bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Characterization of Micro/Nanoscale Wires/Tubes Using Pulsed Laser-assisted Thermal Relaxation
Authors: Guo Jiaqi , Wang Xinwei , Geohegan David , Eres Gyula , Vincent Cecile
Published: April 2011

A novel transient technique is developed to measure the thermal diffusivity of one-dimensional microscale wires. In this technique, the thin wire is suspended over two copper electrodes. Upon fast (nanosecond) pulsed laser irradiation, the wire's temperature will quickly increase to a high level and then decrease gradually. Such temperature decay can be used to determine sample's thermal diffusivity. To probe this temperature evolution, a dc current is fed through the wire to sensor its voltage variation, from which the thermal diffusivity can be extracted. A 25.4-μ;m thin Pt wire is characterized to verify this technique. Sound agreement is obtained between the measured data and reference value. Applying this pulsed laser-assisted thermal relaxation technique, the thermal diffusivity of multi-wall carbon nanotube bundles and microscale carbon fibers is measured. Detailed analysis is conducted to study the effect of the wire embedded in the paste/base on the final measurement result.
Electrical Switching Using Compliant Metal Infiltrated Multi-Wall Nanotube Arrays
Authors: Bult Justin , Sawyer W. Gregory , Voevodin Andrey , Muratore Chris , Dickrell Pam , Pal Sunil , Ajayan Pulickel , Schadler Linda
Published: April 2011

The topology of conventional noble-metal-coated switch counterfaces creates modes of switch failure via fouling, arcing, and local melting when impacted. To avoid these failure phenomena, compliant conductive contact surfaces of vertically aligned multi-wall nanotube arrays grown on conductive substrates have been fabricated. Infiltration of the array by noble metal results in a robust compliant switch contact surface. Cyclic hot-switch testing of the nanotube based switch, via modified nano-indentation, results in performance surpassing conventional designs with stable resistance of 0.4Ω over 3000 cycles. Investigating the physical performance of the array shows the array is compacted less than 3% over the first 500 cycles with no observable compaction through the remaining cycles. The improvement in performance of the nanotube based switch is attributed to the ability for the compliant contact surface to conform to the probe tip geometry, increasing the effective contact surface area.
Moisture Effects on Gold Nanowear
Authors: Pendergast Megan , Volinsky Alex A. , Pang Xiaolu , Shields Robert
Published: April 2011

The addition of water results in the higher wear rate of gold compared to experiments performed in the ambient environment (approximately 60% humidity). This higher wear rate in water has been observed with the AFM, Hysitron Triboindenter, and additionally in single pass scratch tests performed with the Taber Shear/Scratch tester. These tests were preformed using silicon nitride cantilevers on the AFM and a conical diamond tip in the Taber instrument. Tests performed in the ambient atmosphere resulted in slightly reduced surface roughness, while much higher wear rate was observed in the wear tests performed in water. Ambient scratch tests produced slightly shallower scratch trenches than wet scratches consistently as a function of the varied normal load. Single scan lines provide valuable information about the mechanisms and progression of the nanoscale wear. The different components of scratch friction are investigated to explore the main contributors to the nanoscale scratching of gold.
Fractal Dimensions of Soy Protein Nanoparticle Aggregates determined by Dynamic Mechanical Method
Authors: Jong Lei
Published: April 2011

The fractal dimension of soy protein aggregates can be estimated by dynamic mechanical methods when the particle aggregates are imbedded in a polymer matrix. Composites were formed by mixing hydrolyzed soy protein isolate (HSPI) nanoparticle aggregates with styrene-butadiene (SB) latex, followed by freeze-drying and compression molding methods. The dynamic shear moduli of the elastomeric composites containing different particle fractions were measured. A logarithmic plot of shear modulus vs. particle fraction in rubber plateau region at 140 oC can be fitted with a linear line. From the slope of the fitted line, the fractal dimension of the particle aggregates was estimated using the Cluster-Cluster Aggregation (CCA) model developed by Kluppel and Heinrich. The CCA model can also be used to extract fractal dimension from dynamic strain sweep experiments. The reversible strain sweep data was then fitted with a CCA model expression developed by Huber and Vilgis to yield the fractal dimension of the particle aggregates. The results show that the fractal dimensions extracted from both linear and non-linear viscoelastic data have a good agreement with each other. The model fitting indicates HSPI has a greater fractal dimension and therefore a more compact structure than the un-hydrolyzed soy protein aggregates.
Simulations of an Interface Crack Nucleation During Nanoindentaion : Molecular Dynamics and Finite Element Coupling Approach
Authors: Hara Shotaro , Izumi Satoshi , Sakai Shinsuke , Eguchi Yoshiyuki , Iwasaki Tomio
Published: April 2011

We carried out the nanoindentation simulations for the Ru (superlayer) / Cu (film) / SiO2 (substrate) system using the finite temperature MD-FEM coupling method. The calculations are performed for the different adhesion energies of Cu/SiO2 ranging from 0.2 to 0.6 J/m2. During loading, it was found that the interfacial crack nucleation occurs at three to four times the contact radius, driven by the tensile stress acted on the Cu/SiO2 interface. We also show that the asymmetric defect behavior have a great effect on giving birth to the crack nucleation. The observation of our simulation indicates that the mechanism of the crack nucleation strongly depends on the interfacial bonding energy.
Stress Assisted Grain Growth in Ultrafine and Nanocrystalline Aluminum Revealed by in-situ TEM
Authors: Mompiou Frederic , Legros Marc , Caillard Daniel
Published: April 2011

In-situ straining experiments on nanocrystalline (nc) and ultra fine grain (UFG) Aluminum were performed at room and intermediate temperatures. Both materials exhibit significant stress assisted grain growth. The strain induced by grain boundary motion has been measured in UFG Al, and was found to be on the order of a few percents. These results cannot be interpreted solely within the framework of Displacement Shift Complete (DSC) dislocation motion. We propose here that GB motion occurs via both shuffling and secondary DSC dislocation motion.
Kinetic- or Thermodynamic-Growth Formation of Pd Nanocrystals: a combined TEM-DLS Approach
Authors: Berhault Gilles , Bausach Marta
Published: April 2011

The kinetics of formation of palladium nanoparticles with well-defined morphologies (rods, cubes, MTP icosahedra, bipyramids) was studied using a combination of TEM and dynamic light scattering (DLS). The present study was focused on the role of the concentration and the size of seeds on both the kinetics of growth and the morphology distribution. Results clearly emphasize the role of the seed concentration (and not the size) on the growth kinetics in agreement with a collision theory model.
Read-Shockley Grain Boundaries and the Herring Equation
Authors: Shekhar Shashank , King Alexander H.
Published: April 2011

We compute the strain fields and the interactions between dislocations at the junctions of classical small-angle grain boundaries. It is shown that, in contrast with the results for infinite small-angle boundaries, there are always forces acting on the dislocations in the arrays that define the grain boundaries, and that there is also an excess elastically stored energy associated with the triple junction (TJ). The forces on the dislocations and the excess stored energy of the TJ are shown to vary with the dihedral angles formed by the grain boundaries, and that the “equilibrium” dihedral angle based upon the Herring equation and the energies of the individual grain boundaries does not correspond to any kind of force or energy minimum. This relates to an unwarranted assumption in Herring's original derivation, that no interactions occur between the grain boundaries that make up a TJ.
Electric Field Assisted DNA Surface Reactions on the Sub-ms Timescale
Authors: Cabeca Ricardo , Prazeres D. M.F. , Chu V. , Conde J. P.
Published: April 2011

The on-chip application of single, sub-ms voltage pulses promotes the immobilization of single stranded DNA (ssDNA) probes from a solution to a chemically functionalized SiO2 surface and as well as the hybridization between ssDNA targets from a solution to covalently immobilized ssDNA probes (E-assisted DNA reactions). Compared to diffusion-based surface reactions (in the absence of the applied electric field), an improvement of several orders of magnitude in the kinetics of the immobilization and hybridization reactions is observed with low amplitude (below 2 V) and short duration (100 ns to 1 ms) voltage pulses. E-assisted DNA reactions are demonstrated using mm-size macroelectrodes and then optimized using μm-size microelectrodes.
Production of Highly Ordered Nanoporous Alumina and its Application in Cell Cultivation
Authors: Hoess Andreas , Staeudte Andrea , Thormann Annika , Steinhart Martin , Heilmann Andreas
Published: April 2011

Nanoporous alumina membranes were utilized as cell culture substrates. Two different anodization processes were applied in order to obtain highly ordered, self-supporting nanoporous alumina membranes. The resulting membranes exhibit uniform nanopores with constant diameters having aspect ratios (pore depth:pore diameter) larger than 1000. Tentative experiments evaluating the cellular interaction of a hepatoma cell line (HepG2) with the nanoporous alumina membranes will be described. Furthermore, cell proliferation as well as the adhesion behavior of the cells on the porous substrates was investigated. Scanning electron microscopy (SEM) and focused ion beam (FIB) technology were applied to examine the cell morphology. The experiments revealed that the nanoporous membranes can be used as cell culture substrates and that they have no adverse effects on cell proliferation and cell viability. Besides, cells on membranes with pore diameters larger than 200 nm developed small cell extensions (filopodia) which penetrated into the nanopores.
Electric Properties of the Co-nanodots using Kelvin Probe Force Microscopy
Authors: Yamamoto Shin-ichi
Published: April 2011

We have observed the assembly of a chemically adsorbed monomolecularlayer (CAM) into microwires, connections, and an electric path according to the location within field regions of a lithographically patterned array of two platinum (Pt) electrodes. A Pt electrode/monolayer/Pt electrode junction was fabricated by the self-assembly of a rigid monomolecular, namely 3-{6-{11-(Trichlorosilyl) undecanoyl} hexyl} thiophene (TEN) with thiophen groups, in the lateral direction between the Pt gap electrodes. The technique of a conductive probe AFM (CP-AFM) has been used to investigate the forward bias conduction properties of a TEN film grown by a wet process deposition on a glass substrate. The self-assembly depends on: (1) the ideal rigidity of the chemically adsorptive monomolecular layer (CAM) and (2) the strong affinity of the thiophen end groups of the CAM for the Pt electrode. The current–voltage (I–V) characteristics of the conjugated thiophen junction exhibited stepwise features at room temperature. From the results in the atmosphere, the conductivity of a lateral conjugated polythiophen group was calculated to be 5.0E4 S/cm.
Use of hydrogel microstructures as templates for protein immobilization
Authors: Koh Won-Gun , Kim Dae Nyun
Published: April 2011

In this study, protein micropatterns were created on the surface of three-dimensional hydrogel microstructures. Poly(ethylene glycol)(PEG)-based hydrogel microstructures were fabricated on a glass substrate using a poly(dimethylsiloxane) (PDMS) replica as a molding insert and photolithography. The lateral dimension and height of the hydrogel microstructures were easily controlled by the feature size of the photomask and depth of the PDMS replica, respectively. Bovine serum albumin (BSA), a model protein, was covalently immobilized to the surface of the hydrogel microstructure via a 5-azidonitrobenzoyloxy N-hydroxysuccinimide bifunctional linker, which has a phenyl azide group and a protein-binding N-hydroxysuccinimide group on either end. The immobilization of BSA on the PEG hydrogel surface was demonstrated with XPS by confirming the formation of a new nitrogen peak, and the selective immobilization of fluorescent-labeled BSA on the outer region of the three-dimensional hydrogel micropattern was demonstrated by fluorescence. A hydrogel microstructure could immobilize two different enzymes separately, and sequential bienzymatic reaction was demonstrated by reacting glucose and Amplex Red with a hydrogel microstructure where glucose oxidase was immobilized on the surface and peroxidase was encapsulated.
Molecular Motor-Based Assays for Altered Nanomechanical Function of Ca2+-Regulatory Proteins in Cardiomyopathies
Authors: Chase P. Bryant , Brunet Nicolas M. , Mihajlovic Goran , Xiong Peng , von Molnár Stephan
Published: April 2011

We propose that a thermo-electrical control system for rapid and reversible actuation of biomolecular motors and their partner filaments can also be used to study molecular mechanisms of cardiovascular diseases. We have previously used this device to evaluate the temperature-dependence of unregulated (absence of cardiac Ca2+-regulatory proteins tropomyosin, α-Tm, and troponin, Tn) actin filament sliding powered by myosin motors, which hydrolyze ATP. These assays using the thermo-electric controller can also be applied to regulated thin filaments (F actin plus α-Tm and Tn) to obtain energetic parameters and functional correlates of structural stability at the level of single filaments. This allows us not only to examine Ca2+-dependent sliding of thin filaments, but also to test for altered function of clinically relevant mutations of cardiac myofilament proteins such as those identified in familial hypertrophic cardiomyopathy (FHC).
Mechanical and Phase Transformation Behavior of Plastically Strained NiTi-based Shape Memory Alloys
Authors: Yu Peng , Li Qizhen
Published: April 2011

This paper examines the effect of plastic deformation on the strength and transformation heat and temperatures of the superelastic Nitinol samples. Two types of compression tests and differential scanning calorimetry tests were conducted. The first type of compression test deformed the samples to final fracture, and the second type included two loading –unloading cycles with or without plastic deformation. The mechanically tested samples were analyzed using differential scanning calorimetry.
From Feldspar Glass to Zirconia: State of the Art of Ceramics for Dental Applications
Authors: Denry Isabelle
Published: April 2011

The evolution of dental ceramics over the past four decades has been remarkable in light of the increase in the diversity of materials and fabrication techniques that have become available. As a consequence, the applications and indications for all-ceramic materials continue to expand. The purpose of the present article is to review the evolution of dental ceramics from the various aspects of crystalline phases, glassy matrix, flaws andin vivoperformance.
Structural and Mechanical Stability of Reduced Nickel Oxide/Yttria-stabilized Zirconia Anode/Electrolyte Structures for Solid Oxide Fuel Cell Applications
Authors: Biswas Somnath , Thangamani N. , Saraswathi N. T. , Zhang J. , Bandopadhyay S.
Published: April 2011

Highly porous Ni-8YSZ anodes supported by a thin and dense electrolyte layer of 8YSZ have been developed for solid oxide fuel cell applications by reducing a NiO-8YSZ anode/electrolye precursor structure in a gas mixture of 5% H2-95% Ar at 800°C for selected time periods up to 8 h. It appears that 2 h of exposure to the reducing conditions is enough to reduce∼80% of NiO. XRD and SEM analyses in the reduced samples disclose the formation of the Ni-8YSZ cermet structure with desired porosity and microstructure. The porosity in the anode samples, which increases with the increase in the fraction of reduced NiO, severely affects the hardness and elastic moduli of the anode samples. Vickers indentation tests show that a hardness value of 5.5 GPa in the unreduced anode samples (12% porosity) reduces to less than 1 GPa in the 8 h reduced samples (36.68 % porosity). Similarly, a decrease of ˜44% in the Young's modulus and ˜40% in shear modulus is observed in the 8 h reduced samples through impulse excitation techniques, in comparison to the unreduced anode precursor. Since the elastic properties of fully dense Ni, NiO and YSZ are comparable to each other, the decrease in the magnitude in elastic moduli and hardness is attributed to the colossal increase in porosity as a result of the reduction of NiO in H2 atmosphere.
Electrical and optical responsivity of thin palladium films during hydrogen exposure
Authors: K Susan , Yalamanchili Kanthi , Kostanic Ivica N , Nazer Mohammed , Pozo de Fernandez Maria , McCay Mary H
Published: April 2011

This paper presents a series of measurements documenting changes in electrical and optical properties of thin palladium films. Palladium is deposited on the glass surface through plasma-assisted physical vapor deposition. This process produces highly uniform films with a surface variation of a few nanometers. The thicknesses of studied films range from 15 to 60 nm. The films are exposed to a constant flow of 2% hydrogen and 98% nitrogen mixture. During the exposure, film resistivity and its reflection properties in visible light were monitored. It is observed that the change in the film resistance during the hydrogen exposure depends on the film thickness. In particular, thicker depositions exhibit larger relative changes of the resistance. The reflectivity of the films in the white light changes during the hydrogen exposure as well. However, the change of the film reflectivity is observed to be independent of the deposition thickness. This paper presents observed measurements, their quantitative analysis and briefly discusses the use of findings in development of low-cost, single-use commercial grade hydrogen sensors.
Study of Ageing and Fluctuation Effects in MgB2Superconductor
Authors: Rajput Suchitra , Chaudhary Sujeet
Published: April 2011

For device applications of a superconducting material, its stability to ambient conditions is an issue of critical concern. The study of the ageing effects of the recently discovered intermetallic compound MgB2 is vital for knowing the degree of usefulness of this material. We report here the study of ageing and fluctuation conductivity behavior in bulk MgB2 pellets and stainless-steel sheathed, in-situ synthesized MgB2 tapes. A possible degradation mechanism is proposed based on ac-magnetic susceptibility and XRD investigations of MgB2 samples exposed to ambient over prolonged durations of time. In addition, the fluctuation induced conductivity behavior is also analyzed based on the observed resistivity (ρ)-vs-T measurements in MgB2 tape samples. This study indicated a three dimensional character of the MgB2 with reasonably good estimates of coherence the length. The scaling of fluctuation induced conductivity enhancement is also investigated from the ρ(H) vs T data obtained for different applied field strengths. These findings support the three-dimensional nature of thermodynamic fluctuations operative in MgB2 in contrast to that prevalent in several other high-temperature superconductors (HTSCs).
Plasma Texturing and Porous Silicon Mirrors for Epitaxial Thin Film Crystalline Silicon Solar Cells
Authors: Kuzma-Filipek Izabela Jozefa , Duerinckx Filip , Van Nieuwenhuysen Kris , Beaucarne Guy , Poortmans Jef
Published: April 2011

Thin film silicon solar cells, consisting of an epitaxially grown active layer on a low quality highly doped silicon substrate, incorporate many attractive features usually associated with their sister cells based on bulk silicon. However, the efficiency of the current epitaxial semi-industrial screen printed cells is limited to 11-12% mainly due to optical shortcomings. This paper will give an overview of our work aimed at tackling the 2 most important problems: (i) Finding and implementing an adequate front surface texture and (ii) the simulation, fabrication and incorporation of an intermediate reflector.

The former issue has been addressed by the development of plasma texturing based on halogen species. This method allows us to fulfil the sometimes contradictory requirements for the textured surface, i.e. a uniform and reduced reflection, a strong lambertian character to scatter the light and a limited removal of silicon. It will be shown that the scattering efficiency is dependent on both the wavelength of the impinging light and on the silicon removal during the texturing process.

The second and main issue of this work is the limited absorption volume of the epitaxial layer. To resolve this drawback, an intermediate reflector is placed at the epi/substrate interface to enhance the path length of the low energy photons through the epi-layer. In practice, a multi-layer porous silicon stack is created by electrochemical anodization of the substrate. The reflection at the epi/reflector/substrate interface is a combination of several different effects including a Bragg mirror and Total Internal Reflection (TIR). Measurements of the external reflectance as well as extraction of the internal reflection parameters are used to clarify the issue. Advanced structures, including chirped porous silicon stacks, are introduced. Finally, the benefits of the reflector on the level of the epitaxial silicon solar cell are analysed. Efficiencies close to 14% are obtained for epitaxial cells incorporating an advanced porous Si reflector.
New Light Management Concepts for Thin-Film Silicon Solar Cells
Authors: Stiebig Helmut , Haase Christian , Jorke Silvia , Obermeyer Philipp , Moulin Etienne , Schulte Melanie
Published: April 2011

An efficient utilization of the sun spectrum is a key issue in the field of thin-film silicon solar cell technology. Therefore, different strategies for enhanced light absorption were presented in the last years. In order to achieve a better understanding of light scattering at nanotextured interfaces the optical properties of a large variety of samples were studied. The angle resolved scattering behavior was analyzed by means of a developed ray tracing model. As an alternative to randomly textured substrates, the influence of periodically textured substrates on the light propagation in solar cells was experimentally and numerically studied with respect to improved light in-coupling and light trapping. Based on a deeper understanding a new tandem cell structure with a diffractive element between the top and bottom cell was developed. Finally, the influence of metallic nanoparticles on the cell performance was studied.
Periodic textures for enhanced current in thin film silicon solar cells
Authors: Haug Franz-Josef , Söderström Thomas , Cubero Oscar , Terrazzoni-Daudrix Vanessa , Niquille Xavier , Perregeaux Stephanie , Ballif Christophe
Published: April 2011

For thin film silicon solar cells it is vital to increase the optical path of light in the absorber because this allows for thinner cells with better stability and higher production throughput. We discuss the effect of periodically textured interfaces for the case of thin film silicon solar cells in n-i-p configuration using embossed plastic substrate which allows us studying the effect of a wide range of random or periodic textures. Due to the moderate thickness of the individual layers the texture is carried into each interface with a high degree of conformity even for the front contact which is the last layer. Solar cells on periodic structures show excellent performance; in a microcrystalline cell on a simple sinusoidal grating we achieved a gain in current density of 30%. Furthermore, the periodicity serves as a useful tool for the study of light management because the underlying phenomena like diffraction or grating coupling to plasma excitations of the metallic back reflector are governed by a relatively low number of well defined parameters like the periodicity and the amplitude of the grating.
Single Carrier Resonant Tunneling Design for Improving Carrier Collection in Quantum Confined Solar Cells
Authors: Alemu Andenet , Freundlich Alex
Published: April 2011

Promising nanostructured device concepts with staggering theoretical efficiencies where quantum confined states are embedded in the intrinsic region of conventional p-i-n solar cells have been proposed. However, practical realizations remain inefficient as these devices suffer from an inherent difficulty in the extraction of photo-generated carriers from the confined states. Within the framework of a “single particle in the box” theory, such shortcomings could be addressed by the use of resonant quantum tunneling designs that can expedite carrier escape. Nonetheless, in material systems studied thus far, the implementation of such design becomes elusive as band offsets between the nanostructure and the host material are distributed between the conduction and valence band leading to the confinement of both holes and electrons (i.e. two particle problem). Our studies of such p-i-n Multi-Quantum Well (MQW) solar cells, only differing by their MQW region composition and geometry, have shown a strong dependence of device performance on quantum wells composition and thickness. Leveraging on the special property of dilute nitrides and using a carefully chosen material system and device design we show the possibility of circumventing this problem by separating the optimization of the valence and conduction band and reducing the issue to a single particle problem. Band structure calculations including strain effects, band anti-crossing models and transfer matrix methods are used to theoretically demonstrate optimum conditions for enhanced vertical transport. High electron tunneling escape probability, together with a free movement of quasi-3 D holes, is predicted to result in enhanced PV device performance. Furthermore, the increase in electron effective mass due to the incorporation of N translates in enhanced absorptive properties, ideal for PV application.
Electronic Structure and Photoemission in Plutonium Chalcogenides
Authors: Shick Alexander , Havela Ladislav , Gouder Thomas
Published: April 2011

The electronic structure of Pu chalcogenides is investigated making use of static around-mean-field LDA+U and dynamical LDA+HIA (Hubbard-I) methods. The LDA+U calculations provide correct non-magnetic ground state for PuX (X = S, Se, Te) with 5f-manifold non-integer filling (∼5.6(PuS)-5.7(PuTe)). This is an indication of a mixed valence ground state which is a combination of f5 and f6 multiplets. The photoelectron spectra are calculated in good agreement with experimental data. The 5f-manifold three-peaks feature near EF is well reproduced by LDA+HIA, and follows from mixed valence character of the ground state.
Scanning Transmission X-ray Spectromicroscopy of Actinide Complexes
Authors: Shuh David , Copping Roy , Tyliszczak Tolek , Castro-Rodriguez Ingrid , Shuh David K.
Published: April 2011

The fundamental characterization and understanding of 5f electron behavior in actinide complexes is imperative to provide an enhanced basis for the rational and accelerated development of improved processes relevant to nuclear energy. Soft x-ray absorption spectroscopy utilizing the scanning transmission x-ray microscope (STXM) at the Advanced Light Source-Molecular Environmental Science (ALS-MES) Beamline 11.0.2 has been used to probe the electronic characteristics of a nitrogen donor ligand 2,6-Bis(2-benzimidazyl)pyridine (BBP) and its resulting U(IV) complex. The nitrogen K- and carbon K-edges have been collected from both ligand and uranium complex, as well as the uranium 4d-edge from the complex. Upon complexation, the light element absorption spectra change markedly and the uranium spectra from the complex is compared to the reference spectrum obtained from U(IV)Cl4. The evolution of the spectral features are described and interpreted within a simple conceptual framework. Based on spectral evidence alone, the uranium is bound through the pyridine-like nitrogens and the oxidation state of the uranium is consistent with a U(IV) species.
Suppression of Hidden Order and Emergence of Ferromagnetism in URu2-xRexSi2
Authors: Butch Nicholas P. , Sayles Todd A. , Yukich Benjamin T. , Maple M. Brian
Published: April 2011

Measurements on URu2-xRexSi2 single crystals indicate that substitution of Re for Ru in URu2Si2 reduces the transition temperature of the hidden order state and quickly destroys superconductivity. At intermediate Re concentrations, weak ferromagnetism emerges and non Fermi liquid (NFL) behavior is observed in the low-temperature specific heat and electrical resistivity. A scaled Arrott analysis of the magnetization indicates the onset of ferromagnetism at x =0.15, where the hidden order disappears, and that the quantum phase transition is associated with novel critical exponents.
Physical Property Changes in Aging Plutonium Alloys
Authors: Chung Brandon W. , Thompson Stephen R. , Hiromoto David S.
Published: April 2011

Plutonium, because of its self-irradiation by alpha decay, ages by means of lattice damage and helium in-growth. These integrated aging effects will result in microstructural and physical property changes. Because these effects would normally require decades to measure, studies are underway to asses the effects of extended aging on the physical properties of plutonium alloys by incorporating roughly 7.5 wt% of highly specific activity isotope 238Pu into the weapons-grade plutonium to accelerate the aging process. This paper presents updated results of self-irradiation effects on enriched and reference alloys measured from the immersion density, dilatometry, and mechanical tests. After nearly 90 equivalent years of aging, both the immersion density and dilatometry show that the enriched alloys at 35°C have decreased in density by ∼0.19 % and now exhibit a near linear density decrease, without void swelling. Both tensile and compression measurements show that the aging process continues to increase the strength of plutonium alloys.
Meta-Autunite Solubility as Related to Uranium Minerals in Concrete Waste Forms
Authors: Mattigod Shas , Wellman Dawn , Glovack Julie , Arey Bruce , Wood Marcus
Published: April 2011

Previous in situ examination of U(VI) spiked concrete indicated that uranyl-oxyhydroxide phases that were initially formed, later led to the formation of mixed uranyl-oxyhydroxide/silicates, which subsequently transformed into uranyl-silicates, and finally altered into mixed uranyl-silicate/phosphate and uranyl-phosphate phases. We conducted solubility studies of the identified final uranyl-phosphate phase (calcium meta-autunite) in phosphate solutions ranging in concentration from 0.001 – 0.1M as a function of pH. These studies indicated a secondary phosphate phase that formed during the solubility of meta-autunite regulated the uranium concentrations at relatively low levels under high pH conditions (>12) typically encountered in cement pore waters. The importance of uranyl-phosphate minerals in concrete waste forms has, to date, been neglected because of the minimal amount of phosphorus present in most concrete compositions. However, because concrete is a continuously reacting solid, the thermodynamic stability of uranyl minerals that form at the later stages of reaction may have a substantial impact on the long-term fate of uranium in the waste forms. This study suggests that any future investigations should consider the potential benefit of including phosphorus in concrete waste forms.
Excitation Energy Dependence in Near-infrared Photoluminescence Spectra and Dynamics of PuO22+ in Cs2U(Pu)O2Cl4
Authors: Berg John M , Wilkerson Marianne P
Published: April 2011

Recently we reported the observation of near-infrared photoluminescence from metal-centered 5f electronic excited states of PuO22+ doped into polycrystalline Cs2U(Pu)O2Cl4.[1] Photoluminescence dynamics following pulsed excitation show complicated decay patterns suggesting that multiple luminescent states are involved. Here we report the results of two recent sets of experiments showing that photoluminescence processes depend significantly on the energy of photoexcitation. In the first case, decay kinetics following excitation at a lower energy are missing an in-growth term that is present when exciting at higher energy. In the second case, we have observed that lower excitation energy produces significantly reduced number of emission transitions than higher excitation energy. Both observations suggest that higher energy excitation populates feeder states that decay to emitting states, causing signal from the latter to have an in-growth followed by a decay characteristic of their intrinsic lifetimes, whereas lower energy excitation leads to more direct population of luminescent states.
Evolution of Superconducting and Hidden Order Phases in URu2Si2 Under Applied Pressure
Authors: Maple M. Brian , Jeffries Jason R. , Butch Nicholas P. , Yukich Benjamin T.
Published: April 2011

Electrical resistivity measurements performed under applied hydrostatic pressure and in magnetic fields have been used to probe the hidden order (HO) and superconducting (SC) states of URu2Si2, which have ambient-pressure transition temperatures TO = 17.5 K and Tc = 1.5 K, respectively. TO increases with applied pressure and a distinct kink in its pressure dependence is observed at 15 kbar; this feature is associated with the onset of antiferromagnetism. The pressure dependence of the SC upper critical field has been measured with the external field aligned parallel to both crystalline axes. The SC phase is smoothly suppressed to a critical pressure of about 15 kbar and no qualitative change in the critical field curves is observed. The co-evolution of the HO and SC phases is discussed within the context of a model in which the two phases compete for Fermi surface fraction.
Mechanism of Ion Exclusion by Sub-2nm Carbon Nanotube Membranes
Authors: Fornasiero Francesco , Park Hyung Gyu , Holt Jason K , Stadermann Michael , Grigoropoulos Costas P , Noy Alexandr , Bakajin Olgica
Published: April 2011

Carbon nanotubes offer an outstanding platform for studying molecular transport at nanoscale, and have become promising materials for nanofluidics and membrane technology due to their unique combination of physical, chemical, mechanical, and electronic properties. In particular, both simulations and experiments have proved that fluid flow through carbon nanotubes of nanometer size diameter is exceptionally fast compared to what continuum hydrodynamic theories would predict when applied on this length scale, and also, compared to conventional membranes with pores of similar size, such as zeolites.
For a variety of applications such as separation technology, molecular sensing, drug delivery, and biomimetics, selectivity is required together with fast flow. In particular, for water desalination, coupling the enhancement of the water flux with selective ion transport could drastically reduce the cost of brackish and seawater desalting. In this work, we study the ion selectivity of membranes made of aligned double-walled carbon nanotubes with sub-2 nm diameter. Negatively charged groups are introduced at the opening of the carbon nanotubes by oxygen plasma treatment.
Reverse osmosis experiments coupled with capillary electrophoresis analysis of permeate and feed show significant anion and cation rejection. Ion exclusion declines by increasing ionic strength (concentration) of the feed and by lowering solution pH; also, the highest rejection is observed for the salts (A=anion, C=cation, z= valence) with the greatest zA/zC ratio. Our results strongly support a Donnan-type rejection mechanism, dominated by electrostatic interactions between fixed membrane charges and mobile ions, while steric and hydrodynamic effects appear to be less important. Comparison with commercial nanofiltration membranes for water softening reveals that our carbon nanotube membranes provides far superior water fluxes for similar ion rejection capabilities.
The UK National Nuclear Laboratory and Waste Management R&D
Authors: Fairhall Graham A.
Published: April 2011

In the autumn of 2006, the UK government declared its expectation to set up a National Nuclear Laboratory (NNL) as soon as possible (subject to satisfactory contractual terms). The aim would be to base the Laboratory around Nexia Solutions and its ‘state of the art’ facility at Sellafield in Cumbria. The initial phase of the work to recommend formation of the laboratory is well advanced, and the NNL is expected to have a remit for the following roles:

— to play a key role in supporting the UK's strategic R&D requirements

— to operate world-class facilities

— to ensure key skills are safeguarded and enhanced

— to play a key role in the development of the UK's R&D supply base.
Accelerated Weathering of Composite Cements Used for Immobilisation
Authors: Borges Paulo H. R. , Milestone Neil B. , Streatfield Roger E.
Published: April 2011

Trying to estimate the long-term durability of cemented wasteforms is a difficult task as the cement matrix is a reactive medium and interactions can occur with the encapsulated waste as well as with the environment. There are few studies of samples that have been stored under controlled conditions for more than 10-15 years. Wasteforms are now being expected to last hundreds of years, much of that likely to be in some form of storage where sample integrity is important. There is also the concern that results from any long-term samples may only be indicative as both formulations and materials change with time.

This paper discusses changes in physical properties that occur in composite cements when some of the short-term accelerated procedures employed in construction testing are applied to encapsulating matrices. Changes after increased temperature of curing, wetting/drying and accelerated carbonation are discussed.

Many of the encapsulating formulations currently used are composite cements where large replacement levels of OPC with supplementary cementing materials (SCMs) such as PFA or BFS are made, primarily to reduce heat output. Accelerating the exposure conditions, either by increasing temperature or through wetting/drying has the effect of changing the hydration pattern of the composite cement by generating more hydration in the SCMs than would normally occur. The large amount of porosity that occurs because of limited hydration allows intrusion of gases and ready movement of water, so the samples subjected to accelerated testing do not appear as durable as expected if stored at ambient.
High Temperature Behaviour of Polyoxometalates Containing Lanthanides
Authors: Kinoshita Hajime , Brewer Marcus , Talbot-Eeckelaers Caytie E. , Reeves Nik , Copping Roy , Sharrad Clint A. , May Iain
Published: April 2011

The possibility of a simple heating process of POM to obtain tungsten bronze was investigated for nuclear waste immobilisation via DTA/TG and high temperature XRD. Heating process up to 900°C caused the decomposition of structure for both systems. Cooling process seemed to have little effect on the final product for the K11[Nd(PW11O39)2]·xH2O, whereas the cooling profile showed a significant effect on the K13[Nd(SiW11O39)2]·xH2O. Nd formed two types of tungsten bronzes, namely Nd2WO6 and Nd4W3O15 in K11[Nd(PW11O39)2]·xH2O and K13[Nd(SiW11O39)2]·xH2O, respectively.
Immobilization of Liquid Radioactive Waste in Mineral-Like Matrices Derived From Inorganic Cenosphere-Based Sorbents as Precursors
Authors: Vereshchagina Tatiana A. , Anshits Nataly N. , Fomenko Elena V. , Vereshchagin Sergei N. , Anshits Alexander G.
Published: April 2011

The progress in study of immobilization of liquid radioactive waste in mineral-like aluminosilicate matrices (feldspar and feldspathoids) derived from cenosphere-based microspherical zeolite sorbents is reported. Based on the analysis of ‘composition – morphology –C characteristics’ correlation obtained for more than 70 cenosphere products with a high content of one morphological type of imperforated cenospheres, optimal ranges of cenospheres composition were identified for the synthesis of zeolites with the predetermined structural type. Given that the cenosphere-based zeolite sorbents are precursors of the final waste form, further activity proceeds toward developing a highly efficient zeolite sorbent of NaP1 type, which would ensure the effective trapping of Cs+ and/or Sr2+ ions and the phase transformation under relatively mild conditions (T≤1000°C). The paper details the main criteria for realization of the ‘precursor’ approach for fixation of Cs-Sr fraction using cenosphere-based systems; also shown are experimental results indicating practical realization of the proposed approach.
Development of Borosilicate Glass Compositions for the Immobilisation of the UK's Separated Plutonium Stocks
Authors: Harrison Mike T. , Scales Charlie R.
Published: April 2011

The UK inventory of separated civil plutonium is expected to exceed 100 tonnes by 2010. Whilst the majority of this could be used in the manufacture of MOx (Mixed Oxide) fuel in future power generation scenarios, options for the disposal of surplus plutonium are currently being investigated by Nexia Solutions Ltd on behalf of the UK's Nuclear Decommissioning Authority (NDA). One of the options being considered is immobilisation in a durable glass matrix followed by long term storage and subsequent final repository disposal.

A preliminary experimental survey assessed a selection of potential glass systems on the basis of Pu-surrogate (cerium) loading, durability, and ease of processing. Following this, a number of borosilicate compositions have been taken forward into a more detailed investigation in order to fully qualify their potential for Pu-immobilisation. The selected compositions are lanthanide borosilicate (LaBS), alkali tin silicate (ATS) and high-lanthanide alkali borosilicate (modified-MW). For this second series of experiments, hafnium was selected as the Pu surrogate, and a study of the potential waste loading as a function of temperature for the three selected compositions is described in this paper. Furthermore, several variations of the LaBS composition were fabricated in order to investigate the effect of total lanthanide content on melting temperature. The benchmark of 10 wt% HfO2 incorporation is achievable for all three glasses with temperatures of 1200, 1300 and 1400 °C required for ATS, modified-MW and LaBS respectively.
Towards a Single Host Phase Ceramic Formulation for UK Plutonium Disposition
Authors: Stennett Martin C. , Hyatt Neil C. , Gilbert Matthew , Livens Francis R. , Maddrell Ewan R.
Published: April 2011

The UK has a considerable stockpile of separated plutonium; a legacy of over 50 years of civilian nuclear programmes. This material has been considered both as an asset for future energy generation and a liability due to the proliferation threat. A proportion of the PuO2stocks may be consumed by nuclear fission, in mixed oxide (MOx) or inert matrix (IMF) fuels but a quantity of waste PuO2will remain which is unsuitable for fuel manufacture and will require immobilisation. A research program is currently underway to investigate the potential of various single phase ceramic formulations for the immobilisation of this waste PuO2 fraction. In this work a number of synthetic mineral systems have been considered including titanate, zirconate, phosphate and silicate based matrices. Although a wealth of information on plutonium disposition in some of the systems exists in the literature, the data is not always directly comparable which hinders comparison between different ceramic hosts. The crux of this research has been to compile a database of information on the proposed hosts to allow impartial comparison of the relative merits and shortcomings in each system.
Experience in Progressing the Planning Application for New LLW Disposal Facilities for Dounreay
Authors: Broughton David , Tait Michael S
Published: April 2011

An integral part of decommissioning the Nuclear Decommissioning Agency's (NDA) Dounreay site is the management of the solid low level radioactive waste (LLW). The United Kingdom Atomic Energy Authority (UKAEA) has developed and progressed a technical and stakeholder programme that has enabled it to submit a robust Planning Application to Highland Council (HC) for New LLW Disposal Facilities at Dounreay and to submit substantive preliminary safety and environmental cases to the Nuclear Installations Inspectorate (NII) and the Scottish Environment Protection Agency (SEPA). To UKAEA’s knowledge this is the most advanced project in the UK for new LLW disposal facilities. Experience has been gained in progressing the Best Practicable Environmental Option (BPEO) Study, working with regulators in unfamiliar areas, and undertaking groundbreaking stakeholder consultation. Key lessons learnt are that stakeholders should be engaged in dialogue on the project as early as possible, documentation must be high quality and tailored to its audience, and internationally respected and credible consultants must be involved.
Changes on the Mineralogical and Physical Properties of FEBEX Bentonite Due to Its Contact With Hyperalkaline Pore Fluids in Infiltration Tests
Authors: Fernández A. M. , Melón A. , Sánchez D.M. , Galán M.P. , Morante R. , Gutiérez-Nebot L. , Turrero M.J. , Escribano A.
Published: April 2011

Two infiltration tests with a synthetic hyperalkaline solution at pH 13.5 were performed. The aim was to analyse the interaction of concrete solutions with compacted smectitic bentonites. The experiment was performed inside an anoxic glove box at 30-35 °C with FEBEX bentonite compacted at a dry density of 1.65 g/cm3 and a water content of 13.4%. Outflowing water coming from the bentonite was collected over time. A total of three times the bentonite pore volume was recovered and twelve chemical analyses of the resulting pore water were obtained. The ionic strength of the pore waters decreases with time from 0.20 M to 0.03 M and the pH increases from 7.9 to 9.0. After a test period of 595 days, the cells were dismantled, and the study of the state and alteration of the bentonite was undertaken. A modification in the a sorbed cation population, an increase in the Na- and K-smectites type, and the presence of a tri-octahedral smectite (saponite) and zeolites (phillipsite and chabazite) were observed.