Dehydration sequence of gibbsite by electron-beam irradiation in a TEM

To understand the dehydration mechanisms of aluminum hydrates, the dehydration sequence of gibbsite (gamma-Al(OH),) 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 chi-alumina to eta- or gamma-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.