STUDY OF SURFACES PROPERTIES OF FUMED ALUMINA SILICA MATERIALS/

Highly-disperse fumed alumina/silica (AS) with different content of al umina was studied by X-ray, Al-27 MAS NMR, optical spectroscopy of ads orbed color indicator, electrophoretic and quantum chemical methods, i n addition, original silica and alumina were studied for comparison wi th AS. The alumina phase formed in AS for C-Al203 above 20 wt%, when s ix-fold coordinated AI atoms appear, is amorphous. The alumina patches are covered by a silica shell in aqueous suspension as electrophoreti c mobility of the AS particles is practically independent of the conce ntration of alumina and an effective diameter of the particles in susp ension considerably larger than the size of primary particles due to a ggregation and agglomeration. The Bronsted acidic sites =Al-O(H)-Si= a re observed on the AS surface and the intensity of the corresponding b ands in the adsorbed Hammet indicator spectra depends nonlinearly on t he concentration of alumina. (C) 1997 Elsevier Science B.V.