FOURIER-TRANSFORM MECHANICAL SPECTROSCOPY OF THE SOL-GEL TRANSITION IN ZIRCONIUM ALKOXIDE CERAMIC GELS

The gelation of a ceramic precursor, zirconium alkoxide, has been studied using dynamic oscillatory measurements. The gelation time is controlled by varying the concentrations of zirconium propoxide, hydrolysis with water, and acetylacetone concentration which acts as a chelating ligand. Gelation times were varied from minutes to months. The gelation time varied with zirconium concentration to the -10 power, hydrolysis to the -7 power, and ligand concentration of the -17 power. The sol-gel transition was monitored using the criteria of Winter in which G'similar to G''similar to omega'' and tan (delta=tan (n pi/2). It is shown that the use of multiple superimposed sinusoidal waves to simultaneously measure the moduli at several frequencies is faster than using individual frequency sweep experiments. The selection of rate and strain criteria for brittle network gels is discussed in detail.