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Diffraction Studies of Glasses, Liquids and Nanoclusters

Description: Amorphous SiO{sub 2} is classically understood as a continuous random network forming glass. Typically amorphous materials possess no translational symmetry, which is the signature of a crystal. Our interest in investigating SiO{sub 2}, grown as a thin film (100, 500 {angstrom}) on Si(001), is to observe how this particular amorphous phase is able to couple to the crystalline substrate and reflect a peculiar degree of order.
Date: January 24, 2005
Creator: Castro-Colin, Miguel; Donner, Wolfgang & Moss, S. C.
Partner: UNT Libraries Government Documents Department
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Theoretical and Computational Studies of Pattern Formation

Description: This is the final report in connection with the project ''Theoretical and computational studies of pattern formation''. The objectives of this research are to improve the understanding of the mechanisms underlying the formation of complex spatio temporal patterns in systems that are driven outside of thermodynamic equilibrium, to characterize the macroscopic properties of such states, and to apply the methodology to situations of interest in fluid mechanics, materials processing and engineering.
Date: August 10, 2004
Creator: Vinals, Jorge
Partner: UNT Libraries Government Documents Department
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Mechanisms of Plastic and Fracture Instabilities for Alloy Development of Fusion Materials. Final Project Report for period July 15, 1998 - July 14, 2003

Description: The main objective of this research was to develop new computational tools for the simulation and analysis of plasticity and fracture mechanisms of fusion materials, and to assist in planning and assessment of corresponding radiation experiments.
Date: July 14, 2003
Creator: Ghoniem, N. M.
Partner: UNT Libraries Government Documents Department
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Experimental Studies of the Vibrational Entropies of Alloy Phases

Description: This is the annual progress report for the Grant DE-FG03-96ER45572. This research is on the entropy of materials, particularly alloy phases. It is an experimental effort utilizing inelastic neutron scattering facilities at two DOE facilities: Oak Ridge National Laboratory (HFIR) and Argonne National Laboratory (IPNS), and the NIST Center for Neutron Research. It includes an overview of completed research in 2000, a list of publications, and personnel supported under this grant.
Date: February 18, 2001
Creator: Fultz, Brent
Partner: UNT Libraries Government Documents Department
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Structure and dynamics in low-dimensional guest-host systems

Description: This is the final report of the fourth of four three year grants of the same title. The program evolved from an earlier DOE grant on graphite intercalation compounds. Since its inception eight years ago, the focus evolved continuously from conjugated polymers to fullerenes, disordered carbons for Li-ion battery applications, and most recently carbon nanotubes, with side excursion back to GIC's to exploit a recent advance in synthesis of a potentially exciting new phase. The unifying themes are the versatility of carbon in forming novel solids, and the flexibility of intercalation chemistry to provide new materials with potentially useful properties.
Date: May 1, 2000
Creator: Fischer, John E.
Partner: UNT Libraries Government Documents Department
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Electropolishing as a Decontamination Process: Progress and Applications.

Description: Electropolishing is a rapid and effective technique for removing plutonium and other radionuclide contamination from a variety of metal surfaces. The major objective of this continuing research is to develop electropolishing into a large-scale decontamination technique that can completely and economically remove transuranic and other surface contamination from large volumes of metallic waste. These research studies have demonstrated the ability of electropolishing to reduce the radiation levels of steel tools and stainless steel vacuum system components, which were heavily contaminated with plutonium oxide. Other examples of objects that have been decontaminated within minutes using electropolishing include hot cell manipulator assemblies, analytical instrument components, laboratory transfer containers, offsite shipping containers, fission product storage capsules, laboratory animal cages, and nuclear reactor process tube components. One of the major activities of this research has been the establishment and intensive operation of a 400-gal immersion electropolishing system designed specifically to develop and demonstrate decontamination techniques for representative plutonium- and beta/gamma-contaminated components. Substantial progress has also been made in developing in situ electropolishing techniques that can be used to decontaminate metallic surfaces that cannot readily be transported to or immersed in a conventional electropolishing tank. Sectioning/pretreatment studies are underway to develop and demonstrate optimum disassembly, sectioning, surface preparation, and gross contamination removal procedures. Other supporting studies are also in progress to provide a sound technical basis for scale-up and widespread application of this new decontamination process.
Date: July 28, 1978
Creator: Allen, R. P.; Arrowsmith, H. W.; Charlot, L. A. & Hooper, J. L.
Partner: UNT Libraries Government Documents Department
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Characterization of Mo/Si multilayer growth on stepped topographies

Description: Mo/Si multilayer mirrors with nanoscale bilayer thicknesses have been deposited on stepped substrate topographies, using various deposition angles. The multilayer morphology at the stepedge region was studied by cross section transmission electron microscopy. A transition from a continuous- to columnar layer morphology is observed near the step-edge, as a function of the local angle of incidence of the deposition flux. Taking into account the corresponding kinetics and anisotropy in layer growth, a continuum model has been developed to give a detailed description of the height profiles of the individual continuous layers. Complementary optical characterization of the multilayer system using a microscope operating in the extreme ultraviolet wavelength range, revealed that the influence of the step-edge on the planar multilayer structure is restricted to a region within 300 nm from the step-edge.
Date: August 31, 2011
Creator: van den Boogaard, A. J. R.; Louis, E.; Zoethout, E.; Goldberg, K. A. & Bijkerk, F.
Partner: UNT Libraries Government Documents Department
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The Thermoelastic Phase Transition in Au-Cd Alloys Studies by Acoustic Emission

Description: The acoustic emission generated during the thermoelastic phase transitions in polycrystalline Au-47.5 at.% Cd and in Au-49 at.% Cd alloys was recorded and analyzed. The emission detected is a manifestation of the frictional energy dissipated by the moving interfaces during the nucleation and growth stages of the reversible phase transitions. It was found that the amount of energy dissipated depends upon the direction of the transformation, the heating or cooling rates, and the specific crystallographic features of the martensitic phases. Premartensitic acoustic activity was detected in both alloys at temperatures of about 25 {degrees}C before the M{sub s} point. The dynamics and kinetics of martensitic thermoelastic phase transformations are discussed in terms of the accompanying generation of acoustic emission.
Date: March 1, 1980
Creator: Baram, I. & Rosen, M.
Partner: UNT Libraries Government Documents Department
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Degradation of Thermal Barrier Coatings from Deposits and Its Mitigation

Description: Ceramic thermal barrier coatings (TBCs) used in gas-turbine engines afford higher operating temperatures, resulting in enhanced efficiencies and performance. However, in the case of syngas-fired engines, fly ash particulate impurities that may be present in syngas can melt on the hotter TBC surfaces and form glassy deposits. These deposits can penetrate the TBCs leading to their failure. In experiments using lignite fly ash to simulate these conditions we show that conventional TBCs of composition 93wt% ZrO{sub 2} + 7wt% Y{sub 2}O{sub 3} (7YSZ) fabricated using the air plasma spray (APS) process are completely destroyed by the molten fly ash. The molten fly ash is found to penetrate the full thickness of the TBC. The mechanisms by which this occurs appear to be similar to those observed in degradation of 7YSZ TBCs by molten calcium-magnesium-aluminosilicate (CMAS) sand and by molten volcanic ash in aircraft engines. In contrast, APS TBCs of Gd{sub 2}Zr{sub 2}O{sub 7} composition are highly resistant to attack by molten lignite fly ash under identical conditions, where the molten ash penetrates ~25% of TBC thickness. This damage mitigation appears to be due to the formation of an impervious, stable crystalline layer at the fly ash/Gd{sub 2}Zr{sub 2}O{sub 7} TBC interface arresting the penetrating moltenfly- ash front. Additionally, these TBCs were tested using a rig with thermal gradient and simultaneous accumulation of ash. Modeling using an established mechanics model has been performed to illustrate the modes of delamination, as well as further opportunities to optimize coating microstructure. Transfer of the technology was developed in this program to all interested parties.
Date: December 31, 2011
Creator: Padture, Nitin
Partner: UNT Libraries Government Documents Department
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Hydrogen Dissociation on Pd4S Surfaces

Description: Exposure of Pd-based hydrogen purification membranes to H,S. a common contaminant in coal gasification streams, can cause membrane performance to deteriorate, either by deactivating surface sites required for dissociative H, adsorption or by forming a low-permeability sulfide scale. In this work. the composition, structure, and catalytic activity of Pd4S, a surface scale commonly observed in Pd-membrane separation of hydrogen from sulfur-containing gas streams, were examined using a combination of experimental characterization and density functional theory (DFT) calculations. A Pd,S sample was prepared by exposing a 100 f1m Pd foil to H2S at 908 K. Both X-ray photoemission depth profiling and low energy ion scattering spectroscopic (LEISS) analysis reveal slight sulfur-enrichment of the top surface of the sample. This view is consistent with the predictions of DFT atomistic thermodynamic calculations. which identified S-terminated Pd,S surfaces as energetically favored over corresponding Pd-terminated surfaces. Activation barriers for H2 dissociation on the Pd,S surfaces were calculated. Although barriers are higher than on Pd(lll). transition state theory analysis identified reaction pathways on the S-terminated surfaces for which hydrogen dissociation rates are high enough to sustain the separation process at conditions relevant to gasification applications.
Date: January 1, 2009
Creator: Miller, J. B.; Alfonso, D. R.; Howard, B. H.; O'Brien, C. P. & Morreale, B. D.
Partner: UNT Libraries Government Documents Department
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The Parabolic Growth Op Oxide Solid Solutions on Binary Alloys: A Semi-Empirical Approach.

Description: The growth of solid solution oxide scales on alloys has been described by considering either the transport of the cations themselves, or that of the defect species in the oxide lattice. The two approaches have been shown to be similar. However, it has become apparent that the simplified defect model implicitly assumed in previous analyses using the ionic transport approach is not adequate to fully describe the variation of ionic diffusivities with oxygen potential or oxide composition. Further analyses, using a combination of the two approaches, are suggested.
Date: October 1, 1980
Creator: Whittle, D. P.; Gesmundo, F. & Viani, F.
Partner: UNT Libraries Government Documents Department
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Corrosion and Creep of Candidate Alloys in High Temperature Helium and Steam Environments for the NGNP

Description: This project aims to understand the processes by which candidate materials degrade in He and supercritical water/steam environments characteristic of the current NGNP design. We will focus on understanding the roles of temperature, and carbon and oxygen potential in the 750-850 degree C range on both uniform oxidation and selective internal oxidation along grain boundaries in alloys 617 and 800H in supercritical water in the temperature range 500-600 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the temperature rang 750-850 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the temperature range 750-850 degree C over a range of oxygen and carbon potentials in helium. Combined, these studies wil elucidate the potential high damage rate processes in environments and alloys relevant to the NGNP.
Date: June 21, 2013
Creator: Was, Gary & Jones, J. W.
Partner: UNT Libraries Government Documents Department
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Surface structure of protonated R-plane-sapphire (1-102) studied by sum frequency vibrational spectroscopy

Description: Sum frequency vibrational spectroscopy was used to study the protonated R-plane (1{bar 1}02 ) sapphire surface. The OH stretch vibrational spectra show that the surface is terminated with three hydroxyl moieties, two from AlOH{sub 2} and one from Al{sub 2}OH functional groups. The observed polarization dependence allows determination of the orientations of the three OH species. The results suggest that the protonated sapphire (1{bar 1}02 ) surface differs from an ideal stoichimetric termination in a manner consistent with previous X-ray surface diffraction (crystal truncation rod) studies. However, in order to best explain the observed hydrogenbonding arrangement, surface oxygen spacing determined from the X-ray diffraction study requires modification.
Date: April 1, 2011
Creator: Sung, J.; Zhang, L.; Tian, C.; Waychunas, G. A. & Shen, Y. R.
Partner: UNT Libraries Government Documents Department
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A New Technique for Observing the Amorphous to Crystalline Transformation in Thin Surface Layers on Silicon Wafers

Description: Thin amorphous ({alpha}) films of silicon created by ion-implantation have been studied in-situ while undergoing the amorphous to crystalline transformation in the electron microscope. The specimens were prepared in such a manner that the amorphous/crystalline interface was viewed edge-on and its advance during annealing was easily observed over distances of several microns. Growth rates and activation energies were measured. The active role that defects play during the regrowth process was also studied. An additional advantage of the technique was that in a single specimen different segments of the recrystallization front advanced along several different growth directions simultaneously, hence the effect of regrowth direction on the interface migration rate and defect formation was graphically displayed in a single specimen.
Date: February 1, 1980
Creator: Drosd, B. & Washburn, J.
Partner: UNT Libraries Government Documents Department
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UV laser ablation of parylene films from gold substrates

Description: Parylene films, coating gold substrates, were removed by laser ablation using 248 nm light from an excimer laser. Each sample was processed by a different number of pulses in one of three different environments: air at atmospheric pressure, nitrogen at atmospheric pressure, and vacuum. The laser-induced craters were analyzed by optical microscopy and x-ray photoelectron spectroscopy. Multi-pulse ablation thresholds of gold and parylene were estimated.
Date: November 19, 2009
Creator: Musaev, O. R.; Scott, P.; Wrobel, J. M. & Kruger, M. B.
Partner: UNT Libraries Government Documents Department
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