bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure-Sensitive Vibrations in Zeolites as Studied by Raman Scattering
Authors: Buckley R. G. , Deckman H. W. , Newsam J. M. , McHenry J. A. , Persans P. D. , Witzke H. 
Published: March 2011

AbstractIn this paper we demonstrate the usefulness of a nearest neighbor force model for studying the structural dependence of the lattice dynamics of zeolites. Interpreting Raman scattering in the context of this model confirms earlier empirical vibrational assignments in zeolites and underlines the importance of short range forces in determining the frequencies of certain zeolite vibrational modes. The model describes fully the low frequency bond bending mode of A1 symmetry, although long range forces are shown to be required to model complete zeolite vibrational spectra.
The Reactions of C2H2 and CH3C2H on Ag Powder
Authors: Dorain Paul B. , Boggio Joseph E. 
Published: March 2011

AbstractAg powder is activated by pulsing it with NO2 gas which forms fresh Ag microclusters. This powder is then exposed to subsequent pulses of C2H2 or CH3C2H (3.7% in N2 ). The surface enhanced Raman scattering (SERS) spectra show dramatic intensity variations due to rapid changes in adatom concentration. Normalization of these time-dependent SERS spectra to the background scattering intensity, which is proportional to the adatom concentration, provides spectra which represent adsorbate coverage if major surface reconstruction does not occur. The temporal development of the SERS spectra of C2H2 shows rapid degradation with no evidence for adsorbed species. In contrast, propyne reacts more slowly, as evidenced by the behavior of the intensity at 1980cm−1 due to adsorbed -C2-. The reactions observed are in accord with the models developed by Barteau and Madix[1] and Vohs, Carney, and Barteau[2]. Exposure to both alkynes results in the appearance of SERS active NO, an adsorbant not previously observed at room temperature. Ellipsometric measurements are consistent with the presence of a carbon overlayer, which may stabilize the NO and render the system inert to further chemical reaction.
Small-Angle X-Ray Scattering of Carbon-Supported Metal Catalysts
Authors: Goodtsman J , Phillips M. G. , Brumberger H. 
Published: March 2011

AbstractThe slit-smeared intensity of X-radiation scattered from carbon-supported metal catalysts behaves as clh−1 + c2h−3 for higher h-values in the small-angle region (h+4πλ−1 sinθ, λ + X-ray wavelength,θ + half of scattering angle, c1, c2 are constants). For three-phase systems with sharp phase boundaries, uniform electron-densities in the metal and void phases, and lamellar electrondensity fluctuations in the carbon phase, the small-angle X-ray scattering (SAXS) can be described in terms of inter- and intraphase electron-density correlation functions, and can be shown to yield the observed behavior. Further assumptions are required to separate these contributions and calculate interfacial specific surfaces. SAXS measurements on Pt, Ru, Pd, and Rh/C are presented.
Pillared Clays and Micas
Authors: Johnson Jack W. , Brody John F. 
Published: March 2011

AbstractThe interest in the petroleum industry in converting heavier feeds to liquid fuels has led to a search for microporous materials with pore sizes larger than those found in the faujasitic zeolites which form the basis of many petroleum processing catalysts. Materials with zeolite-like pores in the 10 Å range can be synthesized by intercalating large polyoxocations between the layers of smectite clays. Subsequent calcination dehydrates the cations and converts them into oxide pillars that prop the clay layers apart, resulting in permanent microporosity in the interlayer region. Pillared clays have been studied extensively during the last decade due to their potential use in petroleum processing as cracking and hydrocracking catalysts. Previous workers have primarily utilized smectite clays such as montmorillonite and hectorite as the starting layered material for pillared clay. We now report that synthetic fluoromicas, clay-like materials of layer charge density higher than that of smectites, can also be pillared with polyoxoaluminum cations to form aluminapillared fluoromicas that are thermally stable up to 700°C.
VPI-5: A Novel Large Pore Molecular Sieve
Authors: Davis Mark E. , Saldarriaga Carlos , Montes Consuelo , Garces Juan , Crowder Cyrus 
Published: March 2011

AbstractThis paper reports a novel family of aluminophosphate based molecular sieves denoted as VPI-5. These molecular sieves are the first to contain pores larger than 10 Å. The large pores of the VPI-5 sieves consist of long channels circumscribed by eighteen membered rings and are capable of adsorbing molecules excluded from other molecular sieves.
High Dispersion Metal Oxide/Molecular Sieves: New Bifunctional Shape Selective Catalysts
Authors: Szostak R. , Nair V. , Shieh D. C. , Thomas T. L. 
Published: March 2011

AbstractHighly dispersed metal oxide/molecular sieve catalysts can be prepared through modification of metallosilicate molecular sieves. The resulting materials have been shown to exhibit enhanced catalytic activities for selected reactions. The metallosilicates examined include the gallosilicates, iron (ferri-) silicates and cobalt silicates. The size of the metal oxide particles as well as their location (in the pores or on the surface) can be controlled through post-synthesis methods. Thermal or mild hydrothermal treatment of the metallosilicate produces a highly dispersed metal oxide phase, while higher temperatures or longer treatment causes the metal oxide to migrate and form larger agglomerates of the metal oxide phase. The size of these agglomerates are strongly dependent on the conditions of hydrothermal treatment. Dispersion, location and agglomeration of the metal oxide phase have been characterized for the iron silicates using both physical and catalytic techniques. The magnetic properties of the iron silicates are described.
Theoretical Studies of Pt Chemisorption on γ Al2O3.
Authors: Low J. J. , Ellis D. E. 
Published: March 2011

AbstractGeneralized Valence Bond (GVB) and Local Density Functional (LDF) calculations were carried out to explore the influence of electronic structure on the metal-support interaction in Pt/γAl2O3. On the basis of GVB calculations it was found that ethylene can form either di-σ- or π complexes on Pt depending on the oxidation state of the metal. The LDF calculations showed that chemisorbed Pt transfers charge to γ-Al2O3. These results and experimental observations led us to propose a model of the metal-support interaction in which the Pt exists in two oxidation states for reduced Pt/ Al2O3 catalysts.
Structure and Reactivity of RH in the SMSI State
Authors: Braunschweig Ehrich J. , Logan A. David , Datye Abhaya K. 
Published: March 2011

AbstractHydrogenolysis of n-butane and CO hydrogenation were used to charac-terize the behavior of TiO2supported Rh in the SMSI state. The Rh was supported on a model support consisting of nonporous spherical particles of TiO2. The simple geometry of the support permits the metal crystallites to be imaged ‘edge-on’ in a transmission electron microscope. This allows detailed examination of the metal surface and the metal-oxide interface as a function of pretreatment. After high temperature reduction in H2, there is no significant change in the morphology of the Rh crystallites. However, the presence of amorphous overlayers 0.2–0.4 nm thick is clearly evident on the Rh surface. These overlayers can only be partially removed after oxidation at 473 K. The presence of these overlayers is well correlated with the drop in hydrogen chemisorption and altered reactivity. While the butane hydrogenolysis activity of Rh is considerably suppressed in the SMSI state, the CO hydrogenation activity is increased by a factor of 3. The H2uptake and the butane hydrogenolysis activity can be only partially restored after oxidation at 473 K. Treatment at 773 K in oxygen is necessary for restoring the pre-SMSI behavior.
Investigation of Novel Iron Oxide-Chromia on Alumina or Magnesia Aerogel Catalysts for the Selective Reduction of Nitric Oxide by Ammonia
Authors: Willey Ronald J. , Olmstead J. , Djuhadi V. , Teichner S. J. 
Published: March 2011

AbstractA series of iron oxide-chromia on alumina and iron oxide on magnesia materials were made by the aerogel process. These materials had high surface areas (300 to 700 m2/g) and demonstrated good activity for the selective reduction of nitric oxide by ammonia.A combination of 4 parts Fe to 1 Part Cr gave the best catalyst for the reaction. Fe-Cr to alumina ratios were varied from 0.1 to 0.4. Activity per unit weight increased with increasing Fe-Cr/A12O3ratios, however, activity per unit Fe-Cr favored the lower Fe-Cr to alumina ratios.The fresh material from the autoclave was found reduced (Fe3O4) and initially had poor activity for the selective reduction of nitric oxide by ammonia (525 ppm NO & 525 ppm NH3in air feed conditions). However, after several testing cycles, in which the catalyst was in continuous contact with oxygen (as air), activity improved dramatically. Upon removal from the reactor the material had a distinct color change (from brown to reddish brown) and magnetic properties were lost. This suggests that Fe2O3is part of the active site for the selective reduction of nitric oxide by ammonia. At higher temperatures activity decreased because of a competing reaction, ammonia oxidation to nitric oxide.
51V NMR: A New Probe of Structure and Bonding in Catalysts
Authors: Eckert Hellmut , Wacjs Israel E. 
Published: March 2011

AbstractSolid State 51V NMR spectra are sensitive to changes In the surface structure of V2O5 dispersed on Al2O3 and TiO2 supports. For V2O5 supported on alumina, wideline and magic-angle spinning experiments at 4.7 and 7.0 T reveal the presence of two vanadium species with different bonding environments. The relative proportions of these species change monotonically as a function of the vanadium concentration. In contrast, supported vanadium oxide on TiO2 substrates show a much more V2O5-like environment. Structural inferences are discussed In connection with solid state 51V NMR studies on model compounds with known crystal structures and site symmetries.
Mössbauer and Exafs Study of 57Fe Labelled Pt/SiO2 Catalysts
Authors: Sawicki J. A. , Rolston J. H. , Julian S. R. , Tyliszczak T. , McCrimmon K. D. 
Published: March 2011

AbstractSpecimens of highly dispersed Pt/Silicalite catalyst, decorated with 57Fe by impregnation in aqueous ferric nitrate solution, have been studied after decoration, and various pretreatments including exposure to carbon monoxide, by in situ Mössbauer spectroscopy. The form of Pt was followed by EXAFS analysis near the Pt LIII edge. The microstructural studies were combined with CO chemisorption and infrared absorption measurements. It is observed that iron in Pt clusters is very reactive even at ambient temperatures and that the interaction of Fe with CO is strongly accelerated by platinum.
Fixation of Cesium by Calcium Aluminosilicate Hydrates
Authors: Hoyle Susan L. , Grutzeck Michael W. 
Published: March 2011

AbstractRecent work by the authors has demonstrated that cesium was being incorporated in a hydrated phase as their cement-based waste forms cured. The objective of the present study was to identify the hydrated phases responsible for the observed cesium incorporation. Four calcium aluminosilicate glasses having a 1:2 Al2O3/CaO ratio and a 25–70 mole % silica content were mixed with ˜0.3 molar CsOH or CsCl solutions (water/solid ratio = 10) and allowed to hydrate at 38° and 90°C for periods up to 90 days. Paste equivalent samples, having a water/solid ratio of 1.0 were also prepared to gauge the cementing properties of these mixtures. Solutions were analyzed for Ca, Al, Si, and Cs while solids were characterized using x-ray powder diffraction and scanning electron microscopy.Glasses exposed to the CsOH solution were more reactive than their counterparts exposed to the CsCl solution. In addition, reactivity as well as crystallinity seemed to be higher at 90° than at 38°C. At least two cesium-containing zeolites were identified in the 90°C CsOH solution experiment: A cesium-containing wairarkite analogue and possibly another cesium-containing zeolite unidentified at this time. The relatively complete removal of cesium from the solution, in one case, as well as the fact that the mixtures are self-cementing suggests that the glasses may be “engineered” to serve as overpack material in a deep-seated geologic repository.
Diffusion in the Matrix of Granitic Rock Field Test in the Stripa Mine
Authors: Birgersson Lars , Neretnieks Ivars 
Published: March 2011

AbstractThree similar migration experiments in the matrix of granitic rock are presented. The experiments have been carried out in “undisturbed” rock, that is rock under its natural stress environment. Since the experiments were performed at the 360 m level (in the Stripa Mine), the rock was subjected to nearly the same conditions as the rock surrounding a nuclear waste repository as proposed in the Swedish concept (SKB).A mixture of three non-sorbing (conservative) tracers, Uranine, Cr-EDTA and I−, were injected into the granitic rock matrix for time periods of months up to years. The subsequent overcorings of the injection holes showed that the tracers had in some cases migrated at least ≈ 400 mm (measuring limit) into the rock matrix for the experiment with the longest injection time. It could also be seen that there were large differences in migration distance into the rock matrix for samples taken fairly close to each other. One example where the tracers have diffused through fissure coating (filling) material located in “undisturbed” rock is also presented.The results from all three experiments show that all three tracers have migrated through the disturbed zone close to the injection hole, through the fissure coating material and a distance into the “undisturbed” rock matrix.These results therefore indicate that dissolved compounds may migrate into the rock matrix. This migration into the rock matrix will increase the area available for sorption of radionuclides significantly and may therefore increase the migration times for radionuclides by order(s) of magnitude.Diffusivities and hydraulic conductivities obtained in this in-situ experiment compare well with those obtained in laboratory experiments.
3–-D Migration Experiment in Sparsely Fractured Crystalline Rock
Authors: Abelin Harald , Birgersson Lars , Gidlund Jard , Moreno Luis , Ågren Thomas , Widén Hans , Neretnieks Iivrs 
Published: March 2011

AbstractA large scale tracer experiment has been performed in sparsely fractured granitic rock at 360 m depth. Nine different conservative tracers were injected at distances ranging between 10 and 56 m from a drift excavated for this experiment. The upper part of the test site was covered completely with plastic sheets. All the water entering into the drift could be collected. Water flow monitoring shows that water flow takes place in small areas with large dry areas in between. Of the nine injected tracers six reached the test site during the experiment. The fitting of the breakthrough curves to different models could not satisfactorily explain the actual processes involved in the tracer migration. The results of the tracer experiments and the Tritium measurements gave strong support to the notion that a non–negligible portion of the flow takes place in more or less isolated channels.
Sensitivity Surfaces for the Assessment of Waste Package Performance
Authors: Leneveu D. M. , Garisto N. C. 
Published: March 2011

AbstractSensitivity surfaces have been developed to analyse the performance of engineered barriers of an underground nuclear fuel waste disposal vault. The major engineered barriers are the waste form, the containers and the buffer surrounding the containers. A modular computer code has been developed that calculates the release rate from each barrier. The modules are linked together through the use of time-series-management routines. By systematic variation of the model input parameters, sensitivity surfaces are constructed that illustrate the behaviour of an objective function such as maximum fractional release rate in response to the changes in the input parameters.
Validation of a Nuclear Waste Repository Performance Assessment Model:Comparison of Theory With Experiment
Authors: Geldart R. W. , Mcgrail B. P. , Rhoads K. C. , Apted M. J. 
Published: March 2011

AbstractLaboratory tests were conducted to validate a radionuclide mass transfer model. During the experiments, cesium and uranium releases from a simulated waste form embedded in an isotropic medium of quartz sand were measured. A 0.01 M NaH2PO4 buffer solution flowed past the waste form. Downstream concentrations obtained from computer simulations were compared with experimentally measured concentrations of cesium and uranium. Uranium release was found to be controlled by solubility-limited mass transfer, while cesium release was controlled by waste form dissolution kinetics. It was also found that the effects of dissolution on groundwater chemistry must be coupled with solubility-limited mass transfer models to defensibly predict radionuclide release rates under realistic repository conditions.
Application And Results Of A Reinjection Technique For Hydrothermal Experiments In Dickson Autoclaves
Authors: Gardiner M. A. , Kacandes G. H. , Ulmer G. C. , Grandstaff D. E. 
Published: March 2011

AbstractCohassett basalt was reacted with synthetic Hanford groundwater in a Dickson rocking autoclave at 300°C and 30 MPa for ca. 7600 hours. During the experiment fresh solution was twice reinjected into the reaction cell, raising the nominal water:rock mass ratio from 50:1 to 140:1. The reinjection experiment is intermediate between closed-system Dickson experiments and flow-through tests in that the fluid and solids can remain in contact for extended periods of time before the solution is replaced. This allows more time for equilibrium to be approached. Data from this experiment suggest:(1) After reinjection many solution parameters quickly (hrs-days) returned to near preinjection values. (2) The redox buffer capacity of the basalt was not exceeded, i.e. fO2 values remained near magnetite-hematite values, although the nominal water:rock mass ratio was raised to ca. 140 during the experiment. (3) After reinjection the stable high-temperature pH value was only slightly less than the initial pH value. (4) The silica concentration stabilized near apparent quartz saturation rather than the cristobalite saturation value found in closed-system experiments. (5) Short-term relationships between cations appear to be controlled by ionexchange between the solutions and clay minerals.Reaction products identified from the experiment include: Fesmectite, illite, hematite, minor cristobalite and possibly Ti-maghemite.
Experimental Interaction of Basalt, Bentonite, and Water: Implications for Groundwater Chemistry in Waste Package Packing Material in a Nuclear Waste Repository
Authors: McKeon Gail L. , Thornton E. C. , Halko D. J. , Wood M. I. 
Published: March 2011

AbstractExperiments have been conducted by the Basalt Waste Isolation Project (BWIP) to assess changes in solution chemistry in the near-field environment of a nuclear waste repository in basalt. These Dickson autoclave experiments were carried out using Grande Ronde basalt ± bentonite and synthetic groundwater or deionized water at 300°C, 30 MPa, and solution-to-solid mass ratio of 10 for up to two years. Groundwater solution changes during reaction of the basalt and basalt/bentonite included initial decreases in pH and sodium concentration presumably due to smectite formation. This initial trend subsequently reversed in the basalt system with pH rising to ca. 7.5 and sodium increasing to the starting value. Steady state pH values for the basalt/bentonite system were ca. 6.4. The basalt + deionized water test exhibited a constant rise in pH to ca. 7.9 and release of sodium to solution in response to basalt dissolution. Slightly oxidizing conditions characterized the early part of all of the experiments followed by a decrease in fO2 to 10−31 to 10−32 These results are consistent with other work at similar and lower temperatures, suggesting that the packing material will react in the waste package environment to produce slightly alkaline, reducing conditions.
Spent UO2 Fuel Corrosion in Water; Release Mechanisms
Authors: Werme Lars O. , Forsyth Roy S. 
Published: March 2011

AbstractAn update of the status of the joint SKB/Studsvik fuel leaching programme is given. High burnup BWR fuel has been leached for up to 5.5 years cumulated contact time. Data for leaching of PWR fuel are also presented. The present results confirm earlier results from the programme, i.e., in groundwater and deionized water under oxidizing conditions uranium rapidly attains saturation at about 1 mg/l and 10 μg/l, respectively.Under reducing conditions, the uranium saturation levels are below 1μg/l. The plutonium saturation level under oxidizing conditions is at about 0.3 μg/l. Under reducing conditions, the plutonium concentrations in solution appear to be controlled by the solubility of the fuel matrix.Most of the detected fission products appear to be released through selective leaching of fuel/cladding gap, fuel cracks and fissures, and grain boundaries.
Radionuclide Release Behavior of Light Water Reactor Spent Fuel Under Hydrothermal Conditions
Authors: Neal William L. , Rawson Shirley A. , Murphy William M. 
Published: March 2011

AbstractThe Basalt Waste Isolation Project has performed initial characterization of the release behavior of radionuclides from ATM-101 spent fuel reacted under hydrothermal conditions. Results to date indicate that 1) 14C, 90Sr, 129I, and 137Cs exhibit preferential release to solution relative to the actinides, 2) 239+240Pu, 241Am, and 244Cm ratios in solution are consistent with stoichiometric dissolution of the spent fuel matrix, whereas uranium concentrations are higher than those predicted for stoichiometric dissolution, 3) 137Cs release varies as a function of the fluid to solid mass ratio, and 4) 14C, 129I, and 137Cs release is affected by fuel particle size and/or fuel washing.
Analytical Electron Microscopy of Leached Layers on Synthetic Basalt Glass
Authors: Murakami T. , Ewing R. C. , Bunker B. C. 
Published: March 2011

AbstractAnalytical electron microscopy was used to characterize leached layers formed on a synthetic basalt glass after 300 days in deionized water, sodium chloride solutions, or sodium chloride solutions containing magnesium chloride. Ultramicrotomed cross-sections show that the leached layers consist of a mixture of amorphous and crystalline phases whose composition and microstructure are sensitive to solution chemistry. In general, Na, Ca and Mg are selectively leached in all solutions, leaving behind surface alteration products which are rich in Fe, Ti, and Al. In deionized water and the NaCl solution, gibbsite (AI(OH)3) is a major phase; in the Mg-containing solution, Si and Al are retained as smectite clays. Results are compared to the alteration of natural basalt glasses in marine environments, particularly as they relate to the use of basalt glass alteration as a means of verifying the long-term leaching behavior of nuclear waste form borosilicate glasses.