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Figure 8
Boehmite to γ-alumina transformation mechanism. (a) Boehmite structure (arrows indicate two oxygen layers in the hydroxyl group gap); (b) collapse-1 mechanism, where hydroxyl groups are thoroughly removed, and the upper block collapses down with a shear of 0.5a; (c) collapse-2 mechanism, where after the dehydration, the upper block collapses down with a shearing of 0.5c. Only one oxygen layers remains in the gap, which forms an Al–O layer by Al3+ diffusion, as indicated by an arrow; (d) reaction mechanism, where after the dehydration, the space with two oxygen layers remains filled by diffusion, forming two Al−O layers (indicated by arrows) without the occurrence of collapse. In order to get an intermediate structure for analysis, the upper block slightly expands up with a shearing of 0.5a. Outlined in (c)–(d) are the unit cells of the formed intermediate structure. The upper and lower blocks are shown in different color for clarity, and other polyhedra are not shown.

ISSN: 2052-5206
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