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Nonstoichiometry of Al-Zr intermetallic phases

Description: Nonstoichiometry of metastable cubic {beta}{prime} and equilibrium tetragonal {beta} Al-Zr intermetallic phases of the nominal composition Al{sub 3}Zr in Al-rich alloys has been extensively studied. It is proposed that the ``dark contrast`` of {beta}{prime} core in {beta}{prime}/{sigma}{prime} complex precipitates, in Al-Li-Zr based alloys, is caused by incorporation of Al and Li atoms into the {beta}{prime} phase on Zr sublattice sites, forming nonstoichiometric Al-Zr intermetallic phases, rather than by Li partitioning only. {beta}{prime} particles contain very small amounts of Zr, approximately 5 at.%, much less than the stoichiometric 25 at.% in the Al{sub 3}Zr metastable phase. These particles are, according to simulation of high resolution images, of the Al{sub 3}(Al{sub 0.4}Li{sub 0.4}Zr{sub 0.2}) type. Nonstoichiometric particles of average composition Al{sub 4}Zr and Al{sub 6}Zr are observed also in the binary Al-Zr alloy, even after annealing for several hours at 600{degree}C.
Date: June 1, 1994
Creator: Radmilovic, V. & Thomas, G.
Partner: UNT Libraries Government Documents Department

Imaging of SiC in metal matrix composites

Description: TEM has advantages over XRD in determining lattice periodicity. This paper reports an attempt in matching a simulation to an experimental image of SiC in an Al-8.5wt%Fe-1.3 wt%V-1.7 wt%Si composite containing 15 wt% SiC particulates, processed by powder metallurgy. The hexagonal allotrope has predominantly the 6H polytype structure; 1/3 of the 15R polytype is also observed. This SiC structure represents the 87R polytype. 6 refs, 2 figs.
Date: August 1, 1992
Creator: Radmilovic, V.; O`Keefe, M. A. & Thomas, G.
Partner: UNT Libraries Government Documents Department

Reactive Spreading of a Lead-Free Solder on Alumina

Description: The wetting of Sn3Ag-based alloys on Al{sub 2}O{sub 3} has been studied using the sessile-drop configuration. Small additions of Ti decrease the contact angle of Sn3Ag alloys on alumina from 115 to 23 degrees. Adsorption of Ti-species at the solid-liquid interface prior to reaction is the driving force for the observed decrease in contact angle, and the spreading kinetics is controlled by the kinetics of Ti dissolution into the molten alloy. The addition of Ti increases the transport rates at the solid-liquid interface, resulting in the formation of triple-line ridges that pin the liquid front and promote a wide variability in the final contact angles.
Date: December 1, 2005
Creator: Gremillard, L.; Saiz, E.; Radmilovic, V.R. & Tomsia, A.P.
Partner: UNT Libraries Government Documents Department

Validation of Predicted Precipitate Compositions in Al-Si-Ge

Description: Aged alloys of Al-0.5Si-0.5Ge (at.%) contain diamond cubic (A4) precipitates in a dispersion that is much finer than is found in alloys with Si or Ge alone. To help understand this aging behavior, the present work was undertaken to determine alloy composition as a function of aging temperature. The composition was estimated theoretically using a CALPHAD approach, and measured experimentally with energy dispersive spectroscopy (EDS) in a high-resolution electron microscope. Theory and experiment are in reasonable agreement. As the aging temperature rises, the precipitates become enriched in Si, changing from 50 at. % in the low-temperature limit to about 80 at.% Si as temperature approaches 433 C, the high-temperature limit of the precipitate field.
Date: April 21, 2004
Creator: Dracup, B; Turchi, P A; Radmilovic, V; Dahmen, U & Morris, Jr., J W
Partner: UNT Libraries Government Documents Department

Sample method for formation of nanometer scale holes in membranes

Description: When nanometer scale holes (diameters of 50 to a few hundred nm) are imaged in a scanning electron microscope (SEM) at pressures in the 10{sup -5} to 10{sup -6} torr range, hydrocarbon deposits built up and result in the closing of holes within minutes of imaging. Additionally, electron beam deposition of material from a gas source allows the closing of holes with films of platinum or TEOS oxide. In an instrument equipped both with a focused ion beam (FIB), and an SEM, holes can be formed and then covered with a thin film to form nanopores with controlled openings, ranging down to only a few nanometers.
Date: February 24, 2003
Creator: Schenkel, T.; Stach, E.A.; Radmilovic, V.; Park, S.-J. & Persaud, A.
Partner: UNT Libraries Government Documents Department

Nano-crystal growth in cordierite glass ceramics studied with X-ray scattering

Description: The development of monodisperse crystalline particles in cordierite glass doped with Cr3+ after a two-step heat treatment is elucidated by a combination of time-resolved small and wide angle x-ray scattering (SAXS/WAXS) experiments with electron microscopy. The effects of bulk and surface crystallization can clearly be distinguished, and the crystallization kinetics of the bulk phase is characterized. The internal pressure due to structural differences between the crystalline and amorphous phase is measured but the physical cause of this pressure can not unambiguously be attributed. The combined measurements comprise a nearly full characterization of the crystallization processes and the resulting sample morphology.
Date: January 16, 2009
Creator: Bras, Wim; Clark, Simon M.; Greaves, G. N.; Kunz, Martin; van Beek, W. & Radmilovic, V.
Partner: UNT Libraries Government Documents Department

Metal-inducd assembly of a semiconductor-island lattice: Getruncated pyramids on Au-patterned Si

Description: We report the two-dimensional alignment of semiconductor islands using rudimentary metal patterning to control nucleation and growth. In the Ge on Si system, a square array of sub-micron Au dots on the Si (001) surface induces the assembly of deposited Ge adatoms into an extensive island lattice. Remarkably, these highly ordered Ge islands form between the patterned Au dots and are characterized by a unique truncated pyramidal shape. A model based on patterned diffusion barriers explains the observed ordering and establishes general criteria for the broader applicability of such a directed assembly process to quantum dot ordering.
Date: August 28, 2005
Creator: Robinson, J.T.; Liddle, J.A.; Minor, A.; Radmilovic, V.; Yi,D.O.; Greaney, P.A. et al.
Partner: UNT Libraries Government Documents Department