Vapor phase synthesis and consolidation of nanophase oxides

Bulk nanostructured materials are becoming increasingly important in structural applications. In order to achieve the desired nanograined structure in the end product, a non-agglomerated powder with < 10 nm particle size is required as starting material. Furthermore, it is important to prevent coarsening of the nanostructure during processing. In recent research, we have developed a scaleable process for the synthesis of non-agglomerated nanoparticles of single phase (alumina, zirconia), multiphase (alumina/zirconia) and multicomponent (gallates, ferrites) oxides, as well as carbides and nitrides. The process, and involves Chemicap Vapor Condensation, is a modification of the Inert Gas Condensation process, and involves pyrolysis of a chemical precursor in a heated tubular reactor with short residence time. Efficient pyrolysis in a low pressure (< 30 mbar) atmosphere, either inert or reactive, has been found to be the key to high rate production of non-agglomerated powders. Studies have also been carried out on consolidation of these powders into dense materials while still preserving the nanoscale structures. For example, near theoretical density with an average grain size of approx. 50 nm, has been obtained by pressure-assisted sintering of nanophase zirconia in air. Similar results have been obtained by pressureless sintering of powder mixtures of nanostructured alumina and zirconia.