Open-cell foams sponges

Cellular solids are a class of materials with low densities and novel physical, mechanical, thermal, electrical, and acoustic properties. Low-density cellular metals can feature a wide variety of topologies to include open-cell foam, closed-cell foam, hollow-sphere foam, periodic/optimized truss structures, and honeycomb. Metallic foams consist of air dispersed in a solid matrix, similar to polymer foams such as polystyrene or food foams such as whipped cream. Closed-cell foams feature solid faces such that each cell is independently sealed from its neighboring cells, whereas open-cell foams (also known as porous metals, metal sponges and truss-type materials) do not contain cell walls they only have cell edges. Hollow-sphere foams consist of an assembly of individual hollow spheres. 

The most Important distinction is between closed- and open-cell foams. In closed-cell (unicellular) foams, each gas bubble is separated from the others by thin walls of polymer these foams are optimal for flotation applications, structural rigidity, and thermal insulation. In open-cell foams, the cells are all interconnecting, and fluids and especially air can flow freely through the foam structure these are optimal for sponge products and for soft flexible materials. In the extreme case, when the last few remaining cell walls (windows) have been chemically dissolved out of an open-cell foam, it is sometimes called "reticulated."... 

Water absorption of sponges results from the ease with which water can replace gas in flexible open-cell foams, because both fluids can flow freely on flexing. 

Water absorption, particularly in flexible open-cell foams, for sponge-type applications. 

Why do you think closed cell foams are used more often in packaging than open cell foams What kind of foam is used for dishwashing sponges Why ... 

Foamed plastics can be classified according to the nature of cells in them into closed-cell type and open-cell type. In a closed-cell foam each individnal cell, more or less spherical in shape, is completely closed in by a wall of plastic, whereas in an open-cell foam individual cells are inter-connecting, as in a sponge. Closed-cell foams are usually produced in processes where some pressure is maintained during the cell formation stage. Free expansion during cell formation typically produces open-cell foams. Most foaming processes, however, produce both kinds. 

This chapter reviews the application of honeycomb monoliths, open-cell foams (also known as sponges) and other structured catalysts to gas/phase selective oxidation processes. 

The word foam refers to a dispersion of gas bubbles in a liquid, but can also be used to describe a uniform dispersion of a gaseous phase in a sobd matrix. Open-celled foams are, in fact, sponge-like strucmres made of intercoimected solid struts which enclose cavities (or pores) communicating through windows. They are commercially available in a variety of metallic and ceramic materials well-established industrial apphcations include thermal insulation, energy adsorption, fabrication of noise-reduction devices, filtration of molten metals, purification of hot gases and others. 

The cells in foams are polyhedral, like grains in a metal (Fig. 25.8). The cell walls, where the solid is concentrated, can be open (like a sponge) or closed (like a flotation foam), and they can be equiaxed (like the polymer foam in the figure) or elongated... 

Until 1920, the only flexible foam available was the natural sponge, but chemically foamed rubber and mechanically foamed rubber latex were introduced before World War II. These foams may consist of discrete unit cells (unicellular, closed cell), or they may be composed of interconnecting cells (multicellular, open cells) depending on the viscosity of the system at the time the blowing agent is introduced. Over 1.5 million tons of foamed plastic is produced annually in the United States. 

Polyurethane sponge foam. One fabricator offers a coalescer design employing an open-celled polvure-thane foam in a horizontal tank (Fig 4). 

In the case of cellular rubber, the ASTM uses several classifications based on the method of manufacture [11,12]. Cellular rubber is a general term covering all cellular materials that have an elastomer as the polymer phase. Sponge rubber and expanded rubber are cellular rubbers produced by expanding bulk rubber stocks, and are open-cell and closed- cell, respectively. Latex foam rubber, which is also a cellular rubber, is produced by frothing a rubber latex or liquid rubber, gelling the frothed latex, and then vulcanizing it in the expanded state. 

Urea-formaldehyde foams are usually brittle structures with low compressive strength (under 50 psi or 0.34 MPa). The term "frangible" may be applied to them. They are open-cell, sponge-like foams that can absorb large quantities of water. Hiese foams also exhibit thermal and acoustical insulating properties common to low-density foams. For example, their thermal conductivities range within the values quoted for polystyrene foam (0.24 - 0.33). This is the result of their low density and snail cell size (5). 

MIL-R-20092L(1) Rubber or Plastic Sheets and Assembled and Molded Shapes, Synthetic, Foam or Sponge, Open Cell, 25 February 1988, 1 p amend + 17 pp base spec (FSC 9320) (SH)... 

The cells of the structure can be either closed or open. The former type is like a foam, in that the matrix can geometrically be compared with the continuous phase of the foam, which consists of thin lamellae and Plateau borders. Here we have thicker lamellae or walls, and beams (struts, ribs) where two lamellae meet if the cells are filled with gas we can call the system a solid foam. Open cells occur when the lamellae contain holes now we speak of a sponge. Some types of sponge structures merely consist of beams. Most plant tissues (see, e.g., Figure 9.4) consist of closed cells that are mainly filled with an aqueous liquid. 

Water absorption in sponge-type applications and use as a filter medium depends on a high percent of open cells to permit easy passage of liquid water through the foam. 

Cellular rubber may be described as an assembly of a multitude of cells distributed in a rubber matrix more or less uniformly. The cells may be interconnected (open cells) as in a sponge or separate (closed cells). Foam rubber made from a Uquid starting material such as latex, described earKer, is of open-cell type. Cellular products made from solid rubber are commonly called sponge (open cell structure) and expanded rubber (closed cell structure). 

FIGURE 41.7 Cellular solids structures, after Gibson and Ashby [1988]. Left synthetic cellular solids (a) open-cell polyurethane, (b) closed-cell polyethylene, (c) foamed nickel, (d) foamed copper, (e) foamed zirconia, (f) foamed mulllte, (g) foamed glass, (h) polyester foam with both open and closed cells. Right natural cellular solids (a) cork, (b) balsa wood, (c) sponge, (d) cancellous bone, (e) coral, (f) cuttlefish bone, (g) iris leaf, (h) plant stalk. 

Cellular forms of neoprene are used primarily for gasketing, insulation, cushioning, and soimd and vibration damping. This material provides compressibility not foimd in solid rubber but still retains the advantageous properties of neoprene. It is available as an open-cell sponge, a closed-cell neoprene, and a foam neoprene. 

Both the solid and the gas phases are continuous in a sponge, in a plastic foam with open cells, in a porous catalyst particle and in a catalyst monolidi. 

FIGURE 11.5 Simplified plan view of defoamer and filter elements in typical cardiotomy reservoir. Both defoamer elements are sponge-like open-celled polyurethane foams coated with PDMS-hydrophohed silica antifoam. Inner particle filter has pore sizes in range of 50-90 microns and outer filter has pore size of 40 microns. (After Servas, F.M., Gremel, R.F., Ryan, T.C. (assigned to Shiley Inc.), US 4,743,371 10 May 1988, filed 28 February, 1986.)... 

Sevastianov [82] reports the preparation of an open-celled polyurethane foam chemically hydrophobed with a perfluorosiloxane as a suitable defoaming material for defoaming blood. This material was initially as effective as the same polyurethane sponge coated with a proprietary PDMS-hydrophobed silica antifoam for defoaming a solution of human albumin (supposedly the main foam stabilizing protein in blood). However, the effectiveness of the latter diminished relatively rapidly... 

Cells are bubbles that have been frozen in size and shape after solidification of a molten plastic. A plastic can contain two types of cells closed structure and open structure. In a closed structure foam system, each cell is an independent closed entity. The cells resemble small glass bubbles that have been dispersed in the plastic. The walls of a closed cell have no holes in them. The cell will contain gas if the plastic is impermeable to the blowing gas. The cells of an open structure are interconnected, thus unable to hold gas. Liquids and gases can usually move through the open cell structure, like common sponges. 

Foamed polyethylene exhibits several desirable physical characteristics that make it useful in a variety of relatively small markets. It can be made as either a closedcell or an open-cell product. In the former case bubbles of gas expand to a limited extent within a molten polymer constrained by pressure. The product comprises cells eompletely bounded by solidified polymer walls. Open-cell products form when bubbles are allowed to expand in a relatively unconstrained manner. The cells so formed have only partial walls and are thus interconnected like those of a sponge. 

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