bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structure and Thermoelectric Properties of SrBiTe3; 12-Fold Superstructure Caused by Distortion of the Two-Dimensional Te-Nets
Authors: Choi Kyoung-Shin , Chung Duck-Young , Heising Joy , Brazis Paul W. , Kannewurf Carl R. , Kanatzidis Mercouri G. 
Published: April 2011

AbstractThe ternary compound, SrBiTe3, was prepared by the molten flux method. It crystallizes in the orthorhombic space group Pmmn with a=4.665(2)Å, b=4.517(2)Å, c=16.129Å, and Z=2. The compound is composed of a NaCl-type [Bi2Te4]2- layer and a flat square (Te2)2- net with equal Te-Te distances of 3.24Å. The Sr2+ ions are stabilized between the layers in monocapped square antiprismatic sites. X-ray and electron diffraction studies reveal a 12-fold superstructure due to subtle distortions within the Te net of the compound. The superstructure was refined in the monoclinic space group C2 with a=27.923(5)Å, b=32.228(6)Å, c=4.5069(9)Å, β=90.000(3)°. The compound is a semiconductor with a band gap value of 0.14 eV. It melts incongruently at 613 °C.
Laser Machining with Ultrashort Pulses: Effects of Pulse-Width, Frequency and Energy
Authors: Bliss D. E. , Adams D. P. , Cameron S. M. , Luk T.S. 
Published: April 2011

AbstractThe benefits of short pulse (femtosecond) laser machining over conventional nanosecond lasers have been well demonstrated: higher aspect ratio features with smaller remelt zones and less recast material. However, shock induced defects can degrade the mechanical, electrical and optical properties of the remaining material, especially in brittle materials. Our focus is to reduce the amount of defects created while maintaining the machining advantages of using ultra-short pulses. Utilizing a chirped pulse amplified Ti:Sapphire laser with a pulse energy of 1 mJ and a pulsewidth of 120 fs we investigated the effects of pulsewidth, laser frequency and pulse energy on the controlled micro-ablation of Kovar and silicon films. Hole morphology and diameter were characterized by SEM. Hole depth was measured by laser profilometry. Hole volumes were determined by a combination of profilometry and SEM to determine the rate of material removal. The ablation thresholds for both Kovar and Si are between 200–300 mJcm−2.
Sequential N-Fold (N<4) Electrodeposition of YBa2Cu3O7-δ HTSC Films on Silver Substrates
Authors: Martín-Gonzilez M. S. , Morán E. , Sáez-Puche R. , Alario-Franco M. Á. 
Published: April 2011

AbstractElectrodeposition of multimetallic films at room temperature on metallic substrates followed by oxidation at high temperature (~ 900°C) has often been employed to prepare high temperature superconducting (HTSC) films. A difficulty with this otherwise cheap and simple process is that the degree of surface covering is usually not very high. We have attempted to remediate this problem by sequentially repeating the deposition process on the same film. In this way, we have improved quite markedly critical current density (Jc) of films obtained on Silver substrates.To quote some figures, Jc at 1 T is ~ 400 A/cm2 after the first deposition/oxidation process and it increases to ~ 2 000 A/cm2 after the fourth one. The evolution of the morphology of the films has been followed by means of scanning electron microscopy (SEM). It shows that, although the degree of surface coverage never attains 100 %, a substantial proportion of the substrate is well coated.We have also studied the influence of mechanical pressure on the metallic film before the thermal treatment; after the fourth deposition, a pressure of ~15 KBar was applied. In this case a ~ 7% increase in Jc was observed and the density after compression (6.98 g/cm3) attains almost 100 % of the theoretical value for YBa2Cu3O7-δ (Ybacuo).
Hydrothermal Synthesis and Electrochemical Properties of Layered Vanadates
Authors: Livage J. , Boujhedja L. , Castro-Garcia S. , Julien C. 
Published: April 2011

ABSTRACTThe synthesis of vanadates from aqueous solutions leads to a large variety of crystalline materials. The nature of molecular precursors mainly depends on pH and three different pH ranges can be distinguished. Cationic precursors are formed at low pH. Precipitation is obtained via the addition of anions leading to materials in which [VO6] octahedra are linked through anions. V2O5,nH2O gels are formed around the Point of Zero Charge (pH=2). They are made of ribbon-like particles and exhibit interesting properties as cathodic materials. Electrochemical properties depend on the drying procedure. Moreover, intercalation reactions lead to a whole range of new inorganic and organic bronzes. Chain metavanadates are precipitated from anionic precursors in basic aqueous solutions. Vanadium coordination decreases and they are made of corner sharing [VO4] tetrahedra. Layered structures are formed in the pH range where negatively charged species such as [VO(OH)4(OH2)]− should behave as precursors. Condensation occurs via V-OH groups in the equatorial plane leading to layered structures in which cations are inserted between the vanadate planes. Some reduction occurs when organic cations such as tetramethyl ammonium [N(CH3)4]+ are used leading to mixed valence vanadates. Electron delocalization is observed in these compounds but Li insertion is hindered by large organic cations. Better electrochemical properties are observed with smaller inorganic cations. Fibrous crystals of NaV3O8,H2O are formed in the presence of NaOH whereas the mixed valence bronze α'-NaxV2O5 is obtained when both NaOH and TMAOH react with V2O5. This fibrous morphology appears to improve diffusion processes at the electrode-electrolyte interface.
Investigations of The Local Structure in Lithium Nickel Cobalt Oxide Cathode Materials
Authors: Castro-Garcia S. , Massot M. , Julien C. 
Published: April 2011

ABSTRACTWe have studied the modifications of structural and physical properties which occur during delithiation of lithium-nickel-cobalt oxide cathode materials. Long-range and short-range orders have been investigated using XRD, Raman and FTIR spectroscopies. Different samples LixNi0.7Co0.3O2 (0.5≤x_≤1) were prepared by electrochemical lithium deintercalation from LixNi0.7Co0.3O2. Electrochemical extraction of lithium was carried out using Li/LiCIO4 in PC/LixNi0.7Co0.3O2 cells in the potentiometric method with potential step of 10 mV. During the first charge of the Li//LixNi0.7Co0.3O2 cell, the change in the cathode structure was followed by x-ray powder diffraction and vibrational spectroscopies at room temperature. A good correlation is found between XRD data and the local environment of the host lattice. Detailled analysis of vibrational spectra shows that the octahedral oxygen environment of Li+ ions remains stable in the investigated domain of concentration.
High Surface Reticulated Ceramics for Catalytic Applications
Authors: Sweeting T. B. , Karst D. L. , Norris D. A. 
Published: April 2011

AbstractThe physical surface characteristics of three reticulated ceramic materials with and without wash coating are presented. The effect of an addition of 30 volume percent, 15-micron fugitive material on these characteristics is also reported. The fugitive increased pore volume but had little impact on surface area and strength.
Production, Consolidation, Sintering, and Stability of Novel Nano-Crystalline Zirconia Catalyst Support Powders
Authors: Darab John G. , Neuenschwander Gary G. , Elliott Douglas C. , Frye John G. , Strauss Joseph T. 
Published: April 2011

AbstractNano-crystalline, zirconium oxide/oxyhydroxide particulates were produced using a novel, continuous, flow-through hydrothermal technology developed at the Pacific Northwest National Laboratory. Homogeneous aqueous solutions containing ZrO(NO 3)2 and urea were pumped at pressures of 6000-8000 psi through a heated stainless steel reaction tube at 340-350°C. Flow at pressure was maintained using a nozzle at the down-stream end of the reaction tube. In this process, termed Rapid Thermal Decomposition of precursors in Solution (RTDS), the formation of zirconium oxide/oxyhydroxide nano-crystals (diameters of generally less than 15-nm) occurred during the solution's brief residence time (<15 seconds) in the reaction tube, yielding aqueous slurries of agglomerated particulates. Powders were separated from these slurries, washed, then dried. RTDS powder prepared from 0.3M ZrO(NO3)2 and 0.6M urea were mixed with binder and formed into pellets using a commercial screw extruder. These extrudates were subsequently sintered at 500°C, yielding zirconia catalyst support pellets with a measured surface area of 113 m2/g. After application of 3% ruthenium metal to the sintered RTDS zirconia extrudates, the resulting catalyst was evaluated for catalytic activity using the hydrothermal hydrogenation of the sugar xylose to xylitol as a model reaction. After 3 hours at 140°C, the RTDS catalyst exhibited useful activity with 92% conversion and 66% selectivity to xylitol formation.
Pillaring of a Layered Titanate With Alumina: Effect of Hydrolysis Solution
Authors: Kooli F. , Sasaki T. , Rives V. , Watanabe M. 
Published: April 2011

AbstractA layered titanate with a lepidocrocite-type structure has been pillared with Al13 Keggin ions to prepare a porous and high-surface-area material. Pillaring was achieved by ion exchange of hexylammonium (HA-Ti) or tetrabuthylammonium (TBA-Ti) intercalated titanates with Keggin Al13 complex. The thermal stability of the Al13 intercalates depended on the amount of aluminum incorporated. The surface area and porosity can be tailored by controlling the amount of aluminum uptake and by the nature of base used to prepare the aluminium pillaring solution. In addition, the material derived from HA-Ti exhibited a sharp pore size distribution with an average diameter of 2 nm, while the pillared product obtained from TBA-Ti showed mostly a broad mesoporous distribution with an average pore diameter of 4 nm.
Synthesis of Hydrotalcite-Like Precursor Compounds MgCo(11) Co(111).-HTlcs
Authors: Zeng H.C. , Xu Z.P. , Qian M. 
Published: April 2011

AbstractPrecursor compounds of MgCo(11)Co(111)-HTlcs for Mg-Co oxide catalysts have been synthesized by coprecipitation in an ammoniacal solution and hydrothermal treatments under various O2/N2 atmospheres. Using elemental analysis (EA) and redox titration, it is found that about 23% of original Co2+ are oxidized to Co+3, resulting in formation of hydrotalcite-like (HTI) structure. The anion (NO3) intercalation increases with the rise in O2 partial pressure. X-ray diffraction pattern shows a conversion from brucite-like to HTl structures with increase of O2 partial pressure. It is found that thermal stability of the HTl-compounds is proportional to the Mg content. Higher specific surface areas are observed for decomposed products with low Co/Mg ratio. A trace amount of CO3O4 is also detected by FTIR for samples synthesized under high O2 partial pressures, which can be attributed to a deeper oxidation of Co2+.
Resorbable Structures for Schwann Cell Enhanced Peripheral Nerve Regeneration
Authors: Silva A.E. , Summerhayes LC. , Trantolo D.J. , Wise D.L. , Catftaneo M.V. , Gresser J.D. , Holway A. , Wang K-K , Bryan D.J. 
Published: April 2011

AbstractSchwann cells play a dual role serving as a physical framework for regenerating nerves, providing extracellular matrix proteins and specific adhesion molecules facilitating attachment and cell movement, and as a source of stimulatory factors mediated by the release or reception of different ligands important in growth and cell signaling events. To investigate the role of one such ligand, glial growth factor (GGF), in peripheral nerve regeneration, a bioabsorbable nerve guide, prepared from a poly(lactic-co-glycolic) acid (PLGA) foam was seeded with autogenous Schwann cells in the presence and absence of growth factor and evaluated in vivo using a rat sciatic nerve regeneration model. Four weeks post-operatively peripheral nerve regeneration was evident. The resorbable foam implant demonstrated extensive neo-vascularization in and around the guide with no evidence of an inflammatory response or encapsulation. The study showed a statistically significant increase in all measured parameters of nerve regeneration in the presence of GGF. Increased numbers of blood vessels in the regenerated tissue accompanied increased total axon counts after twelve weeks. The addition of exogenous Schwann cells resulted in reduced total axon counts perhaps due to the competition for limited growth factors released by the regenerating tissues. The Schwann cell groups, however, displayed the highest myelination indices recorded likely reflecting the role of Schwann cells in the myelination process. Measurements of conduction velocities (EMGs) revealed the highest conductance velocities recorded in nerves regenerated in the presence of both GGF and Schwann cells. Clearly, the inclusion of GGF in the nerve regenerative process is beneficial with respect to both the generation of new axons and the establishment of a functional endpoint.
Volume Effects in Bulk Metallic Glass Formation
Authors: Yavari A. R. , Inoue A. 
Published: April 2011

AbstractAtomic volume effects in amorphous alloys obtained by rapid solidification and in bulk glasses are briefly reviewed. It is recalled that at high undercoolings, the release at the growth fronts, of the volume corresponding to the reduction of the molar volume upon solidification can sharply accelerate crystal growth in the melt through viscosity reduction. A method is then proposed for estimating the volume of mixing ΔVmix which is negative for elemental additions to glass-forming liquid alloy. It is argued that negative ΔVmix reduces atomic mobility in easy glass-forming alloys thus allowing the suppression during cooling, of nucleation and growth of crystallites. The ZrCuNi system is used as an example for applying this reasoning. It is shown that Al or Ti addition to ZrNiCu alloys lead to strongly negative ΔVmix and expected sharp drops in diffusion-controlled crystal growth kinetics in the melt.
Distribution Coefficients and Apparent Diffusion Coefficients of Cesium in Compacted Bentonites
Authors: Okamoto Akiko , Idemitsu Kazuya , Furuya Hirotaka , Inagaki Yaohiro , Arima Tatsumi 
Published: April 2011

AbstractDistribution coefficients and apparent diffusion coefficients of cesium in some compacted bentonites were determined by the penetration profile method. Cylindrical compacted bentonites with the dry density of 0.8 to 1.6 Mg/m3 were contacted with tracer solutions containing 1000, 100 or 10 ppm of cesium. The apparent diffusion coefficients were obtained from the concentration profiles of cesium in compacted bentonites. The distribution coefficients were obtained concurrently by dividing the intercepts of the profiles by the concentration of the tracer solution. The apparent diffusion coefficients of cesium in compacted bentonite were obtained in the range of 0.42 to 9.6· 10−12 m2/s. The apparent diffusion coefficients in the compacted bentonite contacted with three different concentrations of cesium tended to decrease with increasing dry density of the specimen; but, they had no dependence on cesium concentration within a factor of 3 at the same dry density. The distribution coefficient of cesium for the specimens contacted with three different concentrations of cesium were obtained in the range of 0.3 to 90 L/kg and had little dependence on dry density. The distribution coefficients obtained in the compacted bentonites were dependent on pH of the solution rather than concentration of cesium. These distribution coefficients obtained in the compacted bentonites were 10 to 1000 times smaller than those obtained by batch experiments. The data suggest that not all sorption sites for cesium are available in highly compacted bentonite. It is necessary to consider surface diffusion as a significant migration mechanism of cesium through the compacted bentonites at very high pH condition such as 12.
Modelling the Activity of Sulphate-Reducing Bacteria and the Effects on Container Corrosion in an Underground Nuclear Waste Disposal Vault
Authors: King Fraser , Kolar Miroslav , Stroes-Gascoyne Simcha , Bellingham Peter , Chu James , Dawe Paula V. 
Published: April 2011

AbstractA mathematical model has been developed to predict the extent of sulphate reduction by sulphate-reducing bacteria (SRB) in an underground nuclear waste disposal vault and the consequences for corrosion of the waste package. The model is based on a series of massbalance equations that describe the kinetics of sulphate reduction by two types of SRB (one organotrophic and one chemoheterotrophic), the growth and death of SRB, the supply and consumption of nutrients (acetate and hydrogen) and reactants (SO42−) and the consumption of sulphide by precipitation with aqueous Fe(II) or by container corrosion. The disposal vault is described by a series of 1-D mass-transport barriers representing the buffer and backfill materials and fractured rock. The model can also be used to simulate the effects of γ-radiation and desiccation of the buffer and backfill materials on the extent of microbial activity.
A Quantitative Assessment of Microbiological Contributions to Corrosion of Candidate Nuclear Waste Package Materials
Authors: Lian T. , Martin S. , Horn J. , Jones D. 
Published: April 2011

AbstractThe U.S. Department of Energy is contributing to the design of a potential nuclear waste repository at Yucca Mountain, Nevada. A system to predict the contribution of Yucca Mountain (YM) bacteria to overall corrosion rates of candidate waste package (WP) materials was designed and implemented. DC linear polarization resistance techniques were applied to candidate material coupons that had been inoculated with a mixture of YM-derived bacteria with potentially corrosive activities, or left sterile. Inoculated bacteria caused a 5- to 6-fold increase in corrosion rate of carbon steel C 1020 (to approximately 7-8μm/yr), and an almost 100-fold increase in corrosion rate of Alloy 400 (to approximately μm/yr) was observed due to microbiological activities. Microbiologically Influenced Corrosion (MIC) rates on more resistant materials (CRMs: Alloy 625, Type 304 Stainless Steel, and Alloy C22) were on the order of hundredths of micrometers per year (μm/yr). Bulk chemical and surfacial endpoint analyses of spent media and coupon surfaces showed preferential dissolution of nickel from Alloy 400 coupons and depletion of chromium from CRMs after incubation with YM bacteria. Scanning electron microscopy also showed greater damage to the Alloy 400 surface than that indicated by electrochemical detection methods.
Ion Exchange in High-Level Nuclear Waste Encapsulation: Atomistic Modeling of Equilibrium Coefficients and Isotherms
Authors: Kletskova T. , Czerwinski K. , Gelbard E. , Yip S. 
Published: April 2011

AbstractA computational modeling approach, based on molecular dynamics and related atomistic simulation techniques, is formulated to analyze the confinement of radionuclides in prepared nuclear wasteform for long-term disposal. While the intent is to exploit the ability of simulation to provide a unified treatment of chemical as well as kinetic processes at the molecular level, it is recognized that the problem is too complex to be studied in its entirety at the outset. To demonstrate the feasibility and effectiveness of the atomistic modeling approach, a first step is to determine an equilibrium isotherm for cation exchange, on the premise that a predominant release mechanism is likely to involve ion exchange. As a prototypical application, Cs-Na exchange on sodalite is studied using explicit interatomic potential models. Initial results for the equilibrium Cs concentration in dehydrated sodalite suggest that the effects of frame relaxation need to be taken into account. The present study will be extended to treat an aqueous environment for the loaded wasteform, as well as the effects of radiation damage to the zeolitic framework.
Oxidative alteration of Ce-rich pyrochlore: HRTEM/EELS investigation
Authors: Xu Huifang , Wang Yifeng 
Published: April 2011

AbstractTransmission electron microscopy (TEM) and associated electron energy-loss spectroscopy (EELS) study show intergrowth of Ce4+-rich pyrochlore (metamict) and Ce3+-rich pyrochlore (partially metamict) in a Ce-rich pyrochlore from a rare earth element (REE) ore deposit of Inner Mongolia, Northern China. The partially metamict material is Ba-free and dominated by Ce3+. However, the metamict material is Ba-bearing and dominated by Ce3+,. The Ce4+-rich pyrochlore may result from radiation damage by alpha decay that also causes oxidation of Fe 2+ in titanite, and the interaction with a Ba-bearing oxidizing fluid. The oxidation of Ce3+ in the primary pyrochlore is accompanied by in the loss of REE, Ca, and Pb, a daughter product of U via alpha decay, during the alteration. However, most REE were incorporated in the alteration product, the Ce4+-rich pyrochlore. Based on EDS and EELS analyses, the chemical formulae of the partially metamict Ce3+-rich pyrochlore and metamict Ce4+-rich pyroeblore can be written as: (Ca, Ce3+, U, Pb) 2(Ti, Nb)2O7−x(OH)x, and (Ba, Ca, Ce4+, U)2 (Ti, Nb)2O7−y(OH)y, respectively. Ce is the most abundant element among all REE. It is proposed that the alteration takes place in solid-state with oxidizing fluid as a catalyst. The alteration kinetics is controlled by diffusion processes of aqueous species in metamict pyrochlore.
Molecular Dynamics Study of a Nuclear Waste Glass Matrix With Plutonium
Authors: Meis C. , Delaye J. M , Ghaleb D. 
Published: April 2011

AbstractMolecular dynamics simulation techniques were applied to model the incorporation of plutonium in the French nuclear waste glass matrix. Born-Mayer-Huggins analytical potentials were established to characterize short-range interactions between Pu–O and Pu–Pu pairs; the potentials were fitted to the structural properties of plutonium dioxide in the light of a recent experimental study showing that plutonium is found as Pu(IV) in the glass. The transferability of the established potentials to the glass structure is discussed, and the potential parameters are further refined by molecular dynamics simulations in an aluminoborosilicate glass to obtain mean Pu–O interatomic distances and firstneighbor coordination numbers matching the experimental values as closely as possible. Previously published Born-Mayer-Huggins potentials supplemented by Stillinger-Weber three-body terms were used for oxygen-cation and cation-cation interactions. The difficulties encountered in establishing a Pu–O potential that provides satisfactory results in both oxides and glasses are also discussed.