Silica Glass from Aerogels

by Michel Prassas

Aerogel evolution during sintering


Regarding the considerable research effort devoted in the beginning of the sol-gel adventure on solving the monolithic problem for making bulk glass, George Scherer and Jeff Brinker, authors of the first book on sol-gel, made the following comment.


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Glass from gels
Hypercritical drying
Gel to glass transformation
References & Links

"This is a bit ironic in retrospect, as it is evident that monoliths are the least technologically important of the potential applications of the gels. However, the allure of a room-temperature process for the preparation of bricks and windows was irresistible for research directors around the world, and enormous effort has been devoted to demonstrating that that objective is nonsense".

It is obvious today that this initial "nonsense" research effort, essentially conducted by glass researchers and material scientists, and the breakthrough of making a monolithic piece of silica glass of appreciable size at  1100°C,  considerably helps the development  of the technique and its widespread to other scientific disciplines . This effort tremendously increase the fundamental understanding of sol-gel chemistry, drying and consolidation techniques. It helped bring together physicists, solid state chemists, glass and ceramic scientists, and prepared the basements of  a versatile materials chemistry. and naturally oriented the technique in areas where it makes sense to use it. Materials nano-manufacturing, films, new organic-inorganic hybrids, nanocomposites, morphologically and structurally tailored nanoparticles.

It doesn't prevent people of still continuing to improve sol-gel process in more traditional areas like glass or ceramics. 

Today monolithic gels can be made without the need of hypercritical drying and converted to useful materials. 
Lucent researchers achieved what was considered impossible 25 years ago; produce meter size monoliths which can be densified to pure silica glass and used as clad material for today optical fibers. 





  1. M. Yamane, S. Aso, T. Sakaino, J. of Mater. Sci., Vol 13, 1978, 865
  2. B.E. Yoldas, J. of Mater. Sci., Vol 10, 1975, 1856
  3. Synthesis of monolithic silica gels by hypercritical solvent evacuation
    M. Prassas, J. Phalippou, J. Zarzycki, J. of Mat. Sci. Vol 19, 1984, 1656
  4. Glasses from aerogels Part 1: The synthesis of monolithic silica aerogels 
    J. Phalippou, T. Woignier, M. Prassas, J. of Mat. Sci. Vol 25, 1990, 3111
  5. Glasses from aerogels Part 2 : The aerogel-glass transformation 
    T. Woignier, J. Phalippou, M. Prassas, J. of Mat. Sci. Vol 25, 1990, 3118
  6. G.A. Nicolaon et S.J. Teichner, Bull. Soc. Chem. Fr, 1968, 1906



Silica Aerogels  
from the Microstructured Materials Group at
Lawrence Berkeley National Laboratory. "The" starting point for aerogels.
Carbon aerogels
Description of the elaboration of carbon aerogels
SOL-GEL: A low temperature process for materials of the new millennium
by Prof. J. Phalippou
A short introduction to the Sol-Gel methods and the ways to obtain materials for a variety of applications
Gel preforms for optical fibers at Bell Labs
Process overview 
Particulate Silica Gels and Glasses from the Sol-Gel Process (An excellent review)
by Eliezer M. Rabinovich
AT&T Bell Laboratories, Murray Hill, New Jersey

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