Preparation Of One Dimensional γ-Al₂O₃ And Its Characterization

One dimensionγ-alumina has broad applications in various fields of functional ceramic,absorption and separation,catalyst and so on,due to their high-elastic modulus,unique optical characteristics and special thermal and chemical stability.In this paper,theγ-Al₂O₃ nanorods,nanolaths and nanofibers were obtained via "the surfactant template method","hydrothermal processing" and "solvent-thermal approach" using H₂O₂-precipitated boehmite from sodium aluminate solutions as the precursor reported by El-Katatny et al.Theγ-Al₂O₃ nanorods were prepared via "the surfactant template method" using CTAB as the template.The effects of the precipitated time,H₂O₂ titration rate, annealing temperature were studied.The results showed that the alumina particles were obtained at 5ml/min of H₂O₂ titration for precipitation time of 10h with amorphous crystallite structure,and at the same H₂O₂ titration rate for precipitation time of 16h,the nanorods were obtained with diameters of 10～20nm and lengths of 60～80nm,but the structures of the products were indentified as amorphous alumina. After precipitation for 22h,the alumina film was obtained and the structure was transformed to boehmite.Theγ-Al₂O₃ nanolaths were obtained by "the hydrothermal processing" using the prepared boehmite as the precursor.The effects of aging time,precipitated time,the pH value of the solution,NaAlO₂ concentration,hydrothermal time and temperature were also investigated.It was indicated that the solution obtained by the reaction of H₂O₂ with sodium aluminate was unstable,i.e.,parts of boehmite nanostructures were converted to the bayerite after 0.5h of aging time.The precipitated time had an obvious impact on the morphologies of the hydrothermal products,but little influence on their structures,the hydrothermal products were indentified as AlOOH.The pH value of the solution had a negligible impact on structures,but very obvious effect on their morphologies.Both hydrothermal time and temperature played very important impact on the structures and morphologies.With increase of the hydrothermal temperature,the appearance time of laths became shorter,and with increase of the hydrothermal time,the products were dispersed better.When the NaAlO₂ concentration was reduced,the morphologies of products were converted from the particles to fibers and then to the laths.The laths were obtained with widths of 20nm and lengths of 200—300nm at precipitated time of 16h and the pH value of 10 under 250℃for 8h.The nanofibers were obtained via "solvent-thermal approach" using the prepared boehmite as the precursor.The products were characterized by XRD,TEM and FT-IR. The results showed that the morphologies of the products were converted from the needles to fibers and then to the laths with the increase of the solvent polarity when using pyridine,ethanol and distill water as the solvent.The solvent polarity has no effect on the crystal structure of the precursor,but great effect on the crystallization of the product,which was enhanced with the increase of the solvent polarity.