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The United States of America As Represented by the United States

Sten A Henning

Leif Svensson

Guy Von Dardel

Ravindra Shrikrishna Upadhye

A method is described for making hollow aerogel microspheres of 800-1200 .mu. diameter and 100-300 .mu. wall thickness by forming hollow alcogel microspheres during the sol/gel process in a catalytic atmosphere and capturing them on a foam surface containing catalyst. Supercritical drying of the formed hollow alcogel microspheres yields hollow aerogel microspheres which are suitable for ICF targets.

Production of hollow aerogel microspheres

Silica aerogel in the form of a substantially crack-free, preferably transparent block is described, together with a method for the preparation of such aerogel and use thereof in solar panels. The preparation is effected by means of hydrolysis of a tetraalkoxysilane, preferably tetramethoxysilane, in an alcohol, preferably methanol, in the presence of a catalyst, preferably ammonia, for the formation of an alcogel which is aged for approximately 10 days and washed with alcohol for removing water. The alcogel is thereafter treated in an autoclave by means of a temperature increase to above the critical point of the alcohol, isothermic pressure drop by means of the release of alcohol vapor, and temperature drop. The temperature increase, the pressure drop and the temperature drop take place at such low mean rates that the aerogel does not crack. To this end, a total treatment time in the autoclave of at least 24 hours is required. After the autoclave treatment, a heat treatment at 500.degree. to 750.degree. C. is possibly carried out for further improving the transparency of the aerogel.

Silica aerogel

Silica aerogel in the form of a substantially crack-free, preferably transparent block is described, together with a method for the preparation of such aerogel and use thereof in solar panels. The preparation is effected by means of hydrolysis of a tetraalkoxysilane, preferably tetramethoxysilane, in an alcohol, preferably methanol, in the presence of a catalyst, preferably ammonia, for the formation of an alcogel which is aged for approximately 10 days and washed with alcohol for removing water. The alcogel is thereafter treated in an autoclave by means of a temperature increase to above the critical point of the alcohol, isothermic pressure drop by means of the release of alcohol vapor, and temperature drop. The temperature increase, the pressure drop and the temperature drop take place at the such low mean rates that the aerogel does not crack. To this end, a total treatment time in the autoclave of at least 24 hours is required. After the autoclave treatment, a heat treatment at 500.degree. to 750.degree. C. is possibly carried out for further improving the transparency of the aerogel.

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Dalby, Sweden

Sten A Henning