Time and temperature based gellability zones in modified titanium alkoxidesols

Titanium hydroxide derived from stoichiometrically hydrolysed modified prec ursors usually takes as much as 14 days to gel under ambient conditions. Th ese systems can however be made to gel within a few hours by raising the so l temperature to above 80 degrees C or alternatively by lowering it to belo w 10 degrees C. A gellability zone has been identified between 10 degrees C and 80 degrees C on the temperature axis and between 0 and 14 days on the time axis, for all chelate ratios up to 1:4. The spread of the acetyl aceto ne gellability zone is wider than that for ethyl acetoacetate leading to a wider range of microstructural controls that may be imposed upon such syste ms. The locus of gel points on the gellability zone separates the sol state from the precipitated state. Thermoreversible gelling is seen within the t itania gellability zone. (C) 1999 Elsevier Science Ltd and Techna S.r.l. Al l rights reserved.