bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effect of Grain Size on Corrosion Fatigue of A537 Steel
Authors: Wang Qing , Song Yu-Jiu
Published: April 2011

The influence of grain size on corrosion fatigue behavior of A537 steel in 0.1M HCL solution has been studied. The results show that the increase of grain size can improve the corrosion fatigue crack growth resistance. But the change of crack growth rate da/dN with average grain diameter D is not monotonic. When D>40 μm, crack propagates little faster when grain is larger. When D>40 μm, crack propagates slower when grain is larger. According to the fractographic features, corrosion fatigue mechanism is anodic dissolution under fine grain condition but hydrogen embrittlement under coarse grain condition.
Grain Size Dependent Mechanical Properties in Nanophase Materials
Authors: Siegel Richard W. , Fougere Gretchen E.
Published: April 2011

It has become possible in recent years to synthesize metals and ceramics under well controlled conditions with constituent grain structures on a nanometer size scale (below 100 nm). These new materials have mechanical properties that are strongly grain-size dependent and often significantly different than those of their coarser grained counterparts. Nanophase metals tend to become stronger and ceramics are more easily deformed as grain size is reduced. The observed mechanical property changes appear to be related primarily to grain size limitations and the large percentage of atoms in grain boundary environments. A brief overview of our present knowledge about the grain-size dependent mechanical properties of nanophase materials is presented.
Formation of Amorphous and Nanocrystalline Phases in Mechanically Alloyed Zr-, Al-, and Mg-Base Transition Metal Alloys
Authors: Seidel M. , Eckert J. , Bauer H.-D. , Schultz L.
Published: April 2011

Zr-, Al-, and Mg-base transition metal alloys have been prepared by mechanical alloying and investigated by x-ray diffraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Amorphous phases with significant supercooled liquid region form directly during milling from the crystalline starting materials for Zr- and Mg-base alloys. For Albase alloys the formation of mixtures of amorphous and nanocrystalline phases is observed. The results are compared with data for melt-spun and quenched materials. Possible mechanisms for glass formation and crystallization are discussed.
Mechanical Properties of Nano-Scale Mechanically-Milled NiAl
Authors: Smith Timothy R.
Published: April 2011

This work reports on the mechanical properties of nanocrystalline NiAI materials. Mechanically- milled NiAl with and without Al2O3 additions was forged to 94% of the theoretical density of stoicheometric NiAl at < 0.5 Tm in air. Mechanical properties were investigated by microhardness measurements and the Miniaturized Disk-Bend Test (MDBT). Analysis of the hardness data indicates that most of the compression strengthening is due to the refined microstructure. MDBT results are consistent with tensile tests indicating that the tensile strength is controlled by the strength of grain boundaries.
Crack Velocity Measurements in Sea Ice
Authors: Gluschenkov Oleg , Petrenko Victor
Published: April 2011

To study crack dynamics in sea ice fast measurements of ice electrical resistance and an electromagnetic emission (EME) from cracks were used. The sample dimensions ranged from 0.05 to 30 meters. In a laboratory grown fresh water ice crack velocities varied from a few hundreds to a thousand meters per second while in the natural sea ice crack velocity was very low, about 10 m/s. This remarkable difference in the crack velocities is likely due to the dynamic resistance of unfrozen water in brine pockets and channels and to the high ductility of sea ice. It was found that the cracks propagate in ice discontinuously owing to the strong interaction with such microstructural elements as liquid inclusions and grain boundaries. The high sensitivity of the method allowed to detect nucleation of very first microcracks.
Preparation of Zinc Oxide Films by Low-Pressure Chemical Vapor Deposition Method
Authors: Nishino Junichi , Ohshio Shigeo , Kamata Kiichiro
Published: April 2011

ZnO and Al-doped ZnO films prepared using a low-pressure chemical vapor deposition (LP-CVD) method were studied. The films were prepared on fused quartz substrates using bis(2,4-pentanedionato)zinc and tris(2,4-pentanedionato)aluminum which are inexpensive and stable source materials. The highly c-axis oriented ZnO films were grown on the substrates above 500°C. The minimum electrical resistivity of ρ=6.5×10−5Ωm was obtained for the ZnO film, and of ρ = 3.5×10−5Ωm was obtained for the ZnO:Al film.
Visualization of Atmospheric Pressure Chemical Vapor Deposition and Powder Spray Pyrolysis by Laser Light Scattering
Authors: Mao Limin , Stewart Ogie , Reck Gene P. , Proscia James W.
Published: April 2011

Atmospheric Pressure Chemical Vapor Deposition (APCVD) and powder spray pyrolysis are both pyrolytic thin film deposition techniques that are used to coat glass with thin films at atmospheric pressure. In the present study, the fluid dynamics of each process was investigated by laser light scattering. For each system, a 193 nm ArF excimer laser pulsed at 7 Hz was used for the analysis. In the case of the APCVD reactor, the difference in Rayleigh scattering between helium injected in the reactor and ambient air was used to characterize the process. For the powder spray process, laser scattering off the sprayed powder was used. The effect of various parameters is discussed.
Mixtures in Slit-Micropores with Pore-Walls Structured on Both the Atomic and Nanoscale
Authors: Curry J. E. , Cushman J. H.
Published: April 2011

The grand canonical Monte Carlo method is used to study a binary mixture of Lennard-Jones atoms confined to various corrugated slit-micropores which are in thermodynamic equilibrium with their bulk phase counterpart. The micropore walls have the structure of the (100) face of an fcc lattice. In addition to this atomic scale structure, one wall possesses nanoscale structure in the form of rectilinear grooves (corrugation). The grooved surface divides the confined fluid film into two strip shaped regions. The confined film is studied in each region as a function of groove width, bulk phase composition, and the size of the wall atoms.
Dynamical Buckling Transitions of a Confined Colloidal Monolayer
Authors: Murray Cherry A. , Sprenger Wolfgang , Seshadri Raj , Cerise Jane E.
Published: April 2011

When a rigid two-dimensional triangular crystalline layer of colloidal spheres confined between two smooth repulsive walls is gradually given freedom to move out of plane, it buckles dynamically undergoing several Peierls transitions involving different soft phonon modes before forming a two layer crystal with square in-plane symmetry. We have mapped out the complex phase diagram of the buckling transitions as a function of sphere density and wall separation. Digital imaging is used to study the instantaneous particle positions and trajectories of the uniform, highly charged 0.3 μm diameter polystyrene spheres that comprise the crystalline layer in water suspension. Brownian motion of the spheres creates a true thermodynamic system with a real temperature, which is studied using video microscopy. We follow the collective dynamics of the system as well as individual particle motions and the motions and rearrangements of topological defects and domains. At sufficiently low sphere densities the system melts into a fluid. As the wall separation increases to the point of two layer formation we observe square symmetry in the fluid correlation volumes.
Depression of the Glass Transition Temperature in Ultra-Thin, Grafted Polystyrene Films
Authors: Keddie J. L. , Jones R. A. L.
Published: April 2011

We have used ellipsometry to measure the glass transition temperature (Tg) of ultrathin films of polystyrene (PS) (less than 10 nm thick) obtained by grafting PS-COOH on the native oxide of Si. We find that Tg in these ultra-thin films is depressed from the bulk value by as much as, 35 K. This is in qualitative accord with our earlier results on thicker non-grafted films of PS.
Robustness of Methane Diffusion in Geometrically Restricted Molecular Sieve Pores
Authors: Nivarthi Sriram S. , Davis H. Ted , McCormick Alon V.
Published: April 2011

NMR measurements of sorbate mobility in zeolites are especially attractive because of their capability of measuring multicomponent and anisotropic self-diffusion. We have recently reported the application of the pulsed field gradient NMR technique using very large zeolite crystals to study how easily methane can diffuse when we attempt to slow its migration by crowding the pore space. Here we analyze the implications of these PFG NMR experiments involving (i) ethylene blocking of methane in zeolite NaY; and (ii) methane molecules trying to pass one another in the molecular sieve A1PO4-5.
Adsorption on Rough Surfaces
Authors: Segars Ronald , Piscitelle Louis
Published: April 2011

A new model for adsorption on rough surfaces is derived. The model predicts behavior regarding surface smoothing that agrees well with experimental observations. Computer simulations show the model capable of matching a wide variety of isotherm patterns with reasonable physical constants. These simulations also show that a significant error results in applying the standard BET equation to adsorption data obtained on rough surfaces.
X-ray Scattering Studies of Molecular Ordering Phenomena in Confined Films
Authors: Sinha Sunil K. , Tolan M. , Vacca G. , Lit Z. , Rafailovich M. , Sokolov J. , Lorenz H. , Kotthaus J. P. , Feng Y. P. , Grubel G. , Abernathy D.
Published: April 2011

A knowledge of the structural behavior of molecules confined in thin liquid films and the way in which they differ from bulk behavior is of great importance to a variety of technological applications. We discuss X-ray scattering studies of the conformation of liquid polymer wetting layers on laterally structured substrates in order to test theories of the conformality of the wetting layer to the substrate. Recent work on guided X-ray beams confined to the thin film opens up the possibility of detailed studies of ordering phenomena in molecular layers adjacent to solid surfaces. Recent experiments are discussed.
Microwaves for Reduction of Iron Ore Pellet by Carbon
Authors: Gomez Idalia , Aguilar Juan A.
Published: April 2011

Results of reducibility tests of reduction conducted on iron ore pellets by carbon are presented in this work. Work done is centered on reduction kinetics by carbon with conventional heat supply (heat transfer process) compared with reduction kinetics where heat is supplied by microwaves to whole volume. Ore used in this work is called “Alzada” which has reducibility characteristics well known, and is often used as standard for comparison. Importance of using actual pellet instead of dust is pointed. This work is part of a project related with microwaves for reduction of metallic oxides.
Experimental Study of a Reaction-Diffusion System in a Capillary: Complex Behavior of a Seemingly Simple System
Authors: Lin Anna , Yen Andrew , Koo Yong-Eun , Kopelman Raoul
Published: April 2011

We study a reaction-diffusion system within the confines of a thin capillary tube. Xylenol orange and Cr 3+ are introduced into a capillary tube from opposite ends and meet in the middle forming a reaction front. Unequal initial concentrations of the reactants causes the center of the reaction front to move in time. Characteristics of the front such as the width of the reaction zone, w, the position of the center of the front, xf, the global reaction rate, R, and the local reaction rate, r(xf,t) are determined by continuously monitoring the product concentration in space vs. time. We observe crossover of the global rate from classical to non-classical behavior and a splitting of the reaction front.
Substrate-Dependent Features of Polyethylene Oxide (Peo) Adsorption from Aqueous Solution: Competitive Adsorption Versus Surface Relaxations
Authors: Santore M. M. , Rebar V. A.
Published: April 2011

This work employed total internal reflectance fluorescence (TIRF) to examine the adsorption kinetics of polyethylene oxide (PEO) on silica from aqueous solution in controlled shearing flow. Studies with PEO, fluorescently labeled such that TIRF tracked the chain number on the surface, exhibited an overshoot in the early stages of adsorption. This overshoot was not seen with other polymers such as polyvinyl alcohol, and hydroxyethyl cellulose, possibly because these other polymers were labeled such that TIRF measured the interfacial mass. Indeed, reflectometry studies of PEO adsorption, sensitive to interfacial mass, showed no overshoot. This suggests that the overshoot results from the selectivity of the surface for high molecular weight populations within a polydisperse sample. Initially short chains adsorb because they diffuse to the surface quickly. At longer times, higher molecular weight chains reach the surface and replace the short chains. This evolution occurs as the mass coverage increases (according to reflectivity) but the number of adsorbed chains, and hence the TIRF signal decrease at long times. A study of the impact of the molecular weight distribution confirmed this hypothesis.

Several complications to the molecular weight selectivity hypothesis, however, arose: First, the same PEO samples which overshot during adsorption on silica showed no overshoot on a polystyrene substrate. This suggested that the ability to overshoot was governed by the substratesegment interactions, even though the molecular weight distribution within the sample determined the overshoot shape. Further, the effect of transport conditions (wall shear rate, bulk polymer concentration) were not completely consistent with the molecular weight competition hypothesis, which was based on surface-solution equilibrium, taking into account transport-limited rates of adsorption. Finally certain runs, where the adsorption process was interrupted by solvent flow and later allowed to proceed, never reached the full coverage seen for uninterrupted runs. Hence, the surface coverage and possibly the chain configurations can depend on the history of the adsorption process, a feature which points to surface relaxations and non-equilibrium structures.
Initially Separated Reaction-Diffusion Systems
Authors: Taitelbaum Haim , Vilensky Baruch , Koo Yong-Eun Lee , Yen Andrew , Lin Anna , Kopelman Raoul
Published: April 2011

Characteristics of the A + B → C reaction-diffusion system with initially separated components are studied theoretically and experimentally. When the reaction is slow, the two species will mix before reacting. This leads to a series of crossovers from a rich initial behavior to an asymptotic time behavior. The crossovers depend on the system parameters, such as the diffusion coefficients and initial densities of the two species. In this paper we review our recent studies on this system. We elaborate on a theoretical study of momentum effects, and then focus on theoretical explanations of two experimental phenomena: 1) Non-universal and non-monotonic motion of the reaction front center. The latter occurs when one of the reactants has larger diffusion coefficient but smaller initial density. 2) Existence of more than one front. This occurs when two different transformations of the same reactant (on one of the sides of the system), react with the reactant on the other side with a different reaction constant - the majority slowly, but the minority much faster.
Chemisorption of Self Assembled Alkyl Thiol on Au(111)
Authors: Yeganeh M. S. , Dougal S. M. , Polizzotti R. S. , Rabinowitz P.
Published: April 2011

We have used infrared-visible sum-frequency generation (SFG) to spectroscopically probe the interfacial structure of a self assembled monolayer (SAM) of alkyl thiol on a Au(111) surface. The SFG spectra of the CH3 group measured as a function of azimuthal angle indicates that sulfur atoms cannot be situated at sites of a single type, e.g., hollow or bridge, but must be in a mixed arrangement. SFG is also used to study the reconstruction of the gold substrate by alkyl thiol.
Dewetting of Polymer Bilayers: Morphology and Kinetics
Authors: Faldi Alessandro , Winey Karen I. , Composto Russell J.
Published: April 2011

The kinetics of de-wetting a polycarbonate (PC) film from a poly(styrene-coacrylonitrile) (SAN) copolymer film was monitored using optical microscopy. Whereas the SAN layer was stable upon annealing at 190°C, the PC layer dewetted the SAN and formed holes whose diameter increased linearly with time. Auger electron spectroscopy measurements confirmed that PC was fully removed from the interior of the hole. Upon varying the AN content, the dewetting velocity was found to be a minimum near 0.27 weight percent AN. This result is consistent with the interfacial thermodynamics between PC and SAN. Atomic force microscopy was used to provide a unique image of the hole profile.
Monte Carlo Simulation of a Lattice Model of Microemulsions in Porous Media
Authors: Nowroozi Parisa , Sahimi Muhammad
Published: April 2011

Monte Carlo simulations are used to study various properties of a new lattice model of microemulsions. In particular, we calculate the critical exponent β of the order parameter (water concentration) and the correlation length exponent ν, and find them to be in excellent agreement with those of the 3D Ising model, and also in agreement with the experimental measurements. However, when the same exponents are calculated for the microemulsions in a porous medium, they do not agree with those of either the dilute or the random-field Ising model.
Direct Evidence of Surface Roughness in Small Metallic Particles
Authors: Yacaman Miguel Jose , Tehuacanero Samuel , Zorrilla Cristina , Diaz Gabriela
Published: April 2011

The characterization of nanoparticles is of prime importance in catalysis. High Resolution Electron Microscopy coupled with image processing has produce a lot of new information on the detailed structure of the particles. In this paper we discuss the possibility of applying these techniques to the study of surface roughness.
Electronic and Structural Requisites for Catalytic Activity in Copper-Ruthenium Catalysts
Authors: Malaty M. , Singh D. , Vadel Noel , Gomez M.L. , Palmieri M. , Jansen S.A. , Lawrence S.
Published: April 2011

A system made by combining two non-alloying metals, ruthenium and copper, using alumina as a support was studied. This bimetallic supported catalyst has been used mainly in hydrogenolysis, dehydrogenation and oxidation reactions of hydrocarbons. The samples were characterized by Electron Paramagnetic Resonance Spectrometry (EPR) and X-ray Diffraction (XRD). These two molecular techniques are ideal for studying the electronic and structural changes of the samples at different temperatures and concentrations. Catalytic reactions were performed using the catalyst in the reduced and non-reduced forms on a series of catalytic hydrogenations. A correlation between the electronic, structural and catalytic properties has been made. A correlation of catalytic process to molecular phenomena has yield a better understanding of the catalytic site.
EPR Analysis of Copper Exchanged and Encapsulated Copper (SALEN) Complex in Zeolite - Y
Authors: Ulagappan N , Krishnasamy V
Published: April 2011

Copper exchanged and copper-(salen) complex encapsulated in zeolite-Y were prepared. The encapsulaled complex was analysed by TGA, DRS and IR, which confirms the presence of complex in zeolite. Both copper materials were examined by EPR spectra, and the calculated spin-Hamiltonian parameter indicates the copper complex is more covalent in character than NaCu-Y.
Selective Hydrogenation of Crotonaldehyde Over Cobalt Based Self-Supported Catalysts
Authors: Patil A. N. , Bañares M. A. , Lei X. , Fehlner T. P. , Wolf E. E.
Published: April 2011

Complex cobalt-carbonyl ligand based clusters of clusters are used as molecular precursors for self-supported model catalysts. These precursors consist of two metal layers: an outer of the complex Co-carbonyl ligands, and a core of metal (e.g. Co or Zn) carboxylate groups. Partial thermolysis at low temperature (LT) of these materials under hydrogen results in almost completely decarbonylated material with a mainly unchanged carboxylate metal core. Complete pyrolysis at higher temperatures (HT) in hydrogen leads to mixed metal environment. These materials were used as a heterogenous catalyst in the gas phase hydrogenation of crotonaldehyde. The maximum yield of 27 % of desired product crotyl alcohol was observed when HT-CoCo was used as the catalyst at 423 K. The catalyst activity and the crotyl alcohol selectivity remained unchanged over 2 days of operation. The bimetallic ZnCo catalysts showed lower selectivity to crotyl alcohol than the CoCo catalysts.
Synthesis and Properties of Lanthanide-Exchanged Preyssler's Heteropolyanions
Authors: Antonio Mark R. , Malinsky J. , Soderholm L.
Published: April 2011

Na+ in the Preyssler heteropolytungstate anion [NaP5W30O110]14− can be exchanged for a trivalent lanthanide ion. The potential significance of this new class of lanthanide heteropolyanions relates to their applications in catalysis science. This view follows from the fact that Keggin heteropolyanions and their free acids are used as heterogeneous solid catalysts and homogeneous solution catalysts. We describe synthetic conditions that lead to the incorporation of Ce3+ and Pr3+ within the Preyssler anion, and the coprecipitation of Ce3+ and the Preyssler anion. Initial studies indicate that the latter, coprecipitated, material deserves study for bifunctional catalytic activity.
EXAFS, XPS and TEM Characterization of SnO2-Based Emission Control Catalysts
Authors: Harrison Philip G. , Daniel Wayne , Lloyd Nicholas C. , Azelee Wan
Published: April 2011

Catalysts formed by sorption of Cr(VI) on to tin(IV) oxide have been investigated by EXAFS, XPS and TEM. The latter shows that uncalcined catalysts comprise uniform, homogeneous particles of dimensions 2nm which increase to 4nm on calcination at 400°C. Calcination at higher temperatures results in an increase in particle size to 20nm × 30nm at 600°C, ca. 60nm at 800°C, and 90–100nm at 1000°C. XPS data show the evolution of chromium(III) species upon calcination and both chromium(VI) and chromium(III) species exist at all calcination temperatures. Chromium K-edge XANES also shows the presence of tetrahedral chromium(VI) species at all calcination temperatures, but the relative abundance decreases with increase in calcination temperature. Corresponding EXAFS data indicate that the uncalcined catalyst contains sorbed four-coordinated {Cr2O7} species whereas calcination produces six-coordinated {CrO6} species together with some residual tetrahedrally coordinated chromium. EXAFS data show that adsorbed {Cu(H2O)6} is the copper(II) species present prior to calcination of CuII-SnO2 catalysts.
Co Oxidation by Bi2MoO6-γ(H) Catalyst
Authors: Galván D. H. , Avalos-Borja M. , Fuentes S. , Cota-Araiza L. , Cruz-Reyes J. , Castillón F. F. , Maple M. B.
Published: April 2011

We present a study of a Bi-Mo catalyst, obtained by solid state reaction, for the oxidation of CO. Bismuth-molybdate catalysts form several phases (β3-Bi2Mo2O9, α-Bi2Mo3O12 and γ-Bi2MoO6, among others), depending upon the Bi/Mo ratio and the preparation method [1]. The γ-Bi2MoO6 phase is the one that is stable at high temperatures, according to the phase diagram, and is the one we used as catalyst for the conversion of CO [2].
Preparation, Characterization and Catalytic Activity of Niobium Oxynitride and Oxycarbide in Hydrotreatment
Authors: Kim H. S. , Sayag C. , Bugli G. , Djega-Mariadassou G. , Boudart M.
Published: April 2011

Oxynitride and oxycarbide of niobium present metallic and acidic catalytic functions as evidenced by molecular probe reactions: isomerization of cyclohexane and hydrodenitrogenation of 1–4 tetrahydroquinoline. The proximity of the two functions leads to the concept of “dual site” by selective inhibition of the metallic and acid sites. Substitution of nitrogen of the oxynitride by carbon to form the oxycarbide produces a large enhancement of the metallic character of the surface. The oxynitride was shown to present a more acidic and a less hydrogenating activity as compared to the activity of the oxycarbide. Both compounds of niobium have been compared to molybdenum oxynitride.
Green Technology for the 21st Century: Ceramic Membranes
Authors: Anderson M. A. , Zeltner W. A. , Merritt C. M. , Anderson Professor Marc A.
Published: April 2011

The nineties have brought us to an era of environmental crisis. We are faced with problems of air pollution, both indoor and outdoor, acid rain, water pollution, hazardous wastes, toxic landfills and leaking storage tanks in our soil, to name a few. Our rapid advances into the industrial and technological age have contributed to these problems. However, our advancing technology in the areas of remediation and such “green” engineering tools as ceramic membranes can certainly make a significant contribution in terms of environmental clean-up and a healthier world.
On the Stability of Mo2N During First-Stage Hydrocracking
Authors: Veen J. A. R. Van , Minderhoud J. K. , Buglass J. G. , Lednor P. W. , Thompson L. T.
Published: April 2011

An unsupported sample of Mo2N has been subjected to a first-stage hydrocracking test. The evolution of the HDS and HDN performance indicated a transformation of Mo2N into MoS2. This was substantiated by XPS and TEM, the latter technique showing that the transformation is limited to only a few surface layers.
Characterization of a Catalytically Active Molybdenum Oxycarbide
Authors: Ledoux Marc J. , Delporte Pascale , Pham-Huu Cuong
Published: April 2011

A very active and selective molybdenum based catalyst for C6+ linear alkanes isomerization as been found. Physical characterization of this new active phase, such as XPS, XRD, MASN-MR and HRTEM is described.
Application of Defect Modeling to Materials Design
Authors: Spears Marlene A. , Tuller H.L.
Published: April 2011

Defect chemical models have been found to be useful in establishing defect generation andtransport mechanisms, extracting thermodynamic data and deconvoluting contributions to the total electrical conductivity. In most cases, however, the utility of the approach has been limited due to the imposed simplifications made to make the analysis more tractable, e.g. the simplified neutrality relation and the elimination of defect associates. In thiswork, we treat more complex equilibria with the aid of numerical methods and illustrate how this approach can be used, not only to extractkey thermodynamic and kinetic data, but also to assist in the design and optimization of materials. Some specific examples with application to solid state ionics will be used to illustrate this approach.
Pulse Applications of Electrochemical Cells Containing Insertion Reaction Electrodes
Authors: Huggins Robert A.
Published: April 2011

There is a rapidly increasing interest in energy sources optimized to provide electrical energy at high power levels for short times. Applications include very short pulses for digital electronic devices, the somewhat longer power pulse demands of some implantable medical devices, and the much larger transient power needs in connection with vehicle traction.

Several mechanisms can be used to provide short term energy, with fundamentally different characteristics and applicability to different types of transient output requirements.

Four different electrochemical methods can be used to evaluate the critical materials parameters in insertion reaction materials that might be applicable to such applications, and spreadsheet techniques can be used to model the transient transport behavior of such electrodes under various conditions. LaPlace transform methods can then be used to convert information about the physical mechanisms and parameters of individual components into the dynamic response of an electrochemical system.
Non-Stoichiometry and Cation Tracer Diffusion Studies in the Magnetite-UlvÖSpinel Solution, (Fe,Ti)3-δO4
Authors: Aggarwal Sanjeev , Dieckmann Rudiger
Published: April 2011

Cation diffusion in the spinel solid solution (Fe1-xTix)3-δO4 (0≤ x ≤ 0.3) was investigated at 1200 ºC as a function of oxygen activity, aO2 and cationic composition, x. At different cationic compositions, cation tracer diffusion coefficients, D*Me of Me = Fe and Ti were measured as a function of oxygen activity. Plots of log DMe vs. loga0 show V-shaped curves, indicating that different types of point defects prevail at high anc low oxygen activities. Thermogravimetric experiments were conducted, using a high resolution microbalance, to determine the deviation from stoichiometry in (Fe1-xTix)3-δO4 at 1200 °C. δversus log aO2 curves are S-shaped. An analysis of the oxygen activity dependences of thecation diffusion coefficients and the deviation from stoichiometry with regardto the point defect structure suggests that at high oxygen activities cation vacancies are the predominant defects governing the deviation from stoichiometry and the diffusion ofcations. At low oxygen activities, and at small values of x, cation interstitials determine the deviation from stoichiometry, while they dominate for 0 ≤ x ≤ 0.3 inthe cation diffusion.
Nonstoichiometry and Point Defect Structure of Olivines, (FexMg1-x)2SiO4
Authors: Tsai Tse-Lun , Dieckmann R.
Published: April 2011

A thermogravimetric study was conducted on synthetic olivines (FexMg1-x)2SiO4' prepared either by a conventional ceramic methodor a sol-gel method, to determine the nonstoichiometry and the point defect structure. Measurements were carried out as a function of oxygen activity and cationic composition at elevated temperatures. To avoid the dissolution of transition metal components of the silicate into noble metal containers, commonly used in previous investigations, quartz containers were used. The analysis of the point defect structure of olivines based on the new experimental results is presented.
Study of Ac Conductivity in Dilute CeO2:Y3+ Ceramics
Authors: Vaysleyb A.V. , Lim B.S. , Nowick A.S.
Published: April 2011

The ac conductivity was studied for different compositions of CeO2 ceramics, undoped and doped with Y3+ ions in the composition range 1 to 12 atomic %Y over the temperature range from 50 K to 500 K. It was observed that in temperature range 300-400 K, the ac conductivity (as well as the real part of the dielectric constant, ε',) follows the universal power-law frequency dependence with exponent s ≈ 0.63. No systematic variation of s, either with temperature or with dopant concentration, was observed, although for nominally “pure” CeO2 no power-law regime was observed. The features of the ac behavior were explained on the basis of a percolation approach.
Xas Studies of Peo Based Polymer Electrolytes
Authors: Mcbreena J. , Yang X. Q. , Lee H. S. , Okamoto Y.
Published: April 2011

X-ray absorption spectroscopy (XAS) has been very useful in elucidation the structure of polymer electrolytes, in particular ion-ion and ion-polymer interactions. Several examples are discussed. One is the use of XAS to study the effect of temperature on ion pairing. The other is the elucidation of the mixed cation effect on electrolyte conductivity. Several investigations have indicated abnormally high oxygen coordination numbers for cations. These are discussed.
Polyaniline: Influence of Polymerization Current Density
Authors: Skaarup Steen , Gunaratne L.M.W.K. , West Keld , Zachau-Christiansen Birgit
Published: April 2011

Polyaniline has been synthesized in propylene carbonate by galvanostatic electrochemical polymerization at current densities between 16 and 1000 μA/cm2. Earlier results for polypyrrole have shown that low and high current density films have different properties: The films synthesized at low current density have a higher conjugation length and a more regular structure. The corresponding effect in PANI has been investigated by cyclic voltammetry and UV/visible spectroscopy. Simultaneous measurement of cyclic voltammograms and the absorbtion of selected spectral lines is used because of the complex nature of the PANI system which involves several redox systems as well as forms differing in the degree of protonation and morphology.

The main result is that the method of galvanostatic synthesis at low current densities (-16 μA/cm2) produces polyaniline polymers of different, more conjugated and more regular structure than those prepared at higher current densities. The standard method of in situ layer-by-layer polymerization of conducting polymers during cyclic voltammetry often results in uncontrolled and unmeasured current densities of 0.5-2 mA/cm2 which produces a film that probably has a less regular structure containing more deviations from ideality.
Sensors for Acid-Base-Active Gases
Authors: Maier Joachim , Holzinger Michael , Sitte Werner
Published: April 2011

The theoretical background for potentiometric and conductometric (bulk and surface) sensors is briefly discussed with regard to the usual application, viz. the detection of redox-active gases, and the importance of understanding chemical diffusion is stressed in this context. It is then shown how the analogous concept applied to acid-base interactions leads to powerful possibilities to measure partial pressures of acid-base active gases such as CO2, NH3 and H2O. Two examples of novel sensor principles are discussed: i) The response of the surface ionic conductivity of AgCl or CaF2 upon changes of partial pressures of (Lewis) basic or acid gases can be used to sense NH3 and BF3. ii) In the major part of the paper it is shown how the deliberate use of overall acid-base cell reactions in potentiometric arrangements leads to a fast and precise CO2-sensor. For this purpose, open reference electrodes based on Na2Ti6O13 or Na2SnO3 have been constructed. Owing to the criteria developed in the text the whole cell can be exposed to a CO2 and O2 containing atmosphere without the necessity of sealing. Detailed results are given.
Fabrication of V2O5 Thin Films and their Electrochemical Properties in Lithium Microbatteries
Authors: Julien C. , Gorenstein A. , Khelfa A. , Guesdon J.P. , Ivanov I.
Published: April 2011

Thin films of V2O5 were prepared using the flash-evaporation technique. Amorphous and polycrystalline samples were characterized by X-ray diffraction, Raman spectroscopy and XPS analysis. The electrical properties of the samples were determined. The effect of either deposition parameters or post-deposition treatments, i.e., annealing in various atmospheres and at different temperatures, on transport properties are presented.

Electrochemical characteristics are evaluated in V2O5/LiCIO4-PC/Li microbatteries. The discharge curves present several voltage plateaus, similar to those already observed in cells with bulk V2O5 cathodes. Kinetics of lithium intercalation have been investigated as a function of the growth conditions of V2O5 films. Chemical diffusion coefficient and enhancement factor are calculated as a function of the degree of lithium intercalation. All the results are compared with previous reported results for bulk vanadium oxides. The relationship between the crystallinity of the films and their electrochemical features is also discussed.
Thin Film Fuel Cells
Authors: Van Dieten V.E.J. , Dekker J.P. , Schoonman J.
Published: April 2011

In recent years there has been an enormous increase in the application of thin film technologies in the fabrication of solid state electrochemical devices. Devices in which thin film components are utilized are,e.g.solid oxide fuel cells (SOFCs), thin film rechargeable batteries, and chemical gas sensors. Chemical vapour deposition (CVD) is one of the synthesis techniques for the fabrication of thin film components for solid state electrochemical devices. This paper will focus on the application of novel CVD techniques for the fabrication of the thin film components of one of these devices,i.e.the solid oxide fuel cell. A new SOFC design concept which uses only one gas phase synthesis method will be presented.
Thin-Film Electrolytes for Reduced Temperature Solid Oxide Fuel Cells
Authors: Visco Steven J. , Wang Li-Shun , Souza Selmar , Jonghe Lutgard C. De
Published: April 2011

Solid oxide fuel cells produce electricity at very high efficiency and have very low to negligible emissions, making them an attractive option for power generation for electric utilities. However, conventional SOFC's are operated at 1000 °C or more in order to attain reasonable power density. The high operating temperature of SOFC's leads to complex materials problems which have been difficult to solve in a cost-effective manner. Accordingly, there is much interest in reducing the operating temperature of SOFC's while still maintaining the power densities achieved at high temperatures. There are several approaches to reduced temperature operation including alternative solid electrolytes having higher ionic conductivity than yttria stablilized zirconia, thin solid electrolyte membranes, and improved electrode materials. Given the proven reliability of zirconia-based electrolytes (YSZ) in long-term SOFC tests, the use of stabilized zirconia electrolytes in reduced temperature fuel cells is a logical choice. In order to avoid compromising power density at intermediate temperatures, the thickness of the YSZ electrolyte must be reduced from that in conventional cells (100 to 200 μm) to approximately 4 to 10 μm. There are a number of approaches for depositing thin ceramic films onto porous supports including chemical vapor deposition/electrochemical vapor deposition, sol-gel deposition, sputter deposition, etc. In this paper we describe an inexpensive approach involving the use of colloidal dispersions of polycrystalline electrolyte for depositing 4 to 10 μm electrolyte films onto porous electrode supports in a single deposition step. This technique leads to highly dense, conductive, electrolyte films which exhibit near theoretical open circuit voltages in H2/air fuel cells. These electrolyte films exhibit bulk ionic conductivity, and may see application in reduced temperature SOFC's, gas separation membranes, and fast response sensors.
Lithium Intercalation from Aqueous Solutions
Authors: Li W. , Dahn J. R. , Root J. H.
Published: April 2011

Lithium can be intercalated into a variety of materials using aqueous electrochemical methods, provided that certain criteria are met. The materials must be stable in concentrated Li+ aqueous solution and Li intercalation must take priority over hydrogen intercalation. We use X-ray and neutron diffraction, as well as electrochemical methods to investigate if lithium or hydrogen is intercalated into certain hosts. For example, spinel Li2Mn2O4 can be made from spinel LiMn204 by intercalating one Li per mole in an electrochemical cell with 1 M LiOH electrolyte. If the electrochemical reduction is carried out further, beyond one electron per mole, Mn(OH)2 is then formed, as we prove using neutron diffraction. By carefully selecting electrode materials and electrolyte composition it is possible to make rechargeable lithium-ion cells with aqueous electrolytes. For example, LiMn204/γ-Li0.36MnO2 can be selected as an electrode couple, and5 M LiNO3 in water as an electrolyte to make lithium-ion cells with aqueous electrolytes.
Nanostructured Organic/Inorganic Films from Poly (D-Lysine Hydrobromide) or Poly(N-Methyl.4-Vinyl Pyridinium Bromide) and Hectorite
Authors: Kleinfeld Elaine R. , Ferguson Gregory S.
Published: April 2011

Establishing the generality of any new preparative method is important for its future usefulness in applications of interest. In this paper, we build on results reported earlier for the formation of nanostructured ultrathin films from macromolecular precursors (a particular cationic polyelectrolyte and inorganic sheet silicate) by demonstrating that the method can readily be adapted to different polymers and more complex adsorption schemes. In particular, we used ellipsometry to monitor the regular growth of films incorporating poly(D-lysine hydrobromide) or poly(N-methyl-4-vinylpyridinium bromide) (PMVP) and hectorite. For the PMVP/ hectorite films, X-ray diffraction confirmed the presence of structural order by revealing a lattice spacing of 1.5 nm.
Microstructural Aspects of High-Performance Cement-Based Materials
Authors: Jiang W. , Roy D.M.
Published: April 2011

The goal of this research is to improve the physical properties, mechanical properties and durability of cement-based materials by controlling chemistry and processing to produce the desired microstructures and properties. An accompanying initiative is to establish the basic scientific understanding relating processing and microstructure with physical and mechanical behavior, for the future development of new, special purpose, high performance cement-based materials. The research involves both experimentation and theory elucidating fundamental strengthening mechanisms for materials such as warm-pressed, MDF, DSP, polymer, and fiber composites. SEM and computer image analysis were used. Of interest are creating process models that serve as a basis for real applications such as in the following areas: High-performance highway concrete, and the immobilization of radioactive waste.
Image Analysis of Fly Ash in the Characterization of the Shape of the Grains
Authors: Barrioulet M. , Cros H. , Husson B. , Ringot E.
Published: April 2011

Fly ash from power stations is used as concrete additive to improve strength and durability. Surprisingly, studies of ashes of identical mineralogical composition from two different places have reported different results in terms of the rheological properties of the fresh material. The viscosity of the pastes made from these different fly ashes seems to be linked to the proportion of spherical and smooth-shaped grains found in them. A quantitative image analysis was carried out to characterize the shape of the grains of these two ashes from different geographical origins. The main result proves that the higher the glassy particle content of the fly ash, the more the hydraulic matrix is fluid.
Microstructure and Microchemistry of Calcium Sulfoaluminate Cement
Authors: AndaÇ Ö. , Glasser F.P.
Published: April 2011

Calcium sulfoaluminate, 4CaO • 3Al2O3 • SO3, forms the basis of a new class of structural cements. Microstructural examination of commercial clinker is not easy because it is quite friable. However, backscattered imaging of impregnated clinker is successful and reveals an unusual pattern. The clinker has a sponge-like texture connecting better-sintered, denser regions. The microstructure is, however, very similar between regions of differing density. Irregular to equant, well-shaped crystals of 4CaO • 3Al2O3 • SO3 are enclosed in a matrix composed mainly of Ca2SiO4 together with a little titanium-rich, ferrite-like phase. The minor phases occluded within ferrite include oxide phases one of which concentrates Pb and Bi; the other, Cr, Fe and Ni. Other minor oxide phases in the matrix include lime, periclase, gehlenite and calcium sulfosilicate and probably bredigite. The crystal chemistry and elemental analyses of the individual phases are presented.
An Approach to Quantitative Image Analysis for Cement Pastes
Authors: Wang Yuting , Diamond Sidney
Published: April 2011

Cement paste microstructure as revealed in backscatter SEM presents a number of inherent difficulties that interfere with implementing quantitative image analysis. An approach to overcoming these difficulties is presented, involving gray scale segmentation coupled with application of a hole filling algorithm. Using this approach it is possible to isolate the unhydrated and hydrated portions of phenograins separately, and to combine them for analysis of combined phenograins. Pores and coarse calcium hydroxide masses may also be isolated for feature analysis. Results are reported on mature cement pastes prepared at two water:cement ratios (w:c 0.45 and w:c 0.30) and with and without superplasticizer. It was found that superplasticizer greatly reduced the content and the average size of “visible pores” and increased the content and the average size of coarse CH particles compared to corresponding plain pastes. The area per hydrated phenograin was much smaller in the lower w:c ratio pastes and higher in superplasticized pastes. Among the solid features measured, unhydrated cement particles had the smallest circularity values (at about 2.7) and were the most circular features; Hydrated phenograins had the largest circularity values (at 3.5) and were the most elongated features.
Distribution of Pore Sizes in White Concrete
Authors: Best G. , Cross A. , Peemoeller H. , Pintar M.M.
Published: April 2011

NMR is used to study the evolution of the discrete distribution of proton magnetization fractions in hydrating synthetic white cement. The results at 100 hours hydration time are modelled using a trimodel pore size distribution. A good correspondence is found between the NMR analysis and SANS results reported in the literature.
Multitechnique Approach to Understanding the Microstructure of Cement-Based Systems
Authors: Cocke David L. , Yousuf M. , Mollah A. , Vempati R. K. , Hess T. R.
Published: April 2011

The chemistry of cement, its hydration and the development of microstructure in cement-based systems is extremely complex, and it becomes even more complex in the presence of additives. The elucidation of the mechanisms of these processes is a challenging problem and requires the applications of multiple techniques including the latest microscopic methods. The applications of molecular spectroscopies, surface spectroscopies and microscopies have helpeddevelop models and mechanisms for the retardation of cement setting by Zn, Cd and Pb, the chemical and structural effects of superplasticizers, and the interaction of hydrating cement with aggregates, selective sorbents and fillers. The results of these studies indicated that the inhibition of hydration is controlled by dispersion of various charges present in hyperalkaline solution in cement paste. According to this charge dispersal model, the Ca2+ ions from initial hydration form a tightly-bound bilayer with the negatively charged C-S-H surface. Consequent to this intrinsic process, the metalhydroxy or superplasticizer anions immediately surround the bilayer to constitute a trilayer which inhibits further hydration.
Influences of Interfacial Properties on High-Performance Concrete Composites
Authors: Roy D.M. , Jiang W.
Published: April 2011

There is a strong motivation to study the interfacial properties of concrete composites because the interfacial region is often the phase where fracture first develops. The aim of this study is to understand phenomena which are unique at high-performance concrete composite interfaces, and how these influence the bulk properties of a concrete composite. Since processes at interfaces must be considered over a range of scales varying from the atomic to the macroscopic, multidisciplinary research approaches are desirable. Model cement/rock (aggregate) and matrix/fiber interaction experiments were carried out. Morphology and microstructure of interfacial regions among mortar/rock, and fiber/matrix were examined utilizing SEM. Computer image analysis performed along a perpendicular to the interface revealed compositional and physical irregularities. The variations in the volume of pores adjacent to interface zones are documented and supported by microscopic observation. The influences of interfacial properties on concrete composite strength and durability are discussed, and influences of fibers on the fracture and fracture resistance behavior are also discussed. Analyses of debonding along interfaces are used to define the role of debonding in fiber-reinforced concrete composites.