Abstract
γ-Alumina was synthesized by a sol-gel method with the aluminum ion hydrolysis control performed by urea. The initial saturated Al3+/urea solution presented urea coordinated with the aluminum ion, as shown in the 13C NMR and 27Al NMR spectra and longitudinal relaxation times, T 1, from the latter. The substitution of water molecules in the Al3+ coordination shell by urea controlled the hydrolysis process and provided an extensive nucleation during the initial steps of the aluminum hydroxide formation due to urea thermolysis at 90°C. The resulting sol, composed of Al(OH)3 nanoparticles, coalesced and became a transparent gel permeated by a solution of urea and the polycation ion [Al13O4(OH)24(H2O)12]7+. The freshly prepared gel was transformed, under heating at 300°C, directly to γ-alumina, characterized by FTIR, 27Al-MAS-NMR and SBET techniques, without δ- or θ-phases, as a consequence of the high degree of homogeneity of the γ-alumina precursor.
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Macêdo, M.I.F., Osawa, C.C. & Bertran, C.A. Sol-Gel Synthesis of Transparent Alumina Gel and Pure Gamma Alumina by Urea Hydrolysis of Aluminum Nitrate. Journal of Sol-Gel Science and Technology 30, 135–140 (2004). https://doi.org/10.1023/B:JSST.0000039497.46154.8f
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DOI: https://doi.org/10.1023/B:JSST.0000039497.46154.8f