bluuebunny/crossref_metadata_2025_split huggingface dataset:
Assessing the Natural Performance of Felsic Tuffs Using the Rb-Sr and Sm-Nd Systems-A Study of the Altered Zone in the Topopah Spring Member, Paintbrush Tuff, Yucca Mountain, Nevada
Authors: Peterman Zell E. , Spengler Richard W. , Futa Kiyoto , Marshall Brian D. , Mahan Shannon A. 
Published: March 2011

ABSTRACTCore samples of the Topopah Spring Member of the Paintbrush Tuff from drill hole UE25A#1 were analyzed for Sr and Nd isotopes and selected minor and trace elements to constrain the origin of a zcolitized zone associated with the lower vitrophyre. The Sm-Nd radiogenic isotope system was unperturbed by the alteration, but the Rb-Sr system was severely disturbed in the altered zone. The thick, densely welded high-silica rhyolite is remarkably uniform in composition with only a slight decrease in initial 87Sr/86Sr ratios with depth (0.7129–0.7125). Quartz latite in the upper part of the Topopah Spring has significantly lower initial Sr isotope ratios (0.7095–0.7114). Locally in the altered zone, Sr and Ca were gained in substantial amounts, and K, Rb, and Y were removed. Ti, Zr, Nb, Ba, La, Ce, Sm, and Nd were relatively immobile during the alteration. Sr added to the altered zone had an isotopic composition of 0.7119 ± 0.0002 and was probably derived from dissolution of glass in the bulk Topopah Spring (high silica rhyolite + quartz latite) and transported downward by infiltration.
Natural-Analog Studies for Partial Validation of Conceptual Models of Radionuclide Retardation at the Wipp
Authors: Ward David B. , Brookins Douglas G. , Siegel Malcolm D. , Lambert Steven J. 
Published: March 2011

ABSTRACTTransport by groundwater within the Culebra Dolomite, an aquifer above the Waste Isolation Pilot Plant (WIPP), is the most probable mechanism for long-term release of radionuclides to the accessible environment. Radionuclides could be retarded by sorption if the groundwater is exposed to sufficient amounts of fracture-lining clays. In this natural-analog study, distributions of U and trace metals have been examined to constrain the strength of clay/solute interactions within the Culebra.Uranium solid/liquid distribution ratios, calculated from U concentrations of groundwaters and consanguineous fracture-filling clays, range from ∼80 to 800 mℓ/g and imply retardation factors of 60 to 500 using a fracture-flow model. Retardation factors inferred from uranium-series disequilibria and 14C ages in Culebran groundwaters alone are much lower (∼10), implying that clays may contain a significant unreactive component of U. Such a possibility is corroborated by Rb/Sr ages; these imply long-term stability of the clays, with resetting occurring more than 250 Ma ago. Factor analysis and mass-balance calculations suggest, however, that Mg-rich clays are dissolving in Pleistocene-age groundwaters and/or are converting to Na-rich smectites, and that B and Li are taken up from the water by the clays. Apparently, the solution chemistry reflects gradual equilibration of clays with groundwater, but thus far the bulk of the clays remain structurally intact. Measurements of the distribution of U in the Culebra will be more meaningful if the inert and exchangeable components of the U content of the clays can be quantified.
Radionuclides in Hydrothermal Systems as Indicators of Repository Conditions
Authors: Wollenberg H.A. , Flexser S. , Smith A.R. 
Published: March 2011

ABSTRACTHydrothermal systems in tuffaceous and older sedimentary rocks contain evidence of the interaction of radionuclides in fluids with rock matrix minerals and with materials lining fractures, in settings somewhat analogous to the candidate repository site at Yucca Mountain, NV. Earlier studies encompassed the occurrences of U and Th in a “fossil” hydrothermal system in tuffaceous rock of the San Juan Mountains volcanic field, CO. More recent and ongoing studies examine active hydrothermal systems in calderas at Long Valley, CA and Valles, NM. At the Nevada Test Site, occurrences of U and Th in fractured and unfractured rhyolitic tuff that was heated to simulate the introduction of radioactive waste are also under investigation. Observations to date suggest that U is mobile in hydrothermal systems, but that localized reducing environments provided by Fe-rich minerals and/or carbonaceous material concentrate U and thus attenuate its migration.
The Redistribution of Uranium Series Radionuclides at Koongarra
Authors: Edis Robert 
Published: March 2011

ABSTRACTThe distribution of 238U, 234U, 230Th and 236Ra in rocks from the Koongarra uranium deposit has been examined. Alpha-spectrometry and ICP-MS were used to estimate elements in “accessible” and “inaccessible” phases, separated by a two-phase extraction scheme; and bulk analyses of visibly distinct zones were made using PIXE-PIGME, DNAA and XRF.The secondary U dispersion fan of the Koongarra site is characterised by 234U/238U, 230Th/234U and 236Ra/230Th activity ratios (ARs) below unity in the extractable (accessible) phases, and above unity in the non-extractable (inaccessible) phases. The patterns of the ARs suggest zones of different U deposition and leaching rates with the most rapid accumulation at the base of weathering, especially at the extremities of the dispersion fan.
Effects of Chlorite Alteration on Uranium Redistribution in Koongarra, Australia
Authors: Murakami Takashi , Isobe Hiroshi , Edis Robert 
Published: March 2011

ABSTRACTThe relevance of alteration of chlorite, one of the major constituent minerals of the host rock to uranium ore at Koongarra, to the redistribution of uranium in the vicinity of the ore deposit has been examined. The chlorite alteration is produced by weathering; chlorite is transformed to vermiculite, through regularly interstratified chlorite/vermiculite. The Fe released from chlorite reprecipitates to form iron minerals, possibly ferrihydrite. Vermiculite is then replaced by kaolinite (and possibly smectite), further releasing Fe. On the millimeter scale, an alpha autoradiography study has shown that uranium concentrations are qualitatively proportional to the extent of the alteration; altered chlorite grains having higher uranium concentration. On the meter scale, the X-ray diffraction study has revealed that the abundances of chlorite, vermiculite, and kaolinite correspond well to the low, intermediate, and high uranium concentration zones, respectively. These suggest that the interaction of the uraniferous solution with chlorite causes the alteration of chlorite and the precipitation and sorption of uranium in the alteration products from the solution, and thus, the uranium migration is retarded at Koongarra.
Quantitative Interpretation of Halogen Porewater Concentration Profiles in Lake Sediments
Authors: Eberhard Falck W. , Hooker Paul J. 
Published: March 2011

ABSTRACTHalogen ion migration through clay-rich sediments is particularly well documented in cores from Loch Lomond, Scotland, where distinctive patterns for CI, Br and I have been observed. The sediments are a sequence of marine and limnic silts and clays which cover glacial deposits. The marine band, resulting from a transgression 6900 y B.P. to 5400 y B.P., acts as a source for the halogens.A 1-D conceptual model and code has been developed taking into account variations in the concentration boundary conditions and the accumulation of sediments. The model has been calibrated against the CI concentration distributions for which boundary conditions can be estimated readily.The model has been applied to Br and I profiles. Deviations between the Cl-calibrated model and the measured profiles were attributed to reactive processes. Release rates from the marine band for Br and I are deduced. Their sensitivity with respect to system properties, assumptions over boundary and initial conditions and reaction mechanisms is discussed.
Three-Dimensional Visualization: Breakthrough in Analysis and Communication of Technical Information for Nuclear Waste Management
Authors: Alexander Donald H. , Hill E. Richard , Smoot John L. , Smith Dennis R. , Waldo Karen , Cerny Barbara A. , Krupka Kenneth M. 
Published: March 2011

ABSTRACTComputer graphics systems that provide interactive display and manipulation of three-dimensional data are powerful tools for the analysis and communication of technical information required for characterization and design of a geologic repository for nuclear waste. Greater understanding of site performance and repository design information is possible when performance-assessment modeling results can be visually analyzed in relation to site geologic and hydrologic information and engineering data for surface and subsurface facilities. In turn, this enhanced visualization capability provides better communication between technical staff and program management with respect to analysis of available information and prioritization of program planning.A commercially-available computer system was used to demonstrate some of the current technology for three-dimensional visualization within the architecture of information systems for nuclear waste management. This computer system was used to interactively visualize and analyze the information for two examples: 1) site-characterization and engineering data for a potential geologic repository at Yucca Mountain, Nevada; and 2) three-dimensional simulations of a hypothetical release and transport of contaminants from a source of radionuclides to the vadose zone. Users may assess the three-dimensional distribution of data and modeling results by interactive zooming, rotating, slicing, and peeling operations. For those parts of the database where information is sparse or not available, the software incorporates models for the interpolation and extrapolation of data over the three-dimensional space of interest.
The Importance of Secondary Phases in Glass Corrosion
Authors: Ebert William L. , Bates John K. 
Published: March 2011

ABSTRACTThe analytical expression used to model glass reaction in computer simulations such as EQ6 is compared to the results of experiments used to support the simulations. The expression correctly predicts the acceleration observed in experiments performed at high glass surface area/1eachant volume ratios (SA/V) upon the formation of secondary phases. High resolution microscopic analysis of reacted glass samples suggests that the accelerated nature of the reaction after secondary phase formation is due to changes in the reaction affinity (i.e., is a solution effect) and not a change in the glass reaction mechanism. The composition of solutions in contact with reacted samples reflect the effects of the secondary phases predicted in the model. Experiments which lead to the generation of secondary phases within short reaction times can be used to identify important secondary phases which must be Included in the data base of computer simulations to correctly project long-term glass reaction behavior.
The Formation of Nial Phase and Layered Carbon Precipitates During Ni3Al/SiC Solid State Reactions
Authors: Chou T. C. , Nieh T. G. 
Published: March 2011

ABSTRACTSolid state reactions of Ni3A1 with SiC have been studied at 1000°C. Three layered reaction products consisting of NiAl Ni5,4Al1Si2, and Ni(5.4−x)A11Si2+C were formed in the reaction zone. The Ni5.4AllSi2layer showed carbon precipitation free, while modulated carbon bands were formed in the Ni(5.4−x)A11Si2+C layer. Carbon precipitates were found to exist in either a disordered or partially ordered (graphitic) state, depending upon their locations from the SiC reaction interface. The NiAl layer showed dramatic contrast difference compared to the Ni3Al and Ni5.4Al1Si2layers, and was bounded by the Ni3Al/NiAl and NiAl/Ni5.4A1lSi2phase boundaries. The kinetics of the NiAl formation was limited by diffusion, and the growth rate constant was measured to be 2 × 10−10cm2/s. The thickness of the reaction zone on the Ni3Al side was always greater than that on the SiC side, suggesting that the decomposition of the SiC may be a rate limiting step for the SiC/Ni3Al reactions. An Al-rejection model, based on a lower solid solubility of Al in the Ni-Al-Si ternary phase than in the Ni3A1 intermetallic compound, is proposed to explain the formation of NiAl phase. The rate limiting step for the Ni3Al/SiC reactions is discussed in light of discontinuous decomposition of SiC, which leads to the formation of alternating C and Ni(5 4−x)Al1Si2layers in the reaction zone. Preliminary results on C precipitation behavior in NiAl/SiC system are reported.
Microstructure and Mechanical Properties of Ni3Al-Based Alloys Reinforced with Particulates
Authors: Mckamey C. G. , Carmichael C. A. 
Published: March 2011

ABSTRACTHot-extrusion was used to produce Ni3Al-based alloys to which 10 vol% TiN, NbC, HfO2, or HfN was added for reinforcement. The TiN, NbC, and HfO2 particulates produced Ni3Al-matrix composites in which no reaction was noted at the particle-matrix interface. However, the addition of HfN resulted in extensive reaction in which the hafnium appeared to diffuse into the matrix. Microstructures of this alloy showed a complex array of phases and voids where the HfN particles are presumed to have been originally. Hot hardness, compression, and compression creep tests were performed on specimens cut from the extruded bar of each alloy. No significant strengthening was observed for the alloys containing TiN, NbC, or HfO2. However the HfN-containing alloy did show significant strengthening in simple compression and compression creep. This presentation will include microstructures and the results of the mechanical properties tests.
Phase Diagram Relationships in the Ternary System Ti-Ai-V
Authors: Paruchuri Mohan , Massalski T.B. 
Published: March 2011

ABSTRACTLiquid-solid and solid state phase equilibria in the ternary system Ti-Al-V have been studied using a combination of several experimental techniques. A likely surface of primary seperation (i.e., the liquidus surface) is proposed in the form of the usual projection on the triangular base and the directions of the monovariant lines are defined. Four ternary invariant reactions have been identified in this system. Solid state equilibria have been determined at 900°C and are presented in the form of an isothermal section through the phase diagram. These are very similar to the relationships reported at 800°C by Hashimoto et al. [1].
Phase Transformations and Microstructural Development in Tial-Based Alloys
Authors: Beaven P. A. , Pfullmann TH. , Rogalla J. , Wagner R. 
Published: March 2011

ABSTRACTThe main features of the phase transformations occurring in alloys based on Ti-48 at% Al are described in order to assess their roles in microstructural development during thermomechanical processing and subsequent heat treatment. It is shown that the presence of Al-rich interdendritic γ formed during solidification plays a critical role during these processes.
Phase Stability and Solidification Pathways in MoSi2 Based Alloys
Authors: Frankwicz P. S. , Perepezko J. H. 
Published: March 2011

ABSTRACTThe phase equilibria developed upon substitution of Ti in MoSi2 along the pseudobinary MoSi2-TiSi2 section has been investigated using x-ray diffraction, and electron microscopy. The pseudobinary exhibits orthorhombic (C54), hexagonal (C40), and tetragonal (Cllb) crystalline structures. A hexagonal (C40) ternary silicide (Ti1-xMox)Si2 was observed to exhibit a relatively wide range of solubility with x in the range of 0.50 to 0.75, in contrast to MoSi2 which exhibits limited solubility for Ti. An analysis of the microstructural evolution following solidification reveals that the hexagonal β-(Ti,Mo)Si2 phase forms via a peritectic reaction between liquid and MoSi2 (Cllb). The primary dendritic structure during solidification in (Til-xMo2)Si2, where x z 0.80, has been determined to be tetragonal (Cllb) MoSi2. The results of this study confirm that substitutional alloying on the transition metal sublattice (Mo) is an effective approach to control of the phase stability and crystal structure in intersilicide reactions.
Metastable Phase Formation in Be-Nb Intermetallic Compounds
Authors: Brimhall J. L. , Charlot L. A. , Bruemmer S. M. 
Published: March 2011

ABSTRACTAmorphous structures or metastable crystalline phases are produced in sputter deposited Be-Nb alloys (5–15 at.% Nb) depending on the substrate temperature. The metastable phases transform to the stable Be12Nb, Be17Nb2 or Be3Nb phases on annealing at temperatures >800°C. No Be5Nb phase was found and the Be17Nb2 phase is stable to low temperature. The Be12Nb phase appeared to have a stoichiometric range of about 5.5 to 7.7 at.% Nb. The formation of the metastable phases is consistent with current models and theories.
Ab

Initio Calculations of Structural Energetics of Transition-Metal Aluminides and Silicides
Authors: Carlsson A. E. , Meschter P. J. 
Published: March 2011

ABSTRACTTotal energies of binary and ternary -metral trialminides in the L12DO22 Do23Structures and binary Transition- metal disilicides in the C1lb, C40, C54, and C49 structures have been obtained by ab initio band-structure calculations. In aluminides the tetragonal Do22 and Do23 structures are stabilized relative to cubic L12P and in silicides the hexagonal C40 structure is stabilized relative to orthorhombic C54 and tetragonal C11b relative to C40, as the transition-metal d-electron count increases. The observed easier stabilization of L12 in Ti(AI,Fe) 3 relative to Nb(AI,Fe)is justified by the calculations. Location of the Fermi level in a quasigap in the density of states distribution rationalizes the observed structural stabilities in aluminides but not in silicides.
From Dislocation Cores to high Temperature Strain rate Effects in L12 Compounds
Authors: Vitek V. , Sodani Y. , Cserti J. 
Published: March 2011

ABSTRACTIt is now generally accepted that in many L12 compounds the yielding behavior is controlled by the special features of the cores of screw dislocations. In this paper we first summarize results of the atomistic studies of the core structures of the <110> screw dislocations in these compounds. At this point we show that, depending on the atomic bonding, two distinct classes of L12 alloys exist. In the first, represented by alloys like Ni3Al, a glissile configuration of the core exists on {111} planes although a sessile configuration is energetically more favored. In the second class, represented by alloys like Pt3A1 and A13Ti modified by alloying into L12 structure, the cores of screw dislocations are always sessile. Using the results of the atomistic studies we present physical models explaining the temperature dependences of the yield stress in both classes of L12 alloys. At this point we also present a further development of the model for the anomalous temperature dependence of the yield stress in alloys like Ni3A1, originally put forward by Paidar et al. [15]. In this development strain rate effects are included and it is shown that the model explains not only the orientation dependences of the yield stress in the anomalous regime but also the very low strain rate sensitivity observed in this regime.
Dislocation Structures and Anomalous Yielding in Ordered Alloys
Authors: Hazzledine P. M. , Sun Y. Q. 
Published: March 2011

ABSTRACTThe strain, strain rate and temperature dependencies of the yield stresses of the model L12materials Ni3Al, Ni3Ga and Co3Ti are described, as well as two associated properties, the initial work-hardening rate and the inverted creep. These mechanical properties, the electron microscope observations of <110> {111} APB coupled slip and the violations of Schmid's laws point to glissile-sessile-glissile transitions by cross slip of screw dislocations as the explanation for the yield stress anomaly. Similar explanations are probable for h.c.p. Be, B2CoTi and tetragonal TiAl and MoSi2. A different kind of model, based on the behavior of edge dislocations is required for h.c.p. Mg, B2 CuZn and DO19Ti3Al.
Room Temperature Deformation in “Soft” Orientation Nial Single Crystals
Authors: Field R.D. , Lahrman D.F. , Darolia R. 
Published: March 2011

ABSTRACTA detailed study of deformation of NiAl single crystals in two soft orientations, <110> and <111>, has been conducted. The Schmid factor favors {100} slip in the former and {110} slip in the latter. Detailed dislocation analysis, critical resolved shear stress measurements, and slip trace analysis have been performed to determine the nature of dislocation motion and interactions in this material. Particular attention is given to prismatic loops formed during deformation, since the shapes of these loops reveal the active slip planes. Similar loop morphologies observed in elevated temperature [001] oriented tensile specimens are also discussed.
Slip Transition in [001] Oriented Nial at High Temperatures
Authors: Kim J.T. , Gibala R. 
Published: March 2011

ABSTRACTThe present work was undertaken to understand the transition in slip direction In [001] oriented NiAl as a function of temperature. Single crystals of [001] NiAl were deformed at room temperature to produce <111> dislocations and were subsequently annealed at various temperatures in order to see the effect of temperature on the stability of the <111> dislocation. These results were compared with corresponding dislocation substructures of specimens deformed directly at high temperatures. During annealing <111> dislocations are dissociated into <001>+<110> dislocations at 773–923 K. It is also observed that <111> dislocations can be dissociated into <001>+<110> dislocations during deformation in the vicinity of the transition temperature of around 773 K. The quantitative details of these changes depend on deformation or annealing temperatures.
Burgers Vector Transition in Fe-Ai-Ni Alloys
Authors: Patrick D. Keith , Chang Keh-Minn , Miracle Daniel B. , Lipsitt Harry A. 
Published: March 2011

ABSTRACTPolycrystalline NiAl exhibits <001> slip at temperatures below about 450°C. In Fe-Al alloys there is a transition in the Burgers vector from a/2<111> at low temperatures to a<001> at intermediate temperatures. The transition temperature is dependent upon composition.A transition in the Burgers vector from a/2<111> to a<001> has been found to exist as a function of composition and temperature in the B2 pseudo-binary (Fe,Ni)-40Al (at%) system. At room temperature, this transition occurs at a composition between Fe-40Al-10Ni, which exhibits <111> slip, and Fe-40Al-3ONi, which exhibits <001> slip. At 400°C this transition shifts further toward the iron-rich compositions. Fe-40Al-10Ni exhibits both <111> and <001> slip, whereas Fe-40Al-20Ni exhibits <001> slip.
Deformation of the Orthorhombic Phase in Ti-Al-Nb Alloys
Authors: Banerjee D. , Rowe R.G. , Hall E.L. 
Published: March 2011

ABSTRACTThe deformation structure of the alpha-2 and orthorhombic phase in two alloys of the Ti-Al-Nb system has been characterised by transmission electron microscopy after plastic deformation of about 2% in compression at room temperauture. The orthorhombic phase is shown to deform by all slip modes present in the alpha-2 phase. In addition, extensive “c” component slip is observed in the orthorhombic phase on slip planes that are not equivalent to those observed for “c”component slip in alpha-2. Dislocation dissociation on both basal and prismatic planes of dislocations without a c component is observed in both phases.
Dislocation Behaviour in the Octahedral Plane in Ni3Ga Single Crystals
Authors: Couret A. , Sun Y. , Hazzledine P.M. 
Published: March 2011

ABSTRACTWeak beam electron microscopy has been used to study the substructure in octahedral planes in Ni3Ga deformed in the range of the yield stress anomaly. The substructure is formed by screw dislocations in the Kear Wilsdorf configuration, which contain numerous superkinks. A statistical analysis of the superkink height has been performed. The effect of a first high temperature deformation on a second low temperature one has been investigated. The behaviour of the dislocations has been deduced from these experimental results and from those of the literature.