bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molybdate Catalysts
Authors: Ueda Wataru 
Published: March 2011

AbstractIt is possible to classify the solid state catalyst systems into two categories; structure static catalyst and structure dynamic catalyst. The former is the catalyst in which the original structural circumstances of surface active center, such as coordinatively unsaturated state of active element, length and order of metal-ligand bond or of a bond between structural component, and their bond angle, are maintained unchanged during catalysis. The example is molybdenum sulfid which is a good catalyst for the isomerization and hydrogenation of olefins. On the contrary, the catalysts, in which the above circumstances of surface active center are changing dynamically during catalysis, are classified into the latter category. Molybdate catalysts for olefin oxidation by molecular oxygen at high temperature belong to this category. Main difference between two categories is whether the originally coordinated ligand on metal cation, such as sulfur anion of molybdenum sulfid and oxygen anion of metal molybdate, can participate in the catalysis directly or not. When the coordinated ligand is involved in the reaction, resulting abnormal coordinatively unsaturated state of surface active center must be sustained by the dynamic structure changes of both surface and bulk for the steady state catalysis. The bulk structure, therefore, affects strongly the properties of structure dynamic catalysts, whereas the properties of structure static catalysts depend on the surface structure like coner and edge mainly. The relationship between catalytic properties and structural stability of molybdate catalysts in the selective oxidation of propylene was discussed on the basis of18O tracer study.
A New Polymer-Based Hydrogen Getter
Authors: Gilliom Laura R. 
Published: March 2011

AbstractStyrene-butadiene triblock copolymer PS-PB-PS was hydrogenated in the bulk using the Crabtree catalyst [Ir(COD)(py)(tcyp)]PF6(COD = 1,5-cyclooctadiene, py = pyridene, tcyp = tricyclohexylphosphine). Since this polymer/catalyst mixture reacts rapidly with hydrogen at ambient temperature and low hydrogen pressures, it should act as an effective hydrogen getter.
Auger Electron Spectroscopy of Amorphous Cu-30 at.% ZR Activated for Catalysis
Authors: Vanini Fabiano , Erbudak Mebmet , Kostorz Gernot , Baiker Alfons 
Published: March 2011

AbstractAmorphous Cu70Zr30 ribbons heat treated at 473 K in a hydrogen atmosphere yield a very active catalyst for the hydrogenation of ethene and buta-diene. The catalytic activity is due to finely dispersed Cu particles formed on a surface containing numerous cracks. Auger depth profiles and scanning electron micrographs reveal details of the surface chemistry and morphology. The observations are related to the free-energy curve of bulk amorphous Cu-Zr.
Substantially Transparent Pt, Pd, Rh, And Re Films: Preparation and Properties
Authors: Aspnes D. E. , Heller A. 
Published: March 2011

AbstractFilms of Pt, Pd, Rh, and Re with metal volume fractions of 0.3 to 0.5 have been prepared by mass-transport-limited photoelectrodeposition onto (001) p-InP photocathodes from ∼5 × 10−5 M solutions of the metal ions in 1 M HClO4. These films exhibit their normal catalytic activities (e.g., in hydrogen evolution) and have normal crystal structures, yet are substantially more transparent than equivalent dense films of the same metal loading per unit area. Effective-medium analysis of the spectroellipsometrically measured dielectric functions of these films shows that the anomalous transparency is due to microstructure: depolarization factors and metal packing fractions obtained by best-fit model calculations indicate dendritic (Rh), particulate (Pt, Pd), or platelet (Re) forms that are poorly interconnected in directions parallel to the surface, and whose dimensions are all small compared to the wavelength of light. Transmission electron micrographs confirm these results and reveal that these films consist of primary building blocks of ca. 5 nm crystallites that are organized into relatively loosely packed secondary structures. Potential applications of these films include the formation of efficient metallic-catalyst-coated photoelectrodes on poor-quality semiconductors.
The Composition and Stability of Nicu Surface Alloys Grown by Ni(CO), Decomposition on Cu
Authors: Alkemade Paul F.A. , Fortuin H. , Balkenende R. , Habraken F. H. P. M. , Weg W. F. Van Der 
Published: March 2011

AbstractThe composition of NiCu surface alloys, prepared by decomposition of nickel carbonyl on a Cu(100) surface, has been studied before as well as after annealing using MeV Rutherford Backscattering Spectroscopy.NiCu films with a thickness of 2 nm and of 10 nm, respectively, having a sharp interface with the copper substrate, were grown. The nickel fraction is found to be 65% and 93% respectively. The outermost monolayer is slightly enriched in copper. During annealing interdiffusion between the film and the interface occurs and the enrichment of the surface increases. In case of the 10 nm film the observed diffusion rate is much higher than is expected on the basis of diffusion coefficients published in the literature. This is ascribed to the presence of defects and/or grain boundaries in the grown surface alloy.
Kinetics and Mechanism of the Copper-Catalyzed Etching of Silicon by F2
Authors: Selamoglu N. , Mucha J. A. , Flamm D. L. , Ibbotson D. E. 
Published: March 2011

AbstractThe copper catalyzed fluorination of silicon is first-order in [F2] and in [Cu]s until the coverage reaches ∼4 monolayers. Above ∼4 monolayers the reaction rate is zero order in copper, suggesting a limited number of catalytically active Cu/Si sites. Surface diffusion of copper leads to decrease in the etch rate as a function of time as well as feature size-dependent etch depths. The copper compounds CuF2, CuO, and copper silicides, Cu5 Si and Cu3 Si all catalyzed the F2-Si reaction which suggests that they are all converted to the same active species. The results can be explained by mechanisms involving copper fluorides or copper silicides as active intermediates.
Atomic Force Michoscxpy-Feasibility for Materials Research.
Authors: Bryant P. J. , Yang R. , Miller R. 
Published: March 2011

AbstractThe applicability of atomic force microscopy (AFM) to both conductive and dielectric materials is the subject of this study. A representative conductor, Cu, and two dielectrics, mica and selenite, were examined. Microstructure and single lamellar steps were resolved. Surface areas on Cu and mica generated reproducible images when scanned repeatedly. There was no evidence of damage to the probe or the sample as a result of the AFM investigations. Selenite did show evidence of change after repeated scans with an AFM lever of 12 N/m spring constant exerting a 10−6N force.
High Temperature limit for the Growth of Carbon Filaments on Catalytic iron Particles
Authors: Tibbetts Gary G. , Rodda Eric J. 
Published: March 2011

AbstractCarbon filaments of macroscopic length may be produced by heating transition metal catalyst particles in a hydrocarbon-hydrogen mixture. Because the nanometer-sized catalyst particles contain relatively many surface atoms, they melt at a temperature considerably below that of bulk material; this depression of the melting point is difficult both to calcu-late and measure. This work addresses the fundamental question of whether the catalyst particles are in the liquid or solid state during filament growth.We present measurements of the average number of filaments grown per unit area of substrate as a function of temperature which show that the the activity of the catalyst particles drops precipitously above 1030°C and nearly disappears above 1120°C. This compares with the melting point of the Fe-C eutectic of 1154°C. TEM observations show that the average dia-meter of an active catalyst particle is 15±7 nm. Calculations based on the model of Ross and Andres [1] for the melting temperature of small clusters of atoms predict a drop in activity above 1050°C similar to our observa-tions.
Entropy and Melting in Small Particles
Authors: Ajayan P. M. , Marks L. D. 
Published: March 2011

AbstractWe describe theoretical results for part of the Gibbs free energy surface as a function of shape and temperature for small particles. We predict the existence of true ‘quasi-melting’ at temperatures much below the conventional melting points and also phase transitions between different stable forms as the temperature is varied. A phase diagram for small particles is constructed for the first time, showing the stability ranges for different particle shapes as a function of size and temperature.
Perspective on the use of gas Adsorption for Particle-Shape Control in Supported Metal Catalysis
Authors: Shi A -C. , Fung K. K. , Welch J. F. , Wortis M. , Masel R. I. 
Published: March 2011

AbstractThis paper explores the possibility of using gas adsorption for particle-shape control in supported metal catalysis. Calculations are done to identify the kinds of shape changes which are possible due to treatment in an appropriate adgas. Experiments are done to try to verify the concepts. The results show that gas adsorption can be used for particle shape control in supported metal catalysis.
NMR and Quantum Effects in Metal Particles
Authors: Halperin W. P. , Yu Insuk 
Published: March 2011

abstractThe considerable interest in metallic clusters spans a wide range. In this paper we discuss quantum effects and we suggest that there may be important interrelationships between such behavior and heterogeneous catalysis. Of course, the physical and chemical behavior of the metal particle are the key to understanding principles of catalytic activity. The quantum effects are found at progressively lower temperatures where the metallic properties change. In both cases a fundamental question is posed, “Do these particles exhibit metallic behavior?;” One of the common features of research in these two areas is the important role played by nuclear magnetic resonance(NMR) techniques since the signatures of a metal and an insulator are so dramatically different. The issue of metallic or nonmetallic behavior is therefore best addressed with this experimental approach and we will review the current situation by comparing a number of results on quantum size effects deduced from NMR experiments
Technical Challenges Facing Regulators–Assessment of Long-Term Materials Performance
Authors: Stephens Kenneth W. 
Published: March 2011

AbstractFor a number of years, nuclear regulators have grappled with difficult questions such as: “How safe is safe enough?” Such issues take on new dimensions in the long time-frame of high-level waste disposal.Many of the challenges facing regulators involve assessment of long-term materials performance. Because real-time experiments cannot be conducted, it is necessary to rely extensively on modeling. This raises issues regarding the extent to which long-term extrapolations of short-term data are justified, the question of how closely models must represent reality to be trusted, and practical matters such as methods for validating unique computer codes.Issues such as these illustrate how regulators must make decisions in a climate of uncertainty. Methods used by non-technical disciplines to make decisions under uncertainty have been examined and offer solutions for regulators and licensees alike.
The Radlonuclide Migration Experiment at the Grimsel Rock Laboratory, Switzerland
Authors: McKinley Ian G. , Alexander W. Russell , Bajo Claudine , Frick Urs , Hadermann Jörg , Herzog Franz A. , Höhn Eduard 
Published: March 2011

AbstractThis paper describes the programme for an in-situ radionuclide migration experiment in fractured crystalline rock and presents the first results of site characterisation work. This study is particularly notable for its extensive hydrologic/geochemical support programme and the use of radiotracers identified as important in safety assessment studies.
Immobilization of Technetium and Nitrate in Cement-Based Materials
Authors: Tallent O. K. , McDaniel E. W. , Cul G. D. Del , Dodson K. E. , Trotter D. R. 
Published: March 2011

AbstractThe leachabilities of technetium and nitrate wastes immobilized in cement-based materials (i.e., grouts) have been investigated using ANS 16.1 test procedures. Factors found to affect the leachabilities include (1) grout mix ratio, (2) grout fluid density, (3) dry solid blend composition (including ground blast furnace slag), and (4) waste concentration.
Natural Radionuclides in Hanford Site Ground Waters
Authors: Smith M. R. , Laul J. C. , Johnson V. G. 
Published: March 2011

AbstractUranium, Th, Ra, Rn, Pb and Po radionuclide concentrations in ground waters from the Hanford Site indicate that U, Th, and Ra are highly jorbed. Relative to Rn, these radionuclides are low by factors of 10−3 to 10−6. Uranium sorption is likely due to its reduction from the +6 state, where it is introduced via surface waters, to the +4 state found in the confined aquifers. The distribution of radionuclides is very similar in all of the confined aquifers and significantly different from the distribution observed in the unconfined and surface waters. Barium correlates well with Ra over three orders of magnitude indicating that stable element analogs may be useful for inferring the behavior of radioactive waste radionuclides in this candidate geologic repository.
Radionuclide Transport through Perforations in Nuclear Waste Containers
Authors: Aidun Cyrus K. , Bloom Sanford G. , Raines Gilbert E. 
Published: March 2011

AbstractPrevious analytical models for the steady-state radionuclide release rate through perforations in nuclear waste containers into the surrounding medium, are based on a zero wall thickness assumption. In this paper we investigate the effect of the wall thickness on the mass transfer rate through isolated circular holes. We solve the steady-state diffusion equation for the concentration field and derive a model based on the analytical solution. By direct comparison, we show that the zero wall thickness model overpredicts the mass transfer rate by about 1300 percent for a circular hole with 1 cm radius and a wall thickness of 10 cm. As expected, the zero-thickness model becomes even less accurate as the hole radius decreases; it predicts a greater release rate from a large number of small holes than the mass transfer rate from an uncontained waste form cylinder. In contrast, the results predicted by our model remain bounded for isolated holes and never exceed the mass transfer from an uncontained waste form.
Gas-Phase Transport of Carbon-14 Released from Nuclear Waste into the Unsaturated Zone
Authors: Ross Benjamin 
Published: March 2011

AbstractGas-phase carbon-14 dioxide released from spent fuel buried in unsaturated rocks will move upward by molecular diffusion and advection. The flux resulting from molecular diffusion will be determined by the concentration gradient of gaseous carbon-14 dioxide. Advection will be caused by density-driven flow of the pore gas. Such flow occurs under present conditions as a result of annual and diurnal temperature changes and differences in chemical composition between pore gas and air, and it will be enhanced when the spent fuel heats the rock. The advective flux will be determined by the gas-phase concentration of carbon-14 and by the velocity of convective flow of the pore gas. Gas-phase concentrations of carbon-14 dioxide will be strongly influenced by isotopic exchange with bicarbonate dissolved in water that is retained in the unsaturated zone by capillary forces. Isotopic equilibrium between these two phases will be attained very rapidly on repository time scales. If the liquid phase is saturated with calcium carbonate, precipitation of calcite may provide a sink for removal of carbon-14 from the mobile phases.
Three-Dimensional Code for Groundwater Flow and advection Diffusion With a Decay Chain of Radioactive Materials Using Finite Element Method
Authors: Kawamura Ryuji , Ishihara Takehiko 
Published: March 2011

AbstractA code(PER8MIGR) for the finite element method (F.E.M.) using 8-node point isoparametric elements has been developed for solving three-dimensional groundwater flow and advection diffusion equations with a decay chain of radioactive materials. Galerkin's method is applied to discretize the equations, and asymmetric band matrix method is used to solve the equation. Some simple problems for groundwater flow and migration of nuclides were solved by the code to compare the results for groundwater flow with the one- and three-dimensional analytical solutions. The results for migration of nuclides were also compared with the results obtained by some existing available codes. Our results and those by the other codes were in good agreement. The present work makes it possible to solve the groundwater flow and diffusion problems more accurately for radioactive waste disposal in complex geometry.
Geochemical Simulation of Reaction Between Spent Fuel Waste Form and J-13 Water at 25°C and 90°C
Authors: Bruton Carol J. , Shaw Henry F. 
Published: March 2011

AbstractGeochemical simulations of the degradation of spent fuel waste form in the presence of groundwater at the candidate Yucca Mountain, Nevada repository have been carried out to attempt to predict elemental concentrations in solution and to identify potential radionuclide-bearing precipitates. Spent fuel was assumed to dissolve congruently into a static mass of J-13 groundwater at 25°C and 90°C. No inhibitions to the precipitation and dissolution of secondary phases were assumed to exist. The elements Ac, Zr, Nb, Pd, Sm, Mo, Sb and Cm were not considered in the simulations because of a lack of thermodynamic data.Simulation results indicate that haiweeite, soddyite, Na2U2O7(c) and schoepite are potential U-bearing precipitates. Na2U2O7(c) is only predicted to occur at 90°C. U concentrations in solution and the identity of the U-bearing precipitate depend on the activity of SiO2(aq) in solution. U concentrations are limited to < 1 mg/kg when sufficient SiO2(aq) exists in solution to precipitate uranyl silicates. Depletion of SiO2(aq) in solution by the precipitation of silicates results in predicted increases of U concentrations to 87 and 619 mg/kg at 25°C and 90°C, respectively. Subsequent reaction and precipitation of schoepite cause U concentrations to decrease.Radionuclides other than U commonly precipitate as oxides in the simulations. The precipitation of solid phases appears to be extremely effective in limiting the concentrations of some radionuclides, such as Pu and Th, in solution. Concentrations of other elements are held constant (Sn) or are alternately held constant and then increase (Am, Ni, Np) as various solid phases precipitate and pH decreases from 8.5 to 6.5 at 25°C and 8.7 to 8 at 90°C. No solid phases containing Cs or Tc are predicted to form. Increasing the temperature from 25°C to 90°C does not impact greatly the identity of precipitated phases or solution composition, except in the case of U.A technique involving isotope dilution measurements may allow determination of the rates of spent fuel dissolution in future experiments.
Experimental Glass-Ceramic Products to Immobilize ICPP HLW
Authors: Baker Roseanne S. , Staples Bruce A. , Knecht Dieter A. , Berreth Julius R. 
Published: March 2011

AbstractCandidate products are being evaluated to immobilize the routinely calcined waste at the Idaho Chemical Processing Plant (ICPP). A potential product with minimal volume for immobilizing ICPP high-level waste (HLW) for final disposal is a high-waste-loading and high-density glass-ceramic. Glass-ceramics are formed by Hot Isostatic Pressing (HIPing) the HLW with selected additives, such as SiO2, B2O3, Li2O, Na2O, and Y2O3. Glass-ceramic products have been formed with calcine loa ings up to 80 wt% and densities up to 3.4 g/cm3. Crystalline phases observed in the glass-ceramic products include calcium fluoride, monoclinic and cubic zirconia, calcium- and yttrium-stabilized zirconia, and zircon. An interstitial amorphous phase also exists consisting of the oxides of silicon, aluminum, boron, and alkalis. The glass-ceramic waste forms give leach rates comparable to simulated HLW glass products.
Structural Thermodynamic Model for the Durability and Viscosity of Nuclear Waste Glasses
Authors: Feng Xiangdong , Barkatt Aaron 
Published: March 2011

AbstractA model based upon structural thermodynamic considerations has been proposed for both chemical durability and viscosity of nuclear waste glasses. This model assumes the bond strength between atoms in the glass to be the predominant factor in controlling the composition dependence of physical properties such as viscosity and chemical properties like durability. These characteristic bond strengths in the glass are obtained from known heats of formation of the constituent oxides with a few simple structural rules deduced by distinguishing the structural roles of the various oxides, i.e., separating those components that are clearly “network-formers” (e.g. SiO2, Al2O3, ZrO2) from those that are clearly “network-breakers” (e.g. alkali oxides). This model has been successfully applied to the correlation of glass composition with modified MCC-3 leach test results on nuclear waste glasses measured at various laboratories on one hand and with the viscosities of numerous glasses over a temperature range of 850°C to 1600°C with remarkable accuracy on the other hand.
Temperature Dependence of R7T7 Nuclear Waste Glass Alteration Mechanisms
Authors: Vernaz E. Y. , Dussossoy J L. , Fillet S. 
Published: March 2011

AbstractThe French LWR reference glass R7T7 was leached at temperatures between 100°C and 300°C at a pressure of 10 MPa.An activation energy of 25 kJ/mole was found between 100°C and 250°C which is different from the 60 kJ/mole previously found between 25°C and 70°C. It is suggested that a potential glass hydration mechanism becomes predominant when dissolution is significantly slowed by high concentrations of silica in solution. At 300°C, a complete change in the corrosion mechanisms is found as the glass undergoes a rapid hydrothermal alteration
Leaching of Am-241 from a Radioactive Waste Glass Corroded in the Presence of Stainless Steel Corrosion Products and/or Bentonite
Authors: Tsukamoto Masaki , Björner Inga-Kari , Christensen Hilbert , Hermansson Hans-Peter , Werme Lars 
Published: March 2011

AbstractThe release of Am-241 during corrosion of the radioactive waste glass, JSS-A, has been studied in the presence of corrosion products and/or uncom-pacted bentonite. The corrosion behaviour of Am-241 has been analyzed using gamma spectrometry. Adsorption of Am-241 on bentonite is observed in all cases. The contents of Am-241 in centrifuged leachates are in most cases less than 1/100 of total values. The normalized elemental mass loss of Am increases initially with corrosion time, and the values in the presence of bentonite and corrosion products are larger than those in the presence of bentonite alone. This tendency is in agreement with results previously found for other elements. The release of Am is low, only about 10–20 % of the corresponding total mass loss.