bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular Modeling of Free Volume Distributions of Amorphous Membrane Polymers
Authors: Hofmann Dieter , Heuchel Matthias , Yampolskii Yuri , Topchiev A. V. 
Published: April 2011

ABSTRACTThe paper deals with important differences in the distribution of free volume in high and low free volume polymers as indicated by a joint investigation utilizing molecular modeling and positron annihilation lifetime (PALS) studies. The main focus of this paper is on the molecular modeling approach. The first set of polymers in question are the ultra-high free volume polymer poly(1–(trimethylsilyl)-1-propyne) (PTMSP) and two polystyrene derivatives containing Si and F. Extended equilibration procedures were necessary to obtain reasonable packing models for the polymers. The transition state Gusev-Suter Monte Carlo method was utilized to prove a reasonable agreement between simulated and measured diffusivity and solubility values for the model structures. The free volume distribution was analyzed for the validated packing models and compared with respective PALS data. In both cases a bimodal distribution of free volume was observed for PTMSP while the polystyrene derivatives as other conventional glassy polymers showed a more or less monomodal behavior. Good qualitative agreement is demonstrated between size distributions of free volume elements in these polymers obtained via molecular computer modeling and PALS experiments. In addition a series of conventional and high performance polyimides was considered. There a major result is that polyimides with conventional permeabilities for small molecules always show just a monomodal distribution of free volume element sizes in the radius range up to about 5 Å, while all polyimides with high permeabilities have a wider, often bimodal, distribution extending up to a radius between 6 and about 8 Å.
Transport Properties of Reconstructed Alumina and Vycor Membranes
Authors: Kainourgiakis M. E. , Kikkinides E. S. , Steriotis Th. A. , Stubos A. K. 
Published: April 2011

ABSTRACTAim of the present work is the investigation of the transport properties (Knudsen and molecular diffusivity, permeability) of 3-dimensional binary domains that represent two model mesoporous materials, namely Vycor glass and alumina membrane. A process-based technique producing a random packing of equal spheres is used for the reconstruction of the alumina membrane, while a stochastic reconstruction procedure is employed in the case of Vycor. The comparison between computed and reported transport coefficients confirms that the random sphere pack represents quite well the porous structure of the alumina membrane, while the stochastic reconstruction technique is sufficient for an accurate representation of the porous matrix of Vycor glass.
Mesoscopic modeling of binary diffusion through microporous zeolite membranes
Authors: Snyder Mark A. , Vlachos Dionisios G. 
Published: April 2011

ABSTRACTThe mesoscopic framework describing single-component diffusion through microporous materials is extended here to characterize binary diffusion in the absence of intermolecular forces. Two diffusion mechanisms, single-file diffusion characteristic of confined pore structures and species-species exchange consistent with diffusion modes in less-confined pore topologies, are incorporated at the Master Equation level. Derived fundamentally via rigorous coarse-graining of the underlying Master Equation, the binary mesoscopic relation is validated via direct comparison to gradient continuous time Monte Carlo (G-CTMC) simulations. We further show the capability of this fundamentally derived model to capture the macroscopic diffusion phenomenon of ‘overshoot’ or ‘roll-up’ in the transient uptake and flux. Exploration of the species-species exchange mechanism reveals its strong effect on the transient ‘overshoot’ behavior through relaxation of the constrained single-file diffusion.
Fabrication of Electrochemical Ceramic Membrane with Assistance of Metallization by the Electroless-plating Technique
Authors: Liu Y-Y. , Hong L. , Shao Z-C. , Jiang H-X. 
Published: April 2011

ABSTRACTThis work developed a metal-reinforced ceramic membrane processing approach [by using perovskite La0.2Sr0.8 CoO3-x (LSCO-80) as the model membrane] with the aim of overcoming the membrane-cracking problem. A thin layer of Ag/Pd alloy was incorporated into the LSCO-80 membrane made by dip coating and sintering. It is not viable to obtain a Pd/Ag alloy film using the co-plating method because Ag+ ion strongly inhibits chemical reduction of Pd2+ ion, and the alkaline plating bath causes severe etching of LSCO-80. This obstacle was circumvented through a layer-by-layer deposition procedure, in which Ag and Pd layers were deposited subsequently onto LSCO membrane. The Ag and Pd layers undergo alloying when the laminar structure was subjected to calcinations at 1000°C. It was found that the Pd/Ag alloy drifts beneath into pores in the LSCO layer. The resultant metal-ceramic composite membrane shows excellent structural integrity and free of micro-cracks.
Ion Beam Modification of Matrimid® Gas Separation Membrane—Evolution in Chemical Structure, Microstructure and Gas Permeation Properties
Authors: Xu Xinglong , Hu Ling , Coleman Maria 
Published: April 2011

ABSTRACTMatrimid® is a widely used polyimide that has both attractive thermal and gas transport properties. In addition, it has been used as a precursor polymer for production of carbon molecular sieving membranes with commercially interesting gas separations. Ion beam irradiation over a wide range of doses was used to modify a series of Matrimid® membranes. A combined analysis of impact of ion irradiation on the chemical structure, microstructure and gas transport properties of Matrimid® will be presented. Specifically, the evolution in gas permeation properties following irradiation over a wide range of doses will be discussed. Ion irradiation resulted in combined increased permeability and permselectivity for several gas pairs of interest.
Use of Electrodialysis to Bentonitics Clays Dispersions
Authors: Amorim L. V. , Gomes C. M. , Silva F. L. H. , França K. B. , Lira H. L. , Ferreira H. C. 
Published: April 2011

ABSTRACTThe aim of this work is to study the uses of electrodialysis to bentonitics clays dispersions from Boa Vista City, PB, to improve the rheological properties. The dispersions were prepared with natural clay in the concentration of 4.86% w/w and submitted to electrodialysis process by using cationic polymeric membranes. Following, the dispersions were treated with Na2CO3. After cure, it was evaluated apparent (AV) and plastic (PV) viscosity and water loss (WL). The tests was setting up according to 22 experimental design, with three measures in the central point, to estimate the best applied voltage and time and the influence on AV, PV and WL. The results showed that variables (voltage and time) have significant influence on the rheological properties. It was observed an increase in PV and decrease in WL, with values that satisfy the specifications for water based drilling fluids.
Organic/inorganic Nanohybrid Membranes for Nanofiltration of Nonaqueous Solutions
Authors: Tsuru Toshinori , Kondo Hiroyasu , Yoshioka Tomohisa , Asaeda Masashi 
Published: April 2011

ABSTRACTSilica/zirconia (SZ; Si/ Zr molar ratio = 9/1) membranes having pore sizes in the range of 1∼ 3 nm were prepared by the sol-gel process. Organic/ inorganic hybrid membranes were developed by modifying the surface of the silica-zirconia porous membranes via a gas-phase reaction with trimethylchlorosilane (TMCS) to give a surface that was modified with a monolayer of TMCS. Using nanopermporometry, it was found that the inner surface of membrane pores with diameters larger than several nms were successfully modified with TMCS. TMCS-modified membranes showed approximately the same permeability, Lp, irrespective of water concentration (10 and 100 ppm) in hexane. In contrast, an unmodified membrane, showed a decrease in Lp with increasing water concentration, which was pronounced at low permeation temperatures. This suggests that small amounts of water adsorbed to the inner surface of unmodified silica-zirconia membranes and blocked the permeation of hexane.
Interfacial Ion Fluxes at Nanostructured Thin Films
Authors: Kariuki Nancy N. , Luo Jin , Han Li , Maye Mathew M. , Patterson Melissa J. , Moussa Laura , Hepel Maria , Zhong Chuan-Jian 
Published: April 2011

ABSTRACTThin films derived from nanocrystal cores and functionalized linkers provide large surface-to-volume ratio and three-dimensional ligand framework. This paper describes the results of an investigation of the interfacial ion fluxes associated with redox reactivity and structural properties of such films using cyclic voltammetry, electrochemical quartz-crystal nanobalance, surface infrared reflection spectroscopy, and X-ray photoelectron spectroscopy. Films from gold nanocrystals of 2 nm core sizes and 11-mercaptoundecanoic acid were studied as a model system. First, the film coated on electrode surface displays redox-like voltammetric waves characteristic of the deprotonation-reprotonation of the carboxylic acid groups in the nanostructured network. This process is accompanied by mass changes. Secondly, the film exhibits capability for the complexation of copper ions via the nanostructured carboxylate framework. This process is also accompanied by interfacial fluxes of electrolyte cations across the electrode | film | electrolyte interface which compensate electrostatically the fixed negative charges in the reduction process.
Hardening by Point Defects and Solutes in B2 Intermetallics
Authors: Pike L. M. , Chang Y. A. , Liu C. T. , Anderson I. M. 
Published: April 2011

ABSTRACTThis paper provides a review of recent progress on point defect and solute hardening in binary and ternary B2 intermetallics. As is the case for disordered metallic solutions, the presence of point defects and solute atoms in ordered intermetallic compounds results in solid solution hardening (SSH). However, factors unique to ordered systems are often responsible for unusual hardening effects. Binary compounds with identical crystal structures can exhibit significantly different hardness behavior. Ternary solute additions to ordered compounds can give rise to apparent solid solution softening as well as unexpectedly rapid hardening. These effects arise from the interaction of multiple defect types as well as the presence of multiple sublattice sites available for solute occupation. Therefore, before the SSH behavior of ordered intermetallics can be properly studied, it is necessary to develop an understanding of the types and quantities of the point defects which are present. Three recent studies by the authors are reviewed. Much of the work was done on NiAl and FeAl in binary form as well as with ternary additions. Defect concentrations over wide ranges in alloy composition and quenching temperature were determined using the ALCHEMI (atom location by channeling enhanced microanalysis) technique combined with vacancy measurements. Hardness values were also measured. It was found that most of the observed SSH effects could be rationalized on the basis of the measured point defect concentrations.
Alignment of the lamellar orientation of multi-component TiAl alloys by directional solidification (DS) and mechanical properties of DS ingots
Authors: Omiya Y. , Muto S. , Yamanaka T. , Johnson D. R. , Inui H. , Yamaguchi M. 
Published: April 2011

ABSTRACTBy using an appropriately oriented seed from the TiAl-Si system (Ti-43Al-3Si), the TiAl/Ti3Al lamellar structure has been successfully aligned parallel to the growth direction for TiAl ingots of the Ti-Al-Nb, Ti-Al-Nb-Si, Ti-Al-Ta-Si systems on the basis of the recently proposed method to predict the appropriate compositions. The Al equivalents for Nb and Ta are reevaluated in order to extend the proposed method to large addition (above a several at. %) of these alloying elements. These DS ingots with the lamellar structure all aligned parallel to the loading axis exhibit creep properties far better than conventionally produced TiAl ingots so far reported.
Microstructural Changes of a γ-TiAl Based Alloy with a Fully Lamellar Microstructure Due to Annealing at Elevated Temperatures
Authors: Beschliesser M. , Appel F. , Kestler H. , Clemens H. 
Published: April 2011

ABSTRACTThe changes of a fully lamellar microstructure caused by annealing at 700 and 800°C for up to 10,000 hours in air have been investigated for a Ti-46.5at.%Al-4at.%(Cr,Nb,Ta,B) sheet material. Changes in morphology as well as in chemical composition and volume fraction of constitutional phases were recorded by means of transmission electron microscopy. Thermodynamic equilibrium calculations performed with the software package ThermoCalc provide baseline information upon both the chemical composition and the amount of constitutional phases of the investigated multi-component alloy. It could be demonstrated that due to high cooling rates which are required to adjust a “defect-free” undisturbed fully lamellar microstructure, composition and amount of the α2 phase are far from the thermodynamic equilibrium. However, during high temperature exposure the composition as well as the amount of α2 phase move towards the values predicted by the calculation. Furthermore, former perfectly shaped γ/α2 lamellae interfaces are disturbed, α2 lamellae decompose and new phases appear instead. Dislocations emitted from dissolving α2 lamellae move into the γ lamellae. Mechanisms responsible for decomposition of lamellae and formation of new phases are explained by thermodynamic equilibrium calculations and diffusion considerations. Finally, results of tensile tests conducted at room temperature and 700°C on long-term annealed specimens are presented and discussed. This work is a basis for understanding microstructural changes and their impact on mechanical properties of γ-TiAl based alloys with a fully lamellar microstructure during service at elevated temperatures.
Effects of the Variation in α-Phase Volume Fraction on the Thermal Stability of TiAl Alloys with Lamellar Microstructures
Authors: Kim S. W. , Lee H. N. , Oh M. H. , Yamaguchi M. , Wee D. M. 
Published: April 2011

ABSTRACTThe thermal stability of lamellar microstructure in Ti-Al-Mo PST crystals containing C or Si, was investigated. In addition, the variation of α-phase volume fraction in Ti-Al-Mo-(C,Si) systems was investigated at several temperatures. Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys were found to be very stable during heat treatments at various heating rates and temperatures. Moreover, the α-phase volume fractions of Ti-46Al-1.5Mo-0.2C and Ti-46Al-1.5Mo-1.0Si alloys, which were stable compositions, changed less than those of Ti-47Al and Ti-46–1.5Mo alloys, which were unstable compositions. From these results, it was determined that the instability of the latter alloys was caused by their relatively higher variation of α-phase volume fraction during heating. Therefore, it is suggested that the variation of α-phase volume fraction is an important factor in controlling the thermal stability of lamellar microstructure.
Annealing induced structural changes and microcracking in Mo-Mo3Si
Authors: Wang X.-L. , Schneibel J. H. , Wang Y. D. , Richardson J. W. 
Published: April 2011

ABSTRACTCast Mo-Mo3Si intermetallic composites develop microcracks after annealing at high temperature. Neutron diffraction, x-ray diffraction, composition analysis, and scanning electron microscopy have been used to characterize the structural changes induced by annealing of Mo-Mo3Si. It is shown that the observed cracking cannot be attributed to differential thermal stresses that developed on cooling from the annealing temperature. Instead, the experimental data suggest that the cracks were initiated at high temperature, possibly due to diffusion of Si atoms from supersaturated α-Mo to Mo3Si.
Kinetic Calculation of L10 Ordered System Based on Phase Field Methodand Cluster Variation Method
Authors: Ohno M. , Mohri T. 
Published: April 2011

ABSTRACTDuring ordering process, anti-site ordering proceeds in atomistic scale and anti-phase domain structure evolves in microstructural scale. In order to describe both the processes, a hybridized calculation of the Phase Field Method(PFM) and Cluster Variation Method(CVM) is attempted. The main objective of the present study is focused on the time evolution of atomic configuration during L10 ordering processes below and above the spinodal ordering temperature and their resultant microstructures. In order to investigate the interplay between atomistic and microstructural processes, we conducted two types of calculations. One is for a homogeneous system without an anti-phase boundary and the other is for an inhomogeneous system in which microstructure is formed by anti-phase domains.For the homogeneous system, the relaxation curve of Long-Range-Order parameter(LRO) indicates a transient appearance of an L12-like atomic configuration below the spinodal ordering temperature. Such an L12–like state corresponds to a saddle point configuration in the CVM free energy surface. When the composition of an alloy is located near L10 + L12 phase field in the phase diagram, the L12–like phase becomes highly ordered state.For the inhomogeneous system, it is implied that the appearance of the L12-like phase affects the resultant microstructure by providing the nucleation sites for the L10 ordered phase.
Pulse-Field Activation of Collinear Magnetic Single Crystals
Authors: Jenkins C. A. , O'Handley R. C. , Allen S. M. 
Published: April 2011

ABSTRACTSingle crystals of nickel-manganese-gallium, a ferromagnetic shape memory alloy (FSMA), show up to 10% elongation in response to an applied magnetic field or mechanical stress. The change in dimension is not a result of magnetostriction but of twin boundary motion through the material. The field-induced extension has previously been reversed only by a compressive mechanical stress from a spring or orthogonal field. The use of a second crystal of Ni-Mn-Ga to provide the reset force is unreported.Data are shown here of the stress and strain behavior of two FSMA crystals connected in series and subjected alternately to a magnetic field. Two samples, one initially in full extension and the other in compression, are arranged in series in a rigid frame such that their total length is held constant. A pulsed magnetic field is alternately applied to the samples, with the output energy of the extending crystal tending to apply a resetting force to the other. This setup shows up to 1.5% resetting strain in single crystal laminates.
Brittle to Ductile Transition in Intermetallic Alloys
Authors: Kysar Jeffrey W. 
Published: April 2011

ABSTRACTTwo distinct approaches are commonly invoked to explain the brittle to ductile transition of a material in the presence of a crack. In one approach, dislocation mobility plays the key role. In the other approach, the competition between crack tip dislocation nucleation and cleavage failure plays the key role. The two approaches are reconciled in the present study.
Evaluation of the Thermodynamic Properties and Phase Equilibria of the Ordered γ’ and Disordered γ Phases in the Ni-Al-Ta System
Authors: Zhou Shihuai , Chen Long-Qing , MacKay Rebecca A. , Li u Zi-Kui 
Published: April 2011

ABSTRACTThe phase equilibria and thermodynamic properties of the ternary Ni-Al-Ta system on Ni-rich side were analyzed. Thermodynamic descriptions of the liquid, γ-fcc, γ'-L12, and π-Ni6AlTa phases were obtained using the CALPHAD (CALculation of PHase Diagrams) technique. The thermodynamics of γ-fcc and γ'-L12 phases were modeled with a single Gibbs energy function taking into account the crystallographic relation between the two phases. The ternary interaction parameters of the liquid and fcc phases were also determined. The calculated phase diagrams of the ternary Ni-Al-Ta system show a good agreement with experimental data.
Vibrational Spectroscopy and MAS NMR Studies of A Cryptomelane Family of Mixed (7Li+, 2 H+) Form Manganic Acids
Authors: Tsuji Masamichi , Paik Younkee , Grey Clare P. , Murao Satoshi 
Published: April 2011

ABSTRACTCryptomelane-type manganic acids (CMAs) synthesized by a soft-chemical redox process of KMnO4 with MnSO4 in H2SO4 and α-MnO2s by a decomposition-oxidation process of (CH3)3COK and MnCO3 at 530°C were studied by using the vibrational spectroscopy and 7Li- and 2H-MAS NMR. The infrared absorption bands of the α-MnO2s at 706cm-1 were not changed irrespective of the sort of alkali cations and their uptake amount, while large shifts of this band were observed on the CMA exchanged by alkali cations. Hence, cation-exchange sites of these solids will occupy crystallographically different positions. 7Li-MAS NMR spectra of these manganic acids showed different two chemical shifts depending on their synthetic routes. These findings suggest that different ion-exchange sites are formed at a local level in the 2×2 type tunnel, strongly depending on their synthetic conditions. These are crucial for the control of the cation affinity. These details at a molecular level cannot be obtained by using the conventional XRD analyses.
Surfactant and temperature influence on Co nanocrystal structure and shape
Authors: Puntes V.F. , Zanchet D. , Erdonmez C. K. , Alivisatos A.P. 
Published: April 2011

ABSTRACTInorganic nanoparticles of a variety of materials have been obtained by chemical methods. Under the kinetic control, small variations in the synthesis recipe may yield crystals of different sizes, shapes and structures. Co nanocrystals are of particular interest: besides achieving size control, at least three nearly isoenergetic crystal structures (face-centered cubic, hexagonal close-packed and epsilon) can be synthesized, and shape control (spheres, prisms, cubes, rods and disks) is also possible. Although shape and structure should be intrinsically related, the relationship between these two characteristics has not been deeply explored up to this moment. Here, we present our latest results on Co nanoparticles, analyzing the influence of some parameters on particle shape and structure. In particular, the influence of ligand type and temperature has been tackled.
The Migration Concept for Ionic Motion in Materials With Disordered Structures
Authors: Funke K. , Banhatti R. D. 
Published: April 2011

ABSTRACTThe dynamics of the mobile ions in materials with disordered structures are a challengingly complicated many-particle process. In this paper, we consider characteristic frequency-dependent conductivities and permittivities of such materials and show that they can be well reproduced within the framework of the MIGRATION concept. The meaning of the acronym is MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. In the MIGRATION concept, we attempt to grasp the essence of the ion dynamics in a simple set of rules which convey a physical picture of the most relevant elementary processes. The rules are expressed in terms of three coupled rate equations which then form the basis for deriving frequency-dependent model conductivities and permittivities.