bluuebunny/crossref_metadata_2025 huggingface dataset:
Freezing/Melting Transition of Physically Restricted n-Decane
Authors: Hoffmann P. M. , Malhotra V. M.
Published: April 2011

We undertook differential scanning calorimetry (DSC) measurements at 170 K < T < 300 K on n-decane, physically confined in 8 nm (= diameter D) porous silica derivatized with various functional groups, to understand how surface structure of the confining media affects the freezing or melting transition of the n-decane. Though we observed a typical depression (ΔT) in the freezing or melting transition temperature of the physically confined decane, our results failed to manifest usual linear dependence of ΔT on D−1 when the expected contraction in D, due to the presence of aminopropyl-, hexyl-, phenyl- or trimethyl-groups on the silica surface, was taken into account. However, it is worth noting that a linear behavior was observed between ΔT and D−1 if only alkane-chain derivatized hosts were considered. Our results also indicate that a large fraction of physically confined n-decane (35 to 70 %), depending on the host silica, does not participate either in the melting or freezing transition. The most interesting behavior observed in the present study is the occurrence of the unusual two peaks associated with the freezing transition of physically confined decane. This bimodal behavior is strongly dependent on the chemistry of the confining silica host's surface.
Study of an A+2B--->C Reaction-Diffusion System with Initially Separated Components
Authors: Yen Andrew , Kopelman Raoul
Published: April 2011

The presence of a reaction front is a characteristic feature of a variety of physical, chemical and biological processes. A chemical reaction exhibits a front (spatially localized region where concentration of product is non zero), provided the diffusing reactants are separated in space. We study the reaction front dynamics of a termolecular A+2B--->C reaction with initially separated components in a capillary. The reaction tetra+2Ni2+--->1:2 complex is used, where ‘tetra’ is disodium ethyl bis(5-tetrazolylazo) acetate trihydrate. We measure and compare with theory the dynamic quantities that characterize the kinetic behavior of the system: the global reaction rate R(t), the location of the reaction center xf(t), the front's width w(t), and the local production rate R(xf,t). The non-classical nature of this dynamical system is confirmed.
Adhesion Force Between High Energy Surfaces in Vapor Atmosphere
Authors: Crassous Jerome , Loubet Jean-Luc , Charlaix Elisabeth
Published: April 2011

We report experimental measurements of the adhesion force between metallic substrates in undersaturated heptane vapor atmosphere, with a surface force apparatus. The attractive force between the substrates is strongly dependant of the condensation of a liquid bridge connecting the surfaces. The results show the importance of wetting phenomena for the maximum attractive force: we find that this maximum attraction varies as the power two-third of the curvature of the meniscus connecting the surfaces, in good agreement with the theory of Van der Waals wetting.
Molecular Motion through a Fluctuating Bottleneck
Authors: Eizenberg N. , Klafter J.
Published: April 2011

Molecular motion in a series of cavities dominated by time dependent bottlenecks is studied as a model for molecular pathways in biomolecules. The problem is formulated by coupled rate and Langevin equations and is shown to be equivalent to n-dimensional reaction-diffusion equation where n is the number of cavities visited by the molecules. Results are presented for two cavities and a comparison is made between steady state and non steady state results.
The Escape of Particles from a Quantum Well
Authors: Lavine James P.
Published: April 2011

The escape rate is calculated for an electron in a one-dimensional potential well. First-order time-dependent perturbation theory is used with solutions of Schrödinger's equation and a set of coupled rate equations is numerically solved. The time evolution of an ensemble of one-electron systems is followed and the fraction of systems that remain in a bound state is found to decay exponentially as time passes. The characteristic time constant for the decay grows exponentially with an increase in the well depth. This is analogous to Kramers' result for the classical escape problem.
Diffusion-Controlled Reactions in Micellar Systems
Authors: Tachiya Masanori , Barzykin Alexander V.
Published: April 2011

Reaction kinetics in micellar solutions are studied theoretically with an emphasis on diffusioncontrolled luminescence quenching. Different spatial arrangements of reactants within individual micelles are analyzed and a general method for treating diffusion-controlled reactions in a finite volume employing an effective potential approximation is developed. Several models are considered for the exchange of reactants between micelles including migration mediated by the bulk phase and successive multiparticle hopping through transient channels connecting micelles during their sticky collisions. These results are combined in a general stochastic theory of reaction kinetics in micellar solutions with exchange. The theory is further extended to reactions in clusters of micelles using a continuous time random walk approach. Once the principal features of micellar kinetics are understood, one can extract important structural and dynamic information on the aggregates and their guest molecules by analyzing suitably designed experiments.
Global Reaction Rates from Local Cluster Distributions
Authors: Argyrakis Panos , Kopelman Raoul , Lindenberg Katja
Published: April 2011

The well-known model reactions A+A⇢0 and A+B⇢0 are examined in terms of the microscopic geometric arrangements of the reactants that may possibly lead to reaction. The reaction takes place only upon physical short-ranged collision of the reactants. Different dimensionalities are examined, and for each one of these arrangements all possible arrangements of the reactants are enumarated. Then, the frequency (probability) is taken into account, and an overall rate is formed. This rate is monitored in the course of the reaction in the simulation calculation and compared to the overall rate derived the traditional way from the densities. These two rates agree very well. Finally, the pair correlation functions are calculated as a function of time from the simulation data, and they are also in good agreement with previous studies.
Reaction Kinetics at a Fluctuating Surface: Proton Exchange in Proteins
Authors: Dewey T. Gregory
Published: April 2011

Experimental data for the exchange of protons between proteins and the aqueous solvent is re-examined using a fractal model. The fraction of protons unexchanged from the protein, f is seen to follow a stretched exponential, at long times. For the protein, lysozyme, data over a range of temperatures were considered and accurate fits were obtained with a single, unadjusted scaling exponent, α. The time constant, τ, followed an Arrhenius law and gave an activation energy comparable to that obtained for free peptide exchange. A model is proposed where proton exchange occurs as a result of solvent reacting at the fractal surface of the protein. The protein itself is not treated as static but has units that diffuse to the surface. The diffusion of these units in the long time domain is assumed to be classical. In this model the scaling exponent, α, is related to the spectral dimension of the system. Treating the problem as a reaction of the type A+B→C in a confined region, the exponent is given by: α = (3 − ds)/4 where dS/4 is the fractal surface dimension of the protein. Using the value of 2.17 previously established for the surface dimension of lysozyme, data at 6 different temperatures could be fit with the corresponding α of 0.21. These results show that the fractal structure of a protein can influence difflusional processes of small molecules associating with the protein.
Dynamics of Ferroelectric and Nematic Liquid Crystals Confined in Porous Matrices
Authors: Aliev Fouad M.
Published: April 2011

We performed dielectric spectroscopy measurements to study dynamics of collective modes of ferroelectric (FLC) and molecular motion of nematic (NLC) liquid crystals with polar molecules confined in silica macroporous and microporous glasses with average pore sizes of 1000 Å (volume fraction of pores 40%) and 100 Å (27%) respectively. For FLC the Goldstone and the soft modes are found in macropores. The rotational viscosity associated with the soft mode is about 10 times higher in pores than in the bulk. These modes are not detected in micropores although low frequency relaxation is present. The last one probably is not connected with the nature of liquid crystal but is associated with surface polarization effects typical for two component heterogeneous media. The difference between the dynamics of orientational motion of the polar molecules of NLC in confined geometries and in the bulk is qualitatively determined by the total energy Fs of the interaction between molecules and the surface of the pore wall, which is found Fs ≈ 102erg/cm2.
Critical Dynamics of Contact Line Depinning
Authors: Ertaş Deniz , Kardar Mehran
Published: April 2011

The depinning of a contact line is studied as a dynamical critical phenomenon by a functional renormalization group technique. In D = 2 - ∈ “line” dimensions, the roughness exponent is ζ = ∈/3 to all orders in perturbation theory. Thus, ζ = 1/3 for the contact line, equal to the Imry-Ma estimate for equilibrium roughness. The dynamical exponent is z = 1 – 2∈/9 + O(∈2) < 1, resulting in unusual dynamical properties. In particular, a characteristic distortion length of the contact line depinning from a strong defect is predicted to initially increase faster than linearly in time. Some experiments are suggested to probe such dynamics.
Synthetic Design of Cobalt Fischer-Tropsch Catalysts
Authors: Soled Stuart L. , Baumgartner Joseph E. , Reyes Sebastian C. , Iglesia Enrique
Published: April 2011

We describe synthetic strategies for designing cobalt Fischer-Tropsch catalysts in order to maximize synthesis rates and C5+ selectivity. The support cobalt-precursor interaction must be balanced to maximize dispersion yet allow facile low temperature reduction. The cobalt time yield is independent of support and varies directly as the cobalt dispersion for dispersions in the 0.02 to 0.12 range [1].
Encapsulated Silver Clusters as Oxidation Catalysts
Authors: Crane R. A. , Chao L. C. , Andres R. P.
Published: April 2011

A novel supported metal catalyst has been prepared, that consists of Ag clusters a few nanometers in diameter which are encapsulated in an amorphous silica coating only a few Ångstroms in thickness and are deposited on an oxide support. The synthesis of this catalyst and its physical characterization are described. Its potential use as a selective oxidation catalyst is discussed.
Performance Characteristics of Low-Temperature Co Oxidation Catalysts
Authors: Hoflund Gar B. , Gardner Steven D. , Schryer David R. , Upchurch Billy T. , Schryer Jacqueline , Kielin Erik J.
Published: April 2011

A series of Au/MnOx catalysts with the Au content ranging from 0 to 10 at%, a 19.5 wt% Pt/SnOx catalyst and a commercially available 2 wt% Pt/SnOx catalyst have been examined for activity toward low-temperature CO oxidation. A 1 atm, 10 sccm stoichiometric mixture of CO (1 vol.%) and O2 in He were reacted at 55°C over 100 mg of each catalyst for time periods as long as 20,000 min. Under these conditions a 10 at% Au/MnOx catalyst exhibits the highest activity and the lowest decay. Outgassing experiments indicate that CO2 retention is primarily responsible for the activity decay of the Pt/SnOx catalysts and that the 10 at% Au/MnOx catalyst is not significantly affected by this process.
Preparation and Characterization of New Molybdenum Nitride or Oxynitride Phases
Authors: Marchand Roger J. , Gouin X. , Tessier F. , Laurent Y.
Published: April 2011

Several methods of synthesizing molybdenum nitride or oxynitride fine powders are presented.

We have prepared a γ-Mo2N type oxynitride phase by reacting ammonia with MoO3. The surface area and morphology of the oxynitride powders depend on the synthesis conditions. Characterization of the solids by elemental analysis, X-ray and neutron diffraction, and thermogravimetric analysis shows dramatic modification of the stoichiometry of conventional Mo2N nitride. Aging at room temperature under air results in decreasing the material surface area. The initial surface area can be recovered be fine tuning of experimental conditions. MoCl5 and Ca3N2 are reacted in a molten CaCl2 medium leading to a new Mo2N structure type.

The reaction between molybdenum sulfide and NH3 produces two different phases depending on the reaction conditions. They are structurally related to δ-MoN.
Novel Microfabricated Pd-Au/SiO2Model Catalysts for the Hydrogenation of 1,3-Butadiene
Authors: Krauth Anthony C. , Wolf Eduardo E.
Published: April 2011

Model Pd-Au/SiO2catalysts were prepared via a microfabrication methodology and their catalytic activity was evaluated using the hydrogenation of 1,3-butadiene as a probe reaction. The catalytic particles of the microfabricated catalyst were Pd-Au squares, ranging in composition, each approximately 4 µm in size and separated by 4 µm on a silica/silicon support. The reaction was carried out at atmospheric pressure with a hydrogen to hydrocarbon ratio of 125. The bimetallic catalysts exhibited lower apparent activation energies than the pure Pd catalyst with a minimum occurring at ˜65 at% Pd. Corresponding to the decrease in activation energy, there is an increase in the turnover frequency over the monometallic catalyst at low temperatures, i.e. room temperature. At high temperatures (above 200°C) the pure Pd catalyst has the highest conversion (0.61) and the largest pre-exponential factor (4.71×1016cc/g Pd/s), while the 73 at% Pd catalyst has the lowest conversion (0.45) and the smallest pre-exponential factor (5.59 × 106cc/g Pd/s). The bimetallic catalysts also showed a higher selectivity towards 1-butene than the monometallic catalyst; however, at lower conversions (less than 25%) the pure Pd catalyst was more selectivity towards 1-butene. AFM was used to characterize the surface morphology of each of the samples.
Fine Chemicals Synthesis by Heterogeneous Asymmetric Catalysis
Authors: Wan Kam T. , Davis Mark E.
Published: April 2011

The application of heterogeneous asymmetric catalysis to fine chemicals synthesis is discussed. The asymmetric synthesis of naproxen, a non-steroidal antiinflammatory drug, using a novel, heterogeneous, chiral catalyst is used as an example to illustrate the feasibility to industrial application.
Surface Assembled Hybrid Polymers
Authors: Rose Philip L. , Manziek Larry , Gallagher Michael K.
Published: April 2011

Novel copolymer composite resins have been synthesized using the surface assembled hybrid technology. Monodisperse polystyrene/DVB microspheres with diameters of 5.3 and 7.5 μm and polydisperse carbonaceous and acrylic microspheres with diameters ranging from 5–30 μm have been assembled onto the surface of styrene and acrylonitrile based gel and macroreticular resins.

Carbonaceous adsorbents with holes of controlled diameter on their surfaces have been prepared using the surface assembling technique. Core-shell carbonaceous adsorbents with divergent surface chemistries have been prepared using this technique

Novel catalytic materials have been made and are envisioned using the assembling technique to form short-diffusion path reactive systems. The range of surface functional groups include: strong acid, strong base, palladium, silver, gold and reductive amine-borane.
Synthesis and Characterization of Supported Metal Cluster Catalysts with Well-Defined Structures
Authors: Gates B. C.
Published: April 2011

Nearly uniform supported metal clusters are the focus of this summary, which addresses their synthesis, characterization, and catalytic properties. Supported clusters represented as Ir4and Ir6were prepared on MgO powder by thermal decarbonylation of [HIr4(CO)11]−and [Ir6(CO)15]2−, respectively. The most useful characterization technique for supported clusters is extended X-ray absorption fine structure spectroscopy, but the structure data are limited by the precision of the coordination numbers (about ±20%). Ir4and Ir6clusters on supports catalyze hydrogenation of cyclohexene and of toluene, and they are catalytically distinct from larger iridium particles, although the reactions are structure insensitive (proceeding at about the same rate per exposed metal atom) when catalyzed by metal particles larger than about 1 nm. Thus the concept of structure insensitivity does not extend to supported metal clusters, which are regarded as quasi molecular.
Reticulated Ceramics for Catalyst Support Applications
Authors: Sweeting Truett B. , Norris David A. , Strom Laurie A. , Morris Jeffrey R.
Published: April 2011

The primary use of reticulated ceramics is in molten metal filtration. However, other applications have emerged which utilize the porous nature of these materials, including low mass kiln furniture, low NOx. infrared burners, gas diffusers, hot gas filters, sensors and catalyst supports. In this paper, the use of reticulated ceramics as catalyst supports will be reviewed with emphasis on the manufacture, structure and properties.
Ceramic Foam Catalyst Supports Preparation and Properties
Authors: Richardson James T. , Twigg Martyn V.
Published: April 2011

Successful catalyst supports must fulfill different requirements simultaneously [1]. By serving as a base for catalytic components, they provide good activity and selectivity, but certain physical properties are equally important. For example, small catalyst particles are desirable in order to avoid external heat and mass transfer limitations and to provide high effectiveness for the active component dispersed throughout the particle. However, small particles pack with low bed porosities and unacceptable pressure drop results. Open-pore ceramic foams show promising properties that could overcome these difficulties. They have good high temperature resistance, low bulk density and tortuous flow patterns, together with open porosity as high as 85% formed from megapores 0.04 to 1.5 mm in diameter [2]. Characteristic parameters include cell size, window size and surface area, all correlated with the number of pores per inch [PPI]. Ceramic foams were first used as molten metal filters [3,4] and catalytic combustion devices [5–7]. Catalytic applications are beginning to appear and these have been reviewed by Twigg and Richardson [8].
Preparation of La1−xSrxMnO3 Perovskite Catalysts Supported on Ceramic Foam Materials
Authors: Ismagilov Z. R. , Podyacheva O.Yu. , Ketov A.A. , Bos A. , Veringa H. J.
Published: April 2011

The new method of preparation of La1−xSrxMnO3 catalysts supported on ceramic foam materials was developed. The synthesized supported perovskite catalysts were examined by X-ray diffraction analysis and BET methods. It was shown that in coated samples there is a pure perovskite phase on the support surface up to temperatures of 1000°C.

Unsupported La1−xSrxMnO3 catalysts were synthesized applying co-precipitation technique using La, Sr and Mn acetylacetonates and were studied by X-ray diffraction analysis. Temperature programmed reduction method revealed that catalysts contain 2 types of active centers: low temperature (α) and high temperature (β), the quantity of these centers and correlation between them depend on the value of x. It was shown that supported perovskite catalysts, similarly to the massive ones, maintain two types of active centers (α and β).

The activity of La1−xSrxMnO3 on mullite foam was characterized in the methane oxidation reaction.
Laser Synthesis of Iron Nitride Nanoparticles from Pyrolysis of Fe(CO)5-NH3 System
Authors: Zhao X. Q. , Liang Y. , Zheng F. , Hu Z. Q. , Zhang G. B. , Bai K. C.
Published: April 2011

By vapor-phase pyrolysis of Fe(CO) 5 and NH3 induced by CW CO2 laser, γ'-Fe4N and ε- Fe3N nanoparticles(≤35nm) were prepared in Ar and N2 atmospheres. In Ar, γ'-Fe4N accompanied by a little α-Fe was formed at low temperatures below 650°C, while higher temperatures favored the formation of γ-Fe. In N2 atmospheres, a mixture of Fe4N and Fe3N nanoparticles were obtained at high temperatures. In addition, the influences of synthesis parameters on the structure, morphology and magnetic properties of the nanoparticles were discussed.
Surface Properties of Molybdenum Nitride Thin Films
Authors: Lee Hyuek Joon , Mudholkar Mandar S. , Thompson Levi T.
Published: April 2011

The interaction of NH3 and CH3NH2 with the surfaces of f β-Mo16N7, γ-Mo2N, and δ-MoN films was investigated using thermal desorption spectroscopy. Ammonia temperature programmed desorption (TPD) spectra for the films were similar. Ammonia TPD (adsorption at ∼280 K) produced an NH3 peak at ∼360 K. Some of the NH3 decomposed into H2 and N2. Two H2 desorption peaks were produced: a low temperature peak due to recombination of surface hydrogen and a high temperature peak due to hydrogen that emerged from the nitride subsurface. The N2 desorption spectrum consisted of a peak at ∼340 K and several peaks in the range 500–900 K. The desorption kinetics depended on the structure and composition of the film. 15NH3 TPD experiments indicated that the low temperature N2 desorption peak was due to NH3 decomposition, while the origin of the high temperature peaks was the nitride itself. We believe that nitrogen desorption from the nitride was induced by the presence of hydrogen which altered the Mo-N bonding. Three different CH3NH2 decomposition processes were observed: complete decomposition of CH3NH2 into H2, N2 and C, partial decomposition into HCN, and simple C-N bond hydrogenolysis into CH4 and NH3. The decomposition pathways depended on the structural and compositional properties of the films. All three processes were observed for the β- Mo16N7 (400), β-Mo16N7 (203) and δ-MoN(002) films, while only trace amounts of HCN were detected for the γ-Mo2N(200) film, suggesting that the partial decomposition into HCN was not favored on this surface. The β-Mo16N7 (400) and δ-MoN(002) films had the high selectivities for simple C-N bond cleavage.
Palladium Carbide Formation in Pd/C Catalysts and its Effect on Adsorption, Absorption and Catalytic Behavior
Authors: Krishnankutty Nalini , Vannice M. A.
Published: April 2011

The presence of PdCx, a metastable palladium carbide phase, was detected in Pd dispersed on high surface area carbon blacks using a Pd acetylacetonate precursor. TEM and XRD measurements indicated well dispersed Pd after reduction at 573 K; however, hydride formation and chemisorption of gases was suppressed on these catalysts and this was accompanied by lattice expansion of Pd as seen from XRD. Cleaning pretreatments with O2slightly contracted the Pd lattice and enhanced hydride formation and chemisorption, while a 673 K reduction gave normal hydride ratios and Pd lattice parameters although chemisorption was still suppressed. Pd lattice expansion and suppression of hydride formation and chemisorption are attributed to carbon atoms present both in the bulk and on the Pd surface. The performance of these catalysts in probe reactions was consistent with this model of C contamination of the Pd surface and bulk.
Dissolution-Recrystallization Processes of Nickel Hydroxide, The Active Material of the Ni/CD and Ni/H2Cells
Authors: Delahaye-Vidal A. , Sac-Epee N. , Portemer F. , Beaudoin B. , Figlarz M. , Jamin T.
Published: April 2011

Several examples of dissolution-recrystallization processes at the nickel hydroxide electrode are reviewed. Some of them are very well known and have been studied for a few yearsin the case of Ni/Cd cells. The cycling of the ∝-type nickel hydroxide leads to the ∝→β transformation through dissolution of the a phase in the electrolyte (KOH) and recrystallization of the β phase from the solution. Further cycling of the resulting βex ∝phase causes an ageing effect which occursvia the solution (Oswald ripening). More recently, a strong ripening phenomenon has been observed by studying the behavior of nickel hydroxides cycling in Ni/H2cells. By simulating the ageing of charged and discharged materials under hydrogen pressure inKOH media, it has been shown that in the absence of voltage, hydrogen cannot be responsible for the strong ripening effect. Synergetic effects between hydrogen and voltage have to be considered.
Roughness Effect on the Lithium Diffusivity in WO3 Thin Films
Authors: Maaza M. , Gorenstein A. , Sella C. , Bridou F. , Pardo B. , Corno J. , Rogera G. , Bohnke O. , Julien C.
Published: April 2011

In this work, we investigate the influence of surface roughness on the kinetics of Li+ during the insertion process in the well-known electrochromic material WO3. Thin films 500 Å thick have been grown by rf-sputtering and annealed in therange of 25-350ºC. Grazing angle X-ray reflectometry shows that the film roughnessincreases considerably with thermal treatment. These measurements are correlated with chemical diffusion investigations obtained by electrochemical titration in Li/WO3 cells.
Electrochemical Study, Synthesis and Microstructural Characterization of Lithium and Sodium Inserted W18O49.
Authors: Cruz A. Martinez De La , Torres-Martinez Leticia M. , Garciaalvarado F. , Moran E. , Alario-Franco M. A.
Published: April 2011

The formation of lithium inserted W18O49 phases has been studied byelectrochemical methods. When lithium is inserted, several single phases LixW18O49 are observed in the range 0 ≤ x ≤ 40 between 3 and 1 V. Nevertheless the reaction is reversible only for x ≤ 22. Chemical reactions of W18O49 with different quantities of n-butyllithium have been carried out to isolate and characterize some of these phases. For Li17W18O49, this is ˜1:1 Li/W ratio, electron diffraction experiments clearly indicate that lithium produces a periodicity change, doubling the a, b and c cell parameters. On the other hand, when sodium is inserted in W18O49 two single phase regions NaxW18O49 are observed within the range 0 ≤ x ≤ 1.2 between 3 and 0.5 V.
Properties of LiV308 Cathode Materials Prepared from Gels by Spray-Drying
Authors: Saidi M. Y. , Olsen I. I. , Koksbang R. , Barker J. , Pynenburg R. , West K. , Zachau-Christiansen B. , Skaarup S.
Published: April 2011

LiV308 powder has been prepared on a large scale by spray drying ofan aqueous gel. The material was further dehydrated at 150 and 350ºC. These materials were characterized by TGA, XRD and electrochemical methods. Materials dried at 150 and 350ºC, showed an unusual high reversible capacity, close to 4 Li per formula unit, and cycle well. The material dried at 350ºC is very similar to the crystalline LiV308 prepared by conventional high temperature synthesis.
Calculation of Defect Formation Energy from the Thermal Expansion Data for Lead Fluoride
Authors: Schuler Brenda J. , Aurora T. S. , Pederson D. O. , Day S. M.
Published: April 2011

Lead fluoride is a superionic conductor with the fluorite structure. Results of the measurement of linear thermal expansion of lead fluoride (reported earlier in literature) showed a large increase in the thermal expansion coefficient near 700 K where the ionic conductivity has been shown to exhibit a sharp increase. It is believed that thermally-generated defects in a crystal lattice affect the thermal expansion coefficient. This idea was applied in the present analysis to calculate the defect formation energy (Ef) by using the literature values of the coefficient of thermal expansion. It was assumed that the thermal expansion in excess of that produced due to the lattice anharmonicity (δ∝) is proportional to the concentration of defects (n). With this assumption, one may write: δ∝ = c nº exp(-Ef/kT), where c is a constant. For lead fluoride, a plot of ln(δ∝) versus (l/T) yielded Ef = 0.56 eV which is lower than the literature values. The assumptions in this analysis and the discrepancy in the result are discussed.
A Study of the Electrocatalytic Properties of SrCo0.8Fe0.2O3-δ by Impedance Spectroscopy
Authors: Pham Al Quoc , Jacobson Allan J.
Published: April 2011

The electrocatalytic behavior of the mixed electron - ion conductor SrCo0.8Fe0.2O3-δ, in the form of an electrode on YSZ, has been studied using impedance spectroscopy at low frequencies. The results suggest that the electrode process is dominated by the surface exchange at high temperatures and by the bulk oxygen diffusion at lower temperatures. No limiting current was observed in I-V measurements. The electrode polarization decreased with increasing current density. The creation of additonal oxygen vacancies in the electrode material is suggested to account for the better performance at the higher current densities.
Structural, Electrical and Optical Properties of Laser Deposited Thin Films of Srco0.8Fe0.2O3-δ
Authors: Zhang C. , Deng H. , Varon J. , Abeles B. , Yang Y. , Pham A.Q. , Jacobson A.J.
Published: April 2011

Thin film SrCo0.8Fe0.2O3-δ were made by pulse laser deposition. The electrical conductivity is thermally activated in the temperature 25-500 °C with an activation energy of 0.17-0.19 eV and is temperature independant from 500-800 °C. The optical absorption shows characteristic features which are interpreted qualitatively in terms of a simple band structure diagram.
Measurement of Partial Conductivities in Mixed Conductors Using Blocking Electrodes
Authors: Pham Al Quoc , Jacobson Allan J.
Published: April 2011

The blocking electrode method commonly used for the determination of the partial conductivities in a mixed ionic-electronic conductor has been suspected by several authors to give incorrect results in some cases. Experimental evidence illustrating the limitations of this method are presented. The resistance of three pellets of YSZ, the middle one playing the role of a “mixed” conductor, was studied by ac impedance spectroscopy. The imperfect contacts on a microscopic scale formed at the interface between the blocking electrodes and the sample were shown to give rise to additional resistances which cannot be separated from the total bulk resistance. The method was also used to study the conductivity of gold metal. Despite the presence of the ionically blocking electrodes an electronic current is observed. This electronic leakage current is due to the interaction with the gaseous environment, the mixed conductor playing the role of an electrode for the conversion of oxygen ions to electrons.
Synthesis, Characterization and Electrochemical Study of the Solid Solution LixNa0.875−δFe0.875Ti1.125O4 (0 ≤ δ ≤ 0.4, x ≥ 0)
Authors: Kuhn Alois , Garcia-Alvarado F. , Moran E. , Alario-Franco M.A.
Published: April 2011

The calcium ferrite type structure of Na0.875Fe0.875Ti1.125O4[1] has double tunnels which are occupied by double rows of sodium atoms running along the b-axis. We have partially removed sodium from this compound at moderate temperatures with different oxidizing agents. Electrochemical studies show that the resulting materials, Na0.875Fe0.875Ti1.125O4 (0 ≤ δ ≤ 0.4), can reversibly intercalate lithium at potentials between 3.8 and 1 volt. At the lowest voltages, a compound containing ∼ 0.5 lithium per formula is formed. By chemical reaction of Na0.875Fe0.875Ti1.125O4 with n-butyllithium, the maximum lithium content also corresponds to Li0.5Na0.875Fe0.875Ti1.125O4. This suggests that many more than the one eighth of the empty sodium sites, per unit cell, of the parent phase are now being occupied by lithium.
Molecular Layer Processing of Polyaniline via the Use of Hydrogen Bonding Interactions
Authors: Stockton William B. , Rubner Michael F.
Published: April 2011

Molecular layer-by-layer build-up on a variety of substrates is demonstrated for doped polyaniline (PAn) alternating with non-ionic water soluble polymers. The adsorption is enabled by the strong interchain interactions with PAn, such as hydrogen bonding. Multilayer build-up has been demonstrated with four distinctly different non-ionic water soluble polymers: poly(vinyl pyrrolidone) (PVP), poly(vinyl alcohol) (PVA), poly(acrylamide) (PAAm), and poly(ethylene oxide) (PEO). Thus, non-ionic water soluble polymers containing a wide variety of functional groups such as amide, hydroxyl or ether groups can be used to successfully fabricate multilayer thin films with polyaniline. FTIR spectroscopy measurements show the PAn to be hydrogen bonded in these multilayer films. Conductivities for multilayer films are on the order of 1-4 S/cm for films doped with methane sulfonic acid. Conductivities on the order of 0.1 S/cm can be achieved for a single mixed layer self-assembled from a mixed solution of PAn/PVP or PAn/PAAm.
Performance of Polymer-Based Supercapacitors
Authors: Arbizzani Catia , Mastragostino Marina , Meneghello Luca
Published: April 2011

Supercapacitors are now attracting much attention as an electric vehicle power source. The present study focuses on redox supercapacitors with electronically conducting polymers as electrode materials. Performance data of a symmetric supercapacitor based on p-doped poly(pyrrole), of an unsymmetric supercapacitor based on p-doped poly(pyrrole) and poly(3-methylthiophene), and of a symmetric sypercapacitor based on p- and n-doped poly(dithieno[3,4-b:3',4'-d]thiophene) are here compared.
Electrochromism and Photochromism of WO3 Thin Films
Authors: Lefrou C. , Marrot O. , Garot F.
Published: April 2011

A photochromic effect is observed in WO3-based electrochromic devices with an ion-conducting polymer as electrolyte. Upon exposure to sun light, the electrochromic cells become blue. This is due to a change of color of the WO3 electrode. The photoeffect on this layer is due to a simultaneous insertion reaction (reduction) of the WO3 material and a photooxidation of water contained in the polymer. It is reversible and therefore not destructive for the complete device. The study of the transmittance and rest potential as a function of the time of exposure to light shows that a steady state is reached in c.a. 10 hours. The addition of U.V.-cut filters changes the reached steady-state, indicating that the photochromic effect is dependent upon the structure of the WO3 material.
High Rate Deposition of Nickel Oxide Electrochromic Thin Films by Reactive DC Magnetron Sputtering
Authors: Yoshimura Kazuki , Miki T. , Tanemura S.
Published: April 2011

Nickel oxide electrochromic thin films were prepared by reactive DC magnetron sputtering. As-deposited optical property and electrochromic behavior strongly depended on the target operation mode and the substrate temperature. In the condition of low oxygen flow ratio (∼1%), the deposition rate can be raised up to 40 nm/min at the power of 60 W. The sample with the deposition rate of 30 nm/min exhibited the best electrochromic performance when the substrate temperature was kept to 200°C-300°C during sputtering. The integrated luminous transmittance of the best sample could be controlled from 6.6% to 82.3%.
Proton Intercalation in γ-MnO2 from Ramsdellite to Groutite Through Groutellite
Authors: Chabre Yves , Pannetier Jean
Published: April 2011

This paper presents an investigation of electrochemical proton intercalation in two chemically prepared MDs containing low amounts of structural defects and in a natural MD containing 89%of highly crystalline ramsdellite. XRD examination of equilibrated partly reduced synthetic samples confirms the formation of groutite as a final reduction product and, before mid-reduction, suggests the formation of a solid solution between ramsdellite and groutellite H0.5MnO2. In contrast, electrochemical spectroscopy hint at a two-phase process with an equilibrium potential at –60 m V vs Hg/HgO. The implication of the structural defects on these observations are discussed.
Pore Structure and Moisture Properties of Cement-Based Systemsfrom Water Vapour Sorption Isotherms
Authors: Baroghel-Bouny Veronique , Chaussadent T.
Published: April 2011

This paper presents results obtained for hardened cement pastes and concretes, ordinary and very-high-performance materials, concerning pore structure and moisture properties.

Because of the inadequacy of classical pore investigation methods (mercury intrusion, nitrogenadsorption) to provide the exact pore network characteristics of cement-based systems, notably in the case of very-high-performance materials, a more pertinent type of experiment was carried out: water vapour desorption and adsorption measurements.

From these experiments, isotherms were determined at hygrometrical equilibrium and at constant temperature (T = 23 °C) for every desorption/adsorption path. The analysis of these curves gives textural parameters in the mesopore range, not accessible by most of other methods. Thus, from the adsorption curve, the specific surface area accessible to water molecules was calculated by the B.E.T. method. The statistical thickness of the water film adsorbed on the solid surface was also determined. And finally, application of the B.J.H. method on the desorption branch provides relevant porosity values and pore size distribution of the hardened materials, and especially intrinsic characteristics of C-S-H hydrates.

This makes it possible to point out the similarities and the differences between the materials, regarding microstructure and moisture properties, and to quantify the influence of mix parameters such as water-cement ratio or silica fume content.
Fracture Surfaces of Cement Pastes, Rocks, and Cement/Rock Interfaces
Authors: Mindess S. , Diamond S.
Published: April 2011

Stereo pair imaging in a scanning electron microscope was used to document the details ofthe topography of fracture surfaces at various degrees of magnification. The fracture surfaces had been produced by fracture testing of chevron-notched beam specimens according to ISRM Method I. The surfaces examined included the fracture surfaces of dolomite and andesite rocks, cement pastes with and without silica fume, the fracture surfaces from specimen prepared by casting cement paste on previously fractured rock specimen faces, and the fracture surfaces of mortars prepared using the same rock types and cement pastes. The principal topographic features of the various fracture surfaces are described.
Chemical Models for the Mechanisms that Influence the Nature and Structure of the Interfacial Transition Zone
Authors: Cocke D. L. , Mollah M. Y. A. , Lin T.-C. , Vempati R. K. , Hess T. R.
Published: April 2011

The chemical nature and microstructure of the interfacial transition zone (ITZ) are influenced by the interfacial mechanisms of hydration which are primarily controlled by surface and nearsurface phenomena. Recent works from our laboratory involving superplasticizers, metal anions that retard hydration and interaction with silicate based aggregates have established that the interfacial chemistry is of fundamental importance in understanding the mechanisms of CSH formation, surface chemical compound formation and mineralization of the interfacial transition zone and its interaction with the hydrated cement particles and the aggregate. A surface charge control reaction model that accounts for :he importance of calcium and other cations and anions will be outlined and used to discuss the interfacial physical chemistry of the ITZ and its ultimate chemical nature and structure.
Interface Transition Zone and the Elastic Modulus of Cement-Based Composites
Authors: Simeonov Peter I. , Ahmad S.H.
Published: April 2011

The influence of the Interface Transition Zone (ITZ) on the elastic modulus of concrete is demonstrated as a divergence of the experimental data from the general trend of the theoretical Hashin-Shtrikman bounds. This divergence is well related to the W/C of the composite. With reduction of W/C the influence of ITZ decreases and for values close to 0.4 and lower it is insignificant.

The formation of the ITZ is characterized by a transfer of water from the matrix to the surface of the aggregates. As a result of this a highly porous ITZ is formed while the matrix remains with a reduced porosity. This process can also be described as a transfer of material properties. For some compositions the balance of this transfer can approach zero. The imbalance in this process is more pronounced at higher W/C.

The effect of Interface Transition Zone can be successfully simulated by the help of recently derived Hashin's variational bounds for two-phase composites with imperfect interfaces.
A Method for Estimating the Dynamic Moduli of Cement Paste-Aggregate Interfacial Zones in Mortar
Authors: Cohen Menashi D. , Lee Turng-Fang F. , Goldman Ariel
Published: April 2011

The objective of this paper is to propose a method to estimate the average values of the dynamic modulus of elasticity and the dynamic shear modulus of cement paste-aggregate interfacial zones in mortar by applying the Logarithmic Mixture Rule (LMR). Both portland cement mortars (PC mortars) and portland cement mortars with silica fume (SF mortars) are investigated and compared, The influence of silica fume on the dynamic moduli of interfacial zone is also examined. Results indicate that for the specific ingredients and mix design used, the dynamic modulus of elasticity of interfacial zone falls between 0.4 and 2.0 (×10 6 psi) for PC mortar and 1.2 to 2.2 (× 106 psi) for SF mortar. These values are lower than the values obtained for PC mortar (4.2 ×106 psi), PC paste (2.7 ×106 psi), SF mortar (4.4 ×106 psi), and SF paste (2.5 × 106 psi).
Fibre-Cement Paste Transition Zone
Authors: Agopyan Vahan , Savastano Holmer
Published: April 2011

The characteristics of fibres and paste of ordinary Portland cement transition zone are analysed and correlated to the mechanical properties of the produced composites. The water-cement ratio of the matrix varies from 0.30 to 0.46 and the age of the specimens varies from 7 to 180 days. Composites of vegetable fibres (coir, sisal and malva) are compared with those of chrysotile asbestos and polypropylene fibres. The analysis is made by backscattered electron image (BSEI) and energy dispersive spectroscopy (EDS). Mechanical tests evaluate the composite tensile strength and ductility.

Mainly for vegetable fibre composites the transition zone is porous, cracked and rich in calcium hydroxide macrocrystals. These results are directly associated with the fibre-matrix bonding and with the composite mechanical performance. Further studies considering the impact performance of the composites compare the porosity of the transition zone with the toughness of the composites.
The Microstructure of Wood Fiber Reinforced Cementitious Composites
Authors: Lin X. , Silsbee M.R. , Roy D.M.
Published: April 2011

Wood fiber reinforcing of cement matrices is an economic and an efficient approach to producing high performance cementitious composites. In this study, wood fiber reinforced cementitious composites (WFRCs) were made by using both conventional and novel processing styles. Wood fibers exhibited a considerable ability to improve the flexural strength and the toughness of WFRC when an adequate content of the fibers was used. The morphologies ofvarious type of wood fibers and fracture surface of WFRC were examined by scanning electron microscope (SEM) and an environmental scanning electron microscope (ESEM). The microstructures of wood fiber and WFRC were correlated with their mechanical properties. Results indicate a significant interfacial bonding between the cement matrix and the wood fibers.
Bond-Slip Mechanisms in Steel Micro-Fiber Reinforced Cement Composites
Authors: Banthia N. , Yan N. , Chan C. , Yan C. , Bentur A.
Published: April 2011

Bond-slip characteristics for steel micro-fibers bonded in cement-based matrices were investigated by conducting single fiber pull-out tests. The influence of the following factors was investigated: fiber inclination, fiber size, fiber embedded length and matrix refinement using silica fume. It was found that the bond-slip characteristics of fibers aligned with respect to the loading direction were necessarily superior than those inclined at an angle. Inclined fibers supported smaller peak pull-out loads and absorbed lesser pull-out energies than the aligned fibers. The use of silica fume in the matrix was found to improve both theaverage interfacial bond strengthand themaximum interfacial bond strengthbetween the fiber and the matrix.
X-Ray Microtomography of an Astm C109 Mortar Exposed to Sulfate Attack
Authors: Bentz D.P. , Martys Nicos. S. , Stutzman P. , Levenson M. S. , Garboczi E.J. , Dunsmuir J. , Schwartz L. M.
Published: April 2011

X-ray microtomography can be used to generate three-dimensional 5123 images of random materials at a resolution of a few micrometers per voxel. This technique has been used to obtain an image of an ASTM C109 mortar sample that had been exposed to a sodium sulfate solution. The three-dimensional image clearly shows sand grains, cement paste, air voids, cracks, and needle-like crystals growing in the air voids. Volume fractions of sand and cement paste determined from the image agree well with the known quantities. Implications for the study of microstructure and proposed uses of X-ray microtomography on cement-based composites are discussed.
Effects of Microstructure on Fracture Behavior of Hardened Cement Paste
Authors: Ahmed Asif , Struble Leslie
Published: April 2011

Mechanical properties of any material, including hardened cement paste, are assumed to be controlled by its microstructure. An attempt has been made here to establish a link between bulk fracture parameters of hardened cement paste and its microstructure. Paste microstructure has been varied by changing the initial w/c ratio, curing time and curing temperature, and by addition of chemicals to change the calcium hydroxide morphology. It has been found that, like compressive strength, fracture parameters depend directly on porosity. Contrary to our initial hypothesis, CH morphology was found to have no effect on the fracture parameters.
Molecular Approach to Mesoporous Metal Sulfides
Authors: Anderson Mark T. , Newcomer Paula
Published: April 2011

We have synthesized metal-sulfide/surfactant nanocomposite materials by cooperative assembly of molecular precursors in an aqueous medium. The template-mediated synthetic approach is applicable to metal sulfides that exhibit aqueous thiometallate chemistry. The products are lamellar and have bilayers or interdigitated layers of surfactant molecules sandwiched between metal sulfide layers. The layers of anionic metal sulfide molecules are not completely condensed in the nanocomposites, which results in a negative charge on the metal sulfide layers. The materials are stable at room temperature in water, methanol, 1 M HCl, 30 wt% NH3, and 1 M NaOH. The materials do not dissolve at 80 °C in water and are stable to at least 180 0C in air. The nanocomposites exhibit ion exchange of smaller surfactants, alkali-metal ions, and divalent metal ions.
Interaction of Polar Substrates with Transition Metal Substituted Keggin-Type Heteropolyanions [X(H2O)W11SiO39]6−(X=Co2+, Mn2+) Pillared in a Mg-Al Hydrotalcite-Like Clay
Authors: Salinas Esteban López , Castillo Pedro Salas , Ono Yoshio
Published: April 2011

The intercalation of Keggin-type [X(H2O)W11SiO39]6−(X=Co2+, Mn2+) heteropolyanions by aqueous anion exchange of 10 Å in a synthetic hydrotalcite-like Mg2Al(OH)6(NO3) results in products with interlayer spacing of ca. 10 Å. The layered array of the product and the integrity of the intercalated heteropolyanion are stable below 623 K in air as examined by XRD and IR analyses, respectively. UV-vis Diffuse Reflectance spectroscopy indicates that the water ligand in the intercalated [Co(H2O)W11SiO39]6− can be removed by thermal evacuation at 473 K leaving a coordinatively unsaturated site (in the transition metal) which reversibly coordinates water,methanol, ethanol or ammonia. ESR analysis of the intercalated [Mn(H2O)W11SiO39]6− shows that the shape of a signal at g = 2.00, arising from six-coordinated Mn2+ strongly depends on adsorption-desorption of the water ligand.