Properties of aluminated silica sols

Abstract

Abstract:The properties of colloidal dispersions of "Positive Sol 130M" (E. I. du Pont de Nemours and Co.), which contains silica particles coated with alumina, have been studied in detail. Drifts of pH, leaching of aluminum species, and changes of electrokinetic mobility occurred during aging at room temperature for periods of up to a month, and were attributed to surface reactions. Despite its name, the sol has a point of zero charge (PZC) at pH 9, and consequently the particles carry a positive charge only below this pH. The alumina of the coating dissolves in acidic environments; the extent of leaching of aluminum species is dependent upon pH and length of aging at room temperature. The effect of different anions on this process was examined by using various inorganic acids ; it was shown that phosphate and sulfate ions exhibit the strongest.effects. The removal of alumina changed the surface characteristics as well as the stability of the Sol 130M. The mobilities of the particles were found to be directly related to the composition of the particle surface, regardless of the time of aging or the pH.