Synthesis,characterization and formation mechanism of hexagonal prism polycrystalline γ-Al_2O_3

Novel hexagonal prism polycrystalline γ-Al2O3 particles were hydrothermally synthesized in ammonia medium by using AlCl3·6H2O as aluminum precursor.The γ-Al2O3 particles were characterized by means of XRD,SEM,TEM and nitrogen sorption measurements and the formation mechanism of crystal morphology was investigated.The results indicated that after the hydrothermal treatment of aluminum precursor in ammonia medium as well as the later calcination process,γ-Al2O3 particles with perfect hexagonal prism shape can be obtained;the border size and length of the hexagonal prism are about 0.3 and 2.5 μm,respectively.TEM images show that the hexagonal prism γ-Al2O3 particles are aggregated with fine particles of about 10 nm and then take the polycrystalline gamma phase.Such a γ-Al2O3 material exhibits a BET area of 274 cm2/g and pore volume of 0.51 cm3/g with a narrow pore size distribution centered at 5.5 nm.The results also suggest that the formation of the hexagonal prism γ-Al2O3 particles is closely related to the arrangement of the steady AlOOH precursors interacted with NH+ 4 ions.