bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of storage in aqueous environments on polymer–metal interfacial fracture
Authors: Toivola Yvete , Somerday Brian P. , Shediac Renée , Cook Robert F.
Published: October 2005

The effect of environmental exposure on the fracture characteristics of two polymer–metal interfaces was measured using a four-point bend delamination test. Films of high-molecular-weight polymethylmethacrylate (PMMA) resin were spin-cast on metal-coated silicon wafer substrates, for which the metal was either titanium or aluminum. Sandwich beam specimens were fabricated and stored in one of the following conditions prior to the bending tests: vacuum desiccator at 25 °C, vacuum desiccator at 65 °C, distilled water at 25 °C, or distilled water at 65 °C. Load–displacement behavior measured during bending revealed significant differences between the delamination characteristics of the two PMMA–metal interfaces after vacuum exposure which were eliminated after the degrading effects of water exposure. Three distinctive load–displacement behaviors were observed: plateau, fracture at a single load; R-curve, fracture at increasing load with crack extension; and stick-slip, cycles of gradual load increase and sudden load drop with crack extension. PMMA–Al samples stored in vacuum desiccator at 25 °C exhibited R-curve fracture and the largest average crack driving force, GC, 12.2 (±0.5) J/m2, of all samples tested. After storage in 25 °C water, these PMMA–Al samples exhibited stick-slip fracture and GC decreased to 7.1 (±2.6) J/m2; storage in 65 °C water further decreased GC to 2.1 (±0.7) J/m2. PMMA–Ti samples exhibited stick-slip fracture after storage in vacuum desiccator at 25 °C, with an average GC of 8.0 (±2.6) J/m2; storage in 65 °C water resulted in a transition to plateau fracture and a decrease in GC to 1.6 (±0.3) J/m2. The initial difference and subsequent similarity are interpreted in terms of surface roughness and hydrolysis, respectively.
Optical characterization of ceramic thin films: Applications in low-temperature solid oxide fuel-cell materials research
Authors: Gorman B.P. , Petrovsky V. , Anderson H.U. , Petrovsky T.
Published: October 2005

Characterization of thin film solid oxide fuel-cell materials can be difficult due to the range of porosities in electrodes and electrolytes as well as the nano-sized pores and particles. In this study, optical characterization techniques such as ultraviolet–visible transmission and reflection spectrophotometry are illustrated as methods for achieving information about the film density from the film refractive index as well as the film thickness. These techniques were used to investigate the sintering process of colloidal CeO2 on sapphire substrates and polymeric precursor-derived ZrO2:16%Y (YSZ) thin films on silicon over the temperature range 400–1000 °C, and the results were compared with traditional characterization techniques such as electron microscopy, profilometry, ellipsometry, and x-ray diffraction line broadening analyses. Most of the techniques were in good agreement with the CeO2 grain size changing from 5–65 nm and the film thickness changing from 0.8–0.5 μm. Comparisons of transmission and reflection spectrophotometry with ellipsometry illustrated that scattering effects from the porous CeO2 films caused an overestimation of the refractive index from ellipsometry, but allowed for accurate grain size measurements from transmission and reflection data. Both techniques were in good agreement during the sintering of the YSZ thin films, with the density changing from 90–100% theoretical after heating between 400 and 800 °C.
Growth and characterization of single-crystal lead magnesium niobate–lead titanate via high-pressure vertical Bridgman method
Authors: Soundararajan Raji , Das Rabindra Nath , Tjossem Russ , Bandyopadhyay Amit , Lynn Kelvin G. , Eisser Elgin E. , Lazaroff Jerry
Published: October 2005

We have grown lead magnesium niobate–lead titanate (PMN–PT) single crystals, using the high-pressure vertical Bridgman (HPVB) technique, around the stoichiometric composition of 0.7 PMN–0.3PT [0.7Pb(Mg1/3Nb2/3)O3 + 0.3(PbTiO3)]. The final ingot (about 50-mm diameter, 25-mm long) was machinable using an inner diameter saw. The room-temperature x-ray diffraction on the starting powders and the final single crystal revealed a desirable perovskite structure. The natural growth direction in most of the crystals, as determined using orientation image microscopy, was (110). Examination of the final microstructures and phases/inclusions had been done using optical and infrared microscopy, energy dispersive spectroscopy, and x-ray backscatter techniques. Microstructural characterizations of the final ingots have revealed the presence of pores filled with Mg–Si–O-rich impurity phase, usually found along the cell boundary–like structures, in all the growths. We have measured some piezoelectric properties including d33 (1200 pC/N), k33 (0.85), kt (0.5), and the dielectric constant at the Curie temperature.
Discrete-element method application to mixing and segregation model in industrial blending system
Authors: Yamane Kenji
Published: October 2005

In the pharmaceutical industries, mixing is a critical process. Pharmaceutical products consist of various components, including active ingredient and excipient. After mixing, we should get a homogeneous mixture to ensure the quality of the final products, such as tablets or capsules. For that reason, segregation is an unwanted phenomena in the mixing process. In this study, discrete-element method (DEM) was applied to investigate the mechanism of segregation in a rotating cylinder; basic equipment for powder mixing. In addition, segregation of particles in a rotating cylinder is a very interesting phenomenon and has captured the curiosity of not only industrial engineers, but also physicists. DEM can simulate segregation in a rotating cylinder three-dimensionally. In particular, radial segregation, which was quickly observed, was quantified by computing the granular temperature of the system. Furthermore, particle migration in axial direction, which may be the source of axial segregation, was also shown by the DEM simulation.
Synthesis of ZnO particle–polymer hybrid from zinc–organics
Authors: Yogo Toshinobu , Nakafuku Tomoko , Sakamoto Wataru , Hirano Shin-ichi
Published: October 2005

Nanocrystalline ZnO particle–polymer hybrid was synthesized by controlled polymerization and hydrolysis of zinc acrylate (ZA).13C nuclear magnetic resonance spectra revealed the polymerization of ZA during hydrolysis in the presence of hydrazine at 65 °C for 24 h. Nanocrystalline ZnO particles were dispersed in the organic matrix through the polymerization–hydrolysis reaction of ZA using hydrazine or methylhydrazine. ZnO particles increased in crystallinity with increasing amount of water for hydrolysis in the system using hydrazine. Methylhydrazine was found to yield ZnO with higher crystallinity than that obtained using hydrazine. The nanocrystalline particles were identified to be ZnO by electron diffraction. ZnO particle–polymer hybrid was workable by mild heating into transparent films between silica plates. The absorption edge of the transparent ZnO particle–polymer hybrid film was blue-shifted depending on the size of ZnO particles.
Fluorescence property and dissolution site of Er3+ in Ta2O5 film prepared by sol-gel method and dip-coating technique
Authors: Wada Noriyuki , Kubo Michiyo , Maeda Nobuko , Akira Maegawa , Kojima Kazuo
Published: October 2005

Ta2O5–xEr2O3 (TE) films were produced by a sol-gel method and a dip-coating technique with heat treatment at 600–1000 °C. Their powders were also prepared from the same sol. The Er3+ fluorescence property of the TE films containing various contents of Er3+ was measured as a function of the heat-treatment temperature. In crystallized films, the Er3+ fluorescence was observed because water-related residues (Ta–OH and H2O) and carbon-related residues (–CH3, –CH2–, –(C ⁼ O)–, and C≡C–H) were removed from the films. It is shown from infrared absorption spectroscopy that Ta–O− and Ta ⁼ O structures dissolve the Er3+ ions selectively and play a role in dispersing the Er3+. The strongest Er3+ fluorescence is observed in the TE film with 2 mol% of Er2O3 because of its highest ability to disperse the Er3+ ions.
Stress development and relaxation during reactive film formation of Ni2Si
Authors: Liew K.P. , Bernstein R.A. , Thompson C.V.
Published: October 2005

Using continuous wafer-curvature measurements, stress generation was monitored as nickel thin films reacted with silicon substrates to form Ni2Si during isothermal anneals. A large compressive force developed during the reaction, but gradually relaxed after the reaction was complete. From a model for reactive film formation, a lower limit for the instantaneous stress associated with compound formation was found to be −2.00 ± 0.75 GPa. This instantaneous stress can be explained by a volumetric strain of 1.65 ± 0.62%, which is much smaller than the theoretical volume expansion of 62% in this system. These results suggest that significant inelastic deformation occurs during silicide formation. It was also found that diffusive creep relaxes the growth stress after the reaction. The observed instantaneous stress indicates that the energy of deformation associated with the reaction is of the same order as the energy that drives it, suggesting that stress generation and stress relaxation can play a significant role in the kinetics of reactive film formation.
Nanoscale Morphology and Indentation of Individual Nacre Tablets from the Gastropod Mollusc Trochus Niloticus
Authors: Bruet B.J.F. , Qi H.J. , Boyce M.C. , Panas R. , Tai K. , Frick L. , Ortiz C.
Published: October 2005

The inner nacreous layer of gastropod mollusc Trochus niloticus is composed of ∼95 wt% planar arrays of polygonal aragonite-based tablets (∼8 μm wide, ∼0.9 μm thick, stacked ∼40 nm apart) and ∼5 wt% biomacromolecules. High-resolution tapping mode atomic force microscope images enabled nanoscale resolution of fractured tablet cross-sections, the organic component, and deformation of individual nanoasperities on top of tablet surfaces. Nanoindentation was performed on individual nacre tablets and the elastic modulus E and yield stress σy were reduced from elastic-plastic finite element simulations yielding E = 92 GPa, σy = 11 GPa (freshly cleaved samples) and E = 79 GPa, σy = 9 GPa (artificial seawater soaked samples). Images of the indents revealed extensive plastic deformation with a clear residual indent and surrounding pileup.
Stress Evolution in Sputter-deposited Fe–Pd Shape-memory Thin Films
Authors: Sugimura Y. , Cohen-Karni I. , McCluskey P. , Vlassak J.J.
Published: October 2005

Fe–Pd films with Pd content varying between 26 and 30 at.% have been deposited by means of magnetron sputtering of elemental Fe and Pd targets. As-deposited films are highly supersaturated solid solutions of Pd in Fe that have a body-centered-cubic crystal structure and a very fine grain size. Substrate curvature measurements indicate that the films undergo an irreversible densification when heated above 100 °C. This densification is attributed to a structural change that is also observed in other supersaturated systems with a substantial atomic size difference between the constituents. It is possible to retain the high-temperature austenite phase at low temperature by annealing the films at 900 °C followed by rapid cooling. Depending on film composition, this metastable austenitic phase transforms to either a body-centered tetragonal (bct) or a face-centered tetragonal (fct) martensite around room temperature. Substrate curvature measurements show that formation of the fct martensite is reversible, while that of bct martensite is not. The fct transformation occurs at lower Pd content and higher temperature than reported for bulk materials. Both the fct and the fcc phase show a strong Invar effect at lower temperature and Pd content than observed in the bulk.
Hydroxyapatite/diamondlike Carbon Nanocomposites: A Novel Surface Modification to Extend Orthopaedic Prosthesis Lifetimes
Authors: Narayan Roger J.
Published: October 2005

Conventional plasma-sprayed hydroxyapatite coatings suffer from many difficulties that have limited their use in orthopaedic implants, including uneven resorption rates, poor fracture toughness, and poor adhesion to medical alloys. The placement of a diamondlike carbon buffer layer may overcome these obstacles by providing unique chemical inertness, hardness, and cell-interaction properties at the implant–tissue interface. Nanocrystalline hydroxyapatite and amorphous diamondlike carbon films were prepared by room-temperature pulsed-laser deposition of hydroxyapatite and graphite targets, respectively. Scanning electron microscopy, transmission electron microscopy, x-ray diffraction, and microscratch adhesion testing were used to determine surface morphology, interfacial structure, and adhesion of the bilayer coatings. Nanocrystalline hydroxyapatite/diamondlike carbon coatings have several potential orthopaedic applications, including use in hip prostheses.
Nitrogen Loss and Structural Change of Nitrogen-incorporated SBA-15 Mesoporous Materials Under Different Treatment Conditions
Authors: Wang Jiacheng , Liu Qian
Published: October 2005

Work on nitrogen loss and structural change of nitrogen-containing SBA-15 mesoporous materials after heat treatment in air or water treatment is described herein. The nitrogen-containing SBA-15 lost nitrogen after being treated in air at high temperature or in water, the mesoporous structure of which was very well maintained and did not collapse. HRTEM, N2 sorption, powder XRD, and SEM were used to study the structural ordering and morphology of the mesoporous silicon oxynitride materials before and after treatment. FTIR and C/N/H elemental analysis confirmed that nitrogen loss occurred after the mesoporous silicon oxynitride material was treated. Nitrogen was lost via hydrolysis of ammonium groups when mesoporous silicon oxynitride material was treated in water and by being substituted by oxygen from air when it was heated in air at high temperature.
Effect of Electroless Copper on the Growth of ZnO Nanowires
Authors: Chiou Wen-Ting , Wu Wan-Yu , Ting Jyh-Ming
Published: October 2005

ZnO nanowires along with ZnO thin films were obtained on copper-metallized silicon substrates using an radio frequency-reactive sputter-deposition technique. Residual tensile stresses were found in both the copper layer and the ZnO layer. The ZnO nanowires were observed exclusively at the grain boundaries of the ZnO thin films. The average diameter of ZnO nanowires varies only slightly with the ZnO deposition time, while the average length increases linearly with the ZnO deposition time. Based on the observations a growth model involving stress-assisted diffusion of copper and reaction-controlled catalytic growth of ZnO nanowires is suggested.
Electrochemical Synthesis and Room Temperature Oxidation Behavior of Cu Nanowires
Authors: Liu Xingmin , Zhou Yanchun
Published: October 2005

Highly oriented copper nanowires were electrochemically synthesized in a porous alumina membrane template using a new type of weak-acid electrolyte. The Cu nanowires that were deposited have (110) preferred orientation, which is different from most electrochemically deposited Cu nanowires, and they can grow homogeneously. Transmission electron microscopy was used to investigate the room-temperature oxidation behavior, and it was observed that sample treatment methods greatly influence the oxidation rate of the wires. Cu nanowires with different diameters have different resistance to oxidation. The orientation relationship between oxide layer and small-diameter Cu nanowire was determined to be (001) Cu2O // (111) Cu, (110) Cu2O // (110) Cu, and [110] Cu2O // [112] Cu. The possible oxidation process is also discussed.
Microstructural Evolution During Electromigration in Eutectic SnAg Solder Bumps
Authors: Chen Y.H. , Shao T.L. , Liu P.C. , Chen Chih , Chou T.
Published: October 2005

Microstructural changes induced by electromigration were studied in eutectic SnAg solder bumps jointed to under-bump metallization (UBM) of Ti/Cr–Cu/Cu and pad metallization of Cu/Ni/Au. Intermetallic compounds (IMCs) and phase transformations were observed during a current stress of 1 × 104 A/cm2 at 150 °C. On the cathode/substrate side, some of the (Cuy,Ni1−y)6Sn5 transformed into (Nix,Cu1−x)3Sn4 due to depletion of Cu atoms caused by the electron flow. It is found that both the cathode/chip and anode/chip ends could be failure sites. On the cathode/chip side, the UBM dissolved after current stressing for 22 h, and failure may occur due to depletion of solder. On the anode/chip side, a large amount of (Cuy,Ni1−y)6Sn5 or (Nix,Cu1−x)3Sn4 IMCs grew at the low-current-density area due to the migration of Ni and Cu atoms from the substrate side, which may be responsible for the electromigration failure at this end.
Application of Rotational Isomeric State Theory to Ionic Polymer Stiffness Predictions
Authors: Weiland Lisa Mauck , Lada Emily K. , Smith Ralph C. , Leo Donald J.
Published: October 2005

Presently, rotational isomeric state (RIS) theory directly addresses polymer chain conformation as it relates to mechanical response trends. The primary goal of this work is to explore the adaptation of this methodology to the prediction of material stiffness. This multiscale modeling approach relies on ionomer chain conformation and polymer morphology and thus has potential as both a predictive modeling tool and a synthesis guide. The Mark–Curro Monte Carlo methodology is applied to generate a statistically valid number of end-to-end chain lengths via RIS theory for four solvated Nafion® cases. For each case, a probability density function for chain length is estimated using various statistical techniques, including the classically applied cubic spline approach. It is found that the stiffness prediction is sensitive to the fitting strategy. The significance of various fitting strategies, as they relate to the physical structure of the polymer, are explored so that a method suitable for stiffness prediction may be identified.
Aqueous Dissolution of Perovskite (CaTiO3): Effects of Surface Damage and [Ca2+] in the Leachant
Authors: Zhang Zhaoming , Blackford Mark G. , Lumpkin Gregory R. , Smith Katherine L. , Vance Eric R.
Published: October 2005

We have characterized thermally annealed perovskite (CaTiO3) surfaces, both before and after aqueous dissolution testing, using scanning electron microscopy, cross-sectional transmission electron microscopy, x-ray photoelectron spectroscopy, and atomic force microscopy. It was shown that mechanical damage caused by polishing was essentially removed at the CaTiO3 surface by subsequent annealing; such annealed samples were used to study the intrinsic dissolution behavior of perovskite in deionized water at RT, 90 °C, and 150 °C. Our results indicate that, although mechanical damage caused higher Ca release initially, it did not affect the long-term Ca dissolution rate. However, the removal of surface damage by annealing did lead to the subsequent spatial ordering of the alteration product, which was identified as anatase (TiO2) by both x-ray and electron diffraction, on CaTiO3 surfaces after dissolution testing at150 °C. The effect of Ca2+ in the leachant on the dissolution reaction of perovskite at 150 °C was also investigated, and the results suggest that under repository conditions, the release of Ca from perovskite is likely to be significantly slower if Ca2+ is present in ground water.
Copper(I) Halide Nanoparticle-dispersed Glasses Prepared by Copper Staining
Authors: Kadono Kohei , Suetsugu Tatsuya , Ohtani Takeshi , Einishi Toshihiko , Tarumi Takashi , Yazawa Tetsuo
Published: October 2005

Copper(I) chloride and bromide nanoparticle-dispersed glasses were prepared by means of a conventional copper staining. The staining was performed by the following process: copper stain was applied on the surfaces of Cl−- or Br−-ion-containing borosilicate glasses, and the glasses were heat-treated at 510 °C for various times. Typical exciton bands observed in the absorption spectra of the glasses after the heat treatment indicated that CuCl and CuBr particles were formed in the surface region of the glasses. The average sizes of the CuCl and CuBr particles in the glasses heat-treated for 48 h were estimated at 4.8 and 2.7 nm, respectively. The nanoparticles were also characterized by x-ray diffraction and transmission electron microscopy. Depth profiles of Cu and CuBr concentration in the glass heat-treated for 48 h were measured. Copper decreased in concentration monotonously with depth, reaching up to 60 μm, while the CuBr concentration had a maximum at about 25 μm in depth.
Self-assembly-based Thermo-responsible Luminescent Organogels of Chromophoric L-glutamide-derived Lipids
Authors: Yamada Taisuke , Derakhshan Mahnaz , Ansarian Hamid Reza , Takafuji Makoto , Hachisako Hiroshi , Sagawa Takashi , Ihara Hirotaka
Published: October 2005

Three lipophilic L-glutamide derivatives with chromophoric head group were synthesized, and their photo-responsive properties were investigated in organic solution systems. By comparing their spectral behaviors, it was shown that organogels underwent a light blue to purple luminescence change, which was triggered by thermally induced monomeric-to-excimeric phase transition. This switching, based on self-assembly, is supposed to have special advantages in molecular electronics.
Synthesis and Characterization of Oxygen Doped ZnTe for Powder Phosphor Application
Authors: Kang Z.T. , Menkara H. , Wagner B.K. , Summers C.J. , Valdna V.
Published: October 2005

The synthesis of efficient ZnTe powder phosphors is very difficult due to its high moisture sensitivity and chemical instability during processing. In this study, an efficient ZnTe:O powder phosphor for x-ray imaging application was successfully synthesized by vacuum firing ZnTe powder prepared from ZnTe bulk crystals ball-milled in an O2 atmosphere. The phosphors were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, photoluminescence, and cathodoluminescence (CL) measurements and found to exhibit a luminescent efficiency three times that of ZnTe:O prepared by ZnO doping. The ZnTe:O samples exhibited a deep red emission centered at 680 nm and a CL decay time of 1.1μs.
Microstructure and Optical Properties of Au–Y2O3-stabilized ZrO2 Nanocomposite Films
Authors: Sirinakis George , Siddique Rezina , Monokroussos Christos , Carpenter Michael A. , Kaloyeros Alain E.
Published: October 2005

Nanocomposite films consisting of gold nanoparticles embedded in an yttria stabilized zirconia (YSZ) matrix were synthesized at room temperature by radio-frequency co-sputtering from YSZ and Au targets at a 5 mTorr working pressure. The films were subsequently annealed for 2 h in 1 atm argon, with the annealing temperature varied from 600 to 1000 °C in steps of 100 °C. The composition, microstructure, and optical properties of the films were characterized as a function of annealing temperature by Rutherford backscattering spectrometry, scanning electron microscopy, Auger electron spectroscopy, x-ray diffraction, and absorption spectroscopy. An optical absorption band due to the surface plasmon resonance (SPR) of the Au nanoparticles was observed around a wavelength of 600 nm. Furthermore, the SPR band full width at half-maximum exhibited an inverse linear dependence on the radius of the Au nanoparticle, with a slope parameter A = 0.18, indicating a weak interaction between the YSZ matrix and the Au nanoparticles. The experimentally observed SPR dependence on nanoparticle size is discussed within the context of the Mie theory and its size-dependent optical constants.
Fabrication of a Composite Structure of Three-dimensional Macroporous Silica and Carbon Nanofilaments
Authors: Park S.M. , Li H. , Sheldon B. , Du H.
Published: October 2005

We explored the possibility of incorporating carbon nanotubes in a patterned and macroporous silica structure replicated from a thin polystyrene template. A V-shaped thin, vertical channel was constructed and successfully used to assemble 10.06-μm polystyrene spheres into a dense three-dimensionally ordered template of uniform thickness. Infiltration of a single Co/silica precursor sol into the template followed by thermal treatments in vacuum and H2 produced three-dimensionally ordered silica pores with embedded Co nanoparticles. Wormlike carbon nanofilaments of 50–120 nm in diameter were grown on the inner surface of silica pores with plasma-enhanced chemical vapor deposition.
Chemical-mechanical Polishing of Copper Using Molybdenum Dioxide Slurry
Authors: Hegde Sharath , Patri Udaya B. , Babu S.V.
Published: October 2005

Slurries containing molybdenum oxide abrasives (MoO2, isoelectric point ∼pH 2) with potassium iodate (KIO3) as the oxidizing agent were used to polish copper disks and films, yielding relatively high removal rates. The relatively high copper removal rates observed were due to the in situ generation of I2 by the reaction between KIO3 and MoO2. The surface quality of the polished Cu films, however, was very poor with surface roughness values as high as 140 nm. A second polishing step using a dilute colloidal silica suspension containing H2O2, benzotriazole, and glycine at pH 4 improved the post-polish surface quality, final surface having surface roughness values as low as 0.35 nm.
Transparent Conductive In-doped Cd3TeO6 Thin Films with Perovskite Structure Deposited by Radio Frequency Magnetron Sputtering
Authors: Tetsuka Hiroyuki , Shan Yue Jin , Tezuka Keitaro , Imoto Hideo , Wasa Kiyotaka
Published: October 2005

Transparent conductive In-doped Cd3TeO6 thin films were deposited on silica glass substrate by radio frequency magnetron sputtering using targets composed of CdO, TeO2, and In2O3 powders, and their electrical and optical properties were examined. The electrical resistivity of 3.2 × 10−3 Ωcm and an average transmittance above 80% in the visible region (400–800 nm) were obtained for the films deposited at the substrate temperature above 300 °C. The maximum optical band gap was 3.92 eV for the film deposited at 700 °C, demonstrating a large optical band gap comparable to indium tin oxide.
Directional Coarsening of γ′ Phase Induced by Phase Transformation Stress
Authors: Zhao K. , Ma Y.H. , Lou L.H. , Hu Z.Q.
Published: October 2005

It was found that directional coarsening was induced by phase transformation stress due to non-uniform distribution of μ phase in an experimental nickel-based superalloy. The mechanism based on the existing diffusion and coherency strain energy theory has been discussed. It was concluded that directional coarsening was the course of dissolving of γ′ portion with high free energy, diffusing and growing on the existed γ′ particles along a preferential direction.
Assessment of Geometrical and Transport Properties of a Fibrous C/C Composite Preform Using x-ray Computerized Micro-tomography: Part I. Image Acquisition and Geometrical Properties
Authors: Coindreau Olivia , Vignoles Gérard L.
Published: October 2005

Raw and partially infiltrated carbon–carbon composite preforms have been scanned by high-resolution synchrotron radiation x-ray computerized micro-tomography. Three dimensional high-quality images of the pore space have been produced at two distinct resolutions and have been used for the computation of geometrical quantities: porosity, internal surface area, pore sizes, and their distributions, as well as local and average fiber directions. Determination of the latter property makes use of an original algorithm. All quantities have been compared to experimental data with good results. Structural models appropriate for ideal families of cylinders are shown to represent adequately the actual pore space.
Internal Friction Study of a Composite with a Negative Stiffness Constituent
Authors: Jaglinski T. , Stone D. , Lakes R.S.
Published: October 2005

Composites with negative stiffness constituents can exhibit material properties that exceed conventional bounds. Composites with VO2as negative stiffness inclusions and tin as the stabilizing matrix were prepared via powder metallurgy. Specimens were tested over a range of temperature in torsion using broadband viscoelastic spectroscopy. Composites processed via powder metallurgy exhibited internal friction anomalies over a broad range of temperatures, in contrast to the single, sharp anomalies reported previously from cast specimens. The detailed material behavior encompassed a variety of responses, which were also dependent on the number of thermal cycles. Composite theory predictions assuming a distribution of negative shear moduli can account for peak broadening.
Ceramic Coatings for Fiber Matrix Composites: Titania Thin Films on Bismaleimide-glass Fiber Composites
Authors: Razgon Anna , Sukenik Chaim N.
Published: October 2005

Bismaleimide polymer composites were coated with adherent, uniform, crack-free, titania films. Selective deposition of either crystalline (anatase) or amorphous films was achieved as a function of deposition conditions. Films are deposited under near ambient conditions from aqueous solution and thus can be adapted to any sample geometry and still provide complete coating of the polymer composite substrate. They can be obtained crack-free in thicknesses up to 0.5 μm by using drying procedures that combine temperature and humidity control.
Independent Control of Metal Cluster and Ceramic Particle Characteristics During One-step Synthesis of Pt/TiO2
Authors: Schulz Heiko , Mädler Lutz , Strobel Reto , Jossen Rainer , Pratsinis Sotiris E. , Johannessen Tue
Published: October 2005

Rapid quenching during flame spray synthesis of Pt/TiO2 (0–10 wt% Pt) is demonstrated as a versatile method for independent control of support (TiO2) and noble metal (Pt) cluster characteristics. Titania grain size, morphology, crystal phase structure, and crystal size were analyzed by nitrogen adsorption, electron microscopy and x-ray diffraction, respectively, while Pt-dispersion and size were determined by CO-pulse chemisorption. The influence of quench cooling on the flame temperature was analyzed by Fourier transform infrared spectroscopy. Increasing the quench flow rate reduced the Pt diameter asymptotically. Optimal quenching with respect to maximum Pt-dispersion (∼60%) resulted in average Pt diameters of 1.7 to 2.3 nm for Pt-contents of 1–10 wt%, respectively.
Effects of Nano-sized Microalloyed Carbonitrides and High-density Pinned Dislocations on Sulfide Stress Cracking Resistance of Pipeline Steels
Authors: Zhao Ming-Chun , Yang Ke
Published: October 2005

Sulfide stress cracking (SSC) resistance was investigated by comparing acicular ferrite (AF) and ferrite-pearlite (FP) in a microalloyed steel and in a non-microalloyedsteel. In microalloyed steel, AF exhibited better SSC resistance than FP, while in non-microalloyed steel, AF presented far worse SSC resistance than FP. In microalloyed steel, nano-sized carbonitrides and high-density pinned dislocations in AF were analyzed to behave as innocuous hydrogen traps, offering numerous sites for hydrogen redistribution and modifying critical cracking conditions. Dislocations in AF of microalloyed steel in the final analysis are attributed to pinning by the nano-sized carbonitrides.
Influence of Deposition Parameters on the Composition and Structure of Reactively Sputtered Nanocomposite TaC/a-C:H Thin Films
Authors: Evans Ryan D. , Howe Jane Y. , Bentley James , Doll Gary L. , Glass Jeffrey T.
Published: October 2005

The properties of nanocomposite tantalum carbide/amorphous hydrocarbon (TaC/a-C:H) thin films depend closely on reactive magnetron sputtering deposition process conditions. The chemical composition and structure trends for TaC/a-C:H films were obtained as a function of three deposition parameters: acetylene flow rate, applied direct current (dc) bias voltage, and substrate carousel rotation rate. Films were deposited according to a 23 factorial experimental design to enable multiple linear regression modeling of property trends. The Ta/C atomic ratio, hydrogen content, total film thickness, TaC crystallite size, and Raman spectra were statistically dependent on acetylene flow rate, applied dc bias voltage, or both. Transmission electron microscopy revealed a nanometer-scale lamellar film structure, the periodicity of which was affected mostly by substrate carousel rotation rate. The empirical property trends were interpreted with respect to hypothesized growth mechanisms that incorporate elements of physical vapor deposition and plasma-enhanced chemical vapor deposition.
Dy3+-doped Selenide Glasses for 1.3-μm Optical Fiber Amplifiers
Authors: Yang Zhiyong , Chen Wei , Luo Lan
Published: October 2005

The GexGa5Se(95−x) glasses, where x = 20, 22.5, 25, 27.5, 29.17, 30, 32.5, and 35, all doped with 0.05 mol% Dy3+ were prepared and studied. Thermal stabilities, optical properties, and 1.3 μm emission properties of the glasses were investigated. Strong fluorescence centered at 1.34 μm with a bandwidth of 92 nm was observed. Three phenomenological intensity parameters were obtained: Ω2 =12.64 × 10−20, Ω4 =2.94 × 10−20, and Ω6 =1.48 × 10−20 cm2 by Judd–Ofelt analysis. A new method estimating lifetime of overlapping energy level was introduced. Lifetimes of 520 μs were measured for the 1.3 μm transition, and the quantum efficiency was 36.8% according to the new method.
A Hybrid Poly(ethylene oxide)/ Poly(vinylidene fluoride)/TiO2 Nanoparticle Solid‐State Redox Electrolyte for Dye‐Sensitized Nanocrystalline Solar Cells
Authors: Han H. W. , Liu W. , Zhang J. , Zhao X.‐Z.
Published: October 2005

High‐efficiency all‐solid‐state dye‐sensitized nanocrystalline solar cells have been fabricated using a poly(ethylene oxide)/poly(vinylidene fluoride) (PEO/PVDF)/TiO2‐nanoparticle polymer redox electrolyte, which yields an overall energy‐conversion efficiency of about 4.8 % under irradiation by white light (65.2 mW cm–2). The introduction of PVDF (which contains the highly electronegative element fluorine) and TiO2 nanoparticles into the PEO electrolyte increases the ionic conductivity (by about two orders of magnitude) and effectively reduces the recombination rate at the interface of the TiO2 and the solid‐state electrolyte, thus enhancing the performance of the solar cell.
Directed Growth and Electrical‐ Transport Properties of Carbon Nanotube Architectures on Indium Tin Oxide Films on Silicon‐Based Substrates
Authors: Agrawal S. , Frederick M. J. , Lupo F. , Victor P. , Nalamasu O. , Ramanath G.
Published: October 2005

Growing aligned carbon nanotubes (CNTs) on electrically conducting and/or optically transparent materials is potentially useful for accessing CNT properties through electrical and optical stimuli. Here, we report a new approach to growing aligned bundles of multiwalled CNTs on a porous back contact of optically transparent and electrically conducting indium tin oxide (ITO) films on silicon and silica substrates without the use of a predeposited catalyst. CNTs grow from a xylene/ferrocene mixture, which traverses through the pores in the thin ITO film, and decomposes on an interfacial silica layer formed via the reaction between ITO and the Si substrate. The CNTs inherit the topography of the silica substrate, enabling back‐contact formation for CNTs grown in any predetermined orientation. These features can be harnessed to form CNT contacts with other substrate materials which, upon reduction by Si, results in a conducting interfacial layer. The ITO‐contacted CNTs exhibit thermally activated ohmic behavior across a 100 ± 10 meV barrier at electric fields below ∼ 100 V cm–1 due to carrier transport through the outermost shells of the CNTs. At higher electric fields, we observe superlinear behavior due to carrier tunneling and transport through the inner graphene shells. Our findings open up new possibilities for integrating CNTs with Si‐based device technologies.
Energy Collection, Transport, and Trapping by a Supramolecular Organization of Dyes in Hexagonal Zeolite Nanocrystals
Authors: Minkowski C. , Pansu R. , Takano M. , Calzaferri G.
Published: October 2005

The incorporation of guest molecules into the cavities of molecular sieves leads to a large variety of highly interesting materials. Zeolite L—an aluminosilicate with one‐dimensional channels of open diameter 7.1 Å—is a very versatile material for building highly organized host–guest systems. We present materials where organic dye molecules have been incorporated into the channels of zeolite L by means of diffusion, to build artificial photonic antenna systems. The channel entrance can be plugged by adding closure molecules that then connect the guest molecules inside with materials or molecules outside of the zeolite channels, since they can act as extensions of the interior of the zeolite crystal. The photophysical processes taking place in such dye‐loaded zeolite L antennae can be studied either on single‐micrometer‐ or submicrometer‐sized crystals or on crystals dispersed in a solvent or coated as thin layers on a support. The energy‐transfer process occurring is of the Förster‐type, and its transfer rate can be tuned by separating the donor dyes and the acceptor dyes locally by varying amounts of spacer molecules. The distribution of the dye molecules and empty sites within a zeolite crystal has been modeled by means of a Monte Carlo simulation. The Förster energy migration and transfer steps are described as a random walk.
Hierarchical Pattern Formation in Thin Polymer Films Using an Electric Field and Vapor Sorption
Authors: Harkema S. , Steiner U.
Published: October 2005

The experimental observation of electric‐field‐induced instabilities of polymer films exposed to toluene vapors is reported. When using a laterally structured electrode, the pattern that forms in the polymer film is governed by the interplay of the intrinsic film instability and the periodicity of the electrode structure. By adjusting the applied voltage, it is possible to switch between two different pattern‐replication modes. A further important parameter is the aspect ratio of the structured electrode. For high ratios of polymer film thickness to capacitor‐plate spacing, structures with hierarchical length scales have been observed.
Ethylene‐Bridged Bissulfoximines in Copper‐Catalyzed Enantioselective Hetero‐Diels‐‐Alder Reactions
Authors: Bolm Carsten , Verrucci Marinella , Simic Oliver , Hackenberger Christian P. R.
Published: October 2005

Ethylene‐bridged bissulfoximines were applied as chiral ligands in copper‐catalyzed enantioselective hetero‐Diels–Alder reactions. After optimization of the reaction conditions, products with up to 99% ee were obtained.
Anionic Reactions of N‐(trans‐2,3‐Diphenylaziridin‐1‐yl)imines and Their Use as 1,1‐Dipoles in Anionic Cyclizations
Authors: Hwang Jung‐ll , Hong Young‐Taek , Kim Sunggak
Published: October 2005

Reaction of N‐(trans‐2,3‐diphenylaziridin‐1‐yl)imines with alkyllithiums and organocuprates afforded the desired addition products after consecutive fragmentations along with liberation of stilbene and nitrogen gas, while the reaction of N‐(2‐phenylaziridin‐1‐yl)imines under similar conditions gave an anomalous by‐product. Anionic cyclizations of N‐(trans‐2,3‐diphenylaziridin‐1‐yl)imines using unactivated alkenes and alkynes as acceptors proceeded smoothly, yielding cyclized products in good yields.
Substrate‐Controlled Palladium‐Catalyzed Allylic Alkylations of Chelated Enolates – Scope and Limitations
Authors: Lindner Thomas , Kazmaier Uli
Published: October 2005

Chelated enolates of amino acid derivatives were found to be excellent nucleophiles for stereoselective palladium‐catalyzed allylic alkylations via terminal π‐allyl complexes. Neither the olefin geometry (linear substrates) nor the configuration of secondary allylic substrates has an influence on the newly formed stereogenic centre of the amino acid. This is exclusively controlled by the protecting group on the chiral centre. Therefore, depending on the protecting group used, both diastereomeric amino acids can be obtained in a highly stereoselective fashion (up to 96% ds for 1,5 induction) from one allylic alcohol.
Diastereoselective Synthesis of Enantioenriched, Annulated Tetrahydrofurans by Simultaneous Formation of the O‐1C‐5 and the C‐5C‐4 Bonds
Authors: Ünaldi Seda , Özlügedik Mustafa , Fröhlich Roland , Hoppe Dieter
Published: October 2005

Enantiomerically enriched 1‐[2‐(1‐hydroxyalkyl)cycloalkylidene]methyl N,N‐diisopropylcarbamates, which are easily available by an asymmetric homoaldol reaction, condense with aldehydes under the influence of boron trifluoride etherate to form cyclohexano‐ or cyclopentano‐annulated tetrahydrofuran‐3‐carboxaldehydes, bearing two quaternary carbon atoms and four adjacent stereogenic centers, with complete diastereoselectivity.
Stereoselective Synthesis of 3‐Alkylideneoxindoles using Tandem Indium‐Mediated Carbometallation and Palladium‐Catalyzed Cross‐Coupling Reactions
Authors: Yanada Reiko , Obika Shingo , Kobayashi Yusuke , Inokuma Tsubasa , Oyama Munetaka , Yanada Kazuo , Takemoto Yoshiji
Published: October 2005

The first efficient methods for the stereoselective synthesis of various (E)‐, (Z)‐, and disubstituted 3‐alkylideneoxindoles via radical cyclization reactions were investigated using tandem indium‐mediated carbometallation and palladium‐catalyzed cross‐coupling reactions. The proper combination of substrates and reaction conditions is important for good yields. The key step is the first stereoselective carboindation reaction using the strong coordination ability of an indium cation to the amide carbonyl oxygen. We applied this method to the synthesis of TMC‐95A precursor. A new N‐debenzylation method with N‐hydroxyphthalimide‐O2‐Co(OAc)2‐Mn(OAc)2 was also developed using a one‐electron oxidation procedure.
Mannich‐Type Reaction Using Alkenyl Trichloroacetates Catalyzed by Dibutyltin Dimethoxide
Authors: Yanagisawa Akira , Saito Hironao , Harada Masanori , Arai Takayoshi
Published: October 2005

A novel Mannich‐type reaction of alkenyl trichloroacetates with aldimines has been realized by using dibutyltin dimethoxide as a catalyst, which is regenerated by addition of methanol. A three‐component coupling reaction of aldehydes, primary amines, and alkenyl trichloroacetates has been also efficiently achieved. These procedures can provide a variety of β‐amino ketones not only from aromatic aldehydes but also from α,β‐unsaturated aldehydes mainly with syn‐selectivity in high yields up to 99%.
Synthesis of New C2‐Symmetrical Bissulfonamide Ligands and Application in the Enantioselective Addition of Alkynylzinc to Aldehydes and Ketones
Authors: Ni Ming , Wang Rui , Han Zhi‐jian , Mao Bin , Da Chao‐shan , Liu Lei , Chen Chao
Published: October 2005

Novel C2‐symmetrical bissulfonamide ligands were easily prepared in three simple steps and applied in the enantioselective addition of alkynylzinc reagents to aldehydes. Compound 7a was found to be an outstanding ligand for this reaction. When the catalyst loading, 4 mol % of 7a, was used, high enantioselectivity with an ee value up to 97% was achieved under very mild conditions. When the amount of ligand 7a was lowered to 2 mol %, excellent levels of enantiocontrol up to 95% ee were still achieved. So far the most economic catalyst system was developed for the addition of terminal alkynes to aromatic aldehydes in terms of ligand loading and enantioselectivity. Moreover, ligand 7a in combination with Ti(O‐i‐Pr)4 was found to be effective in promoting the addition reaction of an alkynylzinc reagent to unactivated simple ketones under very mild conditions. The corresponding chiral tertiary propargylic alcohols were obtained with enantiomeric excesses of up to 81%.
Iron(III)‐Catalyzed Tandem Sequential Methanol Oxidation/Aldol Coupling
Authors: Lecomte Vincent , Bolm Carsten
Published: October 2005

Iron(III)‐catalyzed methanol oxidations have been performed using hydrogen peroxide as oxidant. Formaldehyde is formed in situ and reacts subsequently with activated ketones to give α‐hydroxymethyl carbonyl compounds in good yields. As side reactions iron‐catalyzed α‐hydroxylations have been observed.
Enantioselective Mannich‐Type Reaction Catalyzed by a Chiral Brønsted Acid Derived from TADDOL
Authors: Akiyama Takahiko , Saitoh Youichi , Morita Hisashi , Fuchibe Kohei
Published: October 2005

A novel cyclic dialkyl phosphate was synthesized starting from (+)‐diethyl tartrate. Its catalytic activity as a chiral Brønsted acid has been examined in the Mannich‐type reaction of a ketene silyl acetal with aldimines as a model reaction. The corresponding β‐amino acid esters were obtained with high enantioselectivity.
Imine Additions of Internal Alkynes for the Synthesis of Trisubstituted (E)‐Alkene and Cyclopropane Peptide Isosteres
Authors: Wipf Peter , Xiao Jingbo , Geib Steven J.
Published: October 2005

Divergent multi‐component reactions (DMCR) involving CC bond formations can provide large increases in structural diversity and allow the rapid assembly of complex products from readily available starting materials. Cascade hydrozirconation‐Zr/Zn transmetalation‐imine addition of alkynes represents a versatile methodology for the synthesis of (E)‐alkene and cyclopropane dipeptide isosteres. Appropriate substitutions at the sp2‐carbon of (E)‐alkene peptide isosteres allow a range of Pd‐catalyzed cross‐coupling reactions, which can be used for the fine‐tuning of the conformational and electronic properties of the parent peptide bond mimic. CC bond formation by microwave‐accelerated Stille coupling of stannylalkenes represents a fast, convergent synthetic approach toward trisubstituted (E)‐alkene dipeptide isosteres.
A New Method for the Generation of Titanium(III) Complexes and its Application in Pinacol Coupling Reactions
Authors: Knoop Christoph Alexander , Studer Armido
Published: October 2005

A new method for thein situgeneration of various Ti(III) complexes is presented. Cyclohexadienyl‐Ti(IV) derivatives, which are readily prepared from the corresponding lithiated cyclohexadienes, afford the corresponding Ti(III) complexes upon thermal CTi‐bond homolysis. The Ti(III) compounds generated using this novel method have successfully been used in the reductive dimerization of benzaldehyde. In particular, TiBr3, TiCp2Cl and Ti(O‐i‐Pr)3have been generatedviathis approach. Moreover, the method also offers an entry to new chiral Ti(III) complexes as documented by the preparation of Ti(III)CpTADDOLate.
Allylation of Aldehydes Promoted by the Cerium(III) Chloride Heptahydrate/Sodium Iodide System: the Dependence of Regio‐ and Stereocontrol on the Reaction Conditions
Authors: Bartoli G. , Giuliani A. , Marcantoni E. , Massaccesi M. , Melchiorre P. , Lanari S. , Sambri L.
Published: October 2005

The cerium(III) chloride heptahydrate/sodium iodide complex (CeCl3 ⋅ 7 H2O/NaI) acts as a useful promoter in the carbon‐carbon bond forming reaction by addition of allyltributylstannanes to aldehydes. The reaction of 2‐butenyltributylstannane shows that the regio‐ and the stereochemical outcomes depend on the reaction conditions. When the promoter is adsorbed on a solid support (aluminum oxide), a highly prevalent formation of the γ‐adduct is observed in solvent‐free conditions. Conversely, when the reaction is carried out in acetonitrile as the solvent, the α‐adduct largely prevails. In the last case, a complete stereocontrol is observed, the less stable (Z)‐isomer being obtained in high geometrical purity.