STABILITY OF SUSPENSIONS OF ALUMINA NANOPARTICLES IN AQUEOUS-SOLUTIONS OF ELECTROLYTES

Studies were performed on the colloidal behavior of aqueous suspension s of nanodisperse powders of alumina prepared by low-temperature plasm a synthesis. The surface charge density, electrokinetic potential, and coagulating power of 1 : 1, 2 : 1, and 1 : 2 electrolytes depend on p H. Coagulation takes place at abnormally high concentrations of electr olytes with univalent counterions and at abnormally low concentrations of electrolytes with bivalent counterions. These facts cannot be expl ained by the classical concepts of the DLVO theory. High stability of suspensions with respect to univalent counterions is explained by the appearance of the structure-related component of the disjoining pressu re due to the ''secondary'' hydration of the surface. This hydration i s associated with the formation of highly charged aquahydroxycomplexes of aluminium on the particle surface brought into contact with acid o r alkali.