bluuebunny/crossref_metadata_2025_split huggingface dataset:
Beam-Metal Surface Interactions Using an Excimer Laser
Authors: Pellegrino Joseph , Partridge Julian P. , Magee A. , Strutt P. 
Published: March 2011

ABSTRACTIn view of material technological developments, studies have been made of the interactive processes involved in irradiation of metals with an excimer laser. These studies involved single-pulse irradiation of Al, Ni, Ti, and Zn at various powers up to about 5 MW. Systematic studies at widely differing, yet reproducible, power densities were facilitated using numerically controlled beam focusing. By changing the incident intensity, different plasma pressures were produced during surface melting. These created various types of unstable ripple patterns which emanated radially from the center of beam incidence and were enhanced by immersion in liquid nitrogen.The results showed only minor differences between substrates possessing different physical properties and the influence of crystallographic orientation was also found to be minimal. An elliptical disturbance zone was produced on the substrates when the beam was defocused and this is attributed to astigmatic effects associated with a lens system incorporating spherical refracting surfaces.
Surface Concentration of Defects on a Constrained System: a Molecular Dynamics Approach
Authors: Rosato Vittorio , Guillope Michel 
Published: March 2011

ABSTRACTWe have performed a systematic study to evaluate the structural response of a {110} fcc surface to an externally imposed elastic deformation, by Molecular Dynamics at a fixed temperature T=0.48T and T=0.68T (T melting point). For high contractions along the dense axis [110], surface concentration of defects (SCD) and diffusion coefficient increase with respect to the equilibrium values. The resulting surface disorder is similar to the one found, at equilibrium, at higher temperatures.
The Nature of the Surface of a Metal-Metalloid Metallic Glass
Authors: Brower W. E. , Tlomak P. , Kowbel W. , Pierz S. J. 
Published: March 2011

ABSTRACTThe surface of a metallic glass has been characterized at the atomic and microstructural levels. On the atomic scale, the glassy surface hal been previously characterized via a model which allows the calculation of surface coordination numbers and the fractal dimension. Catalytic experiments and LEIS measurements appear to confirm the model's prediction of surface roughness on the atomic scale. In this work, the glassy surface has been characterized on the microstructural level via RHEED patterns. In addition, the fresh glassy surface produced by comminution of Fe-B glass has been characterized with respect to the relative stability of the comminuted glass as compared to as-quenched glass.
Defects in Laser Surface-Melted Metals Studied by Pac
Authors: Collins Gary S. , Aliard Carl , Hohenemser Christoph , Draper Clifton W. 
Published: March 2011

ABSTRACTFollowing nanosecond-duration laser surface-melting, lattice locations of illIn probe atoms in Ni and Pt samples were studied using the technique of perturbed gamma-gamma angular correlations (PAC). After melting and annealing, no probe atoms were observed to become associated with unique vacancy clusters observed after other methods of damaging, while many probe atoms were found on non-unique sites. 111In probe atoms were observed to move to the surface and to be expelled at anomalously low temperatures. These observations are partially reconciled by the hypothesis that probe atoms diffusing in the molten surface layer become trapped on dislocations during resolidification, and during later annealing return to the surface via pipe diffusion.
Adsorption of Oxygen on Sodium Saturated Cu{110}
Authors: Grider D. E. , Wendelken J. F. 
Published: March 2011

ABSTRACTThe adsorption of oxygen on a sodium saturated Cu{110} surface is examined with x-ray photoelectron spectroscopy (XPS) in an extension of a previous study of this system which utilized low energy electron diffraction (LEED), and high resolution electron energy loss spectroscopy (HREELS). The sodium overlayer, despite the presence of an initial oxide contaminant, shows metallic character. Intentionally adsorbed oxygen is in a different chemical state than the initial oxygen contaminant and causes a reduction in the metallic character of the sodium. The sticking coefficient for oxygen on the sodium saturated surface is almost three times greater than for the bare Cu{11O} surface.
Characterization of a Ag Monolayer on Pt by Surface Enhanced Raman Scattering
Authors: Miragliotta Joseph , Furtak T. E. 
Published: March 2011

ABSTRACTWe report the results of a surface enhanced Raman scattering investigation of a Ag monolayer (ML) electrochemically deposited on a Pt substrate. The poor electromagnetic enhancing properties of this surface insure that the observed Raman scattering intensity is short–range in origin, arising from an electronic resonant process between the surface adatom and the probe molecule. Raman spectra showed the probe molecule, pyridine, to be bound to an electron-deficient Ag site. This supports earlier vacuum studies of the Ag/Pt surface which reported an electron transfer from the Ag ML into the Pt substrate leaving a partial positive charge in the ML. The transfer is due to the work function difference between Ag and Pt.
Surface Science Investigations of Thin Metal Films on Metal and Metal Oxide Supports
Authors: White J. M. 
Published: March 2011

ABSTRACTChemisorption and catalysis on overlayer metals and metal oxides is rich and complex. Thin film model systems, suitable for UHV surface science, are attractive candidates for studying the fundamental interactions involved. In this paper, we discuss three examples: (1) O2 and N2O dissociative adsorption on Cu-covered Ru(0001), (2) molecular CO chemisorption on K-covered Ag(111), and (3) CO, H2 and NO chemisorption on clean and TiOx covered Pt and Rh. In each of these cases, evidence is presented for significant chemical interactions between the two substrate materials.
Surface Chemistry of Thin Palladium Films
Authors: Neiman David L. , Koel Bruce E. 
Published: March 2011

ABSTRACTThe properties of Pd monolayers on several transition metal substrates are dramatically different from the surface properties of bulk Pd single crystals. The changes include a large rehybridization of the Pd atoms to a noble metal electronic configuration and a concomitant reduction in CO and H2 chemisorption bond strengths. We present here temperature programmed desorption (TPD) studies of CO, NO, H2, and C2H4 chemisorption on thin epitaxial Pd films on Nb(110). Our resuAs confirm for all of these gases a large reduction in the chemisorption bond energy for adsorption on Pd thin (<2 ML) films. Our TPD results for CO, which give a CO binding energy of about 10 kcal/mole, confirm previous UPS studies which show that a Pd monolayer forms only a weak chemisorption bond to CO. Thicker Pd films ( > 5 ML ) have CO TPD spectra that agree qualitatively with previous studies on Pd(111) single crystals, where the CO binding energy is about 30 kcal/mole. These results for Pd/Nb(110) will be discussed with respect to recent work on related systems involving thin Pd films on other transition metal substrates.
Adsorption and Reaction on Thin Metal Overlayers
Authors: Berlowitz Paul J. , Peden Charles H. F. , Goodman D. Wayne 
Published: March 2011

ABSTRACTThese studies have addressed the adsorption of CO on very thin (submonolayer to multilayer) deposits of Cu, Ni, Pd, and Fe on single crystals of Ru and W. The kinetics of the methanation, ethane hydrogenolysis, and cyclohexane dehydrogenation reactions have also been measured over these model bimetallic catalysts. Temperature programmed desorption (TPD) spectra of CO at submonolayer coverages reveal new desorption features which have significantly perturbed peak maxima from those observed on the bulk metals, indicating the unique character of these monolayer metallic films. This behavior has been correlated with LEED, ARUPS, work function, and kinetic measurements.
Structural Energetics of Thin Coherently Strained Metallic Overlayers
Authors: Dodson Brian W. , Taylor Paul A. 
Published: March 2011

ABSTRACTUnderstanding of the growth, stability, and structural properties of coherently strained metal overlayers has achieved considerable importance because of the recent discovery of unique interfacial electronic states and catalytic properties of such systems. The structural stability of coherently strained metal films grown on a substrate composed of a different and lattice-mismatched metal is determined via atomistic calculations. An equilibrium energy balance criterion is used, which is evaluated with a Monte Carlo annealing optimization procedure in which the structural energy of the bimetallic system is obtained using the embedded atom method. The stability of coherently strained (100) bimetallic structures chosen from combinations of the fcc metals Ag, Au, Cu, Ni, Pd, and Pt has been studied. The predicted critical thicknesses agree remarkably well with experimental results, but disagree quantitatively with the continuum models.
A Study of Epitaxial Films of Bcc Nickel on FE{001} with leed Intensity analysis and Total Energy Band Calculations
Authors: Marcus P. M. , Moruzzi V. L. , Wang Z. Q. , Li Y. S. , Jona F. 
Published: March 2011

ABSTRACTAnalysis of LEED intensities of thin films of Ni grown epitaxially on bcc Fe{001} establishes that the structure is bcc up to six layers, but with a contraction of 5% of the first layer spacing and expansion of 5% of the second layer spacing. At thicknesses above six layers there is a gradual change to a new surface and bulk structure with increasing disorder. Spin-polarized total-energy band calculations show that the bcc Ni film is stretched 1.4% from its equilibrium value and thereby changed from nonmagnetic to ferromagnetic. The calculated results on stable and metastable phases of Fe, Co, Ni and Cu show that the equilibrium lattice parameters and differences in binding energies favor mutual epitaxy for any bcc or fcc pair. There are six pairs in which a possible metastable phase is grown epitaxially on a stable substrate.
Oxidation of the (111) Surface of an Al-Be Alloy: Effect of a BeO Layer
Authors: Ahmad M. , Blakely J. M. 
Published: March 2011

ABSTRACTGrowth of a thin BeO layer on the (111) surface of a dilute Al-Be alloy has been studied under oxidizing condition. At 500°C, in the presence of oxygen, Be atoms diffuse to the surface to form BeO. This oxide grows epitaxially with its (0001) basal plane orientation parallel to Al (111). During room temperature oxygen exposure of the AI(111) surface precovered with a BeO layer, it was found that oxygen diffused through the BeO overlayer and formed amorphous Al2O3 at the AI-BeO interface. The thin BeO film remained well ordered even when separated from the substrate by the amorphous layer. The effect of various coverages of BeO on the kinetics of oxidation of Al (111) at room temperature was studied; the influence of the BeO was found to be small in comparison with the case of a polycrystalline sample with predominantly (001) textures.
The Influence of Predeposition of Nonolayer Thin Titanium Filns Upon the Crystallography of Subsequently Formed Pd2Si Layers on (100) Silicon
Authors: McGinn J. T. , Hoffman D. M. , Thomas, III J. H. , Tams III F. J. 
Published: March 2011

ABSTRACTThis paper reports upon a new technique for the formation of epitaxial Pd2Si on (100) silicon using thin predeposited titanium layers. Improvements in the quality of epitaxy in Pd2Si on {111} silicon by this technique will also be shown. A preliminary model for the formation of epitaxy will be given. Discrepancies between this model and results in the literature will be discussed and experiments suggested to resolve the uncertainties.
Optical Second Harmonic Generation from Surface Segregants and Adsorbed Oxygen on an Fe-18Cr-3Mo (110) Surface
Authors: Hamilton J. C. , Anderson R. J. , Foltz G. W. 
Published: March 2011

ABSTRACTOptical second harmonic generation is a new surface diagnostic applicable both in ultra-high vacuum and ambient environments and capable of examining gas-solid, liquid-solid and solid-solid interfaces. Studies of surface segregation of chromium and nitrogen on Fe-18Cr-3Mo(II0) single crystal surfaces in ultra-high vacuum are described. Major increases in second harmonic intensity generated by 700 nm excitation at the surface are seen upon heating to temperatures at which chromium and nitrogen cosegregate. Adsorption of oxygen has also been studied on this surface. Second harmonic generation shows promise in providing structural and electronic information for surfaces and interfaces in a wide variety of environments.
Modification of the Properties of Metal Overlayers oN Nb(110) and Ta(1l0)
Authors: Ruckman M. W. , Strongin Myron , Pan Xiaohe 
Published: March 2011

ABSTRACTModification of the physical and chemical properties of noble and near-noble metal monolayer films supported on Nb(110) or Ta(l10) is demonstrated using photoemission and LEED. Strong adlayer-substrate bonding leads to the formation of commensurate Pd or Pt overlayers at low coverage (8 < 0.7 ML). Ni and Cu form incommensurate structures because the additional interfacial misfit cannot be overcome by substrate-overlayer bonding. Ag and Au form commensurate overlayers at coverages le ss than 3 ML because the lattice misfit is small. The strong overlayer-substrate bonding produces large changes in the chemical activity of near-noble metal overlayers. Photoemission measurements on Pt monolayers show that the hybridized metal d-states are shifted further below the Fermi level “EF” and show a reduction in the surface density of states at EF. This absence of bonding d-states near EF effects CO chemisorption. However, as additional layers of Pd and Pt are deposited, the d-occupancy at EF grows, with “constant” atomic structure and the amount of CO increases. Hence, in these systems chemisorption changes can be studied as a function of changing electronic structure while holding the surface structure fixed.
Microstructure of Cement Paste and Mass Transfer of Gas through Concrete
Authors: Mills R. H. 
Published: March 2011

ABSTRACTGas flow through concrete may be modelled by a relationship:where D* is the specific permeability, N* is the number of unit pores per m2, and α, β and γ are experimental constants.A unit pore is defined by the hydraulic mean radius a* equal to the total porosity divided by the BET surface area. The value of a* is estimated from porosity and hydration parameters to lie between 1.6 and 2.8 nm for water-cement ratios from 0.42 to 0.77 and initial porosities from 0.292 to 0.150. Estimation of pore radius a from gas flow yielded values of a/a* varying from 72 to 6. There appears to be fair correlation between N* and D*, but it appears that flow passes through microcracks rather than the natural pore system.
Relationships Between Microstructure and Engineering Properties
Authors: Pratt P. L. 
Published: March 2011

ABSTRACTThe calculation of such macroscopic engineering properties as elastic modulus and compressive strength for cement pastes and concrete depends upon the establishment of a realistic model of the microstructure. Increasingly complex models are considered, which appear capable of predicting the elastic modulus in terms of a modified Rule of Mixtures. The same models are able to account for the broad features of the compressive strength, because strength is always scaled by the elastic modulus of the material. The actual value of the compressive or the bend strength is determined by the mechanics of crack initiation and crack propagation in the particular test used. Crack initiation is controlled by the defects present in the material and crack propagation by the fracture toughness of the different phases and the porosity in the microstructure. Thus the strength depends upon microstructure in a number of different but interrelated ways, determined by the fracture toughness of the material.
Microstructural Aspects of Stress Corrosion of Cementitious Materials
Authors: Schneider U. , Nagele E. , Dujardin N. 
Published: March 2011

ABSTRACTStress corrosion phenomena, i.e. significant effects of mechanical stresses on the corrosion resistance of materials, have been reported for a large variety of materials, including metals, oxides and halides. Recently it has been shown [1,2] that cementitious materials are also sensitive to stress corrosion. The time dependent decrease in the flexural strength of chemically stressed concrete and mortar depends significantly on the mechanical stress acting simultaneously with the chemical attack.For cementitious materials a comprehensive study of the stress corrosion phenomena has been started. In this paper the latest results from the current research program are presented and the interrelations between the microstructure of hardened cement mortar and the strength reduction caused by stress corrosion, are briefly discussed.
Pore Structure Development in Portland/Fly Ash Blends
Authors: Cook David J. , Cao Huu T. , Coan Everett P. 
Published: March 2011

ABSTRACTPore structure development in portland/fly ash blends was investigated using mercury porosimetry and methanol exchange techniques. The progress of hydration was monitored using compressive strength tests. The specimens were made using four water-cement ratios and were hydrated over a one-year period in lime-saturated water. Mercury porosimetry results indicated that the blended cement pastes generally had higher total porosity than plain cement pastes. The major contribution to this increase in porosity was in the form of smaller pore sizes. With reactive fly ash at 20% replacement, the pore structure of mature paste consists mainly of pores nominally smaller than 0.05 μm in diameter. Diffusion parameters obtained from the methanol exchange results were found to be inversely related to the volume of large pores (nominally <0.05 μm) and also to the volume of small pores (nominally <0.05 μm). The effects of the physical and chemical properties of cements and fly ashes on pore structure development are discussed.
Cement Paste Microstructure in Concrete
Authors: Diamond Sidney 
Published: March 2011

ABSTRACTAn understanding of the microstructure of cement paste in actual field concrete is considered to be the primary objective of cement microstructural studies. Cement paste in concrete is shown to consist of narrow ribbons of the order of 80 to 150 μm separating sand and coarse aggregate grains, and interrupted by frequent air voids. Individual cement grains form shells around themselves early in the hydration process. In subsequent hydration they either deposit dense layers of internal hydration product or empty out in a hollow-shell mode and precipitate hydration products in the empty spaces between nearby shells. Analogous shells are similarly formed around fly ash particles, which then react by progressive etching from within the shells. Interfacial zones around aggregates are pictured as having a complex characteristic structure including at least four different forms of calcium hydroxide particles with various preferred orientations. It is suggested that the conventional picture of the “aureole de transition” derived from successive x-ray diffraction measurements may have been misinterpreted.
TEM Studies of Cement Hydration
Authors: Groves G. W. 
Published: March 2011

ABSTRACTThe application of transmission electron microscopy to the study of the early stages of hydration C3S and the microstructure of very mature C3 S paste is reported. In the former case the effect of water-cement ratio appears to be very important. In the latter, a detailed evaluation of the microstructures of inner C-S-H, outer C-S-H and CH is possible and the relationship of these to models of cement hydration is discussed.
Analysis of Phases in Cement Paste using Backscattered Electron Images, Methanol Adsorption and Thermogravimetric Analysis
Authors: Scrivener Karen L. , Patel H. H. , Pratt P. L. , Parrott L. J. 
Published: March 2011

ABSTRACTIn backscattered electron (bse) images of polished cement sections, anhydrous material, calcium hydroxide, other hydration products (mainly C-S-H) and porosity can be distinguished on the basis of their grey level in the image. Using an image analyzer connected directly to the SEM, it is possible to resolve these four components and so measure their relative proportions and distributions. The effects of magnification and the number of fields measured on the accuracy of bse image analysis are examined. The volume fractions of anhydrous material, porosity and calcium hydroxide derived from bse image analysis are compared with those obtained by other techniques and good correlation was found for the measurement of anhydrous material and porosity.
Measurement and Modeling of Porosity in Drying Cement Paste
Authors: Parrott Leslie 
Published: March 2011

ABSTRACTPreliminary models for predicting the performance of exposed concrete show that the porosity sub-model plays a pivotal role in linking properties with the developing gradients of cement paste microstructure that arise from drying and carbonation. The difficulties of porosity characterization are reviewed and some alternatives to traditional methods are considered. Property/porosity relationships are considered with particular reference to the volume, size-distribution and continuity of the larger pores. The factors influencing porosity under normal exposure conditions, such as cement hydration, drying and carbonation, are reviewed and the possibilities of modeling their effects are considered. Some comparisons between predicted and measured values of porosity are given. It is concluded that progress in modeling the performance of exposed concrete is likely to be linked with improvements in methods of pore structure characterization.
Leachate Composition at an Experimental Test Cell of Coal Combustion Fly Ash
Authors: Labuz L. L. , Viliaume J. F. , Bell J. W. 
Published: March 2011

ABSTRACTIn an effort to characterize the waste streams at a typical utility fly ash landfill, a large outdoor test cell of compacted fly ash was constructed in 1984 at the Pennsylvania Power & Light Company's Montour Steam Electric Station. The test cell is a scaled-down version of the active dry fly ash disposal facility at the plant and includes a liner, a leachate collection system, and surface water runoff perimeter drains. It is 100 feet by 100 feet at the base and 10 feet high with 2:1 vertical:horizontal side slopes, giving a top area of 60 feet by 60 feet. The test cell is instrumented to measure precipitation, infiltration, surface runoff, unsaturated flow, evapotranspiration and leachate drainage. This paper presents a preliminary evaluation of the chemical composition of leachate generated from the test cell during the first year of leachate production. Leachate samples are periodically collected from a concrete sump to which the leachate collection system drains. Leachate first appeared in the sump in October 1985, approximately one year after the test cell was constructed. Samples are analyzed for pH, specific conductance, 22 metals, and 10 ions. The concentrations of parameters present in the test cell leachate are compared to drinking water standards and to standard laboratory extraction results. Parameters not detected in the leachate are also identified. The preliminary findings of the leachate monitoring effort are providing valuable information on the initial quality of leachate generated under field conditions. This data will be useful in the design of leachate control systems, wastewater treatment facilities and ground water monitoring programs for future ash disposal operations.