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Synthesis of Advanced Ceramic Compounds by Intercalation

Description: The U.S. Bureau of Mines investigated the synthesis of advanced ceramics (SiC+AlN, SiAlON, SiC+Al 203 , and Si 3N4 +AlN) from natural clays (kaolin, halloysite, or montmorillonite) by an intercalation and heat treatment method. This process includes the steps of refining a clay, intercalating organic chemicals into its layered structure, drying the intercalated mixture, firing the treated structure at certain temperature ranges in controlled atmospheres to form desired compounds, and grinding the loosely agglomerated structure. Focus of this research is to economically process advanced ceramic structures from abundant natural resources. The advanced ceramic phases produced in this simple treatment are homogeneously distributed at the nanostructure level, and may potentially lead to cost effective manufacturing processes. The intercalation of clay was confirmed by X-ray and BET analyses. The evolution of chemical compositions during carbonization reactions and carbothermal reduction was investigated. The characteristics of refined clays and synthesized powders were studied. Advanced ceramic composites/solid solution have been produced from intercalated clays, without the presence of other compounds.
Date: 1995
Creator: Kwong, Kyei-Sing & Bennett, James P.
Partner: UNT Libraries Government Documents Department

Reactive plasma atomization of aluminum nitride powder

Description: Experiments were performed to synthesize AlN powders by reacting Al with N using a conventional dc arc plasma as heat source. Feeding Al powder into Ar/N plasma open to atmosphere produced mainly Al oxide. Experiments using a chamber backfilled with nitrogen suppressed the Al oxide, but little AlN was formed. A furnace and crucible assembly was designed to feed molten Al directly into a DeLaval nozzle attached to the face of the dc arc plasma gun. Resulting submicron powders show a significant increase in AlN formation. This was dependent on chamber pressure, plasma velocity, and molten liquid feed rate. Experimental parameters, equipment design, effects of atomization/vaporization/condensation are discussed.
Date: February 1, 1997
Creator: Prichard, P.; Besser, M.; Sordelet, D. & Anderson, I.
Partner: UNT Libraries Government Documents Department

Synthesis, characterization and mechanical properties of nanocrystalline NiAl

Description: Nanocrystalline NiAl was produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100-300 C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range 4-10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.
Date: November 1, 1996
Creator: Choudry, M.; Eastman, J.A.; DiMelfi, R.J. & Dollar, M.
Partner: UNT Libraries Government Documents Department

Gelcasting of aluminum titanate. Final report

Description: This Cooperative Research and Development Agreement (CRADA) was undertaken to assess the applicability of the gelcasting process for forming automotive exhaust port liner green bodies using Golden Technologies` proprietary aluminum titanate powder composition. A gelcasting process, specifically tailored to Golden Technologies` powder, was developed and used successfully to form green bodies for property evaluation. Using appropriate milling and firing conditions, it was found that the gelcast material had properties which compared favorably with Golden Technologies` baseline material. Tubular gelcast samples simulating exhaust port liners were prepared and shipped to Golden Technologies for final process evaluation.
Date: August 1, 1997
Creator: Nunn, S.D. & Stephan, J.E.
Partner: UNT Libraries Government Documents Department

Vibrational and electronic transition in InAs quantum dots formed by sequential implantation of In and As in a-SiO[sub 2]

Description: Optical, structural, and thermodynamic properties of materials can be changed by reducing their dimensions. We sequentially implanted In and As into fused silica windows in order to investigate formation and properties of InAs nano-particles. UV/VIS/NIR, FTIR in mid-IR, and far-IR spectroscopy were used to study change in electronic transitions and in vibrational modes (phonons) of the nano-particles InAs. The phonons can be confined to the surface of nano-particles and have frequencies falling between the transverse and longitudinal optical modes of the bulk material. Thermal annealing developed the formation of InAs quantum dots from as-implanted In-As system. At certain annealing temperature a change in UV/VIS transmission spectra and IR reflectance spectra indicated formation of InAs quantum dots. This is particularly evident from the absorption in IR and surface phonon bands are observed, confirming presence of quantum confined InAs.
Date: January 1, 1996
Creator: Ueda, A.; Henderson, D.O.; Mu, R.; Tung, Y.S.; Hall, C.; Zhu, J.G. et al.
Partner: UNT Libraries Government Documents Department

PERFORMANCE OF CHIPPED MAGNESIUM VERSUS HAMMERMILLED MAGNESIUM IN THE BOMB REDUCTION OF TETRAFLUORIDE. PART I

Description: The O. Hommel Company, of Carnegie, Penna., supplied Mallinckrodt Chemical Works with three types of Mg chips or powder (Type 84, 85B, and 87B) formed by machining Mg ingots. This material was tested and compared with standard New England Lime Mg in a series of reduction runs. A new type of powder (Type 93) developed by the O. Hommel Company during the course of the first experiment was also sert to Mallinckrodt Chemical Works foi preliminary testing. As this was superior to the other tynes tested, a large batch was made up and sent to both Electro Metallurgical Company and Mallinckrodt Chemical Works in order to confirm the preliminary results obtained by Mallinckrodt Chemical Works alone. (auth)
Date: June 1, 1945
Partner: UNT Libraries Government Documents Department

Measurement of strain heat in shock-loaded 304 stainless steel: implications to powder consolidation; oral presentation of full paper

Description: Over the past decades there have been numerous papers on the shock response of materials and more specifically towards metal powder compaction and consolidation. In general, the shock process for powdered materials has utilized the traditional pressure-volume shock relationships proportioned to the initial packing densities of the powders. However, this approach and its resulting data are in controversy due to the lack of knowledge of its associated particle strain and strain temperature uncertainties. This paper will describe the current understanding as well as the experimental technique used to obtain the shock response for distended materials. The above parameters are described within a pressure-strain-temperature interdependence. It was found that the experimentally measured strain heat was not only a function of initial packing density but also a function of powder size and distribution.
Date: January 1, 2003
Creator: Staudhammer, Karl P.
Partner: UNT Libraries Government Documents Department

Directed light fabrication of rhenium components

Description: Directed Light Fabrication (DLF) is a direct metal deposition process that fuses powder, delivered by gas into the focal zone of a high powered laser beam to form fully dense near-net shaped components. This is accomplished in one step without the use of molds, dies, forming, pressing, sintering or forging equipment. DLF is performed in a high purity inert environment free from the contaminants associated with conventional processing such as oxide and carbon pickup, lubricants, binding agents, cooling or cleaning agents. Applications using rhenium have historically been limited in part by its workability and cost. This study demonstrates the ability to fuse rhenium metal powder, using a DLF machine, into free standing rods and describes the associated parameter study. Microstructural comparisons between DLF deposited rhenium and commercial rhenium sheet product is performed. This research combined with existing DLF technology demonstrates the feasibility of forming complex rhenium, metal shapes directly from powder.
Date: February 1, 1997
Creator: Milewski, J.O.; Thoma, D.J. & Lewis, G.K.
Partner: UNT Libraries Government Documents Department

Dynamic response of physisorbed hydrogen molecules on lanthanide-modified zirconia nanoparticles

Description: We investigated the microstructure and surface properties of ultrafine Ce- and Nd-modified zirconia powders by a joint adsorption-isotherm and neutron-scattering study. While the average pore size distribution and specific surface area can be determined by BET analysis of nitrogen adsorption, neutron inelastic scattering from surface adsorbed hydrogen provides additional information about the modulation of local potential energies over the substrate surfaces and distinguishes subtle differences in the microporous and mesoporous structure of the two samples.
Date: December 31, 1996
Creator: Loong, C.K.; Trouw; Ozawa, Masakuni & Suzuke, Suguru
Partner: UNT Libraries Government Documents Department

Grain size dependent mechanical properties in nanophase materials

Description: It has become possible in recent years to synthesize metals and ceramics under well controlled conditions with constituent grain structures on a manometer size scale (below 100 nm). These new materials have mechanical properties that are strongly grain-size dependent and often significantly different than those of their coarser grained counterparts. Nanophase metals tend to become stronger and ceramics are more easily deformed as grain size is reduced. The observed mechanical property changes appear to be related primarily to grain size limitations and the large percentage of atoms in grain boundary environments. A brief overview of our present knowledge about the grain-size dependent mechanical properties of nanophase materials is presented.
Date: February 1, 1995
Creator: Siegel, R.W. & Fougere, G.E.
Partner: UNT Libraries Government Documents Department

Test data for the calculation of powder paterns for intermetallic phases

Description: Powder diffraction patterns are often calculated from structural parameters to assist in the identification of materials. To ensure that powder pattern calculations are correct, it is useful to have data to test the computer program doing the calculations. this paper contains test data for each of the crystallographic point groups and 63 of the 230 space groups. An important feature of the data is that many tests involve two high-symmetry structures (sodium and magnesium) that are set in successively lower-symmetry space groups. Thus, the calculated powder intensities for sodium, for example, are identical whatever the setting is. Though the data were chosen to be especially useful for the calculation of the powder patterns of metals and intermetallic compounds, the data have wider utility.
Date: September 1, 1996
Creator: Calvert, L.D.; Mueller, M.H.; Wallace, P.L.; Huang, J.A.; Kaduk, J.A.; Dann, J.N. et al.
Partner: UNT Libraries Government Documents Department

Mechanical properties of nanocrystalline metals, intermetalics and multiphase materials determined by tension, compression and disk-bend techniques

Description: The mechanical behavior of nanocrystalline metallic, intermetallic, and multiphase materials was investigated using tension, compression, and disk-bend techniques. Nanocrystalline NiAl, Al-Al{sub 3}Zr, and Cu were synthesized by gas condensation and either resistive or electron beam heating followed by high temperature vacuum compaction. Disk- bend tests of nanocrystalline NiAl show evidence of improved ductility at room temperature in this normally extremely brittle material. In contrast, tension tests of multiphase nanocrystalline Al- Al{sub 3}Zr samples show significant increases in strength by substantial reductions in ductility with decreasing grain size. Compression tests of nanocrystalline copper result in substantially higher yield stress and total elongation values than those measured in tensile tests. Implications for operative deformation mechanisms in these materials are discussed.
Date: February 1, 1997
Creator: Eastman, J.A.; Thompson, L.J.; DiMelfi, R.J.; Choudry, M.; Dollar, M.; Weertman, J.R. et al.
Partner: UNT Libraries Government Documents Department