White Paper: Reticulated foams expand the boundaries of cellular solids
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Reticulated foams expand the boundaries of cellular solids Paul Everitt, Goodfellow Corporation James Taylor, Goodfellow Corporation
WHITE PAPER
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icture a structure formed by fibers or ligaments that frames open cells. Such a structure would be lightweight, permeable, and shock-resistant while retaining the properties of the parent material. Polymer foams, used for insulation, cushions, and packaging materials, were perhaps the first man-made material to take advantage of the unique characteristics of cellular solids. Today, another type of foam, reticulated foam, made of either a ceramic (typically alumina, silicon carbide, or vitreous carbon) or a metal (typically aluminum, copper, nickel, stainless steel, or zinc), provides an extraordinarily versatile material that can be engineered for particular properties and tailored for specific applications.1 Reticulated foams have a number of features that benefit research and design engineers across many industries. The
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interconnected lattice of continuous ligaments within the cellular structure provides greater strength than shorter fibers and also ensures uniform material characteristics throughout the structure (Figure 1a). Other characteristics that offer further benefits include: High strength-to-weight ratio: Reticulated foam is particularly useful within cores of structural sandwich panels.2 The isotropic properties of the foam allow for a uniform response to impact, regardless of impact angle. These foams also add strength and structure when used as part of a three-dimensional (3D) network of reinforcing fibers in composites. High surface area-to-volume ratio: Deposition of a high-cost catalyst such as platinum or silver onto the ligament surfaces of a reticulated foam allows contact of a gas or liquid with the catalyst
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over a vast surface area.3 This technique is cost-effective and proves to be particularly valuable in the development of fuel cells. In addition, reticulated foam offers an exceptionally large surface area in a compact and lightweight structure for use as a scaffold for biological growth in pollution control and other devices. Conductive or insulating: Depending on the material, a reticulated foam can provide very low bulk thermal or electrical conductivity as well as insulation against high temperatures. In particular, vitreous carbon and silicon carbide reticulated foams are, like the solid material, structurally stable at extreme temperatures but at a fraction of the weight. These characteristics lend themselves for use in aerospace applications, in heat exchangers, porous electrodes, and wherever an exceptionally efficient, lightweight conductor or insulator is required. Low flow resistance: The open, uniform cell structure and rigid geometry of reticulated ceramic or metal foam contribute to a low pressure drop, or little resistance to the flow of liquid or gas for fluid flow. This is useful for applications such as filters, demisters, gas diffusers and mixers, and liquid and gas separators. Resistance to fr
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