抄録
We have found that alumina gels made from aluminum-sec-butoxide by gentle sol-gel reaction exhibited unique crystallization behavior. When corundum-seeded, HCl-catalyzed gel was partially (about 60 %) converted to alpha-alumina around 500 oC, and HNO3-catalyzed gel was completely alpha-transformed at 800 oC. In the present work, structure of these alumina gels was analyzed by X-ray radial distribution function method and Al MAS-NMR spectroscopy, and structure data were compared with those of conventional gel and amorphous boehmite. It was considered that in the HNO3-catalyzed gel dimeric Al2(O, OH)10 units are linked in a similar manner to boehmite, while in the HCl-catalyzed one such a structure unit is rather isolated by Cl-bridging. The Al MAS-NMR data suggested that AlO6 polyhedra are largely distorted in the HCl-catalyzed gel when heat-treated for dehydration, which may lead to alpha-transformation around 500 oC.
