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Acoustic resonance tracking in sol gel materials

The sol-gel synthesis of glasses and ceramics has received a great amount of scientific and technological interest. The close control of its evolution between the sol and gel states allows the elaboration of highly appropriate materials for technical purposes. The sol-gel transition can be characterized by a very rapid increase of the bulk viscosity of the medium. This paper presents a non-invasive technique of investigation based on acoustic resonance, which can trace the sol-gel evolution. Two different sol-gel matrices have been prepared from silica gels using acid and basic agents. The study of the evolution of these sol-gel matrices shows that in the gel phase, several resonance frequencies appear and increase as a function of time. In both matrices the evolution of these resonance frequencies follow an exponential law according to percolation models for a cross-linked polymeric network. In addition, this technique is particularly well suited to investigate the SG matrices with short gelation times.