Structure of amorphous alumina tubes studied by positron annihilation lifetime spectroscopy

Positron annihilation lifetime spectroscopy (PALS) is used to investigate the detailed structure of amorphous alumina tubes prepared via thermohydrolysis of anhydrous AlCl3. The results demonstrate that PALS is a sensitive probe of the structure of amorphous materials, capable of distinguishing between the structures of amorphous alumina tubes and amorphous alumina prepared by a standard procedure, which are shown to differ slightly in the concentration and size of free-volume elements. The observed distinctions can be understood in terms of the anisotropic aggregation of primary alumina particles during hydrolysis in aqueous media or thermohydrolysis in water vapor.