bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Preparation of Kinetically Stable Crystalline Compounds from Modulated Elemental Reactants
Authors: Hornbostel Marc D. , Noh Myungkeun , Johnson Christopher D. , Johnson David C. 
Published: April 2011

AbstractDiffusion distances within elementally modulated reactants can be controlled on an Angstrom length scale. Below a critical repeat thickness, elementally modulated reactants interdiffuse without nucleating crystalline compounds. Using this amorphous intermediate, we can prepare metastable compounds by controlling nucleation: Above this critical repeat thickness, crystalline compounds nucleate at the reacting interfaces. Using the architecture of the initial reactant to control the diffusion distances in the initial reactant, we have found that we can prepare crystalline superlattices. Crystalline superlattice compounds containing integral numbers of inter grown transition metal dichalcogenide layers and alternating layers of transition metal carbides have been prepared through controlled crystallization of superlattice reactants with designed compositional modulation. High quality c-axis oriented dichalcogenide crystalline superlattices result from extended annealing at relatively low temperatures. A large number of [00l] diffraction orders and off-axis [10l] diffraction peaks are observed indicating that these compounds are crystalline in three dimensions. Similar annealing conditions were used to prepare carbide superlattices, however the limited low temperature diffusion rates of the carbides limit the crystallite size to approximately 300Å. The rational synthesis of these intergrowth compounds from superlattice reactants permits the exploratory synthesis of a new class of compounds and the tailoring of physical properties as a function of compositional layer thicknesses and native properties of the parent compounds.
V2O5 and β-CuxV2O5 Thin Films Grown by Mocvd
Authors: Gleizes A. , Bufforn J.-M. , Salzman C. , Virette E. , Senocq F. 
Published: April 2011

AbstractThin films of V2O5 and β-CuxV2O5 have been grown by MOCVD using VO(OiPr)3 and Cu(tmhd)2 (tmhd = tetramethylheptanedionato) as precursor molecules. Films were grown on chips of Si3N4 coated silicon wafers in a cold wall reactor using a H.F. heater. A mixture of helium and oxygen was used as a reactive carrier gas, and depositions were performed at low pressure. The films were examined by SEM, characterized by XRD, and analyzed by EDS and EMPA techniques. All the films proved to be carbon free.For V2O5, the substrate temperature was varied from 450 to 630°C. The films are highly caxis oriented for both ends of the temperature range, and less oriented for intermediate temperatures. For 630°C, the XRD pattern consists almost entirely of reflections (001) and (002).For β-CuxV2O5, the substrate temperature was varied from 450°C to 650°C. Pure β-phase films with x varying from 0.25 to 0.55 have been obtained above 500°C, by using well chosen gas phase composition. Morphology and texture depend dramatically on the temperature. The most oriented films exhibit a strong anisotropy of electrical surface conductivity.
Synthesis Optimization of Mesoporous MCM-41 Materials in Acidic Media
Authors: Karlsson A. , Schmidt R. , Stocker M. 
Published: April 2011

ABSTRACTThe synthesis of MCM-41 in a highly acidic medium has been optimised. It was found that the relatively low-cost synthesis gave a material with extremely high surface areas (more than 1500 m2/g) compared to that obtained in conventional alkaline synthesis (ca 1100 m2/g). Judged by the short synthesis time, high yield, enhanced adsorption capacity, large particle size and thermal stability, the acid route to MCM-41 appears promising from an industrial point of view. Additional cost-reducing steps, such as the recycling of the “acid matrix” and the reduction of the volume of the water/acid mixture were successfully applied.
Synthesis and Catalytic Applications of Novel Mesoporous Aluminosilicate Molecular Sieves
Authors: Reddy Kondam Madhusudan , Song Chunshan 
Published: April 2011

ABSTRACTThis paper reports on the synthesis of four series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different aluminum compounds were examined as Al source in the hydrothermal synthesis of the mesoporous aluminosilicates of MCM-41 type, including pseudo boehmite (alumina), aluminum sulfate, aluminum isopropoxide, and sodium aluminate. Each Al source was examined at three different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the dioo-spacings for the samples prepared with different Al sources: sodium aluminate > Al isopropoxide > Al sulfate > pseudo boehmite. Such differences reveal that Al incorporation in the framework increases in the following order: pseudo boehmite < Al sulfate < Al isopropoxide < sodium aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. 27Al NMR and 29Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and sodium aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. We also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.
Alumoxane Precursors to Designer Catalysts and Catalyst Supports: Catalytic Oxidation of Dichloromethane
Authors: Cook Ron L. , Wong Cynthia , Harlan C. Jeff , Kareiva Aivaras , Barron Andrew R. 
Published: April 2011

ABSTRACTCarboxylato-alumoxanes are aluminum-oxygen macromolecules consisting of a boehmite-like core surrounded by a sheath of carboxylate groups. The alumoxanes may be processed like organic polymers yet when fired are readily transformed into ceramic oxides. The alumoxanes can be precisely doped at room temperature in aqueous solution with a range of metal cations to prepare novel catalyst and catalyst support materials. The ease of introduction of multiple cations into the alumina lattice via the alumoxane approach provides a method for fine-tuning catalyst support properties and the fabrication of new catalyst materials themselves. Manganese-doped alumina (Mn-Al2O3), formed via the doping of an alumoxane with Mn at room temperature, is presented as an example where the alumoxane route provides enhanced catalytic performance over traditional approaches for the low temperature catalytic oxidation of chlorinated hydrocarbons (CHCs). The Mn-Al2O3 formed from the Mn-doped alumoxane is compared with MnO2/Al2O3 prepared by the incipient wetness method, and commercial Pt/Al2O3 for the oxidation/destruction of dichloromethane (CH2Cl2).
Ion-Exchangeable Oxides with Layered Perovskite Structures as Photocatalysts for Overall Water Splitting
Authors: Takata T. , Shinohara K. , Tanaka A. , Hara M. , Kondo J. N. , Domen K. 
Published: April 2011

ABSTRACTA novel series of photocatalysts for an overall water splitting is reported. The catalysts have a layered perovskite type structure with a general formula of A2−xLa2Ti3−xNbxO10 (A = K, Rb, Cs; x = 0, 0.5, 1.0). The catalysts, except for the one with x=1.0, are spontaneously hydrated, and the band gap irradiation induced efficient evolution of H2 and O2 in a stoichiometric ratio from an aqueous alkaline solution when a proper amount of Ni loading was made. The reaction mechanism of water splitting on these catalysts is discussed on the bases of the structural study of the catalysts.
FT-IR Characterization of the Acidic and Basic Sites on a Nanostructured Aluminum Nitride Surface
Authors: Baraton M.-I. , Chen X. , Gonsalves K. E. 
Published: April 2011

ABSTRACTA nanostructured aluminum nitride powder prepared by sol-gel type chemical synthesis is analyzed by Fourier transform infrared spectrometry. The surface acidic and basic sites are probed out by adsorption of several organic molecules. Resulting from the unavoidable presence of oxygen, the aluminum nitride surface is an oxinitride layer in fact, and its surface chemistry should present some analogies with alumina. Therefore, a thorough comparison between the acido-basicity of aluminum nitride and aluminum oxide is discussed. The remaining nitrogen atoms in the first atomic layer modify the acidity-basicity relative balance and reveals the specificity of the aluminum nitride surface.
Fast Dynamics in Glass-Forming Polymers Revisited
Authors: Colmenero J. , Arbe A. , Mijangos C. , Reinecke H. 
Published: April 2011

ABSTRACTThe so called “fast-dynamics” of glass-forming systems as observed by time of flight (TOF) neutron scattering techniques is revisited. TOF-results corresponding to several glass-forming polymers with different chemical microstructure and glass-transition temperature are presented together with the theoretical framework proposed by us to interpret these results. The main conclusion is that the TOF-data can be explained in terms of quasiharmonic vibrations and the particular short time behavior of the segmental dynamics. The segmental dynamics display in the very short time range (t ≈ 2 ps) a crossover from a simple exponential behavior towards a non-exponential regime. The first exponential decay, which is controlled by C-C rotational barriers, can be understood as a trace of the behavior of the system in absence of the effects (correlations, cooperativity, memory effects…) which characterize the dense supercooled liquid like state against the normal liquid state. The non-exponential regime at t > 2 ps corresponds to what is usually understood as α and β relaxations. Some implications of these results are also discussed.
Fragility of Polymeric Liquids: Correlations between Thermodynamic and Dynamic Properties
Authors: Colucci Dina M. , McKenna Gregory B. 
Published: April 2011

ABSTRACTThe effect of polymer structure on fragility was determined by relating the apparent fragility to the relaxation response, heat capacity, and thermal expansion. For the 14 polymers studied, the fragility estimates based on the relaxation behavior (log aT) correlated well with the thermodynamic estimates of ΔCp/Mo, and Δα. In general, polymers with less sterically hindered repeat unit structures exhibited strong behavior. Polymers with sterically hindered backbones containing oxygen or ringed structures in the backbone were consistently fragile using log aT, ΔCp/Mo, and Δα as measures of fragility. On the other hand, using Cp1/Cpg as a fragility criterion resulted in very different fragility classifications.
Spectroscopic Investigations of the Network Structure in Borovanadate Glasses
Authors: Attos O. , Massot M. , Mavi H. S. , Julien C. 
Published: April 2011

ABSTRACTBorovanadate glasses with mixed conductivity, i.e., simultaneous ionic and electronic carriers have been obtained in the system (100−x)[B2O3-Li2O]-xV2O5 (0 ≤ x ≤ 30 mole%). To understand the origin of the conductivity in these glasses, the compositional dependence of the network structure has been studied by Raman and infrared spectroscopy.
New Fe-Ni Based Metal-Metalloid Glassy Alloys Prepared by Mechanical Alloying and Rapid Solidification
Authors: Suñol J. J. , Clavaguera-Mora M. T. , Clavaguera N. , Pradell T. 
Published: April 2011

ABSTRACTMechanical alloying and rapid solidification are two important routes to obtain glassy alloys. New Fe-Ni based metal-metalloid (P-Si) alloys prepared by these two different processing routes were studied by differential scanning calorimetry and transmission Mössbauer spectroscopy. Mechanical alloyed samples were prepared with elemental precursors, and different nominal compositions. Rapidly solidified alloys were obtained by melt-spinning. The structural analyses show that, independent of the composition, the materials obtained by mechanical alloying are not completely disordered whereas fully amorphous alloys were obtained by rapid solidification. Consequently, the thermal stability of mechanically alloyed samples is lower than that of the analogous material prepared by rapid solidification. The P/Si ratio controls the magnetic interaction of the glassy ribbons obtained by rapid solidification. The experimental results are discussed in terms of the degree of amorphization and crystallization versus processing route and P/Si ratio content.
Fast Dynamics in Glass-Formers: Relation to Fragility and the Kohlrausch Exponent
Authors: Ngai K. L. , Roland C. M. 
Published: April 2011

ABSTRACTFrom the Raman spectra and related inferences from low temperature specific heat data, Sokolov and coworkers have established that the ratio of the quasielastic and vibrational contributions at low temperatures (5∼10K) up to Tg correlates well with the degree of fragility and β of the glass-former. As pointed out by Sokolov (see his contribution in this Volume) such a correlation between the fast dynamics and structural a-relaxation at Tg(i.e., m and β) is intriguing, since at and below Tg, the α-relaxation time τα is more than twelve orders of magnitude longer than the quasielastic contribution and the boson peak. We show in this paper how the Coupling Model (CM) may provide an explanation for this correlation.
Electrostatic Potentials at θ = 24° [001] Tilt Boundaries in Undoped and Doped Strontium Titanate Bicrystals
Authors: Mao Z. , Dunin-Borkowski R. E. , Boothroyd C. B. , Knowles K. M. 
Published: April 2011

ABSTRACTPhase contrast techniques in the transmission electron microscope are used to measure directly the electrostatic potentials at θ = 24° [001] symmetrical tilt grain boundaries in both undoped and Nb-doped SrTiO3 bicrystals. The boundaries are all found to have significantly lower scattering potentials than the surrounding bulk material. The depths and the shapes of the potential wells at the boundaries are discussed in the light of both theoretical models of the grain boundary chemistry of pure and doped strontium titanate and other experimental data that we have acquired on these boundaries from high resolution transmission electron microscopy, diffuse dark field imaging, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy.
Interface Effects on the Tensile and Fatigue Crack Growth Behavior of Fiber-Reinforced Metal Matrix Composites
Authors: Majumdar B. S. , Warrier S. G. , Miracle D. B. 
Published: April 2011

ABSTRACTThe effects of the interface on the tension and fatigue crack growth behavior of fiber-reinforced titanium matrix composites were studied using single-ply and single-fiber SiC/Ti-6Al-4V mini-composites with different SiC fibers and coatings. Attention was focused on fiber failure mechanisms in the absence of a matrix crack (tension loading), and on fatigue crack deceleration mechanisms. In contrast to established models of tensile failure, local load sharing behavior was observed for very weak interfaces, with plasticity playing a major role in enhancing stress concentration effects. The approach included statistical evaluation of fiber breaks, their locations, and comparisons between single-fiber and single-ply composites. Under fatigue loading, crack deflection behavior was found to be consistent with a strength based interface debonding model. Crack shielding through modulus mismatch was found to have a significant effect on crack growth rates, independent of bridging conditions, with a stronger interface performing better under such conditions. The ramifications of the different mechanisms on interface optimization for longitudinal and transverse properties of composites are indicated.
Structure of Interfaces in Multilayers
Authors: Fedorenko A. I. , Pershin Yu.P. , Poltseva O. V. , Ponomarenko A. G. , Voronov D. L. , Yulin S. A. 
Published: April 2011

ABSTRACTStructure of interfaces in as-deposited state and after annealling at elevated temperatures was studied in variety of dc-magnetron sputtered multilayers by X-ray diffraction and high resolution electron microscopy. Interfaces in multilayers from materials without phase equilibrium (Mo/Si, W/Si, MO/B4C, Cr/C, Mo/(B+C)) are unstable and has the trend to evolution due to interlayer redistribution of chemical elements. Formation of the extended intermixed transition zones at interfaces is characteristic for multilayers from materials without phase equilibrium with each other. Unhomogeneous structure of materials along and across layers is responsible for nonuni-form proceeding of layer intermixing, development of interface roughness and differences of neighbour interfaces. It was shown that thickness asymmetry of intermixed transition zones at Mo/Si and Si/Mo interfaces in large-period Mo/Si multilayers is caused by different mechanisms of growth of Mo and Si on each other and by different structure of lower and upper parts of polycrystalline Mo-layers. Interfaces in multilayers from materials with phase equilibrium MoSi2/Si, WSi2/Si, OB2/C, TiC/C, Ni/C, MO2B5/B4C) are sharp and stable at elevated temperatures which gives the possibility to treat them for modification of their structure (smoothening, restoring sharp profiles of chemical elements). Multilayers W/Ti and W/TiN showed trend to formation of epitaxial superlattices with coherent or partially coherent (with misfit dislocations) interfaces and pseudomorphic state of layers.
Interfaces and fatigue Damage in a Ti-15–3/SCS-6 [0/90]2s Composite
Authors: Soboyejo W. O. , Rabeeh B. , Li Y. , Rokhlin S. 
Published: April 2011

AbstractThe key role of interfaces in the initiation and propagation of fatigue damage is elucidated for a model eight ply [0/90]2s Ti-15V-3Cr-3Al-3Sn (Ti-15–3) composite reinforced with SiC (SCS-6) fibers. Interfacial strengths obtained from fiber push-out tests are used in the quantification of shielding due to crack bridging. Composite fatigue tests are predicted using an idealized fracture mechanics model. The possible effects of interfacial strength variation on the predicted fatigue lives are also elucidated.
Characterization of Interphase Regions Using Atomic Force Microscopy
Authors: Vanlandingham M. R. , McKnight S. H. , Palmese G. R. , Bogetti T. A. , Eduljee R. F. , Gillespie J. W. 
Published: April 2011

ABSTRACTThe use of the atomic force microscope (AFM) to measure surface forces has been developed to optimize its operation as a surface imaging tool. This capability can potentially be extended to evaluate nanoscale material response to indentation. In this paper, a novel technique is used to probe local property changes in multi-component polymer systems. Changes in indentation response in interphase regions are investigated for an adhesive system involving a diffuse polymer-polymer bond and for two composite systems. To date, diamond-tipped probes with effective spring constants of 150 and 310 N/m have been used to investigate polyimide and epoxy resin matrices reinforced by carbon fibers.
Mo-W Interdiffusion and the Influence on Potassium Bubbles in W Lamp Wire
Authors: Bewlay B. P. , Briant C. L. , Murray M. L. 
Published: April 2011

ABSTRACTThe effects of Mo contamination on the microstructure of lamp-grade tungsten wire are investigated in this study. Mo is often used as the mandrel material in the coiling of lamp filaments, and when utilized during high temperature heat treatments significant amounts of Mo can diffuse into the W. In this study, W-Mo diffusion couples were prepared and heat treated at temperatures of 2500°C and above to intentionally contaminate the W with Mo. After dissolution of the Mo and additional high temperature heat treatments of the W, equiaxed grains were observed in the W and excessive porosity was also observed. Explanations for these microstructural changes are discussed. Microprobe data were also obtained to quantify interdiffusion between the W and Mo.
Toward Optimization of the Grain Boundary Character Distribution in Copper by Strain Annealing
Authors: King Wayne E. , Schwartz Adam J. 
Published: April 2011

ABSTRACTWe have used a two-step (low and high temperature) strain-annealing process to evolve the grain boundary character distribution (GBCD) in fully recrystallized oxygen-free electronic (OFE) Cu bar that was forged and rolled. Orientation imaging microscopy (OIM)[1–4] has been used to characterize the GBCD after each step in the processing. The fraction of special grain boundaries, “special fraction,” was ∼70% in the starting recrystallized material. Three different processing conditions were employed: high, moderate, and low temperature. The high-temperature process resulted in a reduction in the fraction of special grain boundaries while both of the lower temperature processes resulted in an increase in special fraction up to 85%. Further, the lower temperature processes resulted in average deviation angles from exact misorientation, for special boundaries, that were significantly smaller than observed from the high temperature process. Results indicate the importance of the low temperature part of the two-step strain-annealing process in preparing the microstructure for the higher temperature anneal and commensurate increase in the special fraction.
Stacking Fault Energies in TiCx
Authors: Harris R. M. , Bristowe P. D. 
Published: April 2011

ABSTRACTWe have used a Tight Binding model to calculate the surface energies of various (111) stacking faults in TiC1.0 and TiC0.5. Based upon our preliminary results we have identified the stable stacking faults and have examined possible dislocation dissociation reactions.
Applications of Active Thin Film Coatings on Optical Fibers
Authors: Fox G. R. , Muller C.A.P. , Wüthrich C. R. , Kholkin A. L. , Setter N. , Costantini D. M. , Ky N. H. , Limberger H. G. 
Published: April 2011

ABSTRACTActive thin film coatings on optical fibers provide a variety of functions that are being used to develop active all-fiber optical devices. Two types of active coatings that are of interest for device development include resistive and piezoelectric coatings. Resistive coatings can be used to heat an optical fiber, while piezoelectric coatings can be used to strain the fiber. Localized changes in the fiber waveguiding properties can be achieved by electrically activating the fiber coating. These coated fibers show promise for applications such as optical phase shifters and modulators.Recent developments in the fabrication of diffraction gratings within the core of an optical fiber have provided the means for making a variety of intra-core reflection and band pass filters. By combining these passive intra-core fiber devices with active coatings, wavelength tunable devices have been demonstrated. Wavelength tunable devices are expected to have a variety of applications in telecommunications and sensing networks. A review of recent developments in fiber coating and analysis techniques, device fabrication, and applications of active all-fiber devices are presented along with a discussion of which coating materials are of interest in active devices.