Metal Foams: Production and Stability

Abstract

Liquid metal foam can be generated by creating gas inside a liquid or semi‐liquid metallic melt which has been pre‐treated in a suitable way. Such foams are self‐supporting disordered structures in complete analogy to aqueous foams. The stabilisation mechanism of metallic foams is still not fully understood. In order to facilitate discussion of foam stabilisation the various methods for making such foams are classified with respect to the mode of gas generation and the type of melt used for foaming. Metal foams can be produced by gas injection from an external source or by in‐situ nucleation of gas bubbles in the melt for which various possibilities are known. Melts amenable to foaming range from almost pure molten alloys to melts to which particles have been added, formed by in‐situ reactions or which have been already present in the solid precursor prior to melting. Some of the available experimental evidence for the action of stabilising particles in metallic foams is presented. It is found that although stabilisation seems to be based on the presence of a solid constituent in all the foaming processes, the mechanisms might vary. At present the nature of stabilisation is not yet fully understood and many questions remain open.

Low-density three-dimensional foam using self-reinforced hybrid two-dimensional atomic layers

“…These man-made, low-density, highly porous materials called foams, exhibit novel physical properties compared with their bulk counterparts. Large specific area, high energy absorption at impact and outstanding strength to weight ratios make them ideal for catalysis, energy storage, damping and building structural components [3][4][5] . Creating threedimensional (3D) structures using nanoscale elements allow tailoring of properties by integrating specific elements in favourable proportions [6][7][8] .…”

The Study on Fabrication and Sound Absorption Properties of Al-Zn-Mg-Cu Alloy Foams

“…개기공 발포금속은 각각의 기공 이 연결되어 있는 형태를 지니며, 필터나 열교환기 등에 사용 이 가능하며, 폐기공 발포금속은 각각의 기공이 독립된 형태로 존재하며, 충격흡수재나 흡음재 등의 재료로 사용이 가능하다 [6]. 또한, 제조방법에 따라서 주조법, 분말법, 입자분해법, sputtering등이 있으며, 이 방법들은 기공의 형성방법에 따라 크게 직접 발포법과 간접 발포법으로 다시 나누어진다 [7][8]. 직 접 발포법은 용융금속을 직접 처리하는 방법으로 용탕내부에 직접 가스를 분사하거나 발포제를 투입하여 기공을 형성시키며 주로 폐기공의 형상을 가진다.…”

“…직 접 발포법은 용융금속을 직접 처리하는 방법으로 용탕내부에 직접 가스를 분사하거나 발포제를 투입하여 기공을 형성시키며 주로 폐기공의 형상을 가진다. 간접 발포법은 금속 분말을 소 결하여 발포금속을 제조하는 방법이 대표적으로, 발포재의 기공 구조를 미리 결정하는 것으로 추가적인 첨가제가 필요 없는 방 법으로 주로 개기공의 형상을 가지게 된다 [8][9]. 이와 같이 발 포금속은 제조 조건 및 모재에 따라 밀도, 크기, 기공 구조 등 이 각기 다르게 나타나며, 최종 형태도 패널이나 블록 형상에 서부터 정형 부품 등 다양하게 제조되고 있다 [10].…”

Foams and emulsions in space

“…As the films become thinner, they rupture at critical thicknesses around 50 µm, something that must be eliminated to obtain a useful engineering material. This can be done by incorporating solid oxide particles within the films and Plateau borders in order to keep the two interfaces apart and efficiently block flow [11]. This stabilisation technique is largely inspired from the similar effect of powders on emulsions first observed by Pickering.…”