Features of phase transitions upon the thermal treatment of Al₂O₃ nanoparticles

Abstract

Micro- and nanopowders of aluminum oxide with nanoparticles ranging from 200 μm to 40 nm obtained by the sol-gel technique have been investigated and the influence of their dimensions on phase transitions γ-Al₂O₃ → α-Al₂O₃ have been studied using differential thermal analysis, X-ray diffraction, and scanning electron microscopy. The data of X-ray-phase analysis show that the phase transition from γ-Al₂O₃ to θ-Al₂O₃ is typical for aluminum oxide nanoparticles at 900°C, while phase transitions from γ-Al₂O₃ to θ-Al₂O₃ are practically not observed at 900°C for microsized aluminum oxide. The transition to the form α-Al₂O₃ proceeds in the temperature range from 1150 to 1200°C. Generally, the results indicate that a reduction in particle sizes allows us to stabilize the formation of α-Al₂O₃ at lower temperatures.