Transparent aerogel insulation materials

One of the most promising applications of SiOa aerogels is their use as transparent thermal insulation. Extensive studies of transparent aerogels have shown that the thermal resistance as well as the solar transmission are sufficiently high to make these materials most suitable for passive solar usage [72]. However,... 

The most extensively studied chemical system for aerogel formation is the silica system. The sensational images associated with aerogels— free-standing transparent monoliths insulating a hand from a flame or holding up a brick (Fig. 8.2), are almost all of silica materials. The reason for this lies in the well-developed and facile sol-gel chemistry of silica that lends itself to formation of robust monoliths, as well as the intriguing physical properties and associated applications of such materials (11,13). 

Due to the absence of a stabilising pressurisation in mechanically tensioned structures, another type of aerogel insulation is employed. This version is a fleece made of two-component fibres which is sprinkled with aerogel particles. This produces a flexible and pressure-resistant mat which has highly favourable insulating properties. This fleece can be used both in combination with transparent ETFE foils and with translucent membrane materials such as PTFE-coated, glass-fibre fabric - see Fig. 12.4. The... 

In case of the thermal insulation, the technical limits are nearly reached today and a further improvement will affect aspects like the units transparency (yiP - Vacuum Insula-ti(Mi Panels) or their maximum size, not mentioning the costs. A functional transparent vacuum insulating unit with U-values of 0.1 W/(m K) is not available by now due to the technical problems of keeping the system permanently gas-tight. Therefore, the use of translucent Silica Aerogels, as a highly efficient insulating material inside the/Gf/ s cavity, represents the best possible thermal insulation at the moment. 

On the other hand, silica aerogel has also optical function, translucent or transparent, as described in another section (Chapter 3). This excellent thermal insulating material is most ideal for solar energy application. 

Thermal Insulation. In addition to their low thermal conductivity, as discussed in the section above, siUca aerogels can be prepared to be highly transparent in the visible spectmm region. Thus, they are promising materials as superinsulating window-spacer. To take further advantage of its... 

Silica aerogels, a newly developing type of material, also have been produced as thermal insulations with superinsulation characteristics. The nanometer-size cells limit the gas phase conduction that can take place. The aerogels are transparent to visible light, so they have potential as window insulation. The use of superinsulations at present is limited by cost and the need to have a design that protects the evacuated packets or aerogels from mechanical damage. 

In fact, aerogels consist of a thin amorphous solid matrix network surrounded by nanoscale-sized pores, and therefore, they are reasonably described as transparent, highly porous, open-cell, extremely low-density materials. This extraordinary structure provides silica aerogels a variety of unique properties. For example, low thermal and electrical conductivity are a result of the low thermal conductivity of silica and nanometer pores sizes. The low thermal conductivity and other optical properties make them desirable for many applications. For example, they can be an attractive alternative in insulating applications, due to their high insulating value and environment-friendly production methods. They also possess low refractive index, low sound velocity, and low dielectric constant. 

Generally, the incorporation of nanometer-sized aerogel particles into the polymer matrix can enhance the thermal stability by acting as a snperior insulator. These aerogels show optimal thermal conductivity at a relative density of about 0.15 (85% porosity). At a lower density, heat transfer by conduction through the polymer is reduced, but the materials become more transparent to infrared radiation, which iuCTeases thermal conductivity. 

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