bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solid-State Reactions in Model Oxide Systems
Authors: Johnson Matthew T. , Kotula Paul G. , Thompson Ryan S. , Barry Carter C. 
Published: April 2011

AbstractThe kinetics of thin-film solid-state reactions have been investigated in two model spinel forming oxide systems, NiO/Al2O3 and MgO/Fe2O3. In the NiO/Al2O3 system, thin-films of epitactic NiO were reacted with (0001), , and orientated Al2O3 (corundum). The kinetics of the spinel forming reaction for this system were found to be linear-parabolic in nature. Additionally, it was found that the kinetics of the spinel-forming reaction varied by nearly two orders of magnitude between the fastest and slowest diffusion couples. The substrate determines the orientation of the overlayers and thereby the structure of the phase boundaries. In the MgO/Fe-oxide system, thin films of epitactic Fe oxide were reacted with {001} MgO. The kinetics of this spinel forming reaction were parabolic in nature, indicative of diffusion control. In contrast to the N1O/Al2O3 system, the movement of phase boundaries are not the step controlling the reaction rate, but rather the diffusion of one of the cations across the reaction layer. In comparing the reaction rates for the two systems the activation energy for the formation of the spinel product in the MgO/Fe-oxide system was found to be almost a factor of 4 lower in comparison to the NiO/Al2O3 system.
Quantitative Interfacial Chemistry and Bonding in Ceramic Materials
Authors: Gu Hui 
Published: April 2011

AbstractInternal interfaces, between the same phase (grain boundary) or two different phases, often play an essential role in controlling various properties in ceramic materials. Analysis of such interfaces can achieve various newly available quantitative information on a sub-nanometer scale, as well as bonding picture associated with these interfaces. This analysis combines EELS spectrum profiling and advanced near-edge structure (ELNES) data processing, taking advantage from both the high spatial and energy resolutions provided by a dedicated STEM instrument. Demonstrated by chemical and structural study of gram boundary and inter-phase interfaces in Si3N4 ceramics where ∼1 ran thick amorphous phases cover every crystalline boundaries, it reveals that the amorphous boundary films are substantially different to bulk amorphous phase and to the interface between crystalline and amorphous phases. Moreover, the boundaries between two different crystalline phases were found covered with two thin amorphous layers of different composition and bonding. These observations can shed further light on the influence of interfaces on the macroscopic properties of these ceramic materials. This interfacial analuysis method can be extended to broader research area in solid state physics and chemistry.
Surface Stability of Siderite Under Acidic Atmosphere: an Atomic Force Microscopy Study
Authors: Weaver R. M. , Grandstaff D. E. , Myer G. H. 
Published: April 2011

AbstractThe reactivity of siderite (FeCO3) was investigated under ambient atmosphere and acidic aerosols using an atomic force microscope (AFM). Scans of freshly cleaved siderite crystals showed a relatively irregular microtopography, consisting of high-density kink-steps, compared to other isostructural carbonates (e.g. Iceland-spar calcite). Under ambient conditions siderite is inert with no spontaneous surface reconstruction as is reported for calcite. Under controlled conditions of pH and humidity, siderite was exposed to mists of HC1 and H2CO3 and the reaction was imaged with submicron resolution. The kinetics of the reaction varied with pH, humidity levels, and also as a function of the initial microtopography. Preferential growth and dissolution were observed as a function of initial topography and due to crystallographic anisotropies. Although extreme reaction conditions were excluded by certain aspects of AFM (high capillary forces, tip corrosion, charged surface), this technique has allowed real-time, in situ observations of surface reactions.
Influence of Hydrogen Incorporation and Oxygen Removal on Superconducting YBa2Cu3O7-δ
Authors: Hirata T. 
Published: April 2011

AbstractThe influence of hydrogen incorporation and oxygen removal on superconducting YBa2Cu3O7-δ is discussed in comparison with their respective effects. Both hydrogen incorporation and oxygen removal induce the orthorhombic (O)-to-tetragonal (T) transition and antiferromagnetic ordering as well. However, there exist no consistent changes in the c-axis for the O-to-T transition and the superconducting transition temperature Tc upon hydrogen incorporation in YBa2Cu3O7-δ on the other hand, the c-axis certainly increases in the corresponding transition driven by oxygen nonstoichiometry and Tc decreases with increasing δ in YBa2Cu3O7-δ. Plots of Tc vs. the lattice parameter c reveal no significant suppression in Tc upon hydrogenation than oxygen removal. It is concluded that the Cu-O bond distances or the Cu-Cu plane spacings along the c-axis change somewhat differently in two cases; it is believed that the charge-carrier concentration is reduced less significantly upon hydrogenation than oxygen removal in YBa2Cu3O7-δ, giving rise to the aforementioned finding.
Application of a Knowledge-Based Expert System for Assisting in Catalyst Design
Authors: Körting E. , Baerns M. 
Published: April 2011

ABSTRACTThe prototype expert system ESYCAD (expert system for catalyst design) was set up for assisting in the design of heterogeneous catalysts. It selects materials as catalyst components which have all required properties for the various (elementary) steps of a target reaction but which do not catalyze undesired side reactions. If necessary, also secondary catalytic components or promoters are selected; furthermore, reaction conditions are proposed if required by catalyst properties. The application of the system is illustrated by examples for CO-hydrogenation, alkane dehydrogenation, and for oxidative coupling of methane.
A Micro-Raman Study of Niobium Titanium Oxide Powders Obtained by Laser-Induced Synthesis
Authors: Depero L. E. , Sangaletti L. , Bontempi E. , Salari R. , Casale C. , Musci M. , Notaro M. 
Published: April 2011

ABSTRACTMicroraman and scanning electron microscopy studies have been performed on pure TiO2 and Nb-Ti-O nanopowders obtained by laser induced synthesis. The effect of Nb content on the temperature of the anatase to rutile phase transformation, induced by annealing in air at different temperatures, has been evidenced and related to the changes in the particle size distributions obtained from a Fourier analysis of the X-ray diffraction patterns.
Rapid Thermal Response Catalyst for Treatment of Automotive Exhaust
Authors: Carter Robert N. , Roychoudhury Subir , Muench George , Karim Hasan , Pfefferle William 
Published: April 2011

ABSTRACTTo meet the increasingly strict automobile emissions requirements for conventional vehicles, considerable improvements in catalyst technology are required. It is now recognized that a primary challenge in meeting the ultra-low emissions vehicle standards (ULEV) for automobiles is in reducing cold-start emissions, and this generally requires a catalytic converter that has a rapid temperature response. Conventional converters (typically made from ceramic or metal monoliths) have a relatively slow temperature response due to their high thermal mass and limited heat transfer characteristics. We present details of a novel catalyst technology (Microlith™) that offers considerable advantages for this application because of greatly enhanced heat and mass transfer characteristics. Results of performance tests are also presented that demonstrate this catalyst's effectiveness. The effects of thermal aging on microstructure and catalyst performance are also discussed.
Enhanced Catalytic Performances by Desilication and Subsequent Steam Treatment of ZSM-5 Zeolite
Authors: Le Van Mao R. , Borsuk N. , Ohayon D. , Ramsaran A. , Le S. T. , Denes G. 
Published: April 2011

ABSTRACTControlled desilication of ZSM-5 zeolite increases the acid site density of its acid form. A subsequent treatment with steam at 300 °C results in a material with single-sized and slightly larger micropores when compared to the parent zeolite. This is likely the cause of a second increase of the yields of MTBE (methyl terbutyl ether) and ethylene when the steamed desilicated zeolite is used as catalyst in the MTBE synthesis and ethanol dehydration, respectively. Steam appears to be capable of “healing” the zeolite framework at a temperature much lower than that normally required when the desilicated ZSM-5 zeolite is solely heated in air.
Mesoporous Activated Carbon Filaments
Authors: Lu Weiming , Chung D. D. L. 
Published: April 2011

ABSTRACTActivated carbon filaments of diameter ∼0.1 μm, main pore size (BJH) 55 Å, specific surface area 1310 m2/g and yield 36.2% were obtained by activating carbon filaments of diameter ∼ 0.1 urn in C02 + N2 (1:1) at 970°C for 80 min. Prior to this activation, the filaments were surface oxidized by exposure to ozone.
1/f Dielectric Fluctuations at the Glass Transition
Authors: Israeloff N. E. , Wang W. 
Published: April 2011

AbstractThe temperature and frequency dependence of thermal dielectric polarization noise was investigated in glycerol and PVC in the vicinity of their glass transitions. Polarization fluctuations were observed via voltage noise which was produced within a sample capacitance cell. The high sensitivity and accuracy of the technique provides a powerful probe of dynamics in low-loss regimes of various materials. Noise spectra had 1/fβ form at lower temperatures just below the glass transition. In glycerol, the spectral exponent decreased smoothly with temperature, extrapolating to 1, i.e. 1/f noise, near T° where relaxation times diverge. The results support the idea that a glassy phase transition occurs in the static limit.
Protein Dynamics from Intramolecular Electron Transfer
Authors: Nienhaus G. U. , McMahon B. H. , Müller J. D. , Wraight C. A. 
Published: April 2011

ABSTRACTProteins are complex systems that share essential properties with viscous liquids and polymers. Structure, dynamics, and function of proteins are strongly interrelated, and structural and dynamic aspects can be revealed by studying protein function. Here we report measurements of the kinetics of intramolecular electron transfer (ET) from the primary quinone (QA) to the special pair (P) of reaction center (RC) proteins from Rhodobacter sphaeroides as a function of temperature (5 to 300 K) and illumination protocol (cooled in the dark and under illumination from 280 K). From the data, information about structural heterogeneity, relaxations and fluctuations of these molecules is obtained.
Intermediate Range Order in Sodium Tellurite Glasses
Authors: Zwanziger J. W. , McLaughlin J. C. , Tagg S. L. 
Published: April 2011

ABSTRACTInformation about the spatial distribution of sodium cations in sodium tellurite glasses is obtained from the decay rate of sodium spin echoes. The spin echoes decay due to the magnetic dipole coupling between sodium nuclei, with each pair contributing to the rate in proportion to 1/r6, where r is the distance between the pair. The experiment is used to probe the sodium distributions in sodium tellurite glasses as a function of sodium oxide content, and the resulting distance distributions are interpreted by comparison with model distributions. At low sodium contents the distribution is similar to that of a random model in which the sodium ions are constrained to be no closer than a minimum cut-off distance. At higher contents the distributions deviate significantly from the random model, suggesting the onset of medium range order in the distribution of sodium ions. This order is most pronounced at 20% sodium oxide content, the composition at which this glass has been claimed to have maximum stability against devitrification.
Effect of Size Dispersity on the Melting Transition
Authors: Sadr-Lahijany M. R. , Ray P. , Harrington S. T. , Stanley H. E. 
Published: April 2011

ABSTRACTWe present a molecular dynamics simulation study of the liquid-solid transition in a two dimensional system consisting of particles of two different sizes interacting via a truncated Lennard-Jones potential. We work with equal number of particles of each kind and the dispersity Δ in the sizes of the particles is varied by changing the ratio of the particle sizes only. For the monodisperse case (Δ = 0) and for small values of Δ, we find a first order liquid-solid transition on increasing the volume fraction p of the particles. As we increase Δ, the first-order transition coexistence region weakens gradually and completely disappears at high dispersities around Δ = 0.10. At these values of dispersity the high density phase lacks long range translational order but possesses orientational order with a large but finite correlation length. The consequences of this effect of dispersity on the glass transition and on the melting transition in general are discussed.
Liquid-Liquid Phase Separation of Melts and Glasses in Ferric Ferrous Oxide-Silica System
Authors: Yasumori A. , Koike A. , Kameshima Y. , Okada K. , Yano T. , Yamane M. , Inoue S. 
Published: April 2011

ABSTRACTThe existence of liquid-liquid miscibility gap in ferric ferrous oxide-silica system has been reported, however, the phase separation phenomena and the derived morphology of the phase separated glasses are uncertain. In this study, the melt-quenched samples of 5 Fe3O4-95 SiO2 and 15 Fe3O4-85 SiO2 (mol%) were prepared by melting at 2300°C or 2200°C (expected to be above miscibility gap), and subsequently at 1800°C or 1750°C (in immiscible region) by use of infrared image furnace and quenching at the rate of ≈102 K/sec. The glassy materials exhibited phase separation having discrete spherical particles or interconnected structure due to the composition, melting temperature and time. Also, the segregation of Fe component occurred during melting, which was caused by the difference of specific gravity of components in the melt.
Formation and Properties of Amorphous and Nanocrystalline Phases in Mechanically Alloyed Fe-Based Multicomponent Alloys
Authors: Schlorke N. , Eckert J. , Schultz L. 
Published: April 2011

ABSTRACTMulticomponent Fe-Al-P-C-B alloys have been prepared by mechanical alloying of elemental powder mixtures. X-ray diffraction data were recorded to monitor the structural development of the powders. Coexistent amorphous and nanoscale crystalline phases are found for a variety of alloys. Some alloys exhibit an extended supercooled liquid region before crystallization. The compositional dependence of glass formation and the thermal stability of the resulting phases were investigated by constant-rate heating differential scanning calorimetry (DSC), isothermal annealing experiments, and thermomechanical analysis (TMA). The results are compared with data for melt-spun ribbons.
Tendency and Scale of Chemistry and Bonding Changes at SrTiO3 Grain Boundaries by Fe Segregation
Authors: Gu Hui 
Published: April 2011

ABSTRACTUsing a new EELS analysis method the local chemical and structural changes induced by Fe segregation to two types of grain boundaries in SrTiO3 were studied. At Σ5 boundary in bicrystals Fe segregation lowers O/Ti ratio but increases substantially Ti and O concentrations in boundary region. Sr-O bond has been severely changed by the segregation as revealed by ELNES. Grain boundaries in a polycrystalline sample were covered with titania-based amorphous films where Fe content is higher but Ti and O concentrations are both lower than the bulk levels, which are strikingly different from the bicrtysal. More dopants segregated to glass pockets at triple junctions. SiO2 was detected in one of the large pocket but not at the grain boundary films within the detection limit. These observations suggest the equilibrium defect chemistry and the related space charge theory may not be the only explanation for the grain boundary segregation in SrTiO3 Local structure modification at gram boundaries can trigger dramatical change of the chemistry to a degree higher than the segregation level. The existence of titania-based amorphous films at general grain boundaries makes it better to understand Fe segregation from the two phase (SrTiO3-TiO2) equilibrium.
The Adhesion Nature of Ag/MgO Interface: Hartree-Fock Study
Authors: Heifets E. , Kotomin E. A. 
Published: April 2011

AbstractThe atomic and electronic structure of the Ag/MgO interface are calculated using the ab initio Hartree-Fock approach and a supercell model. The electronic density distribution is analyzed in detail for isolated and interacting slabs of a metal and MgO. The energetically most favorable adsorption position for Ag atoms is found to be above the O atoms. The binding energy is 0.20 eV (0.41 eV) for one and three Ag layers atop MgO substrate, respectively. The relevant equilibrium Ag-O distance is 2.64 Å(2.41 Å). Neither appreciable charge transfer in the interfacial region, nor considerable population of bonds between the silver layer and the insulating substrate take place. The adhesion energy arises mainly due to the electrostatic interaction of substrate atoms with a complicated charge redistribution in the metal monolayer, characterized by large quadrupole moments and electron density redistribution towards gap position in the middle of nearest Ag atoms.
Analysis of Adhesion and Interface Debonding in Laminated Safety Glass
Authors: Sha Y. , Hui C. Y. , Kramer E. J. , Garrett P. D. , Knapczyk J. W. 
Published: April 2011

AbstractA tension adhesion test is developed to measure the adhesion of a polymer interlayer to the glass plates in laminated glass. The polymer adhesive is bonded between two cracked glass plates and is loaded under a remote tension P. Typically, a peak load P* exists and its value depends on the adhesion between the polymer interlayer and the glass. The peak load P* is often used to characterize the adhesion strength of the interface. The experimental data is analyzed using a micromechanical model of debonding and simulated using finite element computation. Our analysis allow us to determine the shear and normal strength of the interface and the relation between the peak load and the mechanism of debonding.
Wheel Abrasion Experiment Metals Selection for Mars Pathfinder Mission
Authors: Hepp Aloysius F. , Fatemi Navid S. , Wilt David M. , Ferguson Dale C. , Hoffman Richard W. , Hill Maria M. , Kaloyeros Alain E. 
Published: April 2011

ABSTRACTA series of metals was examined for suitability for the Wheel Abrasion Experiment, one of ten microrover experiments of the Mars Pathfinder Mission. The seven candidate metals were: Ag, Al, Au, Cu, Ni, Pt, and W. Thin films of candidate metals from 0.1 to 1.0 micrometer thick were deposited on black anodized aluminum coupons by e-beam and resistive evaporation and chemical vapor deposition. Optical, corrosion, abrasion, and adhesion criteria were used to select Al, Ni, and Pt. A description is given of the deposition and testing of thin films, followed by a presentation of experimental data and a brief discussion of follow-on testing and flight qualification.
Grain Boundary Engineered Lead Alloys
Authors: Lehockey E. M. , Palumbo G. , Brennenstuhl A. , Lin P. 
Published: April 2011

ABSTRACTThe present work reports oii the effect of grain boundary structure on intergranular corrosion and creep by grain boundary diffusion in polycrystalline lead (Pb). “Special” boundaries characterized by low-Σ misorientations in the Coincident Site Lattice (CSL) model have been shown to exhibit resistance to grain boundary sliding and corrosion. PbCa and PbCaSn alloys having “special” grain boundary frequencies greater than 50% showed a 30 fold reduction in steady-state creep compared with corresponding as-received alloys containing 10% to 28% of low-Σ CSL boundaries in the microstructure of comparable grain size. At the same time, increasing the frequency of “special” boundaries enhanced alloy ductility with no compromize in tensile strength. Results from electrochemical corrosion tests on polarizied Pb alloys immersed in H2SO4 (S.G.=1.28) at 70°C indicate a clear correlation between the frequency of “special” boundaries and the prolifíeration of intergranular corrosion resulting in bulk weight loss from grain-dropping. Collectively, these results advocate adopting a “gram boundary design” approach in developing advanced lead-acid battery electrodes.
Theoretical Calculations of Elastic Properties of Metallic Superlattices
Authors: Yamaguchi Akira , Nakajima Hideo 
Published: April 2011

ABSTRACTElastic constants of metallic multilayered film have been calculated using MEAM (Modified Embedded Atom Method) potential. Structural relaxation has been performed to obtain relaxed model structure of (111) stacked multilayers which consist of two fee metal elements. The composition modulation wavelength dependence of elastic constants was found to be large, and we could not observe any large enhancement of elastic modulus in the calculated systems.
Bicrystals with Strain Gradient Effects
Authors: Shu John Y. , Fleck Norman A. , King Wayne E. 
Published: April 2011

ABSTRACTThe boundary between two perfectly bonded single crystals plays a very important role in determining the deformation of the bicrystal. This work addresses the role of the grain boundary by considering the elevated hardening of a slip system due to a slip gradient. The slip gradients are associated with geometrically necessary dislocations and their effects become pronounced when a representative length scale of the deformation field is comparable to the dominant microstructural length scale of a material. A new rate-dependent crystal plasticity theory is presented and has been implemented within the finite element method framework. A planar bicrystal under uniform in-plane loading is studied using the new crystal theory. The strain is found to be continuous but non-uniform within a boundary layer around the interface. The lattice rotation is also non-uniform within the boundary layer. The width of the layer is determined by the misorientation of the grains, the hardening behavior of slip systems, and most importantly by the characteristic material length scales. The overall yield strength of the bicrystal is also obtained. A significant grain-size dependence of the yield strength, the Hall-Petch effect, is predicted.
Interfaces Studied by Electromechanical Pull-Out Testing
Authors: Fu Xuli , Chung D. D. L. 
Published: April 2011

ABSTRACTThe experimental technique of electromechanical pull-out testing is introduced to study the interface between fiber and matrix. The technique involves measuring both the contact electrical resistivity and the shear bond strength of a fiber-matrix interface. Samples that are identically prepared differ in contact resistivity and bond strength, which correlate. The correlation allows determination of even small differences in bond strength due to differences in sample preparation conditions. It also gives information on the structure of the interface and allows the bond strength to be nondestructively determined by measuring the contact resistivity. The technique is demonstrated for the interface between steel fiber and cement.