Photoacoustic Analysis of the Evolution from Sols to Aged Gels: Comparison of Different Initial Titania Sols

C. MARCHI, R. CASTAÑEDA-GUZMÁN2, A. PÉREZ-PACHECO2, S. ALDABE BILMES1 AND M. VILLAGRÁN

INTERNATIONAL JOURNAL OF THERMOPHYSICS

plenum press

Año: 2004 vol. 25 p. 491 - 502

0195-928X

We propose the use of correlation analysis of the photoacoustic signal changes during the sol-gel-aging evolution of titania sols prepared from the hydrolysis of titanium n-butoxide in alcoholic, aqueous, and micellar medium which provide different initial conditions and different evolution pathways. The photoacoustic experiments were done either at constant temperature for monitoring the initial evolution of the system, or under heating at 2°C for monitoring molecular processes related to drying, syntering and crystallization. Results obtained from photoacoustic measurements display higher sensibility when compared with those from Differential Thermal Analysis (DTA) and Thermogravimetric Analysis (TGA). The evolution of these systems show instabilities below and above gelation, as well as during thermal treatment. These stabilities are minimized when the thermal treatment is performed on gels aged several months, and can be associated to molecular rearrengements or oscillating chemical reactions. For all the systems studied, the sensitivity of the correlation analysis recovered from photoacoustic signals allows to detect a transition in the 100-150°C range.