bluuebunny/crossref_metadata_2025_split huggingface dataset:
RBS and micro-PIXE study of I and Cs Heterogeneous Retention on Concrete
Authors: Alonso Ursula , Missana Tiziana , García-Gutiérrez Miguel , Patelli Alessandro , Ceccato Daniele , Rigato Valentino , Albarran Nairoby , Rojo Henar , Lopez Trinidad 
Published: February 2009

AbstractA combination of two nuclear ion beam techniques, Rutherford Backscattering Spectrometry (RBS) and micro-Particle Induced X-Ray Emission (uPIXE) was tested to evaluate both diffusion profiles and radionuclide spatial distribution of radionuclides (RN) onto cement-based materials. The methodology was tested on a Spanish reference backfill concrete, used as engineering barrier in low-level radioactive waste repositories, using two elements (Cs and I) with different sorption behaviour onto the cement. The applicability and limitations of the selected methodology is discussed for both elements.
Conduction and Disorder in Y3NbO7 - Zr2Y2O7
Authors: Marrocchelli Dario , Madden Paul A. , Norberg Stefan T. , Hull Stephen 
Published: February 2009

AbstractThe construction of interaction potentials for the Y0.5+0.25xNb0.25xZr0.5–0.5xO1.75 system, on a purely ab-initio basis, is described. These potentials accurately reproduce experimental data on both the structure and the dynamics of these systems; the computer simulations also reproduce the experimental trend of the conductivity, which decreases as x increases, and of the level of static disorder within the O2− sublattice, which increases with x. A detailed analysis of these phenomena shows that the static disorder in Y3NbO7 is caused by the high Nb5+ charge and that in this material the conduction is heterogeneous, i.e. some anions are completely immobile while some others are very mobile. The role of the cation sublattice is explained in detail.
Structure and Electrochemistry of Carbon-Bromine Nanocomposite Electrodes for Electrochemical Energy Storage
Authors: Barpanda Prabeer , Amatucci Glenn G 
Published: February 2009

ABSTRACTActivated carbons have been mechanochemically modified by bromine incorporation through high-energy milling route. Varying the milling duration and bromine content, carbon-bromine nanocomposites of different compositions were fabricated. The highly reactive and electronegative bromine reacts with host carbon, which can modify its characteristic properties. We have examined the effect of bromination on the structure, chemistry, morphology and electrochemical properties of a mesoporous activated carbon. Bromination leads to possible charge transfer reaction, structural disordering with polybromide formation. Consequently, the non-faradaic capacitance improves and a faradaic pseudocapacitive reaction occurs at 3.1 V and a more traditional bromine reduction at 3.5V. The formation of carbon-bromine nanocomposites was found to deliver improved gravimetric and volumetric capacity. The effect of bromination on physical and electrochemical properties of activated carbons have been presented and contrasted to that of iodine incorporation.
PtRu Nanoparticle Catalytic Activity Enhanced by the Ligand Effect
Authors: Goto Shuji , Li Yuli , Nagasawa Naomi , Senoo Tadashi , Noda Kazuhiro , Kudo Yoshihiro , Maesaka Akihiro , Hatazawa Tsuyonobu 
Published: February 2009

ABSTRACTWe synthesized a methanol electrocatalyst with high activity and low noble metal content. The electrocatalyst consists of carbon&supported PtRu nanoparticles, which have 1-2 Pt monoatomic layers on Ru nanocores. In spite of the pure Pt surface, the catalyst showed high catalytic activity when used in the anode of a direct methanol fuel cell. Clearly the underlying Ru atoms modified the property of the surface Pt atoms, bringing about the high catalytic activity.
Metallographic and numerical characterization of MgH2-Mg system
Authors: Aurora Annalisa , Celino Massimo , Cleri Fabrizio , Gattia Daniele Mirabile , Giusepponi Simone , Montone Amelia , Antisari Marco Vittori 
Published: February 2009

ABSTRACTThe remarkable ability of magnesium to store significant quantities of hydrogen has fostered intense research efforts in the last years in view of its future applications where light and safe hydrogen-storage media are needed. Magnesium material, characterized by light weight and low cost of production, can reversibly store about 7.7 wt% hydrogen. However, further research is needed since Mg has a high operation temperature and slow absorption kinetics that prevent the use in practical applications. For these reasons a detailed study of the interface between Mg and MgH2 is needed. Further insights are gained by characterizing the Mg-MgH2 system from both the experimental and the numerical point of view.The study of the MgH2-Mg phase transformation in powder samples has been performed to gain detailed metallographic information. A method for studying this phase transformation by cross sectional samples scanning electron microscopy observation of partially transformed material has been developed. This method exploits the peculiar features of this system where the MgH2 phase is insulating and the Mg is a metallic conducting phase. This difference can induce a contrast between the two phases owing to the different secondary emission yield. Further insights are gained by characterizing Mg-MgH2 interfaces by means of accurate first-principle molecular dynamics simulations based on the density-functional theory. Extensive electronic structure calculations are used to characterize the equilibrium properties and the behavior of the surfaces in terms of total energy considerations and atomic diffusion.
Phase Stability and Thermoelectric Properties of Half-Heusler (Ma, Mb)NiSn (Ma, Mb = Hf, Zr, Ti)
Authors: Kimura Yoshisato , Ueno Hazuki , Kenjo Takahiro , Asami Chihiro , Mishima Yoshinao 
Published: February 2009

AbstractAiming to improve thermoelectric properties of half-Heusler (Ma,Mb)NiSn alloys (Ma,Mb = Hf, Zr, Ti), phase equilibria in the (Ma,Mb)NiSn systems were investigated focusing on the phase separation of TiNiSn from ZrNiSn and HfNiSn while (Zr,Hf)NiSn forms all proportion miscible solid solution. Diffusion couples consisting of liquid Sn and solid (Ti,Zr)Ni were used to examine the partitioning behavior which is associated with T-rich and Ti-poor half-Heusler phase separation during the reaction at the interface. Thermal conductivity can be reduced in (Ma0.5,Mb0.5)NiSn and (Ti0.13,Zr0.87)NiSn alloys due to the solid solution effect of M-site substitution. (Ti0.13,Zr0.87)NiSn alloy has high potential as a ecological thermoelectric material.
Microstructure and Tensile Ductility of a Ti-43Al-4Nb-1Mo-0.1B Alloy
Authors: Droessler Laura M. , Schmoelzer Thomas , Wallgram Wilfried , Cha Limei , Das Gopal , Clemens Helmut 
Published: February 2009

AbstractThe microstructural development of a forged Ti-43Al-4Nb-1Mo-0.1B (in at%) alloy during two-step heat-treatments was investigated and its impact on the tensile ductility at room temperature was analyzed. The investigated material, a so-called TNM™gamma alloy, solidifies via the β-route, exhibits an adjustable β/B2-phase volume fraction and can be forged under near conventional conditions. Post-forging heat-treatments can be applied to achieve moderate to near zero volume fractions of β/B2-phase allowing for a controlled adjustment of the mechanical properties. The first step of the heat-treatment minimizes the β/B2-phase and adjusts the size of the α-grains, which are a precursor to the lamellar γ/α2-colonies. However, due to air cooling after the first annealing step, the resulting microstructure is far from thermodynamic equilibrium. Therefore, a second heat-treatment step is conducted below the eutectoid temperature which brings the microstructural constituents closer to thermodynamic equilibrium. It was found that temperature and duration of the second heat-treatment step critically affect the solid-state phase transformations and, thus, control the plastic fracture strain at room temperature. Scanning and transmission electron microscopy studies as well as hardness tests have been conducted to characterize the multi-phase microstructure and to study its correlation to the observed room temperature ductility.
Initial Stages of Lamellae Formation in High Nb Containing γ-TiAl Based Alloys
Authors: Cha Limei , Scheu Christina , Dehm Gerhard , Schnitzer Ronald , Clemens Helmut 
Published: February 2009

AbstractIn this study a two-step heat treatment was applied to high Nb containing γ-TiAl based alloys in order to investigate the initial stage of the lamellae formation in ordered α2-grains as well as in massively transformed γm-grains. The first heat treatment step, conducted in the single α-phase field followed by oil quenching, leads to a microstructure consisting of supersaturated α2-grains and a small volume fraction of γm-grains. The second step of the heat treatment was performed below the eutectoid temperature, i.e. within the (α2+γ)-phase field region and was again followed by oil quenching. There, the formation of ultra-fine γ-lamellae takes place in the α2-grains and (some) fine α2-lamellae are formed in the γm-grains. In both cases the lamellae show a Blackburn orientation relationship with the matrix grain. It was found that the precipitation of γ-laths in the supersaturated α2-grains is faster than the formation of α2-laths in γm-grains. The characteristics of the initial stage of formation were investigated by transmission electron microscopy.
The Role of Fundamental Material Parameters for the Fluorine Effect in the Oxidation Protection of Titanium Aluminides
Authors: Zschau Hans-Eberhard , Schütze Michael 
Published: February 2009

AbstractTo improve the insufficient oxidation resistance of Titanium Aluminides at temperatures above 750°C the fluorine effect offers an innovative way. The focus of this paper is to define the fundamental material variables for the fluorine effect related to the macroscopic behaviour (oxidation resistance) and its long time stability.
The thermodynamic model predicted the fluorine effect for the TiAl within a corridor of total fluorine amount in terms of partial pressures. To realize the fluorine effect the required F-concentration [in at.-%] within the near surface region had to be found. Using fluorine ion implantation several fluences within 5e15 and 5e17 F cm-2 were implanted with an energy of 20 keV. The implantation depth profiles were calculated by using the Monte Carlo simulation code T-DYN and verified experimentally by using the non-destructive PIGE - technique (Proton Induced Gamma-ray Emission). After oxidation tests at 800°C – 1000°C a value of 2e17 F cm-2 / 20 keV was determined as an optimal implantation parameter set. Following these results the maximal fluorine concentration was identified to be a fundamental material variable for starting the alumina formation with a required fluorine amount of about 40-45 at.-%. However this maximum fluorine concentration showed a rapid decrease to values less than 5 at.-% only after a few hours of oxidation (900°C and 1000°C) followed by a slow decrease. Therefore the maximum fluorine concentration Cmax – now located at the metal/oxide – interface – was identified to be a fundamental parameter for the long time stability. An exponential decay function containing a constant term of about 1 at.-% was found to describe the time behaviour of Cmax for isothermal and cyclic oxidation (900°C, 1000°C). Because the alumina scale on the surface acts as a diffusion barrier for fluorine, the stability of Cmax is strongly influenced by the F-diffusion into the metal. From the F-depth profiles the diffusion coefficient of fluorine into the TiAl at 900°C was determined as a fundamental parameter for the long-term stability of Cmax showing a value of 1.56e-15cm2/s.
Microstructure and Compression Behavior of Ti3Al Based Ti-Al-V Ternary Alloys
Authors: Takahashi Tohru , Kiyohara Ayumu , Masujima Daisuke , Nagakita Jun 
Published: February 2009

AbstractThe ordered alloy phase of Ti3Al shows a rather wide solid solution range in aluminum and also in vanadium. Several Ti-Al-V ternary alloys have been prepared to investigate the alloy composition effect upon microstructure, crystallography, and mechanical characteristics. The materials containing 75, 70, and 65 at.% titanium, and 0 or 5 at.% vanadium were prepared by arc melting. Metallographic observation has revealed that the binary Ti-Al alloys contained somewhat coarse grains with about 100 μm grain diameter. In contrast to this, ternary alloys containing 5 at.% vanadium showed smaller grained microstructures with grain diameters around 15 μm. The grain size could not be adjusted to a unified value in the present study. X-ray diffraction study and microanalysis showed that the alloys contained single phase α2. Not every possible diffraction peak of the D019 ordered structure has been observed in the XRD patterns. The lattice parameters, a and c, were observed to decrease as the aluminum content increased and also when vanadium was added. Compression tests have been performed at various temperature ranging from an ambient temperature up to 1300K on rectangular parallelepiped specimens with 2mm×2mm×3mm dimensions. Alloys containing more aluminum showed higher strength, and vanadium addition enhanced the strength of the alloys. In some alloys deformability and strength are both enhanced by vanadium addition in some alloys. Temperature dependence of strength showed a little variation upon chemical compositions.
Plasma-Assisted Surface Modification of Two-Phase Intermetallic Alloy Composed of Ni3X Type Structures
Authors: Kaneno Yasuyuki , Matsumoto Naoki , Tsuji Noriyoshi , Tanaka Shinichi , Takasugi Takayuki 
Published: February 2009

AbstractA two-phase intermetallic alloy composed of Ni3Al (L12) and Ni3V (D022) was plasma-nitrided or -carburized in dependence of temperature and time. It was found that the hardness of the surface layer of the present intermetallic alloy was enhanced by both plasma-nitriding (PN) and -carburizing (PC), and primarily depended on treating temperature; the maximum surface hardness of the alloy was shown by nitriding at around 850 K and by carburizing at 1025 K. In addition, the hardened layers due to PN and PC effectively kept their hardness up to a high temperature. The XRD analysis revealed that vanadium nitride (VN) and vanadium carbide (VC) were formed in the surface of the nitrided and carburized alloy, respectively, suggesting that the enhanced surface hardness was attributed to the dispersion hardening due to the nitrides and carbides.
Surface modification of Ni/Ni3Al two-phase foils by electrochemically selective etching
Authors: Lee H.Y. , Demura M. , Xu Y. , Wee D.M. , Hirano T. 
Published: February 2009

AbstractSurface morphology after the selective etching of the γ matrix was examined in Ni(γ)/Ni3Al(γ´) two-phase foils with various microstructures controlled by the 98 % cold rolling and subsequent heat treatment at 873, 1073 and 1273 K for 0.5 h. In the cold-rolled state, the elongated pancakeshape γ´ precipitates were distributed in the γ matrix, and this structure was almost the same after the heat treatment at 873 K though the recrystallization partly started. These γ´ pancakes were partitioned into the fine blocky particles of 10~100 nm in the edge after the heat treatment at 1073 K and the γ´ blocks significantly became larger at 1273 K. These foils were electrochemically etched in the electrolyte of distilled water with 1 wt.% (NH4)2SO4 and 1 wt.% citric acid at a constant potential of 1.75 V for 5 h. In this etching, the γ matrix was selectively dissolved and the γ´ precipitates were left behind, yielding rough and irregular surface. The surface morphologies corresponded to the γ/γ´ two-phase structures, thus demonstrating that the two-phase structure can be used as a template to make the surface area larger. The foil heattreated at 1073 K had a number of the fine γ´ particles with 10~100 nm in size densely dispersed on the surface. Such fine surface structure was expected to improve the catalytic activity of Ni3Al for the hydrogen production reaction.
Electron Irradiation Induced Crystal-to-Amorphous-to-Crystal (C-A-C) Transition in Intermetallic Compounds
Authors: Nagase Takeshi , Takizawa Kazuya , Nino Akihiro , Umakoshi Yukichi 
Published: February 2009

AbstractMechanical atomic displacement in intermetallic compounds can be introduced by var-ious processes such as severe plastic deformation, mechanical milling and electron irradiation, resulting in the crystal-to-amorphous (C-A) transition and amorphous-to-crystal (A-C) transition in some alloy systems. Recently, unique atomic displacement-induced-phase transitions contain-ing both amorphization and crystallization was found: a crystal-to-amorphous-to-crystal (C-A-C) transition under electron irradiation and a cyclic C-A transition during mechanical milling. The features and predicting factors of alloy systems which undergo C-A-C transition under MeV electron irradiation are discussed based upon the analysis of experimental data reported to date in intermetallic compounds irradiated by High voltage electron microscope (HVEM).
An Intermetallic Precipitate Strengthened Materials for Cryogenic Applications
Authors: Han Ke , Xin Yan , Walsh Robert P. 
Published: February 2009

AbstractIn high field magnets, most of the structural materials operate at very low temperatures (e.g. 1.8 K) and high magnetic fields (e.g. >20 T). Such an extreme environments ask for demanding properties from the materials. Austenite stainless steels have been used for such an application for decades and provide good combination of mechanical strength and toughness at cryogenic temperatures. In the National High Magnetic Field Laboratory, we have studied intermetallic precipitate strengthened alloys for high field magnet and cryogenic applications. An examination of the data from an intermetallic precipitate strengthened alloys shows that intermetallic precipitate strengthened alloys can be used at cryogenic temperatures and have some superior properties in extreme environments. Based on our experimental data, we developed a new alloy that has even better properties than the current intermetallic precipitate strengthened alloys.
Pseudo Fine Particle Effect on Unstable Phase Transition of Gd2Al
Authors: Yazdani A. , Kamali Sarvestani N. , Osaty Araghi R. 
Published: February 2009

AbstractThe unusual duality of magnetic phase transition (especially high transition temperature, remarkable shoulder) is thought to be due to second phase impurities of pure Gd or Gd3Al2 or even both. The temperature dependence and field dependence of magnetization have been studied in the temperature range of 4.2-350 K in three different strengths of magnetic field to investigate the cause or/and the source of metamagnetic character which is a puzzle on Gdintermetallic compounds, IMC, in order to find the critical field needed to overcome the fluctuation field, above which the magnetic behavior of the system is stabilized, and a critical turning field is defined.However for the clearance of intrinsic instability behavior and the nature (and source) of anisotropy in the Gd2Al system, the following experimental works has been prepared.The study of the effect of increasing the magnetic field up to the critical “threshold“ field which is exactly the same as decreasing the conduction electron concentration “c.e.c” from Gd2Al to Gd2Au; The contribution of short range order as well as thermal fluctuation of short range exchange “Jsh” through the long – range interaction “Jl” which can be induced by localized s-f (or d-f) exchange. This effect can be the cause (or the source) of internal magnetic field Hin=<Si.Sj> and fluctuation field Hf=Hin-Hext.
Stacking Faults and Dislocation Dissociation in MoSi2
Authors: Cak Miroslav , Sob Mojmir , Paidar Vaclav , Vitek Vaclav 
Published: February 2009

AbstractThe intermetallic compound MoSi2 crystallises in the body-centred-tetragonal C11b structure and while it is brittle when loaded in tension, it deforms plastically in compression even at and below the room temperature. The ductility of MoSi2 is controlled by the mobility of 1/2〈331] dislocations on {013) planes but the critical resolved shear stress for this slip system depends strongly on the orientation of loading and it is the highest for compression along the 〈001] axis. Such deformation behaviour suggests that the dislocation core is controlling the slip on the {013)〈331] system. Since the most important core effect is dissociation into partial dislocations connected by metastable stacking faults the first goal of this paper is to ascertain such faults. This is done by employing the concept of the γ-surface. The γ-surfaces have been calculated for the (013) and (110) planes using a method based on the density functional theory. While there is only one possible stacking fault on the (110) plane, three distinct stacking faults have been found on the (013) plane. This leads to a variety of possible dislocation splittings and the energetics of these dissociations has been studied by employing the anisotropic elastic theory of dislocations. The most important finding is the non-planar dissociation of the 1/2〈331] screw dislocation that is favoured over the planar splittings and may be responsible for the orientation dependence of the critical resolved shear stress for the {013)〈331] slip system.
Chemical Bonding in Laves Phases Revisited: Atom Volumina in Cs-K System
Authors: Grin Yuri , Simon Arndt , Ormeci Alim 
Published: February 2009

AbstractLaves phases comprise a large group of intermetallic compounds with general composition AB2 and multi-component derivatives. The crystal structures of Laves phases are often regarded as closest packing of spheres. This observation, beginning with very early work on Laves phases, has led many researchers over the years, to emphasize the role of geometrical factors in the formation of Laves phases. In order to develop a firm understanding of chemical bonding in Laves phases and assess the importance of geometrical factors, we undertake a first-principles-electronic structure-based chemical bonding analysis for several representatives. As a first step towards this goal we concentrate on the K-Cs system which contains the Laves phase CsK2 and the hexagonal Cs6K7 compounds. In such alkali-metal-only compounds it is generally expected that chemical bonding effects are minimal. Atom volumina and charge transfer investigations reported here, however, suggest that even in alkali metal-alkali metal Laves phases chemical bonding plays a non-negligible role.
An In-situ Electron Microscopy Study of Microstructural Evolution in a Co-NbCo2Binary Alloy
Authors: Kumar Sharvan , Jain Padam , Kim Seong Woong , Stein Frank , Palm Martin 
Published: February 2009

AbstractThe microstructure in a Co-rich, Co-15 at.% Nb alloy was characterized in the as-cast condition. A predominantly lamellar eutectic morphology composed of a Co-Nb solid solution and the C15 Laves phase NbCo2was confirmed by transmission electron microscopy. The C15 phase was heavily twinned, with only one variant of twins being present in the individual lamella, while the Co solid solution had the face centered cubic structure. In-situ heating to 600°C in the microscope confirmed the decomposition of the metastable Laves phase into a fine equiaxed, ˜10-20 nm grain size microstructure, and the product phase is the monoclinic Nb2Co7. The individual grains appear faulted. The matrix solid solution retained the fcc structure and no change in structure was observed on cooling to room temperature. Heating to temperatures as high as 1130°C leads to rapid grain growth in the Nb2Co7phase, and the nucleation and growth of a few new grains within the original grains; however, the reverse peritectoid transformation previously reported, was not observed.