bluuebunny/crossref_metadata_2025 huggingface dataset:
Sintering of Metal(100) Homoepitaxial Islands: Kink Rounding Barriers, Modified Size Scaling, and Experimental Behavior
Authors: Liu Da-Jiang , Stoldt C. R. , Thiel P. A. , Evans J. W.
Published: April 2011

Near-square islands form during sub-monolayer homoepitaxial growth on metal (100) surfaces. Diffusion of these islands after deposition leads to collision of island pairs, typically corner-to-corner creating dumbbell-shaped clusters. Subsequent coalescence (or sintering) recovers a near-square equilibrium shape. This process is mediated by periphery diffusion (PD) and its study can provide detailed insight into the underlying dynamic processes and energetics. Atomistic modeling reveals that the size scaling of the characteristic relaxation time, τ, depends on the detailed energy barriers of various hopping processes that contribute to PD. Simulations without an extra kink or corner rounding barrier for PD reveals τ ∼ L4, while behavior approaching τ ∼ L3 is observed with a significant extra kink rounding barrier for PD. The latter is consistent with experimental observations for Ag/Ag(100) at 300 K.
Atomic Structure of Ultrathin Iron Silicide Films on Si(111): Metastable Phases and a New Template Structure
Authors: Starke U. , Walter S. , Krause M. , Blobner F. , Bandorf R. , Weiss W. , Müller S. , Hammer L. , Heinz K.
Published: April 2011

The initial stages of iron silicide growth on Si(111) were investigated using LEED, AES and STM experiments together with DFT calculations. In 1:1 stoichiometry, a cubic FeSi develops showing a (1×1) surface periodicity which is stable up to 300°C. The epitaxial strain energy stabilizes this bulk-unstable B2 (CsCl-type) phase for up to 250 Å thickness. The surface is Si terminated, the interface coordination of the so-called B8 type. After annealing at ≈ 600°C, a (2×2)-FeSi2 phase of higher Si content is observed which possesses cubic crystal structure. It is stable below 10 monolayers (ML) initial Fe coverage and grows in an island-like morphology. In the initial growth stage, however, a c(8×4) phase forms that completely covers the surface at 1.5 ML Fe content and appears as potential template for further growth of homogeneous films. The interpretation of atomically resolved STM images suggests that the film contains three Si and two Fe layers in B2 structure with vacancies on Fe positions. The vacancy arrangement seems to be responsible for the c(8×4) periodicity displayed by the Si adatoms in T4-position.
EFFECT OF LANTHANUM MANGANITE MODIFICATION BY CALCIUM AND/OR FLUORINE ON THE BONDING STRENGTH, MOBILITY AND REACTIVITY OF THE LATTICE AND SURFACE OXYGEN
Authors: Sadykov V. A. , Kuznetsova T. G. , Simakov A. V. , Rogov V. A. , Zaikovskii V. I. , Moroz E. M. , Kochubei D. I. , Novgorodov B. N. , Ivanov V. P. , Trukhan S. N. , Litvak G. S. , Bulgakov N. N. , Lunin V. V. , Kemnitz E.
Published: April 2011

Ca and/or F-modified samples of LaMnO3have been prepared by the Pechini method. The bulk structure of samples was characterized by TEM, EXAFS and XRD, while the surface composition was studied by SIMS. Thermal analysis, O2TPD, H2TPR and isothermal pulse/flow samples reduction by CO were applied to characterize the accessible surface/bulk oxygen mobility and reactivity. A reasonable description of the experimental energetic spectrum of the surface oxygen for various types of regular and defect surface sites on the perovskite faces was achieved by using semiempirical Interacting Bonds Method in the slab approximation with a due regard for the surface face termination and relaxation. Fluorine was found to decrease the surface coverage by reactive weakly bound oxygen forms while increasing the bulk oxygen excess and mobility. Calcium generated reactive weakly bound oxygen forms while decreasing the oxygen excess in the lattice and converting the regular M-O oxygen forms into the bridging ones through migration to the surface.
A Structural Comparison of Si(100) Oxidized by Atomic and Molecular Oxygen
Authors: Randjelovic Maja , Yang Judith C.
Published: April 2011

We compared the structural characteristics of a silica layer formed on Si(100) by oxidation in hyperthermal atomic oxygen and molecular oxygen at 493K. The laser detonation method was used to create primarily neutral atomic oxygen with kinetic energy of 5.1eV. The silicon oxides were characterized by High Resolution Transmission Electron Microscopy (HRTEM), Atomic Force Microscopy (AFM), Rutherford Backscattering Spectrometry (RBS), Scanning Electron Microscopy (SEM) and X-ray Photoelectron Spectroscopy (XPS). We determined that atomic oxygen forms amorphous silica that is almost twice as thick and nearly double the surface roughness as compared to molecular oxygen - formed silica at the same temperature and time conditions.
Observations of TiO2 Surfaces Using Totally Reflected X-ray In-plane Diffraction Under UV Irradiation
Authors: Horiuchi T. , Ochi H. , Kaisei K. , Ishida K. , Matsushige K.
Published: April 2011

Surface lattice displacements of titanium dioxide (TiO2: rutile) during ultra-violet (UV) light irradiation have been investigated using a total reflection x-ray diffraction, which provides a high signal to noise ratio (S/N) and superior in-plane surface diffraction. Under the environments in vapors of H2O, CH3OH, C2H5OH and C3H6OH, the photo-catalytic activities of TiO2 (110), (100) and (001) surfaces subject to UV irradiation have been measured. It is found that the diffraction peaks and their full width half maxima (FWHMs) show some peculiarities with respect to the photo-catalytic activities in both surface lattices and adsorbed molecules in vapors. Furthermore, Kelvin force microscopy (KFM) has showed that there exists a very high surface potential, probably due to surface atom displacements induced by UV irradiation. With regard to the origin of the photo-catalytic activities, the induced surface potentials are discussed.
Effect of the Supercooled Liquid Region on Al85Ni7Gd8 Metallic Glass Crystallization Products
Authors: Guo F. Q. , Poon S. J , Shiflet G. J.
Published: April 2011

The effect of the supercooled liquid region on the primary crystallization of Al85Ni7Gd8 metallic glass, which exhibits a clear glass transition before its primary crystallization, was evaluated systematically under different annealing conditions, including isothermal annealing at different temperatures and non-isothermal annealing employing different heating rates. It was found that isothermal annealing within the supercooled liquid region and non-isothermal annealing at small heating rates (≤ 5 °C/min) result in the co-precipitation of fcc-Al and Al compound(s). When isothermal annealing is done at temperatures where partial crystallization is involved, or non-isothermal annealing is carried out at a larger heating rate, the primary crystallization product is a single phase of fcc-Al. The effect of the supercooled liquid region on the crystallization product is discussed in detail.
Effect of high pressure on glass transition in Zr-Ti-Cu-Ni-Be bulk metallic glass
Authors: Wang Wei Hua , Wen Ping , Hui Zhao Yan , Xiang Pan Ming , Qian Zhao De
Published: April 2011

A new method is developed to directly exhibit glass transition in Zr-Ti-Cu-Ni-Be bulk glass-forming alloy under high pressure in metallic glass. Via the method, we derive an increase of glass transition temperature,Tgwith pressure of 5.6 K/GPa, and a formation volume (ΔVf) of 6.5 Å3for diffusion and the migration volume (ΔVm) of 6.5 Å3. The glass transition under high pressure is simulated based on the free-volume theory, and the simulations are consistent with the experimental observations.
Computer Simulations of Hydration, Alteration, and Release from Waste Glasses Using A Cell Model
Authors: Pérez-Cárdenas Fernando C. , Gan Hao , Pegg L.
Published: April 2011

A probabilistic cell model to study the hydration, alteration, and elemental release into solution from nuclear waste glasses is presented. This computational model considers the glass alteration as the product of hydration and multiple phase transformations. The model reveals that the elemental redistribution occurring as a consequence of these transformations can produce transport barriers that would affect the glass alteration and release into a surrounding aqueous solution. Importantly, the model also exhibits anapparentsaturation concentration in solution, which has a kinetic origin and is lower than the true thermodynamic value. We also highlight the interplay among the different mechanisms that give rise to the glass corrosion process.
Modeling Element Concentrations in Äspö Groundwaters
Authors: Emrén Allan T.
Published: April 2011

The chemical properties of groundwater entering a repository for nuclear wastes, have a major impact on the performance of natural and engineered barriers. Thus, accurate models for the chemical evolution of the groundwater are important in connection with performance assessments. Simple mixing of waters is inadequate for describing most chemical properties, like concentrations of iron, pH or redox potential.

In the present work, ground waters from Äspö at the Swedish east coast have been modeled. In the model it is assumed that ancient waters (end member waters) have been able to reach a steady state with respect to the minerals in the fracture walls. Due to groundwater flow, end member waters have been mixed to form intermediate waters. In the sampling process (by pumping), waters from a large number of small units are mixed too rapidly for mineral reactions to be of importance. After the sampling mixture has been formed, the water reaches equilibrium with respect to homogeneous reactions (in the aqueous phase) but not with respect to heterogeneous reactions.

The CRACKER program has been used to simulate groundwater formation and sampling process according to the model. It has been found that the end member waters are fairly stable with respect to observed mineral sets.

Conservative elements like Cl have been used to find the initial mixing ratios for intermediate waters. Evolution of the mixtures was simulated and finally mixing and speciation of waters from some 900 locations have been simulated to describe the final solution. It is found that the model is able to give a good agreement between observed and modeled concentrations for the ten most important elements as well as pH and redox potential.
Effect of Elevated Curing Temperature on Early Hydration and Microstructure of Composite Cements
Authors: Hill J , Whittle B R , Sharp J H , Hayes M
Published: April 2011

The heat of hydration of a number of composite cement systems has been studied using isothermal conduction calorimetry (ICC) from ambient temperature to 90°C. The resulting hardened cement paste, from the high temperature regime, was then examined by scanning electron microscopy. Results showed that increasing the hydration temperature increased the rate of heat output for all systems and, at early ages, decreased the porosity of the sample.
Modelling of Biochemical Processes in Rocks: Oxygen Depletion by Pyrite Oxidation – Model Development and Exploratory Simulations
Authors: Sidborn Magnus , Neretnieks Ivars
Published: April 2011

The purpose of this work is to gain understanding about one of the potential oxygen consuming processes occurring in deep subsurface crystalline rocks. A model for the depletion of oxygen by microbially mediated oxidation of pyrite along a deep subsurface conducting fracture was developed. In the model, a previously undisturbed fracture is suddenly invaded by oxygenated water. This could happen after a glacial period when the melt water penetrates down in the deep rock. We assume that no degradable organic matter is present. The oxygen in the water will be scavenged by the pyrite minerals in the rock matrix and in secondary minerals in any fracture infill. In this study the intrusion depth of oxygenated water is simulated assuming microbially mediated oxidation of pyrite mineral in the rock matrix as the main oxygen consuming reaction. Bacterial growth was modelled using Monod's dual limitation equation with oxygen and dissolved pyrite as the two limiting substrates. The bacteria grow as a biofilm on the fracture surface and are also present in the flowing water. The oxygen is transported to the microbes in the biofilm by the flowing water in the fracture. The ferrous iron and the sulphur from the pyrite move by molecular diffusion in the rock matrix. The rock matrix, near the fracture, is gradually depleted of pyrite and a dissolution front propagates away from the fracture.
Long Term Durability Testing of Simulated Iron-Phosphate Nuclear Waste Glass
Authors: Haworth H. , Wronkiewicz D. J. , Day D. E.
Published: April 2011

An iron phosphate base glass and a simulated Hanford Tank Farm B (TFB) waste loaded iron phosphate glass were reacted under both Product Consistency Test (PCT) and Vapor Hydration Test (VHT) conditions. Solution aliquots were collected following reaction of the TFB glass after the completion of a PCT at 90°C for time periods of 7, 49, 185, 274, and 365 days. Normalized element release patterns for sodium were highest of all the elements present, with values initially decreasing between 7 and 182 days and then increasing thereafter. Normalized release values for phosphorous declined between 49 and 182 days but increased thereafter, whereas calcium contents declined to and remained below the analytical detection limit after 182 days. Normalized element release patterns for Ce, Nd, and Fe were below 0.00045 g/m2 for all time periods tested. Amorphous iron oxide and elongate crystals (possibly apatite?) were noted as alteration products in both long-term PCT and short-term VHT formats.

The VHT samples were reacted at 150°C for time periods of 3, 7, and 35 days for the base glass and 3, 7, 35, 91, 185, and 300 days using the TFB glass. Reacted samples were examined for alteration products, with an emphasis on identifying phases that could potentially occur during geologic disposal. The base glass reacted quickly under the VHT conditions. Phosphorous released from the base glass apparently formed phosphoric acid, which quickly lowered the solution pH to a value of one. The acidic nature of the fluids, in turn, led to an accelerated rate of glass corrosion. The addition of alkali and alkaline earth elements in the TFB glass prevented the low pH excursion seen in the base glass; possibly by ion exchange processes that remove hydrogen ions from solution, sequestering of phosphorous in alteration phases to prevent phosphoric acid formation, or both. This change led to a dramatic decrease in TFB glass reaction rates relative to the base glass composition. Alteration products included an amorphous iron precipitate and several crystalline phases.
Cathodoluminescence of Am3+ in zircon, (Zr,Pu,…)SiO4, and garnet, (Y,Gd,…)3(Al,Ga,…)5O12
Authors: Zamoryanskaya Maria V. , Hanchar John M. , Burakov Boris E. , Garbuzov Vladimir M.
Published: April 2011

Ceramic waste forms based on garnet, (Y,Gd,An‥)3(Al,Ga,An‥)5O12, and zircon, (Zr,An‥)SiO4, where An=U, Pu, Np, Am, and Cm have been proposed for the immobilization of weapons-grade plutonium and other actinides. The lattice capacity of these materials depends on the valence state and ionic radius of the substitute ions. The method of cathodoluminescence (CL) allows the determination of the valence state of different ions (e.g., some transition metals, lanthanides, and actinides) in ceramic. There is a lack of information in the literature concerning CL properties of actinide ions. Cathodoluminescence images and emission spectra of synthetic yttrium-aluminum garnet, gallium-gadolinium garnet and zircon doped with Am were studied. Americium ion has three groups of lines of CL in visible region at 1.6eV, 1.9eV and 2.3eV. The interpretation of these lines has been done using the results of absorption spectra of Am in solution and in crystal LaCl3. There are f-f transitions of Am3+ ion. The ratio of intensities and the structure of these lines depend on the matrix. However, the spectral positions of these lines in two types of garnets and in zircon coincide. It was conclude that these lines can be used for identification of Am3+ ion in different crystalline matrices.
Impact of Atmospheric Pressure Fluctuations on Vadose-zone Contaminant Plumes
Authors: Downs Wayne C.
Published: April 2011

Field and laboratory studies have been underway at the INEEL and BYU to investigate the effect of atmospheric pressure fluctuations on the migration of contaminant plumes.

In the field, two vadose-zone piezometer nests were instrumented to measure soil-pressures and carbon tetrachloride concentrations at depths of roughly 78-ft, 112-ft., and 150-ft., below ground surface in wells 25-ft. apart. At land surface, a manifold was constructed to systematically rotate from port to port at 15-minute increments of time. Contaminant concentrations were measured at each rotation, and soil pressures were measured at all ports at 15-minute increments. Atmospheric pressures were also recorded. Results showed that atmospheric pressure changes propagated downward lagged in time and dampened in amplitude. Carbon tetrachloride concentrations were observed to decrease with pressure increases at each port, suggesting that pressure increases pushed the plume downward. Increases in concentration were observed with decreases in pressure. Concentrations were observed to change at a port by as much as an order of magnitude. Modeling is underway to assist in isolating the transport mechanisms involved and assist in quantifying the effect of varied pneumatic permeability on pressure propagation.

Laboratory work is underway at BYU to more carefully isolate the mechanisms of diffusive transport and pressure fluctuation in unsaturated conditions. A sealed soil column has been packed with sand and instrumented with a contaminant reservoir at one end and concentration sensor at the other. A mechanical syringe is used to vary the pressure within the tube, and pressure sensors have been emplaced.

An affiliation has been established with researchers at the DOE Sandia laboratory to utilize a novel non-invasive vapor detector in our sealed-column laboratory work.
Migration Behavior of Iron Ion in Compacted Bentonite Under Reducing Condition by using Electromigration.
Authors: Idemitsu Kazuya , Yano Seiji , Xia Xiaobin , Kikuchi Yoshiro , Inagaki Yaohiro , Arima Tatsumi
Published: April 2011

Carbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. The lifetime of the carbon steel overpack will depend on its corrosion rate. The corrosion rate of carbon steel is reduced by the presence of buffer material such as bentonite. Buffer material will delay the supply of corrosive materials and discharge of corrosion products through it. Carbon steel overpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The reducing condition will be expected to retard the migration of redox-sensitive radionuclides by lowering their solubilities. Therefore, the diffusion of corrosion products of iron in buffer material is important to discuss the corrosion rate of overpack, properties of buffer material and migration of redox-sensitive radionuclides. Electromigration experiments have been carried out with source of iron ions supplied by anode corrosion of iron coupon. Iron ions migrated as fast as 2mm in 2 or 3 hours under electrical field of 100V/m to the direction of cathode. Because the iron ions displaced exchangeable sodium ions in bentonite at a ratio of 1 to 2 during the electromigration, migrating iron ion could be ferrous ion.
Results of Vertical Scanning Interferometry (VSI) of Dissolved Borosilicate Glass: Evidence for Variable Surface Features and Global Surface Retreat
Authors: J.P. Icenhower , A. Lüttge , B.P. McGrail , M.S. Beig , R.S. Arvidson , E.A. Rodriguez , J.L. Steele , S.R. Baum
Published: April 2011

Two disparate reaction mechanisms have been invoked to explain the reactivity of glass in contact with aqueous solution. One model is based on arguments from Transition State Theory (TST), which postulates that glass dissolution rates are surface reaction controlled. Alternatively, the second model argues that release of elements from glass to solution is governed by diffusion through an altered layer that forms on the surface of glass. Vertical Scanning Interferometry (VSI) is a new technique that allows one to observe surface features of specimens exposed to solution and may, potentially, be used to distinguish between competing models. We performed a series of dissolution experiments with a suite of glass compositions from chemically simple (sodium borosilicate) to complex (sixteen component borosilicate). Dissolution rates were determined using single-pass flow-through (SPFT) apparatus at 90°C and pH = 9 and over a solution saturation interval. Upon termination of the experiments, glass coupons were examined by VSI techniques. Effluent chemistry and VSI measurements indicate a nearly constant rate of 2.2 to 3.4 g m-2 d-1 over the solution interval; rates calculated from both methods are identical within experimental uncertainty. We argue that this glass is phase separated, and propose a model for dissolution based on the relative rates of dissolution of the two glass compositions. The data are consistent with a modified version of TST and indicate the potency of VSI methods to elucidate glass reaction mechanisms.
Fission Product Immobilisation in Secondary Phases Formed During Magnox Waste Glass Dissolution at 60 °C: Experimental Results and Modelling.
Authors: Abraitis Paul K. , Scales Charlie R. , Hyatt Neil C.
Published: April 2011

Dissolution of a complex, simulated Magnox Waste (MW) glass in batch dissolution experiments at 60 °C over a period of 56 days is accompanied by extensive development of secondary gels. Gel development has been followed using a range of chemical, spectroscopic and physical means. Initially, a surface layer comprising (hydr)oxides of Fe, Zr and the lanthanides develops at the glass surface. Aluminosilicate gels containing Si, Al, Mg, Sr, Cs and Rb develop in systems where sufficient quantities of glass derived solutes accumulate in the leachate. These gels are hydrous and readily soluble in acidic oxalate solutions. Solution chemistry data is consistent with the development of Cs,Sr-bearing aluminosilicates, silica gel and (hydr)oxides of hydrolysis prone waste components. The experimental results are compared with the predictions of a model that considers kinetically constrained glass dissolution and the precipitation of secondary phases, including a Cs,Sr-bearing aluminosilicate gel.
The Effect of Radiation Damage on Zirconolite Dissolution
Authors: Smith Katherine L. , Zhang Zhaoming , McGlinn Peter , Attard Darren , Li Huijing , Lumpkin Gregory R. , Colella Michael , McLeod Terry , Aly Zaynab , Loi Elaine , Leung Sammy , Hart Kaye P. , Ridgway Mark , Weber William J. , Thevuthasan Suntharampillai
Published: April 2011

Polished tiles (7×7×2 mm3) of Nd-bearing zirconolite were fabricated and then some were irradiated on both large faces with 3 MeV or 2 MeV Au2+ ions (total fluence of ≥ 1 × 1015 ions/cm2) in order to render the zirconolite amorphous and so simulate displacement damage caused by alpha decay. Both the irradiated and non-irradiated tiles were then subjected to static dissolution tests in 0.01M nitric solution (pH2) at 90 C, for periods of 0–1, 1–7, 7–14 and 14–28 days. It was found that radiation damage did not affect the dissolution rate of zirconolite as indicated by the elemental leach rates of Nd, Ti, Ca and Al. The results of solution analyses are consistent with those obtained from X-ray Photoelectron Spectroscopy (XPS) in that the Ca, Nd, Ti and Al concentrations in the top surface layer (< 5 nm) all decreased with respect to that of Zr after dissolution testing, and the leached surface composition of the non-irradiated zirconolite is very similar to that of the two irradiated specimens. The implications of these results are discussed in the context of previous work.
Preparation and Characterization of a Calcium Phosphate Ceramic for the Immobilization of Chloride-containing Intermediate Level Waste
Authors: Metcalfe Brian L. , Donald Ian W. , Scheele Randy D. , Strachan Denis M.
Published: April 2011

Attention has recently been given to the immobilization of special categories of radioactive wastes, some of which contain high concentrations of actinide chlorides. Although vitrification in phosphate glass has been proposed, this was rejected because of the high losses of chloride through the mobilization of volatile species.

On the basis of non-radioactive and, more recently, radioactive studies, we have shown that calcium phosphate is an effective host for immobilizing the chloride constituents [1]. In this instance, the chlorine is retained as chloride, rather than evolved as a chlorine-bearing gas. The immobilized product is in the form of a free-flowing, non-hygroscopic powder, in which the chlorides are chemically combined within the synthetic mineral phases chlorapatite [Ca5(PO4)3Cl] and spodiosite [Ca2(PO4)Cl]. Data from studies on non-radioactive simulated waste consisting of a mixture of CaCl2 and SmCl3, and radioactive simulated waste composed of CaCl2 with PuCl3 or PuCl3 and AmCl3, are presented and compared.

The XRD data confirm the presence of chlorapatite and spodiosite in the non-radioactive and radioactive materials. The durability of all specimens was measured with a modified MCC-1 test. Normalized releases of Cl after 28 days were 1.6 × 10-3 g m-2 for the non-radioactive specimens and 7 × 10-3 g m-2 for the Pu bearing specimens. Releases of Ca after 28 days were 0.3 × 10-3 and 2.0 × 10-3 g m-2 for the non-radioactive composition and the Pu composition, respectively, whilst release of Pu from the radioactive specimens was higher for the mixed Pu/Am specimen at 1.2 × 10-5g m-2 than for the Pu only specimens. The release of Am from the mixed Pu/Am composition was exceptionally low at 2.4 × 10-7 g m-2. Overall, the release rate data suggest that the ceramics dissolve congruently, followed by precipitation of Sm, Pu and Am as less soluble phases, possibly oxides or phosphates. The differences in behaviour noted between non-radioactive and radioactive specimens are interpreted in terms of the crystal chemistry of the individual systems.
Natural Ground Water Colloids From the USGS J-13 Well in Nye County, NV: a Study Using SAXS and TEM
Authors: Fortner Jeffrey A. , Mertz Carol J. , Wolf S. F. , Jemian R.
Published: April 2011

We report results from ultra small angle x-ray scattering (USAXS) and transmission electron microscopy (TEM) of dilute silicate colloids that occur naturally in groundwater from the USGS J-13 well, located near the Yucca Mountain Site in Nevada. We also examined a separate sample of this groundwater that had been treated by heating to 90 degrees C in contact with crushed Topopah Spring Tuff from the Yucca Mountain. The USAXS measurements were done at the UNICAT undulator beamline at the Advanced Photon Source at the Argonne National Laboratory. Power-law plots (scattering intensity verses momentum transfer) were fitted to the USAXS data. Colloids in the untreated J-13 groundwater were shown to have a fractal dimension of nearly 3, whereas colloids in the treated groundwater (“EJ-13”) have a dimensionality of approximately 2.4 over a length scale of approximately 3 to 300 nm. Similar power-law plots with dimension 3 characterized concurrent SAXS measurements from aqueous suspensions of Na-montmorillonite and NIST Brick Clay (NBS-67). We attribute these results to the sheet silicate layered structure of the clay colloids present in J-13 well water, montmorillonite, and “brick clay” systems. The differences between EJ-13 and as-received J-13 are perhaps owing to exchange of calcium for sodium with the tuff. Radionuclide incorporation into, adsorption onto, or ion exchange with existing groundwater colloids may promote colloidal transport of radionuclides in groundwater. Such radionuclide-bearing colloids could thereby increase the concentrations of actinides in groundwater and enhance migration into human-accessible aquifers. Our results demonstrate the first application of USAXS to study the physical nature of such groundwater colloids, and represent perhaps one of the most dilute systems ever studied by small angle scatering.
Xps and Sem Studies on the Corrosion of UO2Cointaining Plutonium in Demineralized and Carbonated Water.
Authors: Cobos J. , Wiss T. , Gouder T. , Rondinella V. V.
Published: April 2011

An oxidation and dissolution study has been performed on UO2pellets containing ∼10 and ∼0.1 wt. %238Pu, ∼10 wt. %239Pu and on undoped UO2to investigate the effects of radiolysis and composition on the corrosion behavior of spent fuel. The so-called alpha-doped UO2is used to simulate the alpha-radiation field of different types of commercial LWR spent fuel after different storage times. Leaching experiments in demineralized and carbonated water at room temperature under oxidizing conditions showed that relatively high amounts of238Pu were released. The leached surfaces were examined with X-ray Photoemission Spectroscopy (XPS), and the progressive surface oxidation was monitored. The oxidation of the U(IV) during the leaching experiments, in the materials doped with238Pu resulted in precipitation of U(VI) phases: enhanced formation of studtite for the strongest radiation field and shoepite at low radiation field was observed on the surface of the pellet. Essentially no precipitation of Pu-rich phases was directly observed. Leaching in carbonated water and characterization of UO2containing239Pu under the same experimental conditions were performed and the results compared to those for alpha-doped UO2. The chemistry effects due to the presence of Pu in addition to alpha-radiolysis were investigated.
Bone Tissue Scaffold Technologies Based on RP Adopted Droplet Assembly
Authors: Zhang Renji , Yan Yongnian , Lin Feng
Published: April 2011

Tissue engineering tries to grow replacement tissues to repair damaged bones. In this paper, the fabrication technology of Multi-nozzle Deposition Manufacturing (MDM) was adopted to fabricate scaffolds of a tissue engineered bone at low temperature. The composite of poly(L-lactic acid) and tri-calcium phosphate (TCP) was chosen to form bone tissue engineering scaffolds. The new computer aided manufacturing process can make porous PLLA/TCP scaffolds. A new surface processing technology of apatite coating on bone tissue engineered scaffolds was also adopted. This digital forming technology was based on rapid prototyping (RP), in which a digital droplets assembly technology was introduced. The MDM technology of 4 nozzles was developed based on the layer-by-layer manufacturing principle of Solid Freeform Fabrication (SFF) in our laboratory. The bone scaffolds made by the multi-nozzle deposition process in the MDM system have good biocompatibility and bone conductive properties as a molecular scaffold for bone morphogenic protein (BMP) in the implantation experiment of repairing segment defects in rabbits' and dogs' radiuses.
A Process to Make Collagen Scaffolds with an Artificial Circulatory System using Rapid Prototyping
Authors: Sachlos Eleftherios , Reis Nuno , Ainsley Chris , Derby Brian , Czernuszka Jan T.
Published: April 2011

Tissue engineering aims to produce biological substitutes to restore or repair damaged human tissues or organs. The principle strategy behind tissue engineering involves seeding relevant cell(s) onto porous 3D biodegradable scaffolds. The scaffold acts as a temporary substrate where the cells can attach and then proliferate and differentiate. Collagen is the major protein constituent of the extracellular matrix in the human body and therefore an attractive scaffold material. Current collagen scaffolds are foams which limit the mass transport of oxygen and nutrients deep into the scaffold, and consequently cannot support the growth of thick-cross sections of tissue (greater than 500 μm). We have developed a novel process to make collagen and collagen-hydroxyapatite scaffolds containing an internal artificial circulatory system in the form of branching channels using a sacrificial mould, casting and critical point drying technique. The mould is made using a commercial rapid prototyping system, the Model-Maker II, and is designed to possess a series of connected shafts. The mould is dissolved away and the solvent itself removed by critical point drying with liquid carbon dioxide. Processed hydroxyapatite has been characterised by XRD and FTIR analysis. Tissue engineering with collagen scaffolds possessing controlled internal microarchitecture may be the key to growing thick cross-sections of human tissue.
Effect of White and Red Light Illumination on the Degradation of a-Si:H Solar Cells
Authors: Jamali-Beh Taraneh , Chen I.-S , Liu H. , Lee Y. , Wronski C. R.
Published: April 2011

Structures were carried out on the degradation of heterojunction and homojunction a-Si:H solar cells, using Xenon arc and tungsten halogen light sources. The degradations were carried out with both white and red light with the intensities being calibrated using the saturated reverse biased photocurrents. Because of the different light intensities, I, involved, comparisons between the different illumination were made after exposure times, t, where I1.8t = constant. The degraded states of the cells were characterized with light I-V, dark I-V, and quantum efficiency measurements. The same degraded states, as indicated by the all three characteristics, are obtained with either white and red light providing the intensities are calibrated using the actual p-i-n cells. It is also found that the empirical relation for obtaining the same degradation found by L. Yang holds for these illuminations being about 1 and 10 suns. Analysis of the dark I-V's using AMPS with a charged defect distributions of defects indicates that with the exposures used, the light induced defects have a close to uniform distribution throughout the i-layer.
Characterization of 0.5 MHz Silicon-Based Ultrasonic Nozzles Using Multiple Fourier Horns
Authors: Tsai Shirley C. , Song Yu L. , Chou Yuan F. , Tseng Terry K. , Chen W. J. , Yang J. H. , Chen J. W. , Tsai Chen S.
Published: April 2011

ABSTARCT

This paper presents the experimental results of impedance analysis and longitudinal vibration measurement of micro-fabricated 0.5 MHz silicon-based ultrasonic nozzles. Each nozzle is made of a piezoelectric drive section and a silicon-resonator consisting of multiple Fourier horns each with half wavelength design and twice amplitude magnification. The experimental results verified the simulation prediction of one pure longitudinal vibration mode at the resonant frequency in excellent agreement with the design value. Furthermore, at the resonant frequency, the measured longitudinal vibration amplitude gain at the nozzle tip increases as the number of Fourier horns (n) increases in good agreement with the theoretical value of 2n. Using this design, very high vibration amplitude at the nozzle tip can be achieved with no reduction in the tip cross sectional area. Therefore, the required electric drive power should be drastically reduced, decreasing the likelihood of transducer failure in ultrasonic atomization.
A Scheme of Micromanipulation using a Liquid Bridge
Authors: Obata Kenichi J. , Saito Shigeki , Takahashi Kunio
Published: April 2011

This paper presents a scheme of micromanipulation with a liquid bridge and an analysis of the capillary forces involved. The following procedure is considered in this article: (a) PICK UP: a probe, with liquid in the tip, approaches the target object. (b) A liquid bridge forms between the object and the tip of the probe. (c) The object is picked up by means of the capillary force of the liquid bridge. (d) TRANSPORT: The probe ascends, moves to the target point, and descends towards a substrate. (e) PLACEMENT: At a given height, a second liquid bridge made from a drop previously applied at the target point on the substrate, forms between the object and the substrate. (f) The probe ascends and the probe-object bridge collapses.

The collapse can be predicted through the stability analysis of the bridge and its condition can be controlled by the regulation of the liquid volume. The liquid volumes required for the manipulation, in the first and second liquid bridge, are calculated in this paper.
Layer-by-Layer Engineered Microreactors for Bio-Polymerization of 4-(2-aminoethyl) phenol hydrochloride
Authors: Ghan R. , Shutava T. , Patel A. , John V. , Lvov Y.
Published: April 2011

This study presents the results of polymerization of phenol to yield fluorescent polymer encapsulated within shells fabricated via layer-by-layer (L-b-L) assembly. Hollow polyelectrolyte microcapsules (shells) were prepared using weakly cross-linked melamine formaldehyde (MF) particles. Dissolution of the MF cores was achieved by changing the pH of the solution. Horseradish peroxidase (HRP), the catalyzing enzyme, was loaded in these capsules by taking advantage of the “open/close” mechanism of the capsules by altering the pH. The empty shells were then suspended in a concentrated solution of monomer. Since the monomer is a low molecular weight species, it freely permeates through the polyion wall into the shells. Addition of aliquots of hydrogen peroxide initiated the polymerization reaction and the polymer formed from the ensuing reaction was confined in the shells due to its high molecular weight. The model used for demonstrating this synthesis is polymerization of 4-(2-aminoethyl) phenol hydrochloride commonly known as tyramine hydrochloride to its corresponding polymeric form by reacting it with hydrogen peroxide. Fluorescence spectrometry (FS), confocal laser scanning microscopy (CLSM), and atomic force microscopy (AFM) were the characterization methods employed to confirm polymerization in situ shells.
Evaluation of Design and Performance of a Cryogenic Mems Micropump Realized with Si-Based Diaphragm Using Combination of Zygo/Wyko Interferometer and Raman Spectroscopy
Authors: Zhao Yi , Ludlow Daryl , Li Biao , Zhang Xin
Published: April 2011

This paper reports work concerning a silicon-based micro pump for use in a cryogenic cooling system. The diaphragm deflection, which is critical for the control of pumping capacity, was accurately derived using a combination of ZYGO and WYKO interferometer. The relationship between the pumping capacity and differential pressure was further achieved. Stress distribution was obtained using Micro Raman spectroscopy. It was found that Young's modulus derived from the maximum deflection increases with decreasing temperature. The compressive stress concentrates at the edge centers; whereas the tensile stress occurs at the diaphragm center. There is a fairly good match between the theoretical predications and experimental observations.
Novel Electro-Optic Ceramic Materials for Microchip and High Power Lasers
Authors: Chen Xuesheng , Li Kewen , Zou Kevin , Zhang Run , Jiang Hua , Ozen Gonul , Bartolo B. Di
Published: April 2011

This paper reports optical studies on transparent electro-optic ceramics, 2%Er:PLZT and 0.5%Er-2.5%Yb:PLZT. Strong photoluminescence was observed in these polycrystalline ceramics in the 1550 nm region when pumped by diode lasers either at ∼970nm or ∼800nm. Efficient green upconversion luminescence was also observed. Co-doping Yb3+ did enhance the Er3+ emission in the 1550nm region when pumped with ∼970 nm diode laser. This work provides important information for developing microchip and high-power ceramic lasers using Er-doped PLZT ceramics.
Pattern Formation in Directional Solidification
Authors: Greenwood Mike , Haataja Mikko , Provatas Nikolas
Published: April 2011

We simulate directional solidification using the phase field method solved with adaptive mesh refinement. We examine length scale selection for two cases. For small surface tension anisotropy directed at forty five degrees relative to the pulling direction, we observe a transition from a seaweed to dendrite morphology as the thermal gradient is lowered, consistent with recent experimental findings. We show that the morphology of crystal structures can be unambiguously characterized through the local interface velocity distribution. We derive semi-empirically a phase diagram for the transition from seaweed to dendrites as a function of thermal gradient and pulling speed. As surface tension anisotropy is increased and aligned with the pulling direction we observe cellular and dendritic arrays directed in the pulling direction. We characterize wavelength selection and obtain a new universal scaling of the wavelength that differs from previous theories.
Mechanical Characterizations of Laser Microwelds for MEMS Packaging
Authors: Han Wei , Pryputniewicz Ryszard J.
Published: April 2011

Laser micromachining has proven to be a very powerful and successful tool for precision machining and microfabrication with applications in electronics, MEMS, medical, and biomedical fields. For MEMS fabrication and packaging, several approaches based on localized heating and bonding have been proposed such as localized eutectic bonding, fusion bonding, solder bonding, and chemical vapor deposition (CVD) bonding. However, these approaches are based on resistive heating which requires intimate contact at the electrodes, and this is not preferred for MEMS packaging applications. As a good alternative, laser microwelding has advantages of non contact, low heat distortion, high speed, high precision, and consistent weld integrity. Therefore, it is finding increasing use in MEMS fabrication and packaging applications. In laser microwelding, the material in the HAZ of the workpiece experiences heating, melting, and re-solidifying stages, and the final characterizations of the laser microwelds can be influenced by various factors such as the laser beam properties, the system cooling condition, and the surface roughness/reflectivity of the component. This paper presents characterization of laser microwelds, with emphasis on study of deformation and strength of the microwelds made by a Nd:YAG pulsed laser. Optical interferometry is used to nondestructively record fringe patterns of the shape and deformation of the laser microwelded workpiece before, during, and after the microwelding process, and tensile tests are performed to study strength of the laser microwelds as a function of different welding parameters. Results indicate that quality of the laser microwelds depends on selection of an appropriate set of parameters controlling the microwelding process.
Molecular Modeling Computer Simulations of Organic Polymers: A Novel Computer Simulation Technique to Characterize Nanostructured Materials
Authors: Schulz Sarah G. , Kuhn Hubert , Schmid Günter
Published: April 2011

The understanding and prediction of complex nanostructured self-assemblies such as colloidal suspensions, micelles, immiscible mixtures, microemulsions, etc., represent a challenge for conventional methods of simulation due to the presence of different time scales in their dynamics.

We have recently successfully applied a novel computer simulations technique, Dissipative Particle Dynamics (DPD), to model the behavior of diblockcopolymers at the water/oil interface. With the use of a simple model we have performed simulations of polymer/water/oil systems at different concentrations.

We present the results of nanoscale “coarse-grained” simulations with DPD. DPD is a mesoscale simulation technique that has been introduced in order to simulate three-dimensional structures of organic polymer aggregates.

In DPD the polymer is modeled using particles which are interacting by conservative, dissipative and random forces. Particles are not regarded as molecules but rather as droplets or nanoclusters of molecules.

We have successfully applied this technique to simulate the three-dimensional structures of microemulsions, e.g. the bicontinuous phase of a surfactant in water and oil, in domains of less than 100 nm. The different structures of the polymer/water/oil system were effectively characterized with DPD and are in remarkable agreement with the experiment.

The DPD method proofed to be a reliable tool to get a better understanding of the nanostructure of self-assemblies and is therefore applicable to support the often complicated experiments or even to obtain experimentally unavai1able data.
Porous carbon nanoturf using anodized alumina templating
Authors: Rajagopalan Ramakrishnan , Dronavajjala Krishna , Foley Henry C.
Published: April 2011

This paper reports the development of porous carbon nanoturfs using alumina templating method. The nanoporous carbon has a pore size of 4 -5 Å. The length of the pillars in the carbon nanoturf was a function of temperature. It was shown that the pyrolysis of the polymer precursor reduces the dimensions of the polymer only in axial direction as compared to radial direction when it is formed inside the nanochannels.
Controlled Assembly of Carbon Nanotube Fibrils by Dielectrophoresis
Authors: Tang J. , Yang G. , Zhang J. , Geng H. Z. , Gao B. , Velev O. , Qin L.-C. , Zhou O.
Published: April 2011

Although advances have been made in the synthesis of raw carbon nanotube (CNT) materials, the lack of efficient processes for assembly and integration of CNTs into functional forms has hindered the development of CNT-based devices. Here we report a dielectrophorestic method to manipulate, align and assemble CNTs into one-dimensional nanostructures using an alternating-current electric field. Pre-formed CNTs dispersed in water are assembled into micro-electrodes and sub-micron diameter fibrils with variable lengths from 1 μm to over 1 cm. The CNTs within the fibril are bonded by van der Waals forces and are aligned along the fibril axis. This method affords fine control of the fibril length and is capable of parallel fabrication of multiple fibrils using the same material source. The short CNT fibrils can potentially be used as probes for scanning probe microscopes and the long ones as electrodes or conducting nanowires.
Nano-Structured Polymer Coatings for Ultraviolet Protection
Authors: Katangur Phaneshwar , Warner Steven B , Patra Prabir K , Kim Yong K , Mhetre Shamal K , Dhanote Autumn
Published: April 2011

Polymer materials such as Kevlar that are susceptible to UV degradation may be protected by appropriate coatings. We are using zinc oxide and titanium dioxide nanoparticles with an average particle size ranging from 25 to 70 nm. Five weight percent nanoparticles were dispersed in acrylic coatings, the dispersion is assisted by addition of a non-ionic surfactant, mechanical stirring and ultrasonication. The UV protective mechanism of nanoparticle-embedded coatings is theoretically explained using Mie theory. We estimated the minimum thickness of a 5 weight % nanoparticle-embedded coatings that is required to prevent the UV radiation from reaching the base of the substrate. Results obtained from nanoparticle-embedded acrylic-coated Kevlar fabric and neat acrylic-coated Kevlar fabric after exposure to UV radiation in QUV weatherometer show that the nanoparticle coating offers protection. UV-visible spectroscopy was used to obtain quantitative results.