REWE DE PHYSIQUE APPLIQUEE Colloque C4, S,uppl&ment au n04, Tome 24, avril 1989 TEXTURAL CHARACTERISTICS OF AEROGELS OBTAINED FROM SONOGELS N. DE LA ROSA-FOX*, L. E S Q U I V I A S " ~ ~ ~ J. ZARZYCKI Laboratory of Science of Vitreous Materials, CNRS LA-1119, University of Montpellier 11, France *~epartrnent of Structure and Properties of the Materials, Faculty of Science, University of ~Qdiz, Apartado 40, Puerto Real, csdiz, Spain Resum6 - Le traitement ultrasonore de melanges de. TEOS + H20 permet d'obtenir des gels sans utilisation d'alcool comtne s o l v a n t commun. L'influence de l'energie fournie par les ultrasons et de la temperature de gelification sur la texture des aerogels resultants a 6t6 etudi6e pour determiner les conditions optimales pour le frlttage. Abstract - Ultrasonic treatment of mixtures of TEOS + H20 . . enables gels to be obtained without^the necessity of using alcohol as a commom s o l v e n t . The influence of energy supplied by the ultrasounds and gelation temperature on the texture of the resulting aerogels were studied in order to determine the optimal conditions for sintering. 1 - INTRODUCTION Some results on silica gels obtained by hydrolysis of TEOS wlthouc the use of a solvent have been already reported /1-4/. The initially homogeneous liquid 1s obtained by submltting TEOS and water to the action of ultrasounds in the presence of an acid catalyst. Resulting gels are two or three* times more dense than standard gels prepared in alcoholic solution. This method is potentially interesting for preparing highly refractory matrices for ceramic composites. It is welL known that the texture of the aerogels strongly depends on various preparation parameters such as composition, type of catalyst, gelatlon temperature, aging, hypercritical conditions of drying, etc. The present method introduces the dose ,of ultrasonic energy as a parameter to be controlled in order to optimize the initial conditions for final densification treatment. As its influence on the textural characteristics is unknown, a study on hypercritically dried "sonogels" has been undertaken to see how the dose of ultrasonic energy and gelation temperature influence the subsequent evolution of the aerogels during the sintering process. 2 - EXPERIMEIqTAL The Ilyd~:olysls of tetraethoxysllane, TEOS (R.P. FLUKA) , was obtained sub~ectillg a rnlxture of TEOS, water and traces of HCl, used as catalyst, to ultrasounds produced by a sonifler('), operating at 20 kHz with an inox steel transducer ( 1 ) "ULTRASONIC", MEAUX AND M.M., France. Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989438