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

Abstract

AbstractSpherical shaped mesoporous alumina was synthesized by a simple solvothermal process at 110 °C/24 h using aluminum nitrate as precursor in the presence of glycerol, diethyl ether and propanol followed by calcination at 900–1100 °C. The transformation of solid spherical γ‐Al2O3 at 900 °C into layered shell spherical α‐Al2O3 at 1000–1100 °C was governed by stepwise temperature gradient (ΔT) along the radial direction of interface with adhesion and contraction forces. XRD analysis confirmed the formation of γ‐Al2O3 at 900 °C and its conversion to α‐Al2O3 at 1000 °C. The N2 adsorption–desorption results showed BET surface area and average pore diameter of γ‐Al2O3 as 77.58 m2 g−1 and 3.7 nm, respectively. The particle size of alumina spheres was in the range of 1–3 μm as confirmed by FESEM and TEM studies. The HRTEM images indicated lattice spacing of 0.21 and 0.23 nm corresponding to γ‐Al2O3 with (400) plane and α‐Al2O3 with (110) plane, respectively. A tentative formation mechanism and the role of glycerol have been explained.