Synthesis of magnesium aluminate spinel nanopowder by sol–gel and low-temperature processing

Abstract: Nanospinel MgAl₂O₄ powder was obtained by a sol–gel method at low-temperature processing. It was synthesized using aluminum tri-sec-butoxide and magnesium nitrate hexahydrate as precursors, in an acid medium at 80 °C. Heat treatments of the dried gel were performed from 200 to 1000 °C (∆T = 100 °C) and the powders were characterized by SEM, XRD, TG/DTA, FT-IR, and HR-TEM. A mixture of semispherical nanoparticles (<50 nm) of boehmite and unreacted magnesium nitrate was found after the sol–gel reaction. According to HR-TEM and XRD results, a low-crystalline spinel MgAl₂O₄ started forming at 300 °C, which is a lower temperature than the reported for the same phase in other works. A mechanism of reaction is proposed to explain the formation of spinel at low temperature. At 800 and 900 °C a spinel mono-phase totally crystalline was observed. At 1000 °C, the spinel MgAl₂O₄ phase is well defined but a second phase, magnesium oxide, was found to be about 6% of the final composition. The crystal sizes were 2.272 ± 0.054, 5.222 ± 0.030, 11.610 ± 0.064, and 25.140 ± 0.20 nm for the material heat treated at 700, 800, 900, and 1000 °C, respectively.