Solvothermal Synthesis of Spherical Alumina: Delving into the Formation Mechanism and Morphological Change with Phase Transformation

Spherical shaped mesoporous alumina was synthesized by a simple solvothermal process at 110 degrees C/24 h using aluminum nitrate as precursor in the presence of glycerol, diethyl ether and propanol followed by calcination at 900-1100 degrees C. The transformation of solid spherical gamma-Al2O3 at 900 degrees C into layered shell spherical alpha-Al2O3 at 1000-1100 degrees C was governed by stepwise temperature gradient (Delta T) along the radial direction of interface with adhesion and contraction forces. XRD analysis confirmed the formation of gamma-Al2O3 at 900 degrees C and its conversion to alpha-Al2O3 at 1000 degrees C. The N-2 adsorption-desorption results showed BET surface area and average pore diameter of gamma-Al2O3 as 77.58 m(2) g(-1) and 3.7 nm, respectively. The particle size of alumina spheres was in the range of 1-3 mu m as confirmed by FESEM and TEM studies. The HRTEM images indicated lattice spacing of 0.21 and 0.23 nm corresponding to gamma-Al2O3 with (400) plane and alpha-Al2O3 with (110) plane, respectively. A tentative formation mechanism and the role of glycerol have been explained.