Generating Self-Shaped 2D Aluminum Oxide Nanopowders.

The thermal-assisted exfoliation phenomena of boehmite particles under moderate heating rates were examined. The exfoliation that generated flakes of 5−6 nm in thickness can be achieved because of the perfect cleavage on the boehmite particles that are stripped when thermal treatments bring about dehydration and γ-Al2O3 formation in sequential phase transformation of boehmite. Examinations of the exfoliation effects were carried out on calcined boehmite single crystal particles, which were about 500 nm in diameter, and obtained at three heating rates 0.5, 1.0, and 2.0 °C/min with the heating schedules. The TEM techniques, BET-N2 measurements, XRD-Scherrer equation, and AFM images were employed in the examination. That the BET values increased as increasing of exfoliated flakes reflected two stages of exfoliation. In the beginning stage, during which the BET values were <40 m2/g, the exfoliation resulted from the stress produced by dehydration. In the second stage, the increased rate of surface area was due to the additional force, which originated from the γ-Al2O3 formation. Exfoliation occurred on the cleavage planes {010}, the side pinacoid of the boehmite particle. The generation of flakes resulted in the thinning of boehmite particles. Some of the flakes preserved the external form of boehmite crystals. From the surface energy evaluations of boehmite and γ-Al2O3, it can be inferred that exfoliation is a natural way of thermal treatment.