Sponsored by: MDMD Powder Metallurgy Committee and FEMS (Federation of European Materials Societies)
Program Organizers: Dr. David L. Bourell, The University of Texas at Austin, Materials Science & Engineering, MC C2201, Austin TX 78712; Dr. Liisa Kuhn-Spearing, Laboratory for the Study of Skeletal Disorders and Rehabilitation, Harvard Medical School, Children's Hospital, 300 Longwood Avenue, Boston MA 02115; Professor Dr. Herbert Gleiter, Karlsruhe Research Center, P.O. Box 3640, D-76021 Karlsruhe, Federal Republic of Germany
Monday, PM Room: Grand G
February 5, 1996 Location: Anaheim Marriott Hotel
Session Chairperson: Dr. David L. Bourell, The University of Texas at Austin, Materials Science & Engineering, MC C2201, Austin TX 78712
NANOSTRUCTURED MATERIALS - AN OVERVIEW: Jörg Weissmüller, National Institute of Standards and Technology, Bldg 223 Rm A153, Gaithersburg MD 20899
Nanocrystalline materials are polycrystals with a grain size of the order of 10 nm. The earliest studies of these materials were motivated by the strive to explore the limits of metastability of solid matter and to create materials with novel properties. Dimensionality effects and the large fraction of atoms in the core of topological defects (the grain boundaries) with non- lattice atomic short- range order contribute to the unique properties of the materials. The recent past has brought considerable progress in the characterization of the grain boundaries and of the microstructure of nanocrystalline solids. Physical properties are determined not only by the grain size (or rather the distribution of sizes), but also by additional parameters reflecting the thermal and mechanical history of the material. A large number of methods is now available for producing powders with nanometer grain size, but the number of fundamental studies of their consolidation behavior is limited, and producing dense volume materials while avoiding excessive grain growth remains a challenge. The need for controlling the sintering process, together with the observation of grain growth at room temperature in some materials, indicates the fundamental importance of exploring schemes for stabilizing the grain size, and/or for producing nanocrystalline dense volume materials directly, circumventing the powder stage.
NANOSTRUCTURED POWDER SYNTHESIS VIA SELF-ASSEMBLED MEMBRANES: G.M. Chow, M. Markowitz, A. Singh, Laboratory for Molecular Interfacial Interactions, Center for Bio/Molecular Science and Engineering, Code 6930 Naval Research Lab, Washington DC 20375
Nanocrystalline powder can be synthesized using self-assembled molecular membrane structures as reaction vials. This chemical approach has the advantages of producing size-controlled, unagglomerated nanoscale particles. An overview of this approach and our current work at NRL will be presented. In specific, gold and Co/Co(OH)2 nanoparticles have been synthesized inside polymerized vesicles using surface bound palladium ions as catalysts for electroless metallization. HRTEM studies have demonstrated that particle nucleation and growth occurred within the vesicles and that particle growth could be initiated by either single or multiple nucleation sites. Results of formation of nanoscale metal particles using non-polymerized vesicles will also be discussed.
CARBONATED APATITE NANOCRYSTALS FROM BONE: L. Kuhn-Spearing, M.J. Glimcher, Laboratory for the Study of Skeletal Disorders and Rehabilitation, Harvard Medical School, Children's Hospital, Boston MA 02115; H-M. Kim, College of Dentistry, Seoul National University, Seoul, Korea; C. Rey, Laboratoire de Physico-chimie des Solides, I.N.P.T., Toulouse, France
At the microscopic level, bones, antlers and teeth are all composed of numerous, nanometer-sized mineral crystals embedded in an organic matrix. In bone, mineralization is initiated within the organic micro-compartments (40 nm gaps or holes having a 67 nm periodicity) formed when the organic collagen molecules self-assemble into microfibrils. The calcium phosphate crystals (Ca-P) formed in bone are nearly mono-disperse, nm-sized plates of carbonated apatite (a metastable phase of Ca-P), with a unique composition, crystal structure and surface character reflecting the complex biological environment they were nucleated in. A process has been recently developed to isolate and disperse the mineral crystals essentially free of organic matrix -- without any significant change in their composition, overall structure, or internal short range order. The processing, characterization and potential medical applications of the bone mineral crystals will be presented.
NANOCRYSTALLINE PROCESSING FOR STRUCTURAL AND BIO- CERAMICS: Atsushi Nakahira, Department of Chemical Engineering, Darren T. Castro, Department of Materials Science and Engineering, Jackie Y. Ying, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge MA 02139
Nanocrystalline processing has demonstrated exciting potential in deriving oxide ceramics with low- temperature sinterability and net- shape formability. However, such approach has been little explored with more complex ceramic compositions for high-temperature structural or bio- ceramic applications. This talk will focus on two different techniques for generating high- quality nanocrystalline powders. The first involves a modified forced- flow gas- condensation tubular reactor for flexibly producing large quantities of nanocrystalline non- oxide powders, notably Si3N4- based systems. The second exploits wet-chemical precipitation to achieve proper phase control and dopant uniformity in hydroxyapatite- based nanocomposite. The thermal stability and sinterability of the nanostructured ceramics are related to the processing, microstructure and interfacial chemistry of these systems.
THE NANOCRYSTALLINE MATERIALS IN RUSSIA: RESEARCH DEVELOPMENT AND APPLICATION: Prof. Lev I Trusov, Dr. Ampleev, PPP Consulting, Krasnoproletarskaya, 32, 103030, Moscow, Russia
MECHANOCHEMICAL SYNTHESIS OF NANO POWDER: J. Ding, W.F. Miao, T. Tsuzuki, R. Street, P.G. McCormick, Research Centre for Mineral and Materials Processing, University of Western Australia, Nedlands, WA 6097 Australia
The synthesis of nanocrystalline powders by mechanochemical solid- state reduction reactions has been studied. X- ray and transmission electron microscopy measurements showed that Fe, Ni and Cu powders with particle sizes in the range 5- 50 nm were formed during the reduction process. Synthesized Fe powders exhibited coercivities of ~500 Oe, indicative of separated nano- size particles. This study demonstrates that mechanochemical processing has significant potential for the synthesis of a wide range of nanocrystalline powders in an economic and efficient manner.
A NEW APPROACH TO SYNTHESIS OF CERAMIC NANOPARTICLES: Ganesh Skandan, Structured Materials Industries, Inc., 120 Centennial Ave., Piscataway NJ 08855-3908; Yijia Chen, Nick Glumac, Bernard Kear, Rutgers - The State University of New Jersey, P.O. Box 909, Piscataway NJ 08854-0909
Bulk nanostructured materials, and nanostructured coatings are becoming increasingly important in structural and functional applications. In order to achieve the requisite structure in the end product, a non- agglomerated powder with <10 nm particle size needs to be used as starting material for most of these applications. Furthermore, it is important to prevent coarsening of the structure during processing. In recent research carried out at Rutgers University, we have developed a scaleable process for the synthesis of non- agglomerated nanoparticles of single phase (alumina, zirconia, silicon oxynitride), multiphasic (alumina/zirconia composites) and multicomponent oxides (gallates, ferrites), carbides and nitrides. The process, called Chemical Vapor Condensation, is a modification of the Inert Gas Condensation process, and involves pyrolysis of chemical precursors in a hot zone with short residence times. 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 powders with desirable characteristics. Studies have been carried out on consolidation of these powders into dense materials while still preserving the nanostructure. For example, near theoretical densities with an average grain size of ~ 50 nm, have been obtained by pressure assisted sintering of nanoparticles of zirconia in air. Similar results have been obtained by air- sintering powder mixtures of alumina and zirconia. Correlation between powder characteristics, processing and structure will also be discussed.
THE TRANSITIONS "SOL-GEL-STONE-LIKE CONDITION" OF FOUNDRY WASTES: V.A. Mymrin, Scientific Centre for Engineering Geology and the Environment, Russian Academy of Sciences, P.O. Box 145, Ulanski per. 13, Moscow 101000 Russia
It was established by a wide complex of modern investigation methods that the
crystal bodies in burnt foundry sand (foundry slag) may be completely dissolved
in a porous alkaline solution of the same industrial waste, forming a sol. By
increasing the concentration, the sol transforms into a gel. This gel
transforms through several stages to a "stone-like" state. After 28 days, the
strength of the samples was 1.1-2.2 MPa, but after 90 days the strength rose to
5-6.2 MPa. This is the top of the upper level of strength requirements for
Russian standards for reinforced soils at 90 days. The strength almost doubled
at 360 days. These materials possess very high freeze-thaw resistance. These
new materials can be used as environmentally safe, cost effective, low-grade
concrete in potential applications including road bases, industrial/municipal
waste dumps, etc.
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