α‐Alumina nanospheres from nano‐dispersed boehmite synthesized by a wet chemical route

In this work, stable aqueous suspensions of nano-boehmite were developed through a hybrid wet-chemical route that uses hyperbranched dendritic poly(ethylene)imine (PEI) as template material for boehmite formation aiming at the development of a deagglomerated α-alumina nanopowder after calcination. The method involves firstly the interaction between the Al precursor and PEI followed by the hydrolysis and polycondensation reactions. The study was aiming to investigate the effect of solids content and pH during reactions on both the stability of the final suspension and the morphology of the resulting nanocrystals. For this purpose, the suspensions were evaluated through viscosity measurements, zeta potential analyses, FT-IR, DLS and sedimentation studies, whereas after the proper centrifugation, drying, and calcination steps, the as-received nanocrystals were evaluated through SEM, TEM and XRD studies. In addition, the boehmite nanopowder was studied using Thermogravimetric and Differential Thermal Analysis, whereas its sinterability was evaluated by dilatometric measurements. The investigation showed that the conditions employed affect greatly both the morphology of nanocrystals as well as the dispersion and the stability of the suspensions. The boehmite suspension with the optimum dispersion and stability can lead, after calcination at 1050°C, to a fine deagglomerated α-alumina nanopowder with a mean size at about 10 nm.