In this work, two new gel-combustion routes for the synthesis of Al2O3 nanopowders with aspartic acid
as fuel are presented. The first route is a conventional stoichiometric process, while the second one is a
non-stoichiometric, pH-controlled process. These routes were compared with similar synthesis procedures using glycine as fuel, which are well-known in the literature. The samples were calcined in air at
different temperatures, in a range of 600–1200 ◦C. They were characterized by X-ray diffraction, scanning
electron microscopy, transmission electron microscopy and BET specific surface area. Different phases
were obtained depending on the calcination temperature: amorphous, (metastable) or (stable). The
amorphous-to- transition was found for calcination temperatures in the range of 700–900 ◦C, while the
-to- one was observed for calcination temperatures of 1100–1200 ◦C. The retention of the metastable
phase is probably due to a crystallite size effect. It transforms to the phase after the crystallite size
increases over a critical size during the calcination process at 1200 ◦C. The highest BET specific surface
areas were obtained for both nitrate–aspartic acid routes proposed in this work, reaching values of about
50 m2/g.
