Gel formation monitoring by acoustic spectroscopy

• Published in: The Journal of the Acoustical Society of America 2001-05, Vol.109 (5_Supplement), p.2372-2372
• Main Authors: Martinez, Loïc, Serfaty, Stéphane, Senouci, Brahim, Giesmar, Pascal, Gindre, Marcel
• Format: Article
• Language: English
• Subjects: Acoustics; Electronics; Engineering Sciences; Signal and Image processing
• ISSN: 0001-4966; 1520-8524
• DOI: 10.1121/1.4744348

An acoustic technique in the audible range has been developed to characterize the sol–gel process. Resonances appear at the sol to gel transition of a sol–gel matrix when submitted to an acoustic wave. The range of the associated resonance frequencies leads to a very low propagation speed of sound (about 20 m/s). The resonance frequencies versus time curves, corresponding to the harmonic propagation modes, converge to a unique intersection point with the time axis corresponding to the gelation time tg. The temporal evolution of the resonance frequencies features the formation of the network. Actually, the evolution of the matrix is independent of the initial conditions (precursor concentration, hydrolysis rate). Depicting the ‘‘reduced frequency’’ fi/fi(∞) [fi(∞) is the long-term resonance frequency for the harmonic mode i] versus the ‘‘reduced time’’ t/tg for various Si concentrations and hydrolysis rates results in a unique curve, revealing the insensitivity of the matrix formation process to the input parameters. A propagation model of an acoustic wave in a cylindrical cavity is proposed, to compute the resonance frequencies as a function of the longitudinal to transverse propagation velocity ratio CL/CT. The comparison with the experimental data is conclusive.