Effective thermal insulation with aerogel-aerogel composites

Abstract

Aerogels are suitable to be used as thermal insulation material for example in vehicles or in building construction as they are highly porous (up to 99%), nanostructured and therefore have a low density (0.01-0.3 g/cm³) and a low thermal conductivity (< 0.03 W/m.K). In order to improve the handling we fixed highly insulating granular silica aerogel (SiO2) fabricated by industry with resorcinol-formaldehyde (RF) aerogel. RF is an organic aerogel synthesized via a sol-gel reaction of resorcinol (R, 1,3-dihydroxybenzene) and formaldehyde (F) in deionized water (W) with Na2CO3 as the catalyst (C). The molecules undergo an electrophilic aromatic substitution followed by a condensation reaction and form a sol which builds a three-dimensional network. The molar ratios used for RF are R/F = 0.7, R/W = 0.04 and R/C = 1500 leading to a less sensitive RF-aerogel. The composite aerogel is prepared by mixing the hydrophobic granular silica aerogel into the already highly viscous RF-solution. After gelation and aging, the gel can finally be dried under ambient conditions. Plates in the dimension of 21 x 21 x 8 cm³ are obtained in which the volume content, grain size and grain size distribution of granular silica aerogel influence the properties of the latter material. Composites have density between 0.18-0.23 g/cm³ and thermal conductivity at room temperature between 0.027-0.034 W/m.K. According to thermal analysis composites are suitable for thermal insulation in a normal temperature range lower than the decomposition temperature of 250 °C.