Accession Number : ADA265135


Title :   Nanophase and Nanocomposite Materials. Materials Research Society Symposium Proceedings Held in Boston, Massachusetts on December 1-3, 1992. Volume 286


Corporate Author : MATERIALS RESEARCH SOCIETY PITTSBURGH PA


Personal Author(s) : Komareneni, Sridhar ; Parker, John C ; Thomas, George J


Report Date : Jan 1992


Pagination or Media Count : 454


Abstract : Ultrafine particles (UFPs) of aluminum oxide, formed by arc discharge, were sintered in an ultrahigh vacuum (UHV) furnace system and characterized by high resolution electron microscopy (HREM) under UHV conditions. The UFPs produced range in size from 20 to 50 nm and have highly faceted surfaces. The atomic structure of the UFPs corresponds to the cubic (gamma) and orthorhombic (delta) variants of the spinel structure. In UFPS, surface faceting plays a major role in determining the final sintering geometry with sintering occurring predominantly on the closed-packed (111) facets. Surface diffusion is the predominant mechanism for sintering, as evidenced by the fact that many sintered particles have their initial adhesion structure 'locked in' during sintering with no reorientation occurring. Furthermore, the necks formed during sintering have well-defined, atomically-sharp contact angles suggesting that the neck growth process is controlled by the faceted structures and may be modeled by a mechanism similar to crystal growth due to ledges, grain boundaries, and twins. The driving force for sintering can be considered as a chemical potential difference between facet surfaces and the neck region.


Descriptors :   *COMPOSITE MATERIALS , ANGLES , IONS , METALS , SYMPOSIA , CONDUCTIVITY , STRUCTURES , HIGH RESOLUTION , ELECTRON MICROSCOPY , CRYSTAL GROWTH , TITANIUM DIOXIDE , DIFFUSION , GEOMETRY , ALUMINUM OXIDES , PARTICLES , COATINGS , CERAMIC MATERIALS , SURFACES , SPINEL , ULTRAFINES , SINTERING , ATOMIC STRUCTURE , YTTRIUM , ULTRAHIGH VACUUM , GRAIN BOUNDARIES , FURNACES , PHASE , ALLOYS , ADHESION , CHEMICALS , LAYERS , THERMODYNAMICS , POLYMERS


Subject Categories : Physical Chemistry
      Ceramics, Refractories and Glass
      Laminates and Composite Materials
      Crystallography


Distribution Statement : APPROVED FOR PUBLIC RELEASE