| 초록 |
In this work, we investigated the phase transformation of platelet and rod γ-Al2O3 by XRD, BET, HR-TEM, solid state 27Al-NMR and ethanol TPD after sequential annealing in air up to 1100oC. After annealing at 1100oC, commercial γ-Al2O3 transformed to α-Al2O3 with drastic surface area reduction (initially 200m2/g to 25m2/g). However, platelet γ-Al2O3 transformed to θ-Al2O3 not α-Al2O3 and sustained much higher surface area (60m2/g) than commercial ones after same treatment. Rod γ-Al2O3 phase transformed to δ-Al2O3. Interestingly, platelet and rod which showed same XRD transformed to different phases. These results strongly suggest that the phase transformation can be affected also by secondary morphologies. Ethanol TPD from platelet and rod after 1100oC annealing, showed significantly different desorption profiles. These different phase transformations were also supported by solid 27Al-NMR. Commercial alumina shows mostly octahedral Al3+ ions after 1100oC annealing, but others show even higher intensities of tetrahedral Al3+ ions than initial γ-Al2O3. Morphological changes were also confirmed by TEM. These results consistently suggest the morphology dependent phase transformations of γ-Al2O3 and thermal stability of platelet and rod. |
