ENHANCED SURFACE-ACTIVITY IN NANOCRYSTALLINE ALUMINA AS STUDIED BY NEUTRON-ACTIVATION ANALYSIS, X-RAY PHOTOELECTRON AND INFRARED-SPECTROSCOPY

Nanocrystalline alumina was synthesized by the gas phase condensation using the DC are plasma technique. Spherical particles ranging in diam eter between 20 and 80 nm were obtained. The stoichiometric compositio n of the powder was investigated by X-ray photoelectron spectroscopy ( XPS) and the technique of neutron activation analysis after calcinatio n at different temperatures. Enhanced surface activity in the form of an increase in oxygen content was observed to be maximum in the powder calcined around 800 degrees C. This behaviour is attributed to differ ences in microchemical stoichiometry, i.e. presence of active centers which are most likely localised in crystallographically defective conf igurations thereby leading to chemisorptive hydroxyl incorporation at these local sites. This is viewed against the process of microstructur al transformation operative at higher temperatures. The stretching mod es in the infrared spectrum due to the non-hydrogen bonded hydroxyl gr oups confirmed the surface activity of this nanocrystalline alumina. T hermogravimetric analysis was used to study the behaviour of nanocryst alline alumina vis-a-vis coarse grain powder, during the process of ca lcination. (C) 1997 Elsevier Science S.A.