Preparation and properties of alumina-ceria nano-nano composites

Alumina-ceria composites were prepared by the calcination in air of gels obtained by homogeneous precipitation from dilute chloride and nitrate solutions, followed by either microwave treatment, autoclave treatment or air-drying. Microwave treatment and air-drying of the gels yielded amorphous powders whereas autoclave treatment yielded well-crystallised boehmite. The phase evolution during calcination was investigated by in-situ X-ray diffraction (XRD) and by differential thermal analysis and thermogravimetry (DTA/TG). The structures of the calcined powder were investigated by transmission electron microscopy (TEM) and high resolution TEM. A variety of morphologies was found depending on the processing route. The calcined microwave treated gels consisted of nano-size particles of ceria in nanostructured transition alumina i.e, a nano-nano composite structure suitable for catalysis applications. In comparison, the calcined autoclave treated gels consisted of a coarser composite of large agglomerates of ceria in transition alumina which, however, was more stable against transformation to alpha alumina at high temperature. Boehmite sols made with the autoclave treated gels were suitable for making thin films by dip-coating. (C) 1999 Kluwer Academic Publishers.