Lee Meng-Ying, Yen Fu-Su, Hsiang Hsing-I
Department of Resources Engineering, National Cheng Kung University, Tainan 70101, Taiwan.
Nanomaterials (Basel). 2022 Aug 26;12(17):2955. doi: 10.3390/nano12172955.
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.
研究了勃姆石颗粒在中等加热速率下的热辅助剥离现象。由于勃姆石颗粒在热处理导致脱水和γ-Al2O3形成的连续相变过程中发生剥离时存在完美解理，因此可以实现产生厚度为5-6nm薄片的剥离。对直径约500nm的煅烧勃姆石单晶颗粒进行了剥离效果研究，这些颗粒在加热速率分别为0.5、1.0和2.0℃/min的加热程序下获得。在研究中采用了透射电子显微镜（TEM）技术、BET-N2测量、XRD-Scherrer方程和原子力显微镜（AFM）图像。BET值随着剥离薄片数量的增加而增加，这反映了剥离的两个阶段。在初始阶段，BET值<40m2/g，此时剥离是由脱水产生的应力引起的。在第二阶段，表面积增加速率是由于源自γ-Al2O3形成的额外力。剥离发生在勃姆石颗粒的{010}解理面，即侧面平行双面。薄片的产生导致勃姆石颗粒变薄。一些薄片保留了勃姆石晶体的外形。从勃姆石和γ-Al2O3的表面能评估可以推断，剥离是热处理的一种自然方式。
