bluuebunny/crossref_metadata_2025_split huggingface dataset:
Alloy Phase Formation in Isolated Nanometer-sized Particles in the Au-Sn and Sn-Bi Systems
Authors: Lee Jung-Goo , Mori Hirotaro , Yasuda Hidehiro 
Published: April 2011

ABSTRACTAlloy formation in nanometer-sized particles has been studied as a function of the particle size by in-situ transmission electron microscopy using particles in the Au-Sn and Sn-Bi systems. When the size of particles is larger than a critical value, essentially similar phase equilibrium was observed in nanometer-sized particles and bulk materials in the both systems. But a solid amorphous phase was formed over a compositional range near the eutectic composition when the size of particles was smaller than about 7 nm in diameter in the former system, whereas a fluid amorphous phase was formed when the size of particles is smaller than about 10 nm in diameter in the latter system. These amorphous phases directly changed into liquid phases upon heating and solidified into amorphous phases upon subsequent cooling. The formation of these thermodynamically stable amorphous phases can be attributed to the the suppression of the eutectic temperature (Teu) associated with size reduction being so large that Teu is below the glass transition temperature (Tg).
Electron Irradiation Effect on the Microstructure and Phase Stability of Fe-Based Fe71.0Zr9.0B20.0 Metallic Glass with a Wide Supercooled Liquid Region
Authors: Nagase T. , Umakoshi Y. , Sumida N. 
Published: April 2011

ABSTRACTThe effect of electron irradiation on the microstructural change and phase stability of melt-spun Fe71.0Zr9.0B20.0 metallic glass having a wide supercooled liquid region of 71 K was examined. Crystallization from the amorphous phase was accelerated by electron irradiation, and this irradiation was effective in producing a nanocomposite microstructure.
Atomistic Theory of Bulk Metallic Glass Formation
Authors: Egami T. 
Published: April 2011

ABSTRACTBulk metallic glass can be formed only when the critical cooling rate for glass formation is reduced to 100–2 K/sec. However, a cooling rate achievable with molecular dynamics simulation is higher by many orders of magnitude, so the gap has to be abridged by analytical theories. We propose a theory of bulk metallic glass formation based upon our early theories of glass formation composition. The critical concepts include the idea of local glass transition, distributed local glass transition temperatures and coincident local fluctuation for atomic transport. Strong repulsion between small atoms was recognized for the first time as the necessary condition for bulk glass formation.
Two-liquid Separation in Undercooled Co-Cu Alloys
Authors: Lu X. Y. , Kolbe M. , Herlach D. M. 
Published: April 2011

ABSTRACTElectromagnetic levitation and drop tube processing were used to investigate the solidification behaviour of Co50Cu50 alloys. Deep undercooling was achieved down to 241 K, the alloy melts separated into Co-rich L1-phase and Cu-richL2-phase before solidification. In drop tube processing, the Cu-rich phases disperse morehomogeneously than in EML. This is due to the reduced gravity and high cooling rate during free fall and solidification.
Glass-Forming Ability and Crystallization Behavior in High-Density Bulk Metallic Glasses
Authors: Kecskes Laszlo J. , Trevino Samuel F. , Woodman Robert H. 
Published: April 2011

ABSTRACTAlloys of composition (Hfx,Zr1-x)57Ti5Cu20Ni8Al10 and (Hfx,Zr1-x)52.5Ti5Cu17.9Ni14.6Al10, where x = 0, 0.2, 0.4. 0.6, 0.8, and 1.0, were evaluated for glass-forming ability, and the devitrification behavior on heating of the (Hfx,Zr1-x)52.5Ti5Cu17.9Ni14.6Al10 glasses was examined. Glass-forming ability was determined by suction casting 3-mm-diameter rods, followed by neutron diffraction examination. Results show that substitution of Hf for Zr in these alloys degrades glass-forming ability, and that this effect is more pronounced in compositions of the (Hfx,Zr1-x)57Ti5Cu20Ni8Al10 type. To examine devitrification behavior, thermal analysis was used to identify temperatures at which exothermic events occurred on heating in the (Hfx,Zr1-x)52.5Ti5Cu17.9Ni14.6Al10 series. The amorphous alloys were then subjected to annealing treatments corresponding to the exothermic events. Crystal structures formed during annealing were probedby neutron diffraction, and the size scale of features developed examined by small-angle neutron scattering. Results show that the initial decomposition produces a structure witha characteristic length scale, but it is not yet possible to comment on the mechanism.
Relaxation mapping analysis with an hyperbolic heating rate
Authors: Dias C. J. 
Published: April 2011

ABSTRACTThermally stimulated discharge currents (TSDC) together with the Relaxation Map Analysis (RMA) method is a convenient method to study relaxation processes in complex materials. In the RMA technique, one performs repeated TSDC runs while selecting polarization states through the use of a fixed polarization time schedule and a sucessively higher polarization temperature. Each peak has an associated polarization strength and a pair of activation parameters which can be the Gibbs free activation energy and the activation entropy. In the present paper we propose a different approach to RMA. It consists of a global heating of the sample in an hyperbolic manner to determine the activation parameters as a function of temperature. This determination is done by first selecting a value for the activation entropy for each temperature and then calculating the implied activation enthalpy or Gibbs free energy.We have reasoned that normal relaxation processes usually proceed with a null or close to zero activation entropy and that only relaxations associated to the glass transitionand/or cooperative phenomena involve large values of the activation entropy. In those cases and based on the curvature of the TSDC curve one can select a minimum activation entropy value which will fit the TSDC curve at a particular temperature. Using this data one determines the polarization strength associated to each pair of activation parameters. Results for the TSDC relaxation parameters spectra of a liquid crystal polymer will be presented together with comparisons between the thermal sampling method and the proposed method.
Thermodynamics of supercooled liquid silicon and its glass transition
Authors: Miranda Caetano R. , Antonelli Alex 
Published: April 2011

ABSTRACTThe thermodynamic properties of various phases of silicon, namely, crystalline, amorphous, and liquid, have been studied using the Reversible Scaling method within Monte Carlo simulations. The recently proposed Environment Dependent Interatomic Potential was employed to model the atomic interactions. The calculated Gibbs free energy and entropy of both crystalline and liquid phases are in good agreement with available experimental data. The glass transition is continuous, taking place at 1150 K. We have also determined the Kauzmann temperature, TK = 955 K, the thermodynamic fragility, F3/4 = 0.64, which indicates a fragile thermodynamic character to l-Si, and the configurational entropy of the amorphous phase, Sconf ≈ 1.2 kB/atom.
The electronic and magnetic structure of Fe-based bulk amorphous metals: An ab-initio approach
Authors: Wang Yang , Widom Mike , Nicholson Don , Mihalkovic Marek , Naidu Siddartha 
Published: April 2011

ABSTRACTWe applied the locally self-consistent multiple scattering (LSMS) method to the study Fe-based bulk amorphous metals. The LSMS method is an order-N approach to the electronic structure calculation for solid state materials based on density functional theory and local density approximation. Using LSMS method, we performed electronic structure calculations for the supercell samples generated by ab-initio molecular dynamics simulation. The equilibrium atomic volume and the bulk modulus are calculated based on the energy versus volume curve. The magnetic moment distribution in the samples is determined for both collinear and noncollinear cases. A comparison with the experimental results is also made.
Local Order in Amorphous Fe-alloys
Authors: Louca Despina , Ahn Kyungsoo , Ponnambalam V. , Poon S. J. 
Published: April 2011

ABSTRACTThe pair density function analysis of neutron diffraction data of Fe-based metallic glasses of the Zr and Mo series shows how the local atomic structure changes by chemical substitution. The results provide evidence for short-range chemical reorganization accompanied by a volume contraction that could in turn be associated with stronger glass forming ability. While the existence of chemical short-range topological ordering is enhanced in both systems by alloying with a transition metal such as Mn, locally, the atomic structure changes in a way that corresponds to an increase in bonding interactions. The shortening of bonds is also related to volume contraction that can in turn be associated with a reduction of the ferromagnetic coupling of the Fe sublattice and to a lower Curie transition temperature.
Fracture Toughness of Amorphous Metals and Composites
Authors: Lewandowski J.J. , Thurston A.K. , Lowhaphandu P. 
Published: April 2011

ABSTRACTThe effects of changes in notch radius on the toughness of two different Zr-based bulk metallic glasses have been determined. It is shown that increases in notch radius produce large increases to the toughness, accompanied by extensive shear banding and crack bifurcation. The fracture toughness of twenty (20) fatigue precracked specimens exhibiting planar crack growth were in the range 20.3 ± 6.7 MPa√m for the two Zr-based glasses. Increasing the notch radius to 110 μm produced notch toughness in the range 95.3 ± 8.3 MPa√m for nine (9) tests on Vitreloy I, well in excess of that typically observed in most structural materials. Toughness tests conducted on two fatigue precracked specimens of Vitreloy I at 77 K produced values for fracture toughness that were in the range 17.9 ± 2.7 MPa√m, similar to that obtained at 298 K. The fatigue precracked fracture toughness of metallic glass composites containing large crystalline regions of a body centered cubic Zr-Ti-Nb alloy were in the range 29–42 MPa√m, but the values were temperature dependent over the range 148 K to 500 K. Fracture surfaces were analyzed via Scanning Electron Microscopy (SEM).
Consequences of the Anticipated Long-Term Evolution of Spent Nuclear Fuel for the Assessment of the Release Rate of Radionuclides.
Authors: Poinssot Christophe , Lovera Patrick , Ferry Cécile , Gras Jean-Marie 
Published: April 2011

ABSTRACTThe research conducted in the framework of the French research project on spent nuclear fuel (SNF) long - term evolution (PRECCI Project) has enlightened the potential significance of spent nuclear fuel intrinsic evolution in closed system for the assessment of radionuclide (RN) source term in long-term storage or geological disposal. Beyond others, alpha self-irradiation enhanced diffusion and evolution of the grain boundaries cohesion are two major processes which have to be accounted for in view of the RN source term models development. Accounting for these processes, operational models are developed, the aim of which is to quantitatively define the RN release rates from SNF in long-term storage or geological disposal. They distinguish basically an instantaneous contribution (IRF in geological disposal) and a time-dependent contribution (matrix oxidation or alteration). RN inventories associated to these two different processes have to be modeled since they are time-dependent due to the RN diffusion within the pellet. The present paper details the models that are developed in France in terms of assumptions, conservatism and robustness. It comes out from this work that for the instant release fraction, we have to consider a much higher instant release fraction than classically assumed (5–6% in geological disposal) in particular for geological disposal.
Effects of Volatilization on Groundwater Chemistry
Authors: Pulvirenti A. L. , Needham K. M. , Adel-Hadadi M. A. , Bishop E. J. , Barkatt A. , Marks C. R. , Gorman J. A. 
Published: April 2011

ABSTRACTBoth concentrated and dilute simulated solutions of saturated J13 and unsaturated UZ pore water were concentrated through distillation of the solutions under atmospheric pressure. It was observed that condensed vapors from the pH of J13 waters steadily rose during the distillations to a value of 10, while the pH of UZ waters remained steady until 90% of the volume of the solution had been distilled, after which the pH of the condensed vapors dropped precipitously, often below 1. Residual solutions analyzed when most of the solution had been distilled away were also found to be extremely acidic. The temperature of these residual solutions was around 144°C due to their high solute content causing boiling point elevation. All experiments were performed with the condenser open to ambient air at atmospheric pressure. The pH drop during the distillation of UZ water is attributed largely to the presence of large amounts of magnesium. Specimens of Alloy 22 tested in the residual solutions of at their boiling temperature (around 144°C) showed significant rates of general corrosion over a broad range, often approaching 1 mm/year. Similarly high corrosion rates were also observed in tests on Alloy 22 specimens in condensates obtained during the late stages of the distillation. These tests were performed eitherin situat 75–80°C using a Soxhlet extractor, or in separate pressure vessels at temperatures between 90 and 130°C.
Cesium and Niobium transport through poorly cemented sandstone from Krasnoyarsk-26 (Russian Federation): From Batch to Transport experiments
Authors: Casas Ignasi , Giménez Javier , Merino Joan M. , Arasanz Emilio , de Pablo Joan , Torras Josep , Rovira Miquel 
Published: April 2011

ABSTRACTWe have studied the sorption of Cs and Nb onto poorly cemented sandstone (drillcore from – 250 m depth) from the radioactive waste disposal site at Krasnoyarsk-26 (Russian Federation). Results were evaluated in terms of KD-values and Langmuir isotherms. These values have been used to model the transport of Cs and Nb through a sandstone column using the RETRASO code (REactive TRAnsport of Solutes), which is able to simulate simultaneously groundwater flow, heat transport and multicomponent reactive solute. Good agreement between experimental data and modeling has been achieved for both elements. Cs transport has been modeled using rapid sorption equilibrium, while for Nb a kinetically controlled transport has been considered. The results obtained in this work have been used to predict the 1D transport of Cs and Nb taking into account some parameters of the hydrogeology of Krasnoyarsk-26.
Sensitivity Studies of Waste Package Performance in High-Level Waste Management
Authors: Rivera-Feliciano N. , Bloomer T. , Ahn T. , Pensado O. 
Published: April 2011

ABSTRACTAn important attribute of the high-level waste (HLW) disposal program in the United States (U.S.) is the estimated long life of waste packages (WPs). The outer container of the WP is proposed to be constructed of a nickel-based alloy, Alloy 22 (58Ni-21Cr-14Mo-3W-4Fe), which is highly corrosion resistant. Under nominal conditions of the proposed repository at Yucca Mountain (YM), Nevada, WPs are anticipated to have a long life because of their extremely slow uniform corrosion rate. The technical basis for this expected long life of geological scale is still subject of discussion. In this paper, the NRC Total-system Performance Assessment (TPA) Code is used to evaluate uncertainties associated with the WP performance within a 10,000-year period. Early WP failure may occur due to localized corrosion or high frequency of manufacturing defects. Localized corrosion may occur under mixed salt deposits on the WP surface at temperatures above 100°C. High frequencies of WP juvenile failure are considered to account for the limited industrial experience with Alloy 22 and uncertainty in the long-term performance of Alloy 22 as container material. The localized corrosion and the high frequency of manufacturing defects were simulated with the TPA code by lowering the critical relative humidity for the onset of aqueous corrosion, RHc, and increasing the fraction of initially defective WPs. By sampling RHc from various normal distributions, the mean annual total effective dose equivalent (TEDE) approached 1 mrem/year at 10,000 years. Assuming a fixed fraction of initially defective WPs (1 percent), the mean annual TEDE approached 0.07 mrem/year at 10,000 years.
Long-Term Extrapolation of Passive Behavior of Alloy 22
Authors: Pensado Osvaldo , Dunn Darrell S. , Cragnolino Gustavo A. 
Published: April 2011

ABSTRACTCommon assumptions to extrapolate the lifetime of proposed high-level waste disposal containers made of Ni-Cr-Mo alloys, in the absence of environmental and electrochemical conditions leading to localized corrosion and stress corrosion cracking, are evaluated based on a mechanistic model for passive dissolution. The predominant charge conduction mechanism through the oxide film formed on Ni-Cr-Mo alloys is hypothesized to be interstitial transport of metal cations. Dissolution of the alloy and conduction of interstitial species through the film create vacancies in the alloy. The anodic current density under potentiostatic control decreases as a function of time, and potentiostatic decays in the current density are rationalized on the basis of vacancy accumulation at the metal-oxide interface. It is concluded that the dissolution process is regulated by vacancy-enhanced diffusion of the elements in the alloy. Long-term stoichiometric dissolution arises if the diffusion coefficients of the alloying elements are similar. No credible scenario is envisioned by which catastrophic failure may occur as a result of longterm passive dissolution.
Cold Crucible Vitrification of NPP Operational Waste
Authors: Lifanov Feodor A. , Ojovan Michael I. , Stefanovsky Sergey V. , Burcl Rudolf 
Published: April 2011

ABSTRACTOperational radioactive waste is generated during routine operation of nuclear power plants (NPP). This waste must be solidified in order to ensure safe conditions of storage and disposal. Vitrification of NPP operational waste is a relative new solidification option being developed for last years. The vitrification technology comprises a few stages, starting with evaporation of excess water from liquid radioactive waste, followed by batch preparation, glass melting, and ending with vitrified waste blocks and some relative small amounts of secondary waste. Application of induction high frequency cold crucible type melters facilitates the melting process and significantly reduces the generation of secondary waste. Two types of glasses were designed in order to vitrify operational waste depending on the reactor type at the NPP. For the NPP with RBMK-type reactors the glass 16.2Na2O 0.5K2O 15.5CaO 2.5 Al2O3 1.7Fe2O3 7.5B2O3 48.2SiO2 1.1 Na2SO4 1.2NaCl (5.7 others) was produced. For NPP with WWER reactors the glass 24.0Na2O 1.9K2O 6.2CaO 4.3Al2O3 1.8Fe2O3 9.0B2O3 46.8SiO2 0.8Na2SO4 0.9NaCl (4.3 others) was produced. The melting temperatures of both glass formulations were 1200–1250 C, specific power consumption was 5.2 ± 0.8 kW h/kg, 137Cs loss was within the range 3 - 4 %. The specific radioactivity of glass reached 7.0 MBq/kg. Glass blocks obtained were studied both in laboratory and field conditions. Long-term studies revealed that vitrified NPP operational waste has the minimal impact onto environment. Since the glass has excellent resistance to corrosion it gives the basic possibility of maximal simplification of engineered barrier systems in a disposal facility. The simplest disposal option for vitrified NPP waste is to locate the packages directly into earthen trenches provided the host rock has the necessary sorption and confinement properties.
Effects of Iron and pH on Glass Dissolution Rate
Authors: Jeong Seung-Young , Ebert William L. 
Published: April 2011

ABSTRACTShort-term static tests were conducted with a surrogate high-level waste glass to measure the effects of pH and dissolved iron on the glass dissolution rate. The tests were conducted to determine if a term to account for the effects of dissolved iron is needed in the glass degradation model developed for Total System Performance Assessment (TSPA) calculations for the Yucca Mountain disposal system license application. The glass degradation model includes terms for dependencies on temperature, pH, and chemical affinity. A series of tests was conducted at 90 °C in various pH solutions without iron and with added FeCl3, Fe2O3, Fe3O4, and FeOOH. Tests were conducted at glass surface area/solution volume (S/V) ratios about 2 and 10 m-1for between 2 and 21 days. Solution concentrations of boron were used to measure the extent of reaction and calculate the glass dissolution rates. Similar rates were measured in tests conducted with and without iron at each pH. Both the results of the tests with and without iron showed V-shaped pH dependence curves with minima at near-neutral pH values. The pH dependencies (η) are about 0.44 in basic solutions and –0.49 in acidic solutions, based on the combined results of tests with and without iron. These are within the range of values for the pH dependence in the TSPA model for site recommendation.
Structural characterization of polycrystalline (Nd,Al)-substituted zirconolite
Authors: Loiseau Pascal , Caurant Daniel , Baffier Noël , Fillet Catherine 
Published: April 2011

ABSTRACTZirconolite (formally CaZrTi2O7) is a crystalline phase particularly well adapted to actinide immobilization because of its excellent long-term behavior and its good containment capacity. Most of the French studies on zirconolite deal with minor actinides that are mainly responsible for the long-term radiotoxicity of high-level radioactive wastes. For these kind of studies, trivalent minor actinides (Am3+, Cm3+) can be simulated by a lanthanide ion with an ionic radius similar to that of Nd3+. Thus, several materials having the composition Ca1-xNdxZrTi2-xAlxO7 (0 ≤ x ≤ 0.8) were prepared by solid state reaction. These polycristalline materials were first characterized by X-ray diffraction and scanning electron microscopy associated with energy dispersive X-ray analysis in order to determine the nature of the crystalline phases formed. For low neodymium content (x ≤ 0.1), electron spin resonance of Nd3+ ions revealed that a significant proportion of these ions entered into trace amounts of perovskite. Nevertheless, all Ca1-xNdxZrTi2-xAlxO7 samples with x ≤ 0.6 can be considered as almost single phase zirconolite-2M. Structure refinement by the Rietveld method of Ca0.7Nd0.3ZrTi1.7Al0.3O7 showed that Nd3+ and Al3+ ions mainly entered respectively into the calcium site and into the split five-fold coordinated titanium site. Structural characterization of Ca0.3Nd0.7ZrTi1.3Al0.7O7 and Ca0.2Nd0.8ZrTi1.2Al0.8O7 samples confirmed that these compositions led to the crystallization of almost single phase zirconolite-3O, an orthorhombic polytype of zirconolite, whose structure was also refined by the Rietveld method. Results concerning neodymium location in Ca0.7Nd0.3ZrTi1.7Al0.3O7 and Ca0.3Nd0.7ZrTi1.3Al0.7O7 were qualitatively confirmed by optical absorption spectroscopy at low temperature.