Insulation translucent

Polyethylene is a wax-like thermoplastic softening at about 80-130°C with a density less than that of water. It is tough but has moderate tensile strength, is an excellent electrical insulator and has very good chemical resistance. In the mass it is translucent or opaque but thin films may be transparent. 

Hollomon s ethos, combined with his ferocious energy and determination, and his sustained determination to recruit only the best researchers to join his group, over the next 15 years led to a sequence of remarkable innovations related to materials, including man-made diamond, high-quality thermal insulation, a vacuum circuit-breaker, products based on etched particle tracks in irradiated solids, polycarbonate plastic and, particularly, the Lucalox alumina envelope for a metal-vapour lamp. (Of course many managers besides Hollomon were involved.) A brilliant, detailed account of these innovations and the arrangements that made them possible was later written by Guy Suits and his successor as director, Arthur Bueche (Suits and Bueche 1967). Some of these specific episodes will feature later in this book, but it helps to reinforce the points made here about Hollomon s coneeption of broad research on materials if I point out that the invention of translucent alumina tubes for lamps was... 

Transparent or translucent insulating materials (TIMs) can provide light or solar gains without view. TIMs typically have thermal properties similar to conventional opaque insulation and are thicker than conventional insulating glass units, providing significant resistance to heat transfer. 

The insulating properties are excellent. At ordinary temperatures the resistivity of the translucent form is 10 Qm, and it is capable of withstanding high-frequency discharges at high voltages. See also Table 18.4 for data on other physical properties. 

Many of the properties of urea plastics are similar to those of the phe nolics, but, unlike phenolics, the urea plastics are not dark and are characterized by pastel and translucent colors as well as slightly superior insulating electric properties. Urea is tetrafunctional. As shown in Figure 15.5, linear and cross-linked network products are readily produced. 

Polyethylene. The most straightforward process for the production of polymers from ethylene is that of the direct polymerization of the olefin. The polymerization process usually requires pressures and temperatures of 15,000 to 30,000 pounds per square inch and 200° to 300° C., and may be effected in either gas or liquid phase reactions (9). The polymer of molecular weight above 20,000 is the white, translucent plastic, polyethylene, widely used in electrical insulation, packaging material for foods, cosmetics and pharmaceuticals, liners for paper bags, etc. Articles molded from polyethylene are semirigid or rigid, depending on their thickness, but in thin films the material has excellent flexibility, even at relatively low temperatures. 

Fused quartz or silica tubes are used as insulators through which the wires of a rare-metal couple are threaded, and as outer protecting tubes. The molten quartz may be drawn and worked like glass or the material may be ground and pressed, with a suitable binder, into the proper form and fired in a manner similar to that employed for the manufacture of porcelain. These tubes are translucent like china. Trans-... 

The most common solar collector is the glass-covered flat plate type. Others include concentrating trough and tube-over-reflector collectors, and parabolic collectors. A flat plate collector uses a flat black absorber plate in a container box. Insulation behind the absorber plate and on the sides of the box reduce heat loss. The glazing may be flat glass, translucent fiberglass or clear plastic, on the sun side of the collector, 1 to 2 inches above the absorber. 

Figure 8 Passive solar heating with a translucent aerogel insulation in front of a blackened house wall. Even on cold but sunny days heat gain can be achieved.

Building panels, translucent sheet, corrosion-resistant equipment, thermal insulation... 

Aerogels are particularly well suited for insulation applications because of their exceptionally low density, thermal stability, and high transparency. In fact, they can have a thermal conductivity only one-third that of polyurethane or polystyrene foam, and with recent process improvements that reduce the cost of manufacmre by an order of magnitude their practical use in certain construction applications is now feasible [31]. The insulating properties can be enhanced through the addition of IR opacifiers [32]. The high transparency of aerogels makes them suitable as insulation in windows or translucent panels. 

Stegmaier, T., Linke, M., Planck, H., 2009. Bionics in textiles flexible and translucent thermal insulations for solar thermal apphcations. Philos. Trans. R. Soc. A Math. Phys. Eng. Sci. 367 (1894), 1749-1758. 

Properties Wh. translucent to opaque solid m.w. 400,000-9,000,000 dens. 2.2 useful temp, range cryogenic to 260 C melts to vise, gel 327 C Shore hardness 55-56 tens. str. 3500-4500 psi elong. 200-300% ( break) chem. inert exc. thennal/chem. resist. lowcoeff. of friction high elec, insulation nonflamm. 

Already many lightweight membrane structures are in existence, and an increasing number of them are planned for the future, e.g. football stadium roofs. For such structures the combination of materials produces widely differing properties. Some projects are very cost-effective, while others are used for more expensive building constructions. Some constructions are of a temporary nature, some are erected at a fixed location some are required to be portable, while others may remain in place for decades. Textile roofs or walls may be open or closed according to the time of day or the position of the sun others stay fixed in one position. Some materials are required to have high translucency others may be designed for maximum insulation. 

Encasing constructions can be used with several membrane layers to form an intermediate space that can be filled with air or another insulating material, making U-values from 2.7 to 0.8 W/m K possible. U-values down to even 0.2 W/m can be obtained by using opaque, flexible mineral fibre fills or translucent insulating material, for example blister foils, as well as reflecting intermediate layers which are commonly used in space technology (ref LPS see Rg. 3.12). 

Biomimetic textiles are under development and these include hydrophobic, self-cleaning surfaces analogous to the behaviour of leaf surfaces occurring in nature, such as the lotus plant, and flexible, translucent thermal insulated membranes analogous to the behaviour of the polar bear s fur (Stegmaier and Planck, 2007). 

One of the most promising options of flexible insulation materials to be used for translucent foil structures involves granular silica aerogel as insulation material - see Fig. 12.2 (Cremers, 2008). Not only does aerogel have excellent thermal-insulation properties (see r-values and /-values in Fig. 12.3), but it is translucent as well. 

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