ABSTRACT
Silica aerogels are highly porous, open-cell thermal insulating materials made of amorphous silica nanoparticles, interconnected in a 3D random network. They are made by classic sol–gel process and dried by supercritical drying. However, pure silica aerogels are fragile with low mechanical moduli, and they are transparent to infrared radiation for high temperatures. Making aerogel composite materials by combining fibers with a pre-gel mixture of a gel precursor, or by impregnating a fiber network by such a mixture seems to be a promising way to enhance the mechanical properties of such materials. The addition of fibers as well as a hydrophobic agent allows an ambient pressure drying that is much more energy and cost efficient than the supercritical drying. After drying, the resulting composite is called an aerogel blanket. The aerogel blanket is mechanically strengthened, flexible, opaque, and still has a very low thermal conductivity (≈ 0.015 W.m−1.K−1). Aerogel blankets are—together with vacuum insulation panels—one of the promising new high performances thermal insulation materials for building applications, but only few commercial products exist in the current market. They are not competitive yet in the building insulation market because of their manufacturing costs, and they are mostly used for very specific insulation needs. The latest research efforts are focused on the reduction of manufacturing time and cost, and we expect a threefold increase in the super insulating global market by a few years. This chapter presents a brief overview of the elaboration steps and material properties. It mainly focuses on the hygrothermal properties (thermal conductivity, water uptake, water vapor permeability, and so on), and the characterization techniques to obtain it.
Fourier transformed infrared spectroscopy is used to characterize the aerogel blankets structure and to confirm the graft of water repellent molecules during the hydrophobic process. The texture of aerogel blankets is evaluated using Scanning Electron Microscopy and BET, which provides information about the microstructure, specific surface, and porosity. The hygrothermal properties are measured by using a fluxmeter, a climatic chamber, and a precision balance.
Results show that the aerogel blankets lack sensitivity to humidity in regards to their texture and thermal conductivity, which make them a rising class of insulating materials for the building insulation market.
