Chemical bond change of gibbsite and fumed silica mixture during mechanical activation

Chemical bond changes of gibbsite and fumed silica mixture during mechanical activation were investigated by X-ray powder diffraction (XRD), magic angle spinning nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS). Crystallinity and intrinsic structural change of the mixture during high-energy milling were examined by XRD. Formation of new AlOSi chemical bonds was detected by the changes in Al coordination number of gibbsite in the mixture during milling, and the appearance of new resonance in 29Si NMR spectrum of the ground mixture. The presence of AlO units in silica framework was demonstrated by the increase of Al 2p binding energy and the decrease of Si 2p binding energy.

► Formation of AlOSi bonds during grinding by precursor was confirmed by change of the octahedral AlO units of gibbsite in the starting mixture to tetrahedral and “pentahedral” Al sites in the ground mixture.
► Formation confirmed SiO units bonded to three or four other AlO units reflected by new resonance at −85.25 ppm in 29Si NMR spectrum of ground mixture.
► Formation also confirmed presence of AlO units in silica framework demonstrated by increased Al 2p binding energy to 74.4 eV and decreased Si 2p binding energy to 102.3 eV.