Dehydration Sequence of Gibbsite by Electron-Beam Irradiation in a TEM

To understand the dehydration mechanisms of aluminum hydrates, the dehydration sequence of gibbsite (γ-Al(OH)₃) by electron-beam irradiation has been investigated using transmission electron microscope (TEM). The electron diffraction pattern indicates the formation of chi-alumina in the initial dehydration stage. The intensity distribution in the diffraction pattern of chi-alumina is explained by the random close-packed structure of oxygen/hydroxyl containing gibbsite layer structure. Further irradiation transforms χ-alumina to η- or γ-alumina and to a phase having a more ordered structure. The dehydrated product at this stage consists of crystallites and voids several nanometers in diameter.