Aerogels

This book contains the papers presented at the "First International Sympo­ st sium on Aerogels (1 ISA)", held in September 1985 at. the University of Wiirzburg, Fed. Rep. of Germany. It was the first meet.ing of this kind, wit.h participants from several European count.ries, the United States of America, Canada, South America, and Africa. The meeting was interdisciplinary, with most of the participants being physicists, chemists or material scientists ei­ ther from universities or from industrial research institutes. Let me try to shed some light upon the class of substances the symposium was about: Aerogels are extremely porous high-tech materials, consisting ei­ ther of silica, alumina, zirconia, stannic or tungsten oxide or mixtures of these oxides. Due to their high porosity (up t.o 99%!) and t.heir large inner surface, aerogels serve as especially active catalysts or as catalytic subst.rates, as adsorbents, fillers, reinforcement agents, pigments and gellifying agents. Silica aerogels as translucent or transparent superinsulating fillers in window systems could help to considerably reduce thermal losses in windows and to improve the energy balance in passive solar systems. Aerogels also have fas­ cinating acoustic properties - the sound velocity can be as low as 100 m/s! The production of aerogels starts with the controlled conversion of a sol into a gel: The growth of clusters or polymer chains from a chemical solution, the cross-linking of these primary entities and the formation of a coherent network - still embedded in a liquid.

Inhalt

I Introduction.- Aerogels - a Fascinating Class of High-Performance Porous Solids.- II Production and General Aspects.- Aerogels of Inorganic Oxides.- Advances in Production of Transparent Silica Aerogels for Window Glazings.- Large-Scale Production of Airglass.- Aerogels: Precursors or End Materials?.- The Sol-Gel Process for Non-Metallic Inorganic Materials.- Synthesis and Structure of Borate Based Aerogels.- Preparation, Densification and Characterization of Autoclave Dried SiO2 Gels.- Microporous Silica Fibres.- III Energy Conservation and Thermal Properties.- Translucent Insulation for Passive Solar Energy Utilization in Buildings.- Thermal Transport in Porous Superinsulations.- Thermal Conductivity of SiO2-Aerogel Tiles.- Radiative Heat Transfer in Silica Aerogel.- Thermal Conductivity of Granular SiO2 Aerogel.- Thermal Properties of Silica Aerogel.- Solar Transmission of Aerogel Pellets.- Aerogel as a Transparent Thermal Insulation Material for Buildings.- IV Structural Aspects.- Microstructural Properties of Transparent Silica Aerogels.- Pore Size Distribution of Silica Systems.- Microstructure of Silica Based Aerogel Using High Resolution Transmission Electron Microscopy.- Structural Analysis of Granular Silica Aerogels.- Mechanical and Acoustic Properties of Silica Aerogel.- V Applications.- Aerogel in High Energy Physics.- Silica Aerogel and Space Astrophysics.- On Some Recent Applications of Aerogels.- Index of Contributors.