Effects of peptizers on alkoxy-derived aluminium hydroxide sols and the sol-gel transformation

The effects of a number of inorganic and organic acids (HCl, HNO3, HClO4, CH3COOH, Cl3CCOOH) on the peptization of aluminium monohydroxide derived from aluminium secondary butoxide were examined. The efficiency of peptization, given inversely by the optical density of the sols, varied in the series HClO4> HNO3> HCl for inorganic acids and CH3COOH > Cl3CCOOH for organic acids. A similar series was also valid for the shrinkage pattern of the sols during sol-gel transformation, pointing towards a proportionality between colloidal particle size and the degree of flocculation. The rate of escape of the volatiles, i.e. gelling time as a function of gel volume, could be expressed by a linear regression equation with a correlation coefficient r = -0.9658, indicating a strong relationship, when gelation under the action of low concentrations of the acid was ignored. © 1984 Taylor & Francis Group, LLC