Evaluation of the modified reduction/expansion synthesis in the production of nanoparticulate alumina

Abstract

This study aims to probe the feasibility of a modified reduction/expansion synthesis (M-RES) to generate alumina nanoparticles from nitrate precursors. 1/1 weight ratio mixtures of aluminum nitrate and urea exposed to fast heating at three temperatures (350, 650, 950 °C, under oxidize atmosphere), in order to create the kinetic and thermodynamic conditions to promote chemical reactions and phase transformations leading to the formation of alumina nanoparticles. Crystallographic, morphological and textural properties were evaluated via X-ray diffraction, scanning electron microscopy and nitrogen adsorptions isotherms. Xray revealed little crystallographic development at 350 o C (composed mainly of pseudo boehmite); samples synthesized at 650 and 950 o C presented a welldeveloped crystallographic structure (delta alumina and gamma alumina, respectively). SEM pictures show the transition from amorphous micron aggregates from the 350 o C sample to a more faceted structure material, characteristic of highly crystalline alumina, at 950 o C. M-RES procedure generates powder material with low total surface area and pore volume. Synthesis temperature showed a direct correlation with the development of total surface area and volume pore, the highest values were obtained for the 950 o C synthesized sample (29.5 m 2 /g and 1698 x 10-2 mL/g), while the 350 o C temperature generated the lowest values (4.9 m 2 /g and 3,142 x 10-3 mL/g). M-RES procedure proved to be a suitable procedure to obtain oxidized nanoparticles of sizes ranging from 50 to 200 nm. The M-RES technical simplicity could become a scalable and efficient process for the synthesis of nanoparticles.