Structural and thermal characterisation of nanostructured alumina templates

Nanostructured anodic aluminium oxide materials containing a two dimensional array of high aspect ratio aligned pores of 200 nm diameter have been heat treated in air at temperatures up to 1340 degrees C. Thermal analysis shows two discrete irreversible exothermic events at 850 degrees C and 1020 degrees C. XRD and Al-27 MAS NMR show the progressive development of local and long range order in the heated structures and indicate a reaction sequence of amorphous Al2O3 -> O-Al2O3 alpha-Al2O3 (corundum). NMR shows the co-existence of aluminium in 4, 5 and 6-coordinated sites through most of the heating sequence until the stable (6-coordinated) corundum phase is established. Phosphorus impurities incorporated during the membrane fabrication process crystallise as an AlPO4 phase above.850 degrees C and play an important role in directing the chemical, physical and structural outcomes of the heat treatment. (c) 2005 Elsevier B.V. All rights reserved.