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Aerogels

  1. Nicola Hüsing1,
  2. Ulrich Schubert2

Published Online: 15 DEC 2006

DOI: 10.1002/14356007.c01_c01.pub2

Ullmann's Encyclopedia of Industrial Chemistry

Ullmann's Encyclopedia of Industrial Chemistry

How to Cite

Hüsing, N. and Schubert, U. 2006. Aerogels. Ullmann's Encyclopedia of Industrial Chemistry. .

Author Information

  1. 1

    Anorganische Chemie I, Universität Ulm, 89081 Ulm, Germany

  2. 2

    Institut für Materialchemie, Technische Universität Wien, A-1060 Wien, Austria

Publication History

  1. Published Online: 15 DEC 2006

Chemistry Terms

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Abstract

The article contains sections titled:

1.Introduction
2.Synthesis
2.1.Network Formation and Structure
2.1.1.Inorganic Aerogels
2.1.1.1.SiO2 Aerogels
2.1.1.2.Metal Oxide Aerogels
2.1.2.Inorganic/Organic Hybrid Aerogels
2.1.3.Organic Aerogels
2.2.Drying Methods
2.2.1.Supercritical Drying
2.2.1.1.Drying in Organic Solvents
2.2.1.2.Supercritical Drying with CO2
2.2.2.Freeze Drying
2.2.3.Ambient Pressure Drying
2.3.Modification of Aerogels after Drying
3.Properties
3.1.Structural Properties
3.2.Physical and Chemical Properties
3.2.1.Optical Properties
3.2.2.Mechanical and Acoustic Properties
3.2.3.Thermal Conductivity
3.2.4.Hydrophobicity
4.Applications
4.1.Çerenkov Detectors
4.2.Thermal Insulation
4.3.Catalysis
4.4.Application as Storage Media
4.5.Electrical and Electronic Applications
4.6.Acoustic and Mechanical Applications
4.7.Optical Applications
4.8.Other Applications
5.Future Perspectives

Aerogels are unique among solid materials. They have extremely low densities (up to 95 % of their volume is air), large open pores, and a high inner surface area. This combination of properties results in interesting physical properties, e.g., for silica aerogels extremely low thermal conductivities and low sound velocities are combined with optical transparency. Aerogels are typically prepared via wet chemical processes, such as sol – gel processing, and thus their pore system is initially filled with liquid. Only special drying techniques allow for exchange of the pore liquid against air while maintaining the filigrane solid framework. The most common drying technique is supercritical extraction, and sometimes chemical modification of the inner surface can be used to facilitate drying. The structure of the gel network, and thus the physical properties of aerogels, decisively depends on the choice of the precursors and the chemical reaction parameters for preparing the gels. Therefore, the later materials properties can be deliberately designed in the starting reaction solution.