Reversibility of liosol <-> liogel <-> xerogel transformations, I.

The colloid stability of ferric hydroxide and Al2O3 sols, the formation of liogels from these sols and also, the hydrophilicity, the peptizability of their xerogels were studied as a function of the pH in the medium. Based on the flocculation values determined with KCI, the stability order obtained for the sols is as follows. acidic SiO2, acidic Al2O3, acidic ferric hydrox ide, basic SiO2, basic Al2O3 and basic ferric hydroxide. The flocculation v alues of the acidic sols are an order of magnitude higher than those of bas ic sols and approach those of water-soluble polymers. The high kinetic stab ility of some acidic sols is presumably due to a highly ordered aqueous lay er formed around the particles, and the surface electric charge of the soli d is of less importance. This finding is in line with the statement of the continuity principle by Ostwald and Buzagh.