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Acid-Base Interactions at the Molecular Level: Adhesion and Friction Studies with Interfacial Force Microscopy

Description: To examine the forces of acid-base adhesive interactions at the molecular level, we utilize the scanning probe Interracial Force Microscope (IFM). Unlike cantilever-based atomic force microscopes, the EM is a non-compliant, mechanically stable probe that provides a complete adhesive profile without jump-to-contact. In this way, we are able to quantitatively measure the work of adhesion and bond energies at well-defined, nanometer-scale single asperity contacts. In particular, we will discuss the displacement-controlled adhesive forces between self-assembled monolayer of functionalized alkanethiols strongly bound to a gold substrate and a similarly functionalized tip. We also discuss a method utilizing decoupled lateral and normal force sensors to simultaneously observe the onset of both friction and chemical bond formation. Measurements show that friction can be directly attributed to bond formation and rupture well before repulsive contact.
Date: December 9, 1998
Creator: Burns, A.R.; Carpick, R.W.; Houston, J.E. & Michalske, T.A.
Partner: UNT Libraries Government Documents Department

Wetting of a Chemically Heterogeneous Surface

Description: Theories for inhomogeneous fluids have focused in recent years on wetting, capillary conden- sation, and solvation forces for model systems where the surface(s) is(are) smooth homogeneous parallel plates, cylinders, or spherical drops. Unfortunately natural systems are more likely to be hetaogeneous both in surt%ce shape and surface chemistry. In this paper we discuss the conse- quences of chemical heterogeneity on wetting. Specifically, a 2-dimensional implementation of a nonlocal density functional theory is solved for a striped surface model. Both the strength and range of the heterogeneity are varied. Contact angles are calculated, and phase transitions (both the wetting transition and a local layering transition) are located. The wetting properties of the surface ase shown to be strongly dependent on the nature of the surface heterogeneity. In addition highly ordered nanoscopic phases are found, and the operational limits for formation of ordered or crystalline phases of nanoscopic extent are discussed.
Date: November 20, 1998
Creator: Frink, L.J.D. & Salinger, A.G.
Partner: UNT Libraries Government Documents Department

Reconstruction of surfaces in NiO

Description: We studied the reconstructions of surfaces in NiO by atomistic simulations which utilize Buckingham short range potentials and the shell model. It was found that (hk0) surfaces prefer to reconstruct into (100) surface facets which has the lowest energy. The interaction between these (100) facets is repulsive and converges to zero as size of facets grows. The (111) surface can be stabilized by reconstruction into (100) micro-facets.
Date: July 1, 1995
Creator: Yan, M. & Chen, S.P.
Partner: UNT Libraries Government Documents Department

Surface Modified Coals for Enhanced Catalyst Dispersion and Liquefaction

Description: The aim of this study is to enhance catalyst loading and dispersion in coal for improved liquefaction by preadsorption of surfactants and catalysts on to the coal. During this reporting period, the effects of dodecyl dimethyl ethyl ammonium bromide (DDAB) (a cationic surfactant), sodium dodecyl sulfate (SDS) (an anionic surfactant), Triton X-100 (a neutral surfactant), and ferrous sulfate (as a catalyst precursor) on the coal surface charge at various pH values were determined. The results of the zeta potential measurements suggest that ferrous sulfate as catalyst precursor creates a distinctly different condition on the coal surface compared to that of molybdenum as reported in the previous progress reports. The effects of the adsorption of the surfactants also varied distinctly with the type of surfactant. With the adsorption of DDAB, the cationic surfactant, the surface charge was more positive. The opposite effect was observed for the SDS, the anionic surfactant. The coals treated with Triton X-100, the neutral surfactant, also showed an overall negative surface charge density. The adsorption of the catalyst precursor (ferrous sulfate) resulted in a net negative charge on the coal surface.
Date: December 4, 1998
Creator: Yeboah, Yaw D.
Partner: UNT Libraries Government Documents Department

Optimizing fabrication of electrodeposited 3D surface features

Description: Selective electrodeposition onto specially masked surfaces (producing blind holes with non-conductive side walls) has been investigated. The thick masks are low cost polymer sheet into which holes and other patterns are machined. Plating with this type of masking system is one method of fabricating medium aspect ratio metallic structures (structures whose width to length ratio is greater than 10/1). The experiment was conducted with deposits of OFC copper from an acid sulfate solution, but similar results are expected with other metals. Structure diameter varied from 0.25 mm to 3.8 mm (0.01`` to 0.150``). The effect of current density, electrolyte concentration, solution temperature, and agitation on deposition rate were investigated. Deposit quality, deposition rate, and optimal plating parameters were evaluated.
Date: July 1, 1998
Creator: Steffani, C., LLNL
Partner: UNT Libraries Government Documents Department

Nonlinear optical studies of surfaces

Description: The possibly of using nonlinear optical processes for surface studies has attracted increasing attention in recent years. Optical second harmonic generation (SHG) and sum frequency generation (SFG), in particular, have been well accepted as viable surface probes. They have many advantages over the conventional techniques. By nature, they are highly surface-specific and has a submonolayer sensitivity. As coherent optical processes, they are capable of in-situ probing of surfaces in hostile environment as well as applicable to all interfaces accessible by light. With ultrafast pump laser pulses, they can be employed to study surface dynamic processes with a subpicosecond time resolution. These advantages have opened the door to many exciting research opportunities in surface science and technology. This paper gives a brief overview of this fast-growing new area of research. Optical SHG from a surface was first studied theoretically and experimentally in the sixties. Even the submonolayer surface sensitivity of the process was noticed fairly early. The success was, however, limited because of difficulties in controlling the experimental conditions. It was not until the early 1980`s that the potential of the process for surface analysis was duly recognized. The first surface study by SHG was actually motivated by the then active search for an understanding of the intriguing surface enhanced Raman scattering (SERS). It had been suspected that the enhancement in SERS mainly came from the local-field enhancement due to local plasmon resonances and pointing rod effect on rough metal surfaces. In our view, Raman scattering is a two-photon process and is therefore a nonlinear optical effect.
Date: July 1, 1994
Creator: Shen, Y.R.
Partner: UNT Libraries Government Documents Department

Spontaneous Pattern Formation on Ion Bombarded Si(001)

Description: Pattern formation on surfaces undergoing low-energy ion bombardment is a common phenomenon. Here, a recently developed in situ spectroscopic light scattering technique was used to monitor periodic ripple evolution on Si(001) during Ar(+) sputtering. Analysis of the rippling kinetics indicated that under high flux sputtering at low temperatures the concentration of mobile species on the surface is saturated, and, surprisingly, is both temperature and ion flux independent. This is due to an effect of ion collision cascades on the concentration of mobile species. This new understanding of surface dynamics during sputtering allowed us to measure straighforwardly the activation energy for atomic migration on the surface to be 1.2+0.1 eV. The technique is generalizable to any material, including high temperature and insulating materials for which surface migration energies are notoriously difficult to measure.
Date: April 26, 1999
Creator: Chason, Eric; Erlebacher, Jonah, Aziz, Michael J.; Floro, Jerrold A. & Sinclair, Michael B.
Partner: UNT Libraries Government Documents Department

Lectures on geometrical properties of nuclei

Description: Material concerning the geometrical properties of nuclei is drawn from a number of different sources. The leptodermous nature of nuclear density distributions and potential wells is used to draw together the various geometrical properties of these systems and to provide a unified means for their description. Extensive use is made of expansions of radial properties in terms of the surface diffuseness. A strong case is made for the use of convolution as a geometrical ansatz for generating diffuse surface distributions because of the number of simplifications that arise which are of practical importance. 7 figures. (auth)
Date: November 1, 1975
Creator: Myers, W.D.
Partner: UNT Libraries Government Documents Department

LDRD final report : on the development of hybrid level-set/particle methods for modeling surface evolution during feature-scale etching and deposition processes.

Description: Two methods for creating a hybrid level-set (LS)/particle method for modeling surface evolution during feature-scale etching and deposition processes are developed and tested. The first method supplements the LS method by introducing Lagrangian marker points in regions of high curvature. Once both the particle set and the LS function are advanced in time, minimization of certain objective functions adjusts the LS function so that its zero contour is in closer alignment with the particle locations. It was found that the objective-minimization problem was unexpectedly difficult to solve, and even when a solution could be found, the acquisition of it proved more costly than simply expanding the basis set of the LS function. The second method explored is a novel explicit marker-particle method that we have named the grid point particle (GPP) approach. Although not a LS method, the GPP approach has strong procedural similarities to certain aspects of the LS approach. A key aspect of the method is a surface rediscretization procedure--applied at each time step and based on a global background mesh--that maintains a representation of the surface while naturally adding and subtracting surface discretization points as the surface evolves in time. This method was coded in 2-D, and tested on a variety of surface evolution problems by using it in the ChISELS computer code. Results shown for 2-D problems illustrate the effectiveness of the method and highlight some notable advantages in accuracy over the LS method. Generalizing the method to 3D is discussed but not implemented.
Date: January 1, 2005
Creator: McBride, Cory L. (Elemental Technologies, American Fork, UT); Schmidt, Rodney Cannon & Musson, Lawrence Cale
Partner: UNT Libraries Government Documents Department

Effect of Scratches on Pinch Welds

Description: Fill stems for tritium reservoirs have stringent scratch requirements such that any indications that appear to have depth are cause for rework or rejection. A scoping study was undertaken to evaluate the effect of scratches approximately 0.0015 to 0.002 inch deep on the fitness for service and bond quality. The stems were characterized using borescope before and after welding. The four stems were welded with near optimal weld parameters, proof tested, and examined metallographically. The stems were radiographed, proof tested, and examined metallographically. The scratches did not adversely affect (1) the weld integrity based on radiography, (2) the ability to withstand the proof pressure, and (3) the weld quality based on metallographic cross-sections. Based on these limited results at a nominal weld current, the weld process is very robust. It may be able to recover from manufacturing defects and inspection anomalies worse than those expected for typical fill stem manufacturing processes; additional testing specific to each application over a range of weld heats is needed to verify applicability of these results.
Date: October 11, 2005
Creator: Korinko, P
Partner: UNT Libraries Government Documents Department

Surface effects on tritium diffusion in materials in a radiation environment

Description: Tritium transport and distribution in a material are controlled by chemical potential and thermal gradients and cross-coupling to impurities and defects. Surfaces influence tritium diffusion by acting as sources and sinks for defects and impurities, and surface films restricting tritium transfer between the solid and surrounding fluids. Radiation directly affects boundary processes such as dissociation or adsorption, may erode a surface film or the surface itself, and introduces defects and impurities into the solid by radiation damage, transmutation, or ion implantation, thereby modifying tritium transport within the solid and its transfer across external interfaces. There have been no definitive investigations of these effects, but their practical significance has been demonstrated in tritium release or absorption studies with stainless steel, Zircaloy, niobium, and other materials. (auth)
Date: January 1, 1975
Creator: Caskey, G.R. Jr.
Partner: UNT Libraries Government Documents Department

Examination of Corrosion Products and the Alloy Surface After Crevice Corrosion of a Ni-Cr-Mo- Alloy

Description: The objective of this study is to investigate the composition of corrosion products and the metal surface within a crevice after localized corrosion. The analysis provides insight into the propagation, stifling and arrest processes for crevice corrosion and is part of a program to analyze the evolution of localized corrosion damage over long periods of time, i.e. 10,000 years and longer. The approach is to force the initiation of crevice corrosion by applying anodic polarization to a multiple crevice assembly (MCA). Results are reported here for alloy C-22, a Ni-Cr-Mo alloy, exposed to a high temperature, concentrated chloride solution. Controlled crevice corrosion tests were performed on C-22 under highly aggressive, accelerated condition, i.e. 4M NaCl, 100 C and anodic polarization to -0.15V-SCE. The crevice contacts were by either a polymer tape (PTFE) compressed by a ceramic former or by a polymer (PTFE) crevice former. Figure 1 shows the polarization current during a crevice corrosion test. After an incubation period, several initiation-stifle-arrest events were indicated. The low current at the end of the test indicated that the metal surface had repassivated.
Date: June 9, 2006
Creator: Shan, X. & Payer, J.H.
Partner: UNT Libraries Government Documents Department

Reduction of Oxidative Melt Loss of Aluminum and Its Alloys

Description: This project led to an improved understanding of the mechanisms of dross formation. The microstructural evolution in industrial dross samples was determined. Results suggested that dross that forms in layers with structure and composition determined by the local magnesium concentration alone. This finding is supported by fundamental studies of molten metal surfaces. X-ray photoelectron spectroscopy data revealed that only magnesium segregates to the molten aluminum alloy surface and reacts to form a growing oxide layer. X-ray diffraction techniques that were using to investigate an oxidizing molten aluminum alloy surface confirmed for the first time that magnesium oxide is the initial crystalline phase that forms during metal oxidation. The analytical techniques developed in this project are now available to investigate other molten metal surfaces. Based on the improved understanding of dross initiation, formation and growth, technology was developed to minimize melt loss. The concept is based on covering the molten metal surface with a reusable physical barrier. Tests in a laboratory-scale reverberatory furnace confirmed the results of bench-scale tests. The main highlights of the work done include: A clear understanding of the kinetics of dross formation and the effect of different alloying elements on dross formation was obtained. It was determined that the dross evolves in similar ways regardless of the aluminum alloy being melted and the results showed that amorphous aluminum nitride forms first, followed by amorphous magnesium oxide and crystalline magnesium oxide in all alloys that contain magnesium. Evaluation of the molten aluminum alloy surface during melting and holding indicated that magnesium oxide is the first crystalline phase to form during oxidation of a clean aluminum alloy surface. Based on dross evaluation and melt tests it became clear that the major contributing factor to aluminum alloy dross was in the alloys with Mg content. Mg was identified as the ...
Date: March 17, 2006
Creator: Das, Dr. Subodh K. & Ningileri, Shridas
Partner: UNT Libraries Government Documents Department

Temperature measurements of partially-melted tin as a function of shock pressure

Description: Equilibrium equation of state theory predicts that the free surface release temperature of shock loaded tin will show a plateau of 505 K in the pressure range from 19.5 to 33.0 GPa, corresponding to the solid-liquid mixed-phase region. In this paper we report free surface temperature measurements on shock-loaded tin from 15 to 31 GPa using multi-wavelength optical pyrometry. The shock waves were generated by direct contact of detonating high explosive with the sample. The pressure in the sample was determined by free surface velocity measurements using Photon Doppler Velocimetry. The emitted thermal radiance was measured at four wavelength bands in the near IR region from 1.5 to 5.0 {micro}m. The samples in most of the experiments had diamond-turned surface finishes, with a few samples being polished or ball rolled. At pressures higher than 25 GPa the measured free surface temperatures were higher than the predicted 505 K and increased with increasing pressure. This deviation could be explained by hot spots and/or variations in surface emissivity and requires a further investigation.
Date: January 1, 2009
Creator: Seifter, Achim; Furlanetto, Michael R; Holtkamp, David B; Obst, Andrew W; Payton, J R; Stone, J B et al.
Partner: UNT Libraries Government Documents Department

Singularity fitting in hydrodynamical calculations II

Description: This is the second report in a series on the development of techniques for the proper handling of singularities in fluid-dynamical calculations; the first was called Progress Report on the Shock-Fitting Project. This report contains six main results: derivation of a free-surface condition, which relates the acceleration of the surface with the gradient of the square of the sound speed just behind it; an accurate method for the early and middle stages of the development of a rarefaction wave, two orders of magnitude more accurate than a simple direct method used for comparison; the similarity theory of the collapsing free surface, where it is shown that there is a two-parameter family of self- similar solutions for $gamma$ = 3.9; the similarity theory for the outgoing shock, which takes into account the entropy increase; a ''zooming'' method for the study of the asymptotic behavior of solutions of the full initial boundary- value problem; comparison of two methods for determining the similarity parameter delta by zooming, which shows that the second method is preferred. Future reports in the series will contain discussions of the self-similar solutions for this problem, and for that of the collapsing shock, in more detail and for the full range (1, infinity) of $gamma$; the values of certain integrals related to neutronic and thermonuclear rates near collapse; and methods for fitting shocks, contact discontinuities, interfaces, and free surfaces in two-dimensional flows. (auth)
Date: September 1, 1975
Creator: Richtmyer, R.D. & Lazarus, R.B.
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

Final technical report on Award No. DE-FG02-92ER45465

Description: The motivation of the previous program was to develop methods which could be used in a systematic study of the interface between glass and crystalline oxides. It was recognized that since the mechanical properties of glass-containing oxides are particularly important, it would be desirable to have a method which would also allow a systematic comparison of the mechanical properties of the materials. We found that the geometry of a glass film on a crystalline surface gave several new possibilities: we could develop methods for examining the mechanical properties of the films and the interfaces and we could examine both the crystallization of glass films and their wetting/dewetting behavior. Also, the samples are amenable to examination by the characterization techniques which give information on the chemistry and structure over a wide range of length scales: both chemistry and crystallography can be controlled and changes monitored.
Date: June 18, 2003
Creator: Carter, C. Barry
Partner: UNT Libraries Government Documents Department