Structural evolution of phosphated alumina during sol-gel synthesis.

Phosphated alumina gels were prepared by the sol-gel method. Gels were aged from 1 to 8 days in air. Gel structure evolution, as time went on, was followed by 27Al magic angle spinning nuclear magnetic resonance, X-ray diffraction, and small-angle X-ray scattering. It is concluded that the aging time is a crucial parameter in the formation of coordinately unsaturated sites of aluminum (AlIV and AlV). The gel network is shown to have a fractal structure.