Growth during Unidirectional Solidification of Water-Carbon Dioxide Solution

“…On the basis of this principle, Nakajima et al have systematically investigated to fabricate various kinds of lotus-type porous metals (lotus metals) possessing cylindrical pores aligned in one direction. [1][2][3][4] Owing to the unique porous structure, the mechanical properties of lotus metals are superior compared with conventional porous metals fabricated by sintering or foaming, etc; specific strengths in the direction parallel to the longitudinal axis of pores are almost constant despite the presence of pores. Therefore, lotus metals are expected to be used not only as functional materials but also as structural materials possessing various unique functions.…”