bluuebunny/crossref_metadata_2025_split huggingface dataset:
Catalytic Properties of Vanadium Nitride and the Effect of Preparative Parameters on its Microstructure
Authors: Kwon Heock-Hoi , Thompson Levi T. 
Published: April 2011

AbstractIn this paper we describe the synthesis, morphologies, and catalytic properties of vanadium nitrides prepared via the temperature programmed reaction (TPR) of V2O5 (7 m2/gr) with ammonia. This reaction yielded VN with surface areas up to 60 m2/gr. Among the synthesis parameters, the molar hourly space velocity had the most significant influence on the BET surface areas, crystallite sizes, and pore size distributions. Thermal gravimetric analysis (TGA) and x-ray diffraction indicated that the solid state reaction of V2O5 with NH3 occurred as follows: V2O5 → V4O9 → VO2 → V2O3 → VO0.9 → V.N. Scanning electron microscopy revealed that the surface roughness increased as the transformation proceeded, which corresponds to the increase in surface area. The vanadium nitrides were exceptionally active for the dehydrogenation of butane with selectivities greater than 98 % to C4 olefins. The deactivation was very slow for these catalysts. The reaction rates increased with increasing surface area and were comparable to that of a commercial Pt-Sn/Al2O3 dehydrogenation catalyst.
Preparation of Ti/B Binary Oxides by Sol-Gel Method and Their Photocatalytic Activity for Stoichiometric H2O Decomposition
Authors: Moon S. C. , Tabata S. , Okada K. , Fujiki M. , Mametsuka H. 
Published: April 2011

ABSTRACTA titanium-boron binary oxide has been prepared by the sol-gel method and characterized using SEM, TEM, UV-VIS reflectance, and X-ray diffraction spectroscopies. These measurements indicated that the obtained Ti/B gel with no treatment exhibited an amorphous structure. After calcination in O2, the crystalline structure of titanium oxide species in the Ti/B binary oxide was changed while boron oxide species maintained in the state of amorphous. Titanium oxide species in the Ti/B binary oxide calcined at 673 K showed an anatase phase of TiO2, and changed with the calcination temperatures from anatase phase to rutile phase. The Pt loaded Ti/B photocatalysts in aqueous suspension system decomposed water stoichiometrically under UV-irradiation. Their photocatalytic activities decreased with increasing the calcination temperature, indicating the photocatalytic activities of the Ti/B binary oxides were depended on the crystal phase of titanium oxide in the Ti/B photocatalysts.
A Model for Relaxation in Supercooled Liquids and Polymer Melts
Authors: Pakula T. , Teichmann J. 
Published: April 2011

ABSTRACTA new model for molecular rearrangements in liquids is proposed. The liquids are regarded as dense ensembles of vibrating molecules satisfying the excluded volume condition. A continuity condition is applied on the molecular scale of such systems and is regarded as controlling rearrangements leading to translations of molecules beyond the range of their vibration amplitude. It results in cooperative rearrangements which are considered as taking place in systems with fluctuating density. Rates of rearrangements are considered as being controlled by thermal activation with activation energy barriers dependent on local density. Various dependencies of the activation energy barriers on local density are examined. It is shown, that the model is able to reproduce the extremal cases of temperature dependencies of relaxation times represented on one edge by the Arrhenius relation and on the other edge by the Vogel-Fulcher-Tamman relation. The model can, however, provide a broad spectrum of other dependencies filling the gap between these extremes. All cases are based on the uniform microscopic picture of cooperative molecular rearrangements resulting from system continuity. The model is implemented as a simulation algorithm (Dynamic Lattice Liquid - DLL algorithm) which is used to simulate dynamic properties of liquids and polymer melts. Simulation results obtained for polymers are compared with experimental results obtained by means of the dynamic mechanical measurements on polyisobutylene samples with various molecular weights.
Glassy and Crystalline States in a Model without Disorder: Spin Analog of a Structural Glass
Authors: Gu Lei , Chakraborty Bulbul 
Published: April 2011

ABSTRACTWe have analyzed a non-randomly frustrated spin model which exhibits behavior remarkably similar to the phenomenology of structural glasses. The high-temperature disordered phase undergoes a strong first-order transition to a long-range ordered structure. Using Monte Carlo simulations, we have studied the behavior of the supercooled state by quenching to temperatures below this transition temperature. For a range of supercooling, the system remains ergodic and exhibits dynamics characteristic of supercooled liquids. Below a certain characteristic temperature, however, the system freezes into a “glassy” phase. In this phase, the system is non-ergodic and evolves through a distribution of traps characterized by a power-law distribution of trapping times. This change in the dynamic behavior is concurrent with the appearance of a shear instability.
Local Structure of MD Simulated Soda-Lime-Silicate Glass
Authors: Yuan Xianglong , Cormack Alastair N. 
Published: April 2011

ABSTRACTSimulation of soda-lime-silicate (sis) glass has been performed using molecular dynamics (MD). The local structure of each component is analyzed extensively in terms of total radial distribution function and coordination number and found to be insensitive to the composition change. Because of its big size, Na+/Ca2+ shows a behavior rather like O2− instead of Si4+. It is evident that the CN and local structure of Na+ with O2− are similar to those in crystalline a-Na2Si2O5. Finally, the Na+/Ca2+ cluster phenomenon is discussed.
Simulation of Pressure Effects on Glasses
Authors: Kogure Y. , Doyama M. 
Published: April 2011

ABSTRACTGlass transition and effects of pressure and shear stress on atomic configuration are investigated by means of molecular dynamics simulation. An embedded atom method potential is used for the atomic interaction. A model crystal for Cu is melted and quenched to realize the glass state. Atomic configuration in the glass is examined through the radial distribution function. External stress is applied and displacement of atoms is monitored to investigate the mechanism of mechanical relaxation. Larger displacement of atoms is observed under a shear stress.
Crystallization Pathway in the Bulk Metallic Glass Zr41.2Ti13.8Cu12.5Ni10Be22.5
Authors: Schneider S. , Thiyagarajan P. , Geyer U. , Johnson W. L. 
Published: April 2011

AbstractA new family of multicomponent metallic alloys exhibits an excellent glass forming ability at moderate cooling rates of about 10K/s and a wide supercooled liquid region. These glasses are eutectic or nearly eutectic, thus far away from the compositions of competing crystalline phases. The nucleation of crystals from the homogeneous amorphous phase requires large thermally activated composition fluctuations for which the time scale is relatively long, even in the supercooled liquid. In the Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy therefore a different pathway to crystallization is observed. The initially homogeneous alloy separates into two amorphous phases. In the decomposed regions, crystallization probability increases and finally polymorphic crystallization occurs. The evolution of decomposition and succeeding primary crystallization in the bulk amorphous Zr41.2Ti13.8Cu12.5Ni10Be22.5 alloy have been studied by small angle neutron. Samples annealed isothermally in the supercooled liquid and in the solid state exhibit interference peaks indicating quasiperiodic inhomogeneities in the scattering length density. The related wavelengths increase with temperature according to the linear Cahn-Hilliard theory for spinodal decomposition. Also the time evolution of the interference peaks in the early stages is consistent with this theory. At later stages, X-ray diffraction and transmission electron microscopy investigations confirm the formation of nanocrystals in the decomposed regions.
Electron Speckle and Higher-Order Correlation Functions from Amorphous Thin Films
Authors: Murray Gibson J. , Treacy M. M. J. , Loretto D. 
Published: April 2011

ABSTRACTWe obtain valuable information about medium-range order in amorphous semiconductors from variable coherence microscopy, a new quantitative approach to TEM. The technique reveals three-body and higher-order atomic correlation functions, which are sensitive to medium-range order. Preliminary experimental evidence for structural changes on annealing has been found for amorphous semiconductor films, with pronounced medium-range order seen only in unannealed films.
Network Structure of Oxide Glasses Containing Alkali & Other Ions by Diffraction and MD Simulations
Authors: Yasui Itaru , Nagasawa H. , Matsumoto H. , Mabuchi T. 
Published: April 2011

ABSTRACTNetwork structures of several kinds of oxide glasses were analyzed by means of neutron or x-ray diffraction method and molecular dynamics (MD) simulations including silicate, borate and tellurite glasses. The basic scheme of the structure highly depends on the bonding nature of network forming oxide, but the size of the alkali ions is another important factor to control the network structure of the glass. Structures of silicate glasses are rather easily reproduced by means of MD simulation, whereas borate or tellurite glass structures are hard to be constructed by MD calculation with only 2-body potentials. It is necessary to use adequate potentials to control the bonding angles of O-M-O or M-O-M. The network structure of tellurite glass seems very complex because of the shape of structural units with low symmetry, the use of a new kind of potential was found indispensable to reproduce the glass structure by MD.In addition to the network structure, the polarization of ions seems to be important to understand the whole vision of oxide glass structures. A new kind of MD was developed which took polarization of ions into account to understand the mixed alkali effects in silicate glasses.
Two Species/Nonideal Solution Model for Amorphous/Amorphous Phase Transitions
Authors: Moynihan Cornelius T. 
Published: April 2011

ABSTRACTA simple macroscopic thermodynamic model for first order transitions between two amorphous phases in a one component liquid is reviewed, augmented and evaluated. The model presumes the existence in the liquid of two species, whose concentrations are temperature and pressure dependent and which form a solution with large, positive deviations from ideality. Application of the model to recent data indicates that water can undergo an amorphous/amorphous phase transition below a critical temperature Tc of 217K and above a critical pressure Pc of 380 atm.
Interfacial Segregation in Ionic Conductors: Ceria
Authors: Blom D. A. , Chiang Y.-M. 
Published: April 2011

ABSTRACTGrain boundary segregation in cerium dioxide doped with varying amounts of gadolinium oxide and tantalum oxide has been measured with x-ray energy dispersive spectroscopy using a Vacuum Generators HB603 Scanning Transmission Electron Microscope (STEM). The data has been analyzed in the framework of both elastic relaxation and space charge segregation forces with a limited number of surface sites. Results show that multiple driving forces must be taken into account to explain aliovalent solute segregation.
Grain Boundary Engineering in Ordered Ni3Al for Improving Ductility
Authors: Chaki T. K. 
Published: April 2011

ABSTRACTSeveral techniques of grain boundary engineering for improving ductility in polycrystalline Ni3Al are discussed with the plausible mechanism. Single crystals of Ni3Al are ductile at room temperature, but polycrstalline Ni3Al fails intergranularly with little elongation. The grain boundaries are also embrittled by environmental moisture. The weakness of the boundaries is attributed to the presence of crack-like microcavities at the boundaries. Microalloying with B closes up the microcavities by enhancing relaxation of Ni and Al atoms, thereby improving ductility. In directionally solidified Ni3Al containing low-angle boundaries, large ductility has been reported. Polycrystalline N?3AI produced by recrystallization of rolled single crystals contains a large fraction of Σ3 boundaries and exhibits large ductility. Due to good matching, the low-angle and Σ3 grain boundaries do not contain microcavities and consequently are strong.
A Grain Boundary Engineering Approach to Materials Reliability
Authors: Palumbo G. , Lehockey E. M. , Lin P. , Erb U. , Aust K. T. 
Published: April 2011

ABSTRACTIntergranular degradation processes, (e.g., corrosion, stress corrosion, cracking, creep cracking) are a frequent cause of premature and unpredictable service failure of engineering components. Recent advances in (1) understanding structure-property relationships for grain boundaries, and (2) characterization techniques for grain boundaries in polycrystalline materials, have provided the means for improved component lifetime prediction, and the opportunity to engineer intergranular-degradation resistant microstructures.In this work, we present our previously developed geometric models for grain boundary structure and grain size effects on intergranular degradation susceptibility. Specific examples are presented of the successful application of the ‘grain boundary engineering’ approach to the prediction and mitigation of intergranular corrosion, stress corrosion cracking, and creep cracking in Ni-based materials.
Interfacial Segregation in Bicrystals: A Database for Grain Boundary Design of Polycrystals
Authors: Lejček Pavel 
Published: April 2011

ABSTRACTPhysical meaning of thermodynamic parameters of segregation obtained from measurements of chemical composition of grain boundaries in poly crystals and bi crystals, and calculated for individual grain boundary sites is discussed. It is shown that the mean values of these parameters determined from the measurements on polycrystals can in exceptional cases represent the behavior of general grain boundaries. On the other hand, measurements of grain boundary segregation at individual grain boundaries can provide the values of segregation enthalpies and entropies representing behavior of a specific single grain boundary site. The latter data are appropriate for the use in the grain boundary design concept.
Ab Initio Calculations for Grain Boundaries in Covalent Ceramics
Authors: Kohyama Masanori 
Published: April 2011

ABSTRACTAb initio calculations of grain boundaries in SiC have been performed for the first time by using the first-principles molecular dynamics (FPMD) method. Four-fold coordinated models of polar and non-polar interfaces of the {122}Σ = 9 boundary in SiC have been examined. Interfacial C-C and Si-Si wrong bonds have bond lengths and bond charges similar to those in bulk diamond and Si. The C-C bonds generate greatly localized states at the valence-band edges, which have features similar to the bulk band-edge states of diamond. The wrong bonds have significant effects on the properties of grain boundaries in SiC.
Perpendicular Magnetic Anisotropy and Magneto-Optical Properties of Sputtered Re-Tm(CoGd)/Pd Multilayered Films
Authors: Yang T. , Soe W. H. , Liu B. X. , Yamamoto R. 
Published: April 2011

ABSTRACTThe magnetic properties of sputtered RE-TM(CoGd)/Pd multilayered films were studied. CoGd layers with high Gd concentration were amorphous. Reducing the Gd concentration, CoGd layers changed from amorphous to crystalline gradually. Like in the crystalline Co/Pd multilayered films, perpendicular magnetic anisotropy(PMA) was observed only for CoGd/Pd multilayered films with thin magnetic layer. It is interesting to note that critical magnetic layer thickness, below which the easy magnetization axis is perpendicular to the film plane, reaches 2.5nm for CoGd/Pd multilayered films with amorphous CoGd layers and is larger than that of Co/Pd multilayered films. Kerr rotation was found decreased with the adding of Gd.
Reactive-Sputter Deposition of TiN/ZrN and TiN/CrN Multilayers: Structural and Mechanical Properties
Authors: Soe W.-H. , Kitagaki T. , Ueda H. , Shima N. , Otsuka M. , Yamamoto R. 
Published: April 2011

ABSTRACTPolycrystalline TiN/ZrN multilayers with a 7.5% lattice mismatch between the layers and TiN/CrN multilayers with a 2.3% mismatch were grown by reactive magnetron sputtering on WC/Co sintered hard alloy substrates. Multilayer structure and composition modulation amplitudes were studied using x-ray diffraction method. Hardness and elastic modulus were measured by nanoindentation testing. Hardness of TiN/ZrN multilayers decreased rapidly with increasing bilayer thickness (Λ), peaking at hardness values ≈30% lower than rul e-of-mixtures values at Λ=30 Å, before increasing slightly with further increases in Λ. A comparison with other lattice mismatched systems, TiN/VN and TiN/NbN, showed a similar hardness variation, but a sign was negative. The results suggest that coherency strains were responsible for the larger hardness change. Nanoindenter elastic modulus results showed the same behavior with hardness dependence, i.e., elastic softening at Λ=30 Å. The results of TiN/CrN systems showed no hardness and elastic anomalies within boundaries corresponding to individual values. It was thought too large the difference between hardness (or modulus) of TiN and CrN.
Characterization of TiO2 Thick Films Photoelectrodes Prepared by the Plasma-Spray Coating
Authors: Kubota N. , Ayabe M. , Fukuda T. , Akashi M. 
Published: April 2011

ABSTRACTSemiconducting TiO2 has some photoelectrochemical reactions under ultra-violet irradiation. These photoelectrochemical behaviors studied as possible protection from corrosion. TiO2 thick films were prepared on stainless steel by plasma-spray coating. The film thicknesses were 50∼100μm. The films were characterized by X-ray diffraction, and the diffraction patterns clearly showed a rutile type structure. The crystallization of the films depends on the spray coating conditions. We have investigated the protection properties of the films by measuring the electrode potential. The electrode potential of the films were reduced by about 250m V under ultra-violet irradiation. This potential drop value is sufficient for protection from the corrosion.
Measurement of the Fracture Energy of SiO2/TiN Interfaces Using the Residually-Stressed Thin-Film Micro-Strip Test
Authors: Xu Guanghai , Ragan D. D. , Clarke D. R. , He Ming Y. , Ma Qing , Fujimoto H. 
Published: April 2011

ABSTRACTOne of the key factors affecting the long-term reliability of thin film structures in microelectronics devices is the fracture resistance of their interfaces. Of the many different interfaces formed during device fabrication, the SiO2/TiN interface is amongst the most common. In order to measure the fracture energy of this interface, we have been utilizing a test in which a narrow strip of a material, having a large intrinsic tensile stress, is deposited and lithographically defined onto the SiO2/TiN/Al thin film structure. The elastic strain energy in the micro-strip provides an additional driving force to debond the weakest interface in the structure. Decohesion occurs when the thickness of the micro-strip, and hence the total elastic strain energy, exceeds a critical value. Another measure of the fracture resistance in the same test is the length of the strip that remains intact after debonding at both ends. This is a function of the intrinsic stress, the thickness of the superlayer, and the modulus ratios. In addition to presenting results on the measured fracture energy of the SiO2/TiN interface, evidence for stress-corrosion will be described.
Influence of Ca-Doping on Chemistry and Force Balance at Grain Boundary in Si3N4
Authors: Gu Hui , Rühle Manfred 
Published: April 2011

ABSTRACTHigh-purity HIPed Si3N4 ceramics doped systematically with Ca additives are analyzed quantitatively by EELS. Using an ELNES related method to obtain film composition, we found that the composition difference from film to film is less significant than segregation. This is interpreted as a change of film width related to grain surface faceting. The hexagonal structure associated with anisotropie dielectric function can alter van der Waals attraction for different surface structures to produce variations in film thickness with a uniform film composition. These grain boundary films are better described as a high pressure amorphous oxynitride phase that allows higher but still limited solubility of calcium nitrogen.
Modelling of Adaptive Composite Materials with Embedded Shape Memory Alloy Wires
Authors: Stalmans R. , Delaey L. , Van Humbeeck J. 
Published: April 2011

ABSTRACTVarious models and calculation methods for the description of shape memory behaviour have been developed in recent years by different research groups. Some of the models have already been extended towards the thermomechanical and functional behaviour of matrix materials with embedded SMA-wires. The basic concepts of a thermomechanical model which has found widespread use in the literature on smart materials, are critically reviewed.A recently developed model based on a generalised thermodynamic analysis of the underlying martensitic transformation is discussed more into detail. Experimental verifications indicate that this thermodynamic model can be developed to an effective tool for the materials design of matrix materials with embedded SMA-wires.
Mechanical Properties of Smart Metal Matrix Composite by Shape Memory Effects
Authors: Hamada K. , Lee J. H. , Mizuuchi K. , Taya M. , Inoue K. 
Published: April 2011

ABSTRACTThe thermomechanical behavior of TiNi shape memory alloy fiber reinforced 6061 aluminum matrix smart composite is investigated experimentally and analytically. The yield stress of the composite is observed to increase with prestrain given to the composite. Analytical model is developed by utilizing a shape memory alloy constitutive model of exponential type for the thermomechanical behavior of the composite. The model predicts that the composite yield stress increases with increasing prestrain, and the key parameters in affecting the composite yield stress are prestrain and matrix heat treatment. The model predicts reasonably well the experimental results of the enhanced composite yield stress.
Experimental Analysis of Smart Structure with Damping Treatment and SMA
Authors: Chen Q. , Ma J. , Levy C. 
Published: April 2011

ABSTRACTThe experimental results of a flexible cantilever beam with constrained viscoelastic layer and shape memory alloy layer called smart damping treatment (SDT) are presented. The upper side of the beam is bonded with a viscoelastic layer and then covered with a constraining layer. The lower side is bonded with a shape memory alloy layer, which is used as an actuator. The elastic modulus and loss factor of damping materials are functions of the temperature. The temperature effects on system frequency and loss factor due to heat cycling of SMA layer are evaluated here. It is found that temperature plays an important role on system frequency and loss factor, and thus the temperature effects must be included when discussing such an structure.
Fabrication of Pseudo One-Dimensional Photonic Band System by Grating Pair Method
Authors: Todori K. , Hayase S. 
Published: April 2011

ABSTRACTWe have succeeded in forming a pseudo one-dimensional photonic band by using two gratings facing each other. This pair of gratings had a period of 278 nm. The frequency of the band edge was in the visible region. This method is useful to control the group velocity and the phase velocity of light.