Aerogel granules

Reim M, Reichenauer G, Komer W et al (2004) Silica-aerogel granulate Structural, optical and thermal properties. Journal of Non-Crystalline Solids 350 358-363... 

Beds of aerogel granulate or powder are used for technical thermal insulation (Part 15), because they offer specific advantages in comparison to standard insulation materials, e.g., they can be poured into complicated shaped cavities. Opacified aerogel powders and granulates are used as thermal insulation in space applications [55], automotive applications... 

Figure 23.25. Thermal conductance and the corresponding apparent thermal conductivity of a bed of silica aerogel granulate with a thickness of 22.3 mm as a function of gas pressure. The dashed line is the result of the theoretical modeling of the heat transfer [57].

Reim, M., Komer, W., Manara, J., Korder, S., Arduini-Schuster, M., Ebert, H.P. and Fricke, J., Silica aerogel granulate material for thermal insulation and dayUghting. Solar Energy, 2005. 79(2) p. 131-139. 

Figure 41.7. Visual appearance of the Cabot Aerogel granulate (see Chap. 38).

Mahadik, D.B., A.V. Rao, R. Kumar, S.V. Ingale, P.B. Wagh, and S.C. Gupta. 2012. Reduction of processing time by mechanical shaking of the ambient pressure dried TEOS based silica aerogel granules. Journal of Porous Materials 19(1) 87-94. 

Fig. 3.2 Loss of hydrophobic properties in silica aerogel granules. Left Beaker Unheated hydrophobic aerogels are seen floating on the surface of the water. Right Beaker Heated aerogels turned whitish indicating shrinkage in volume due to infiltration of water into the pores. As a result, the aerogels become denser and settle down at the bottom of the beaker...

Fig. 3.4 Crushing of silica aerogel granules when mixed with epoxy-acetone solution (Gupta and Ricei 2008)...

Another fabrication methodology is via the freeze drying (FD) method. The aqueous solution of gelatin is obtained via sonication as described in flie previous section. However, the solution in this case is not foamed by frothing as described in Fig. 3.12. Instead, the silica aerogel granules are mixed in the solution for about 10 min till a tacky mix is obtained. Thereafter, the mixture is casted onto a 100 mm diameter petri dish or in a metal mold of 75 mm x 50 mm by 25 mm laid witii a porous sheet. The composite mold is covered with transparent porous foil and... 

Fig. 4.1 Non-binding of heat-treated aerogels with gelatin. Aqueous gelatin solution failed to bind with heat-treated silica aerogel granules but was instead absorbed by the aerogels is an indication of loss of hydrophobic properties...

Failed specimen analysis was carried out to purge out the redundant data, which is defined as a specimen already failing at first level but having duphcate data at higher levels. The Failed Specimen Analysis is shown in Appendix 5A. In addition, 55 FD specimens were tested for strain recovery, strength and modulus at 45 % compressive strain as part of the validation data. The data include 40 specimens that were studied for the influence of the silica aerogel granule size on the mechanical properties. 

Influence of Silica Aerogel Granules on Mechanical Properties of GSA-SDS Composites... 

Table 5.3 Summary of density, strain recovery, compressive strength, and modulus of GSA-SDS composites in terms of aerogel granule sizes under optimal conditions...

Fig. 5.17 Influence of silica aerogel granule size on a strain recovery b compressive strength and c compressive modulus...

However, it is observed that the smaller the granule size the higher the strength and modulus. Interestingly, the maximum strain recovery recorded for 2.18 mm silica aerogel granule size also showed the minimum strength and modulus. 

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