SOL-GEL SYNTHESIS OF ALUMINA IN THE PRESENCE OF ACETIC-ACID - DISTINGUISHING GELS AND GELATINOUS PRECIPITATES BY NMR-SPECTROSCOPY

H-1, C-13, and Al-27 NMR spectroscopies were used to characterize the products of sol-gel synthesis with Al(O-s-Bu)3 reactant used in the presence of acetic acid and sec-butyl alcohol. The molar ratio R of acetic acid to Al(O-s-Bu)3 determined the nature of the product. When R was <2, the product was an opaque gelatinous precipitate, and when R was greater-than-or-equal-to 2, the products were transparent gels. The gels were distinguished from the gelatinous precipitate by H-1, C-13, and Al-27 NMR spectroscopies. These techniques provide simple methods for determining the gel point.