bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas Phase Synthesis of Molybdenum and/or Iron Nitrides, Carbides and Sulfides
Authors: Close Michael R. , Petersen Jeffrey L. 
Published: April 2011

ABSTRACTThe thermolytic decomposition of Mo(CO)6 with hydrogen sulfide or ammonia vapor (in a He carrier stream) at temperatures ranging from 300 to 1100 °C produces high surface area molybdenum sulfides (MoS2 or Mo2S3) or molybdenum carbides (hexagonal Mo2C) and carbonitrides, (hexagonal MoN(C) or cubic Mo2N(C)), respectively. The MoS2 surface areas range from 16.7 to 82.0 m2/g, while the surface areas of molybdenum carbides and carbonitrides vary from 14.9 to 21.1 m2/g. The maximum surface area for MoS2 is achieved at 500 °C and decreases with increasing or decreasing temperature. The surface area of the carbonitrides formed from 300 to 800 °C increases with increasing temperature up to 950 °C, where lower surface area Mo2C is formed. Crystallographically pure hexagonal MoN is prepared by decomposing Mo(CO) 6 in pure ammonia. Fe(CO) 5 decompositions in ammonia produce FexZ (where 5.8≥x≥1.6 and Z=C and N), and in some cases elemental Fe. Hexagonal Fe3 N(C) forms when Fe(CO) 5 is thermolyzed in ammonia from 300 to 600 °C, with surface areas ranging from 9.5 to 13.7 m2/g, whereas orthorhombic Fe3C and cubic Fe are produced at 700, 800, 900 and 1000 °C with surface areas of 6.7, 7.6, 2.2 and 2.0 m2/g, respectively. Within the same phase, the surface areas of the carbonitrides increase with increasing reaction temperature. These iron and molybdenum carbonitrides catalyze the conversion of CO/H2 to alkanes and methanol. Based on preliminary catalytic studies, the highest rate of methane (2850 g/kg/hr at 374 °C) and methanol (440 g/kg/hr at 284 °C) formation was accomplished with an FeMo carbonitride prepared by decomposing Mo(CO)6 and Fe(CO)5 in ammonia at 800 °C.
Carbon Nanofibers as a Novel Catalyst Support
Authors: Kim Myung-Soo , Rodriguez Nelly M. , Baker R. Terry K. 
Published: April 2011

ABSTRACTCatalytically grown carbon nanofibers have been prepared by the thermal decomposition of carbon containing gases over copper-nickel and iron surfaces. This material is found to be highly graphitic in nature when prepared from certain catalysts and gaseous reactants. In the as-grown state, carbon nanofibers have surface areas in the range 200 to 300 m2/g, and by following careful activation procedures this value can readily be increased to ˜700 m2/g. Electrical measurements indicate that the material has a conductivity approaching that of single crystal graphite. This material combines the attributes of active carbon and graphite and in addition, the physical form of carbon nanofibers offers some interesting opportunities for the design of unique catalyst systems.
Chemistry of Electrochromic IrOx. Films Deposited Under Variable Redox Conditions
Authors: Klein J. D. , Clauson S. L. 
Published: April 2011

AbstractA thin film deposition technique is described whereby the oxidation condition of as-deposited iridium oxide thin films can be manipulated by varying deposition conditions. Iridium oxide thin films were deposited by reactive rf magnetron sputtering in a H2/O2/Ar gas blend. Optical emission spectroscopy, an in-situ process monitor, was employed to observe redox interactions in the deposition plasma. The plasma spectra exhibited characteristics normally observed in hydrogen flame spectroscopy. A competitive redox balance was found to exist between atomic O and atomic H emissions. Plasma redox conditions defined by the H-O emissions could be accessed by a variety of gas flow conditions. Electrochemical aspects of the IrOx films were examined by cyclic voltammetry. Electrochromic capabilities were demonstrated through optical transmittance.
Sol Gel Intercalation Materials for Lithium Batteries
Authors: Pereira-Ramos J.P. , Bach S. , Farcy J. , Baffler N. 
Published: April 2011

AbstractThis paper emphasizes the interest of sol-gel synthesis in obtaining high performance cathodic materials. New vanadium oxides, vanadium bronzes (MxV2O5) and manganese oxides (MnO2) are prepared via the sol-gel process using inorganic precursors in aqueous medium. Their electrochemical behaviour (working potential, specific capacity, kinetics of Li transport, rechargeability, cycle life) is investigated and discussed in relation with their specific structural, chemical and physical features. In particular, the results are compared to that achieved for the corresponding classical compounds prepared via a synthesis route involving solid state reactions or precipitationreactions.
The Mechanism and Modeling of Conductivity in Polymer Electrolytes
Authors: Lonergan Mark C. , Shriver Duward F. , Nitzan Abraham , Ratner Mark A. 
Published: April 2011

AbstractThe progress of dynamically disordered hopping (DDH) in modelling charge transport in polymer electrolytes is reviewed. The DDH model successfully describes many of the salient features of polymer electrolytes, most notably, the frequency and temperature dependence of the conductivity. Furthermore, analyses and simulations based on the DDH model provide rich mechanistic information. The general picture of charge transport that emerges from the DDH model is one in which two classes of charge carriers exist in thermal equilibrium:quasi-free and bound. The quasi-free carriers dominate the conductivity response and diffuse freely over short distances (≈1Å) with longer range diffusion requiringlocal segmental motions, renewal in the language of DDH, of the polymer solvent. The bound carriers, which are likely polymer solvated ion clusters, are immobile on the time-scale of renewal and contribute relatively little to the conductivity.
Failure of the Frenkel Defect Model to Explain the Trend in Anionic Conductivity in the MF2 Fluorite Structure and Related MSnF4 Materials
Authors: Denes Georges 
Published: April 2011

AbstractThe high fluoride ion conductivity of fluorite type MF2 has been attributed tothe fact that half of the F8 cubes present in this structure are empty and therefore, are potential vacant sites for interstitial fluoride ions in the formation of Frenkel defects. However, the model of long range ion motion through Frenkel defects by use of empty F8 cubes is in contradiction with: (i) the little difference between the conductivities of CaF2 and BaF2, (ii) the conductivity of β-PbF2 being much larger than that of BaF2, and (iii) the much higher performance of MSnF4 even though there is no empty cube to form Frenkel defects in the MSnF4 structures.
Perovskites as Oxide-Ion Electrolytes
Authors: Feng Man , Goodenough John B. 
Published: April 2011

AbstractSubstitution of Nb, Ti, or Sn for In and of La for Ba was used to obtain cubic, anion-deficient perovskites AB03-δ. Neither the ferroelectric character of Nb5+ and Ti4+, nor the more acidic character of Sn4+ suppressed water absorption into the anion vacancies at temperatures T < 500ºC. However, the smaller La3+ ion in Bal-xLaxO2.5+0.5x did suppress the absorption of water for x = 0.4, and Ba0.6La0.4InO2.7 is competitive with yttria-stabilized zirconia as an oxide-ion electrolyte.
Oxygen Permeation Studies of SrCo0.8Fe0.2O3-δ
Authors: Yang Y. L. , Lee T. H. , Qiu L. , Liu L. , Jacobson A. J. 
Published: April 2011

AbstractOxygen permeation fluxes through dense SrCo0.80Fe0.20O3-δ discs have been measured in the temperature range of 620-920 °C under various oxygen partial pressure gradients. The permeation results are compared with the previous measurements. Below 800 °C, the apparent activation energy for the overall permeation is 22±4 kcal/mol. The permeation results are discussed in light of the phase diagram of SrCo0.80Fe0.20O3-δ. Based on experiments in which the membrane thickness is varied, we propose that the surface exchange process is the ratelimiting step in the overall permeation reaction. Preliminary catalytic studies of methane partial oxidation in a membrane reactor are reported.
Diffusion-Reaction in Mixed Ionic Electronic Conductor Solid Oxide Membranes with Porous Electrodes
Authors: Deng Huiming , Zhou Minyau , Abeles Benjamin 
Published: April 2011

AbstractWe solve the transport equations for diffusion-reaction, in the limit of a small O2 pressure gradient, in a mixed oxygen ion-electronic conductor (MIEC) solid oxide membrane consisting of a porous anode and cathode separated by a thin dense layer. The enhancement in ion current due to the porous electrodes calculated for MIEC perovskites is of order 100 for electrode surface area of 106 cm2/cm3.
Structural Chemistry of Alkaline Earth Hexa-Aluminates
Authors: Park Jae-Gwan , Cormack A. N. 
Published: April 2011

AbstractComputer-based atomistic simulation techniques have been used to investigate the crystal chemistry and phase relationships in alkaline earth hexa-aluminates. The lattice energies for hexa-aluminate-related structural models are calculated and successfully predict that barium prefers the β-alumina-type structures with charge-balancing defects, whilst calcium or strontium prefers the ideal magnetoplumbite structure. In the case of magnesium, it is predicted that it does not prefer a hexa-aluminate structure.
Spectrofluorimetric Characterization of an Ionic Conductor: Sodium Sulfate High-Temperature Phases Doped with Europium(III)
Authors: Matithews Lowell R. , Knobbe Edward T. , Dharmasena Gamini , Cole Renée , Frech Roger 
Published: April 2011

AbstractThe highest-temperature polymorph of sodium sulfate, (I), has significant orientational disorder in its structure which allows it to readily accept substitution by di- and trivalent cations. Although Na2SO4 (I) exhibits reasonable ionic conductivity, it cannot be quenched to room temperature without changing phase. However, aliovalent solid solutions of (I) can be quenched to RT and resultant cation vacancies promote conduction via Na+ migration. The closely related but more ordered phase Na2SO4 (III) can also form aliovalent solid solutions which can be quenched to RT.The europium(III) ion is an extremely sensitive and useful probe of its immediate local environment. The presence, location, and intensity of its fluorescence transitions (particularly the 5D0→7F0-2 emissions) can provide detailed information about the symmetry, nature, and multiplicity of the individual Eu3+ site which cannot be gained from X-ray or neutron diffraction techniques.Our research (supported by the National Science Foundation and the State of Oklahoma) involves the structural characterization of two europium-doped sodium sulfate phases via fluorescence spectroscopy.
Electrical Properties of High ion Conductive Polymer Complexes Containing Room Temperature Molten Salt
Authors: Aoshima Norio , Rikukawa Masahiro , Sanui Kohei , Ogata Naoya 
Published: April 2011

AbstractNew ion conductive polymers were obtained by dissolving polycations into room temperature molten salt consisting of methyltriethylammonium chloride (MEAC1) and aluminium chloride (A1C13). These complexes formed viscoelastic solids when the polycation content was increased more than 4 unit mol%. The ionic conductivity of polycation complexes was in the range of 10-4-10-3 Scm-1 at room temperature and were affected by their composition, types of polycations, and counter anion species.
Preparation and Characterization of Polyaniline-Palladium Composite Films
Authors: Li Hongshi , Baer D. R. , Engelhard M. H. , Janata J. , Josowicz M. 
Published: April 2011

AbstractElectrosynthesized polyaniline (PANi) can be chemically functionalized by incorporation of palladium clusters. The functionalization of electrochemically, freshly prepared and dried PANi film occurs spontaneously during the relaxation process. This process is carried out in sulfuric acid containning palladium salt. The material properties of the new composite PANi-Pd film were investigated by applying electrochemical, UV-visible spectroscopic and surface microscopy techniques. The PANi-Pd composite materials behaved electrochemically different than PANi film alone or Pd film deposited electrochemically. This finding is particularly important for developing layers for chemical sensors, electrocatalysis or supercapacitors applications.
Ionic Current Induced Migration of a Hot Spot in GdBa2Cu3O7-δ, Ceramics
Authors: Okamoto T. , Huybrechts B. , Takata M. 
Published: April 2011

AbstractAn electric field sensitive moving hot spot appeared when a dc voltage over 5 V was applied at room temperature to GdBa2Cu3O7-δceramic thin rods under oxygen partial pressures ranging from 0.05 to 1.00 atm (5 kPa to 100 kPa). The spot moved to the negative electrode, and the direction of movement could be reversed time after time by switching the positive and negative electrode. This is believed to be caused by electric field movement of oxygen ions, thereby generating an ionic current. The total current after the appearance of the hot spot was independent of the applied voltage for every oxygen partial pressure, PO2. However the current and spot velocity increased significantly with increasing PO2. By the best of the authors's knowledge this is the first report on the influence of the PO2 on the moving hot spot. The potential use of this phenomenon as an oxygen sensor will be shown.
Crystal Chemistry and Electrochemical Behavior of New Manganese Substituted Nickel Hydroxides
Authors: Guerlou-Demourgues L. , Delmas C. 
Published: April 2011

AbstractAgeing of the manganese substituted nickel hydroxides in 5M-KOH electrolytic medium leadsto a structure interstratification which is related to spontaneous oxidation of trivalentmanganese ions to the tetravalent state, As far as the electrochemical behavior is concerned, the trend to interstratification has a positive influence on the stability of the capacity upon cycling. In addition, the chargeability is improved by the presence of manganese.
Electrochemical Activity of Natural and Synthetic Manganese Dioxides
Authors: Amarilla J.M. , MacLean L.A.H , Tedjar F. , Cras F. Le , Strobel P. , Poinsignon C. 
Published: April 2011

Abstracteven manganese dioxide (MD) forms including natural ramsdellite, β-MnO2 and samples with structures intermediate between these two types, have been analyzed interms of chemical and structural disorder. XRD and IR spectra show that natural ramsdellite contains groutellite, MnO1.5(OH)0.5. The OH absorption band in the 3400cm-1 region is sharp for groutellite, less intense on CMD spectrum, andsuperimposed to a broad and diffuse absorption ranging from 3600 to 2000cm-1 in most γ-MnO2's. The OH groups are associated with Mn+3 defects, while the broad and diffuse absorption band can be assigned to protons in empty MnO6 octahedra, and so related to instable manganese oxydation state between Mn3+ and Mn4+.A potentiostatic study in IM and 7M KOH shows that the stoichiometric oxides, ramsdelliteand β-MnO2, are not reduced, while CMD and EMD are reversibly reduced by H+/-einsertion. In 7M KOH, a reversible reduction occurs for both CMDs and EMDs until -0.2 V, while a heterogeneous mechanism destroys the structure at lower potential (70% capacity loss after 3 redox cycles). Only ramsdellite and β-MnO2 can be cycled reversibly below -0.37 V, but the drained capacity is very low for β-MnO2.The presence of Mn3+ and Mn4+ vacancies associated to structural disorderin synthetic MDs increases their reduction potential and completely modifies the chemicalproperties. This mixed valence state seems to be at the origin of the reduction properties by proton insertion in protonic electrolytes.
Gypsum-Free Portland Cement Pastes of Low Water-to-Cement Rat10
Authors: ŠkvÁra FrantiŠek 
Published: April 2011

AbstractGypsum-free portland cement is a low porosity hydraulic binder based on finely groundportland cement clinker with addition of synergetic system containing an anion-active surface active agent (usually a sulphonated polyelectrolyte) and an inorganic salt (usually sodium carbonate) for regulation of the hardening process. The properties of GF cement are different from ordinary portland cement; they display, for example, higher strength, better corrosion resistance and thermal stability. These positive differences arise from the different mineralogy and microstructure of the hydration products, for example the absence of portlandite crystals. The main component of the binder product in hardened GF cement pastes is C-S-H (mean C/S ratio 2.7, based on EDAX analysis) intergrown with very fine Ca(OH)2 and highly dispersed C-A-H phases (hexagonal and cubic). The absence of crystalline formations in the GF hardened pastes is responsible for highermechanical strength. In the Czech Republic, GF cement is produced in the cement works of CEVA Prachovice Inc. ( Holderbank group) and is used for special works in the building industry.
Microstructure-Electrical Propertyrelationships in Cement-Based Materialss
Authors: Olson R.A. , Moss G.M. , Christensen B.J. , Shane J.D. , Coverdale R.T. , Garboczi E.J. , Jennings H.M. , Mason T.O. 
Published: April 2011

AbstractThere has been much recent progress on the application of impedance spectroscopy (IS) to the study of microstructure and transport in cement-based materials. The IS spectrum allows for the precise determination of bulk resistance, which is a measure of the pore phase interconnectivity, and calculation of the relative dielectric constant, which is related to the capillary pore size and distribution. High values of the relative dielectric constant (σ105) observed in cement paste at early hydration times are the direct result of the microstructure inducing dielectric amplification. Solvent exchange and freezing experiments, combined with digital-image-based computer modeling, have confirmed the role of large capillary pores in the dielectric amplification in young pastes.The conductivities (σ) and relative dielectric constants (εr) of ordinary portland cement (OPC) pastes were monitored during cooling and solvent exchange with isopropanol and methanol. Dramatic decreases in σ and εr, in some cases over two orders of magnitude, occurred at the initial freezing point of the aqueous phase in the macropores and large capillary pores. The same dramatic decreases in a and er were observed at the onset of solvent exchange. Both effects provide experimental support for the dielectric amplification mechanism within the microstructure on the μm-scale. A secondary dielectric amplification was observed in the frozen and solvent exchanged pastes, which produced dielectric constants on the order of 103. This effect is attributed to amplification on the nm-scale within the layered calcium silicate hydrate (C-S-H) gel microstructure. Additional insight into the variable nature of the C-S-H microstructure was obtained by comparing the dielectric behavior of methanol-exchanged OPC pastes to isopropanolexchanged OPC pastes.
The Interfacial Transition Zone and its Influence on the Fracture Behavior of Concrete
Authors: Zampini Davide , Jennings Hamlin M. , Shah Surendra P. 
Published: April 2011

AbstractConcrete specimens of constant water-to-cement ratio and varying amounts of gravel aggregate were tested under 3-point bend. The fracture toughness of the composite and surface roughness of the paste are determined. Fracture parameters obtained from the Two ParameterFracture Model (TPFM) such as the critical stress intensity factor (KIc) and critical effective crack extension (Δao) are found to be related to the average surface roughness of the paste. The Interfacial Transition Zone (ITZ) and the bulk paste are distinguished by different values of roughness. The surface roughness of the area adjacent to the aggregate particle is evaluated as a function of the distance from the aggregate surface. In particular, the surface roughness of the paste near the aggregate is greater than that of the paste far from the aggregate, and it decreases with distance from the aggregate. The higher roughness of the paste near the aggregate indicates that aggregate particles, and more specifically the ITZ associated with them, act to toughen the paste in concrete.
Crack Stability in the Fracture of Cementitious Materials
Authors: Tandon S. , Faber K.T. , Bazant Z.P. 
Published: April 2011

AbstractThe aim of the present study is to investigate the stability of crack propagation in cementitious materials. Tests were conducted on bend specimens in three-point and four-point loading conditions. Three-point bend specimens showed stable crack growth for mortar, normal strength and high strength concrete specimens. Alternatively, four-point bend specimens showed catastrophic failure for mortar and quasi-catastrophic failure for normal strength and high strength concrete specimens. Results will be discussed in relation to brittleness number model and specific microstructural features including the interfacial transition zone between the cement paste and the aggregate and the attendant toughening mechanisms.
Effect of the ITZ on the Leaching of Calcium Hydroxide from Mortar
Authors: Carde Christophe , François Raoul 
Published: April 2011

AbstractThis paper deals with the effect of the ITZ on the leaching process of cement based materials.In order to characterize this effect, we have performed experiments on mortar samples and pure cement paste samples. Two aggressive waters were used, the first one with pH=4.5 and the second one with pH=8.5. These two aggressive waters were modelled by a solution of ammonium nitrate. Compression tests were conducted on micro-cylinder samples (10, 12 and 14 mm of diameter) because of the slow kinetics of degradation due to the leaching.In the case of a sample made with cement paste only, the leaching process leads to a uniform degradation of the samples. The thickness of this degraded zone is the same whatever the size of the sample. The decrease in compression strength is thus completely explained by this degraded zone. In the case of a sample made with mortar, the leaching process leads also to a degradation zone whose thickness is the same whatever the size of the sample. But, the decrease in mechanical properties and the increase in irreversibility couldn't be explained for the different sizes of samples by the same thickness of leaching zone. This is due to the fact that the chemical attack progresses through the interfacial zones because they have a higher porosity than the bulk paste. The relative volume of interfacial zones linked together with the aggressive environment is more important in the case of the smaller sample.
Effect of the ITZ Damage on Durability of Reinforced Concrete in Chloride Environment
Authors: François Raoul , Arliguie Ginette 
Published: April 2011

AbstractThis paper deals with the effect of the ITZ on the service life of reinforced concrete. In the case of reinforced concrete structures, the penetration of chlorides does not depend only on concrete transfer properties but also on the loading applied, on the state of strains and on the exposure to the aggressive environment.In order to take into account these different parameters, we have performed experiments on reinforced concrete elements, over a long period. The samples used have to be of an adequate size (3 meters long) and stored in a salt fog in a loading state so as to be representative of the actual operating conditions of the reinforced concrete structures.The bending of the beams leads to the development of cracks which are neither preceded nor accompanied by microcracks, but the cement paste-aggregate interfaces are damaged in the tensile areas.The service loading of reinforced concrete has two consequences : firstly, a cracking with widths ranging between 0.05 mm and 0.5 mm according to the intensity of the mechanical strength applied. Secondly, a damage of the ITZ in the tensile areas causing an increase of chloride penetration directly proportional to the intensity of the stress applied to the beam.The model of the development of corrosion, worked out in relation with time and based on our results, emphasizes the influence of the paste-aggregate interface damage on the duration of the service life.