Nanostructured Y2O3

It has been shown that a variety of nanostructured (n-) metal-oxide ceramics such as n-TiO2, n-ZrO2, n-Al2O3, n-ZnO and n-MgO can be produced using the inert gas condensation process. Amongst all the nanostructured oxides, the synthesis, microstructure, sintering, and mechanical properties of n-TiO2 have been studied the most extensively. The gas condensation preparation of nanostructured metal-oxide ceramics involves evaporation of metal nanoparticles, collection and post- oxidation. The original synthesis studies of n-TiO2 showed that in order to avoid formation of the many low oxidation state oxides in the Ti-O system, the post-oxidation had to be performed by rapidly exposing the Ti nanoparticles to pure oxygen gas. By doing so, the highest oxidation state and the most stable structure, rutile, was obtained. An undesired feature of this step is that the nanoparticles heat up to high temperatures for a brief period of time due to the exothermic nature of the oxidation. As a consequence, the particles with an average size of 12 nm tend to agglomerate into larger structures up to 50 nm. The agglomerated state of the powder is important since it determines the original density and pore size distribution after compaction, as well as the sintering characteristics and final microstructure of the bulk sample. As a consequence of the preparation procedure of n-TiO2 and the resulting agglomeration, the pore size distribution of n-TiO2 compacted at room temperature is very wide, with pore sizes ranging from 1 to 200 nm. Nevertheless, the n-TiO2 sinters at temperatures several hundred degrees lower than conventional coarse grained ceramics. From the previous results on n- TiO2 it is anticipated that better microstructures and properties can be achieved by reducing the agglomeration of nanostructured powders through a more controlled post- oxidation process