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A metal foam is a cellular structure consisting of a solid metal, frequently aluminium, as well as a large volume fraction of gas-filled pores. The pores can be sealed (closed-cell foam), or they can form an interconnected network (open-cell foam). The defining characteristic of metal foams is a very high porosity: typically 75–95% of the volume consists of void spaces making these ultralight materials. The strength of foamed metal possesses a power law relationship to its density; i.e., a 20% dense material is more than twice as strong as a 10% dense material. Metallic foams typically retain some physical properties of their base material. Foam made from non-flammable metal will remain non-flammable and the foam is generally recyclable back to its base material. Coefficient of thermal expansion will also remain similar while thermal conductivity will likely be reduced.〔(Compare Materials: Cast Aluminium and Aluminium Foam ). Makeitfrom.com. Retrieved on 2011-11-19.〕 Although there is a very large number of patents describing feasible topological structures, constitutive materials, and production methods, metal foams cannot be considered a commodity and relatively few commercial producers are available worldwide of either closed or open cell foams. ==Open-cell== Open celled metal foams have a wide variety of applications including heat exchangers (compact electronics cooling, cryogen tanks, PCM heat exchangers), energy absorption, flow diffusion and lightweight optics. Due to the high cost of the material it is generally used in advanced technology, aerospace, and manufacturing. Extremely fine-scale open-cell foams, consisting of cells smaller than visible to the naked eye, are used as high-temperature filters in the chemical industry. Metallic foams are used in the field of compact heat exchangers to increase heat transfer at the cost of an additional pressure drop. However, their use permits substantial reduction in the physical size of a heat exchanger, and so fabrication costs. To model these materials, most works uses idealized and periodic structures or averaged macroscopic properties. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Metal foam」の詳細全文を読む スポンサード リンク
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