bluuebunny/crossref_metadata_2025 huggingface dataset:
Photochromic Organic-Inorganic Hybrid Nanocomposite Hard Coatings With Tailored Fast Switching Properties
Authors: Mennig M. , Fries K. , Schmidt H.
Published: April 2011

A recently developed photochromic organic-inorganic nanocomposite (Nanomer®) coating system is investigated, which is based on an epoxysilane as network former, different bisepoxides as spacer and an organic amine as thermal cross-linker. This coating system is compatible with different photochromic dyes like oxazines, pyrans and fulgides and also with surface modified ceramic nanoparticles as filler in order to obtain macroscopic “hard properties” without changing the photochromic kinetics. In order to investigate the dye-spacer interactions and influence on the switching kinetic behavior, the matrix composition was diminished to the network former, the thermal cross-linker and two types (polar and nonpolar) of spacers in different concentrations. Four commercially available spirooxazines with different molecular sizes and polarities were incorporated into the matrices and coatings on glass slides were prepared by float-coating and cured at 130 °C for 2 h. The half darkening and half fading times of the coatings were measured by a fast diode array spectrometer as a function of spacer type and concentration for the four different dyes. The “nonpolar” spacer CHMG did not influence the switching kinetic of the dyes significantly and fast switching times of 2 s - 4 s were obtained. The “polar” spacer PCF (aromatic character) showed interactions with the dye molecules, which led to an increase in the switching times of up to 25 s. The retardation of the switching process increased with increasing spacer content and with increasing polar character of the dye molecule. From these results, it could be concluded that the photochromic behavior of the spirooxazines could be adjusted to different applications by interactions with polar spacers.
Sol-Gel Derived Titaniajormosil Composite Thin Films For Optical Waveguide Applications
Authors: Que Wenxiu , Zhou Y. , Lam Y. L. , Chan Y. C. , Cheng S. D. , Kam C. H. , Zhang H. X.
Published: April 2011

We report the preparation of sol-gel waveguide films based on a newly developed recipe to incorporate organic molecules into the inorganic sol-gel glass matrix. The film was derived from a sol that has a higher titanium content in an organically modified silane (ORMOSIL), namely, ÿ-Glycidoxypropyltrimethoxysilane. We have shown that using spin-coating and low temperature baking, a single coating layer can have a thickness of more than 1.5 μm. When such a single layer film is deposited on a microscope glass slide or a piece of silicon with a buffercladding layer, it is able to support the guiding of optical waves. We have characterized the film using scanning electron microscopy, atomic force microscopy, X-ray diffractometry, thermal gravimetric analysis. differential thermal analysis and Fourier transform infrared spectroscopy and have studied the properties of the waveguide film, including the microstructural properties. the chemical bonding properties, and the optical properties. Based on these experimental results, we found that a heat-treatment at a temperature slightly below 200°C is necessary to attain a dense pore-free film. It has also been noted that a purely inorganic and crack-free silica-titania film can be obtained after baking the titania-ORMOSIL composite film at 500°C or higher.
Organic-Inorganic Hybrid Materials From Surface Initiated Polymerization
Authors: Seery Thomas A. P. , Vatansever Fatma
Published: April 2011

A new technique in surface modification is presented where chain growth polymerizations are initiated from tethered ruthenium alkylidene catalysts and organic-inorganic hybrid materials are produced. This approach provides nearly complete control over the polymer layer at the organic-inorganic interface with independent control over the chain length and grafting density. Hybrid particles are characterized using standard methods, i.e. NMR and transmission IR.
Different Solvent Free Synthetic Routes to Organic/Inorganic Hybrid Materials
Authors: Kaddami H. , Gerard J. F. , Pascault J. P.
Published: April 2011

The sol-gel chemistry in low-temperature conditions can be used to produce organicinorganic materials nanocomposite from the in-situ formation of silica-rich phase in a polymer matrix. Different synthetic routes have been proposed: i) hydrolysis and condensation reactions of silane end capped oligomers, ii) polymerization of hydroxyethyl methacrylate, HEMA in presence of preformed functionalized silica nanoparticles, and iii) simultaneous hydrolysis and condensation of tetraethoxysilane and polymerization of hydroxyethymeth-acrylate.

Rheological investigations made during the polymerization of these three systems display many differences. Time for gelation was chosen as the time at which the loss factor, tanδ is independent on the testing frequency, or the time at which the system displays an elastic response. Vitrification phenomenon is associated with a tanδ peak. In some cases vitrification of the inorganic-rich phase interfered with the observation of gelation and the appearance of a non soluble fraction in a good solvent like tetrahydrofurane can help for attribution.

During radical chain-polymerization of HEMA a classical Trommsdorff-effect was observed. It can be at the same time than the macrogelation in the case of neat HEMA or delayed by the presence of grafted SiO2 nanoparticles. During simultaneous synthesis of inorganic and organic phases, vitrification of the inorganic-rich phase occured just after macrogelation of the system.

Final morphologies are strongly dependent on the occurrence of these different structural transformations.
Dendrimer-Metal Nanocomposites
Authors: Balogh L. , Laverdure K. S. , Gido S. P. , Mott A. G. , Miller M. J. , Ketchel B. P. , Tomalia D. A.
Published: April 2011

Dendrimer metal nanocomposites are novel hybride materials that display unique physical and chemical properties as a consequence of the atomic/molecular level dispersion of inorganic and organic molecules. In their synthesis, dendrimers are used as templates to pre-organize metal ions followed by an in-situ reduction, which will immobilize and stabilize atomic domains of the reaction product(s). Size, shape, size distribution and surface functionality of these nanocomposites are determined and controlled by the dendritic macromolecules and may also be influenced by the encapsulated compounds. Solubility of these molecular nanocomposites is controlled by the polymer. Thus, it is possible to solubilize conventionally insoluble inorganic compounds in water or other solvents using dendritic hosts. Conceptually, these materials have enormous potential for applications such as catalysts or molecular devices.

In this work, surface-modified poly(amido-amine) dendrimers were used to prepare {Cu(0)-PAMAM}, {Ag(0)-PAMAM} and {Au(0)-PAMAM} dendrimer-metal nanocomposites containing stable and solvent soluble zero valence metals. Characterization of the resulting nanocomposites has been carried out by TEM, UV-visible spectroscopy, and scattering techniques. Depending on the chemistry of ion preorganization in the dendrimer, internal (“I”), external (“E”) and mixed (“M”) type nanocomposite structures could be identified according to the varying location of the actual metal content.

The effect of structural differences was found to be reflected in the optical properties of the nanocomposites.
Preparation of Novel Hollow Fiber Silica Using an Organic Gel as a Template
Authors: Ono Y. , Hojo J. , Shinkai S.
Published: April 2011

A novel hollow fiber silica was created by the use of the fibrous structures of an organic gel as a template. Its inner diameter ranged from 10 to 200 nm and the outer diameter ranged from 50 to 300 nm. A dichloromethane solution of an organic gelator was mixed with the silicate solution, TEOS/water/catalyst (acetic acid or benzylamine)/solvent (acetic acid or alcohol), which was gelated by the organic gelator. Subsequently, the resultant solution was evaporated in vacuo until the dichloromethane was removed to give a turbid gel. The SEM images of the product showed well-grown fibrous structures. After calcination, it was clearly found by TEM images that these fibers have a tubular structure. The most favorable gelator to form hollow fiber silica is one that has a cationic charge within the molecule, for example, a quaternary ammonium halide salt or a crown ether including a metal cation. In this study, the gel-forming segment of the gelator was a cholesterol derivative. Since the propagation species of silicate in the solution of acetic acid or benzylamine are considered to be anionic, the electrostatic interactions may be important for adsorption of silica onto the template fibers.
A Silicon, Carbon and Deuterium NMR Investigation of Molecular Templating in Amorphous Silicas
Authors: Assink R. A. , Click C. A. , Alam T. M. , Brinker C. J. , Naik S. J.
Published: April 2011

The precise pore sizes defined by crystalline zeolite lattices have led to intensive research on zeolite membranes. Unfortunately zeolites have proven to be extremely difficult to prepare in a defect-free thin film form needed for membrane flux and selectivity. We introduce tetrapropylammonium TPA (a structure directing agent for zeolite ZSM-5) into a silica sol and exploit the development of high solvation stresses to create templated amorphous silicas with pore apertures comparable in size to those of ZSM-5. 29Si and 2H NMR experiments were performed to evaluate the efficacy of our templating approach. The 29Si NMR spectrum of the silica matrix was observed by an intermolecular cross-polarization experiment between the 1H nuclei of TPA and the 29Si nuclei in the silica matrix. The efficiency of the cross-polarization interaction was used to investigate the degree to which the matrix formed a tight cage surrounding the template molecule. Bulk xerogels, prepared by gelation and slow drying of the corresponding sols, exhibited only weak interactions between the two sets of nuclei. Thin film xeorgels, where drying stresses are greater, resulted in significantly increased interactions. Analogous materials were prepared using fully deuterated TPA. The 2H NMR wideline spectra consisted of a partially narrowed resonance, corresponding to template molecules which were undergoing restricted rotational motion, and an isotropically narrowed resonance, corresponding to molecules which were undergoing rapid rotational motion. The number of isotropically rotating template molecules decreased for the thin film specimens, consistent with improved templating of amorphous silica by TPA.
Carborane-Siloxane-Diacetylene Thermosets and Ceramic Precursors
Authors: Armistead J. P. , Houser E. J. , Son D. Y. , Keller T. M.
Published: April 2011

Thermosets and ceramic chars were characterized for three polymeric materials consisting of diacetylene-siloxane repeat units, DaS, diacetylene-siloxane-carborane-siloxane repeat units, DaSCS, and a 90/10 copolymerization. The goal was to incorporate the known thermo-oxidative stability of the siloxane-carborane elastomers into high performance thermosets and ceramic chars. The DaSCS thermoset has excellent thermo-oxidative stability as determined by a low weight loss and tough residue after annealing 100 hours in air at 316°C, however the glass transition is a low 94°C. DaS and 90/10 thermosets do not undergo glass transitions below 350°C and have low weight losses on thermo-oxidative aging, however the residue was quite brittle. The much higher carborane content in DaSCS also seems to help in ceramic char formation. All polymers had similar char yields to 800°C, whereas DaSCS solidified to a 15% denser ceramic.
First-Principle Studies of Permanent-Magnet Materials
Authors: Jaswal S.S. , Sabiryanov R.F.
Published: April 2011

First-principle electronic structure studies complement experimental research on hard-magnet materials. Since the discovery of Nd 2Fel4B in 1984, the research in this area has been concentrated on T(Fe,Co)-rich rare-earth compounds such as RT12 and R2T17 and exchange coupled hard/soft phases. Self-consistent spin-polarized electronic structure calculations are carried out for the sequence YFc2→ YFe3→Y2Fe17→YFe12 to study the variation of the magnetization and Curie temperature as a function of the Fe concentration. Calculations are performed for R2T17 systems which show significant improvements in their Curie temperatures with interstitial and substitutional modifications. The calculated results are compared with the available experimental data. Computer simulations are carried out for FePt/Fe and SmCo5/Co1−x -Fex, hard/soft multilayers.
Emerge: European Magnets with Enhanced Remanence for Greater Efficiency: a new and cost effective magnetic material for use in mid-priced applications
Authors: Archambault V. , Pere D.
Published: April 2011

Emerge is an European project based on the collaboration between three industrial partners (Rhodia, Philips and Magnetfabrik Bonn) and three research laboratories (Centre National de la Recherche Scientifique CNRS (Laboratory Louis NEEL), Trinity College of Dublin TCD, Vienna University IATP). The aim of this project is to improve the coercivity in enhanced remanence material. This three years project used statistical set-ups to reduce the number of samples to be realised and tested. The complete description of the project is developed in this paper and the main conclusions on sample composition and process issues are also discussed.
High Performance Magnets - Microstructure and Coercivity
Authors: Fidler J. , Sasaki S. , Estevez-Rams E.
Published: April 2011

The importance of newly developed permanent magnetic materials in many electro-, magnetomechanical and electronic applications can be attributed to the drastic improvement of the magnetic energy density product and coercive field. A systematic study has been undertaken in order to determine the influence of oxygen content on microstructure and coercivity of high remanence Nd2Fe14B based sintered magnets. The energy density product >400 kJ/m3 (50 MGOe) and the coercive field of 800 kA/m were obtained after a combination of rubber isostatic and transverse die pressing methods. Magnets of the composition Nd151−xFe78+xB6Cu0.03A10.7 [x= 0-2.5] were prepared using strip cast materials. The high oxygen content of the magnets was gradually decreased from values of 4000-6000 ppm to a value < 1000 ppm. Abnormal grain growth (AGG) of the 2:14:1 grains occurred preferentially in magnets with low oxygen content, thus the squareness of the demagnetisation curve drastically decreased. The oxygen content strongly affects the AGG and the magnets with higher oxygen content have the higher critical temperatures at which the AGG occurs. On the other hand, isotropic magnets tend to have the lower critical temperatures than anisotropic magnets by 10-20°C. In the second part of the paper examples of the influence of intergranular phases, grain size and grain shape observed by TEM on coercivity of sintered and melt-spun Nd-Fe-B magnets are compared.
Epitaxial Co/NiAl Thin Film Growth on Si Substrates
Authors: Gong Heng , Yang Wei , Lambeth David N. , Laughlin David E.
Published: April 2011

Quad-crystal Co/NiAl/Ag thin films were epitaxially grown on hydrofluoric acid etched Si(111) single crystal substrates by sputter deposition. The orientation relationship was studied by x-ray 0/20 diffraction and pole figure Φ-scan, and it was determined to be Co(1011) ‖ NiAl(110) ‖ Ag(111) ‖ Si(111). The Ag layer contains two twin-related orientations of grains. NiAl grows with three variants of grains on the Ag(111) layer. Since Co(1011) contains grains with four possible easy axis directions when grown on each NiAl variant, the quad-crystal media consist of grains with twelve easy axis directions and exhibit nearly isotropic in-plane magnetic properties. Meanwhile, uni-crystal Co(1010)/NiAl(112) films were also epitaxially grown on Ag(110)/HF-Si(110) templates. The orientation relationships determined from these epitaxial films were very useful in understanding the texture evolution of the Co alloys on NiAl. It indicates that the Co (1010) texture evolution on the (110) texture of NiAl on amorphous substrates, such as NiP/AlMg or glass, is due to a difficult to observe NiAI (112) texture on the top of the (110) texture.
A Method for Controlled Synthesis of Anisotropic Nanoparticles and Nanosystems
Authors: Khomutov G.B. , Gubin S.P. , Koksharov Yu.A. , Khanin V.V. , Obidenov A.Yu. , Soldatov E.S. , Trifonov A.S.
Published: April 2011

In the present work it has been shown that the shape of ultrafme metallic magnetic particles is controlled by applied magnetic and/or electric fields and the state of reaction media during the nanoparticles formation. The ulraviolet (UV) decomposition of volatile organometallic compound iron pentacarbonyl was used to produce amorphous metallic nanoparticles. The two-dimensional photochemical synthesis of nanoparticles was carried out in a mixed Langmnuir monolayer at the gas/water interface with stearic acid as surfactant matrix and also in a mixed film deposited onto graphite substrate. Scanning tunneling microscopy analysis of deposited nanoparticulate monolayers showed that the size and shape of nanoparticles formed were dependent on the initial mixed monolayer content, compression extent and exposure time to UV, and were changed dramatically from isotropic plate-like to aligned ellipsoidal and needle-like when external magnetic and/or electric fields were applied during the synthesis. Magnetic nanoparticles with diameter exceeding 5 nm formed chain structures alignable by external fields. The one-dimensional aligned metallic string-like nanostructures (nanowires) with cross-section size about 10+20 rm were also formed at elevated temperatures under synergistically applied magnetic and electric fields. Magnetic properties of nanoparticulate multilayer Langmuir-Blodgett films were studied using electron paramagnetic resonance technique. The ferromagnetic resonance and superparamagnetic signals were observed in the material.
Influence of Nanocrystallization on the High-Frequency Magnetoimpedance in Ultrathin Fe83Cu1Nb7B9 Melt-Spun Ribbons.
Authors: Brunetti L. , Rampado O. , Tiberto P. , Vinai F.
Published: April 2011

Ultrathin ribbons of amorphous Fe83Cu1Nb7B9 obtained by planar flow casting, have been submitted to dc Joule heating in vacuum to develop a nanocrystalline phase. Variations in the initial magnetic permeability as high as 1000 times the as-quenched value have been measured in a wide range of nanocrystalline samples. The magnetoimpedance behavior in the microwave region has been studied as a function of the nanocrystalline state. In this work the intensity of the impedance variation has been related to the samples degree of softness.
Magnetic Characteristics of RCo7−xZrx Alloys (invited) (R = Sm, Pr, Er, Gd, and Y)
Authors: Huang M.Q. , Wallace W.E. , Mchenry M.E. , Sankar S.G. , Chen Qun , Rhodia B.M. Ma
Published: April 2011

A brief review is presented of recent work dealing with the structure and magnetic properties of RCo7−x Zrx alloys (R=Sm, Pr, Er, Gd, and Y). The experimental results obtained are consistent with a model in which Zr atoms partly replace dumbbell Co atoms and play an important role in stabilizing the TbCu7 structure while significantly increasing the anisotropy field (HA). For example, when R=Sm, HA increases from 90 kOe for x=O to 130 kOe for x=0.2 at 300 K, and from 140 kOe for x=0 to 220 kOe for x=0.2 at 10 K. In the case of R=Y and Gd, HA is mainly contributed by the Co sublattice. For R=Y alloys, HA increases from 18 kOe for x=0 to 74 kOe for x=0.2 at 300 K and from 20 kOe for x=0 to 82 kOe for x=0.2 at 10 K. For R=Gd alloys, HA shows the largest enhancement. It increases from 35 kOe for x=0 to 140 kOe for x=0.2 at 300 K and from planar for x=0 to uniaxial with 182 kOe for x=0.2 at 10 K. In general, experimental results are in accord with the theory of Greedan and Rao for anisotropies of R-Co alloys. The magnetic moments for cobalt and rare earth in RCo7−xrx compounds (x=0∼A).2) have been estimated from the experimental values. The results show that they are nearly the same as those in RCo5 or R2Co17. The Co moment is 1.5∼;1.6 μB. Some phase transition phenomenon between RCo5, RCo7, R2Co17and R2Co7at different heat treatment conditions will also be discussed.
Discrete Dislocation Plasticity Approach to Fast Moving Dislocations
Authors: Roos A. , Metselaar E. , De Hosson J.Th.M. , van der Giessen E.
Published: April 2011

This paper concentrates on application of the so-called Discrete Dislocation Plasticity to high strain rate deformations. In particular the question is addressed if the DDP approach may capture the specific processes taking place at high strain rates. In particular the paper reports on tests of the validity of some approximations and provides some sample runs to show the applicability of the method. In assessing the results, one has to keep in mind two underpinning aspects: (1) the model is two-dimensional and (2) the results hold only in the regime where linear isotropic elasticity is valid. It was concluded that accelerations can not be neglected at very high strain rate deformations, both for the conventional and the relativistic case.
Modeling Collective Dislocation Dynamics in Ice Single Crystals
Authors: Miguel M.-Carmen , Vespignani A. , Zapperi S.
Published: April 2011

We propose a model to study the plasticity of ice single crystals by numerical simulations. The model includes the long-range character of the interaction among dislocations, as well as the possibility of mutual annihilation of these line defects characterized by its Burgers vector. A multiplication mechanism representing the activation of Frank-Read sources due to dislocation pinning is also introduced in the model.

With our approach we are able to probe the dislocation patterns, which result from the dislocation dynamics. Furthermore, our results exhibit features characteristic of driven dynamic critical phenomena such as scaling behavior, and avalanche dynamics. Some of these results account for the experimental findings reported for ice single crystals under creep deformation, like the power-law distributions of the acoustic emission intensity observed sistematically in experiments.
Amplitude Dependent Internal Friction within a Continuum Simulation
Authors: Greaney P. Alex , Chrzan D. C.
Published: April 2011

The mechanical losses due to the bowing of isolated Frank-Read sources under application of periodic loads is studied within a continuum simulation of dislocation dynamics. The dislocations are modelled within isotropic elasticity theory and assumed to be in the overdamped limit. Dislocation radiation effects are neglected. The mechanical losses are studied as a function of bias stress, amplitude of the periodic stress and frequency. The frequencies studied lie between 10 KHz and 1 MHz. Under high stresses applied at low frequencies, a deviation from the expected Lorentzian resonance shape is observed. The physical origins of this deviation are discussed.
Experimental Study of Mobile Dislocation Densities and Velocities through Transient Mechanical Tests
Authors: Piccolo B. Lo , Martin J.L. , Bonneville J.
Published: April 2011

The use of transient mechanical tests such as repeated load relaxations and repeated creep tests provide some insight on the respective contribution of mobile dislocation densities and velocities to the plastic strain-rate and also on the hardening mechanisms. Improvements of the second technique are reported as well as results on Ni3Al polycrystals. Other materials (e.g. Cu, TiAl) are considered for comparison. Correlations are found between dislocation exhaustion rates, workhardening coefficients and the amplitude of yield point at reloading after the relaxations.
Structure of a Dissociated Edge Dislocation in Copper
Authors: Perondi L. F. , Szelestey P. , Kaski K.
Published: April 2011

The structure of a dissociated edge dislocation in copper is investigated. Attention is given to the structure of the Shockley partials and the equilibrium size of the fault ribbon. The studies are carried out through Molecular Dynamics simulations. The atomic interactions have been modelled through an Embedded Atom Model (EAM) potential. the implementation of which has been specially designed for this study. Our main results show that the equilibrium distance between partials is very sensitive to the type of boundary conditions imposed on the simulated system.
Atomistic Simulation of Transonic Dislocations
Authors: Zimmerman Jonathan A. , Abraham Farid F. , Gao Huajian
Published: April 2011

Recent work has been done on the analysis of elastic stress singularities, such as cracks and dislocations, which propagate at supersonic speeds. Gumbsch and Gao have performed atomistic simulations in which dislocations are created and travel at transonic velocities (speeds which are greater than the material's shear wave speeds but less than the longitudinal wave speed) close to the theoretical value corresponding to the radiation-free state for glide motion. Gao et al. have derived expressions for this radiation-free velocity in both isotropic and anisotropic media. We have performed molecular dynamics simulations showing dislocation nucleation at crystal surface ledges. Dislocations were nucleated at either sub- or transonic velocities, depending upon the ambient temperature, and accelerated to transonic speeds. This paper shows the velocity profiles for the emitted dislocations and compares velocities observed with a theoretical minimum-radiation speed derived by a Strohtype anisotropic elasticity analysis performed by Barnett and Zimmerman. Our findings are particularly exciting considering these simulations were not specifically engineered for the purpose of creating transonic defects, but show agreement with theory nonetheless.
Different Relaxation Modes of Epitaxial Thin Film Alloys With A Large Size Effect
Authors: Thibault J. , Dressler C. , Bayle-Guillemaud P.
Published: April 2011

In epitaxial layers, the mechanism of stress relaxation under consideration is in general dislocations. This paper will present experimental evidences for other modes of relaxation. which may occur in some situations especially where a strong size effect or misfit is present. In fact the stress is the driving force for intermixing, twinning, and phase transformation, which are not expected to occur in the bulk. All these experimental results have been sustained by numerical simulations that will also be presented.
Atomistic Simulation and Experimental Investigation of Ultra Precision Cutting Processes
Authors: Rentsch R.
Published: April 2011

Typical applications for components and equipment with extreme quality requirements regarding surface roughness, shape accuracy and integrity of the generated surface structure can be found in optical and semiconductor industry. Ultra precision machine tools equipped with sharp, single crystalline diamond provide the necessary machining accuracy. Here the actual cutting process can take place at atomic level, which makes the acquisition of typical cutting process data difficult or impossible. However a detailed characterization and understanding of the process is vital for its effective control as well as for further tool and process development.

Therefore an approach is made that focuses on linking results from atomistic simulations with results and observations from cutting experiments. In this work the potential of molecular dynamics (MD) modeling for studying phenomena related to ultra precision cutting processes will be demonstrated. Observations and first results for machining copper will be presented.
Finite Element Simulations of the Deformation of BCC Aggregates Using a Crystal Plasticity Model - Local Orientation Effects
Authors: Arizmendi D. , Raphanel J. L.
Published: April 2011

One has simulated by a finite element computation, the tensile plastic deformation of bcc aggregates with the same initial crystallographic texture but a different spatial distribution of orientations. The computations show fairly large differences between the simulations in terms of axial strain fields: one aggregate presents an homogeneous field, while another one localizes the strain in a narrow band. This “macroscopic effect” is then analyzed at the smaller scale of the crystallite by comparing local re-orientations, glide activity and stress levels. The influence of neighboring grains and of the “local”texture is thus shown. This is an effect that polycrystalline models (Taylor or self-consistent models) cannot account for.
Crack Propagation in Freshwater and Saline Ice
Authors: Donovan Patrick J. , Arakawa Masahiko , Petrenko Victor
Published: April 2011

Crack propagation in columnar saline and freshwater ice has been investigated with high-speed photography, acoustic emission detection and the resistance method. High-speed photography was found to be a single reliable technique. The resistance method proved effective for freshwater ice samples, but not for saline ice samples due to the presence of conductive fluid inclusions. Acoustic emissions pinpointed the moment of crack initiation, but did not correspond to the crack propagation time. Crack velocity has been characterized over a temperature range of -5°C to -30 °C for freshwater and saline ice. Freshwater ice exhibited an overall average velocity of 198 m/s, and did not vary with temperature. Crack velocity in saline ice demonstrated temperature dependence, increasing from an average of 86 m/s in the -5°C to -20°C range, to 131 m/s at -30°C. The crack velocity was also shown to have a general dependence on fracture toughness K' of the material, however, the microstructural variation between samples is also shown to influence significantly the crack behavior in both saline and freshwater ice. Nonuniform crack tip advance and crack reorientation were observed as crack slowing mechanisms in freshwater ice, while in saline ice fracture crack tip blunting on voids greatly reduced average crack velocities.
Void Shape and Distribution Effects on Coalescence in Elastic-Plastic Solids
Authors: Pardoen T. , Hutchinson J.W.
Published: April 2011

An extended Gurson model incorporating the effects of the void shape and distribution on the growth and coalescence is proposed. The emphasis is placed on void coalescence, which is modeled as a transition from diffuse plasticity around the void to transverse localized plastic yielding in the intervoid ligament. Selected results showing the importance of correctly accounting for the void coalescence stage, as well as for the void shape and distribution effects, are presented and discussed.
Atomistic Modeling of Void Growth and Coalescence in Ni+H
Authors: Somerday B.P. , Pattillo P.D. , Horstemeyer M.F. , Baskes M.I.
Published: April 2011

Finite strain rate atomistic simulations were conducted on Ni and Ni+H lattices containing voids to better understand the dislocation-scale mechanisms of void growth and coalescence and how hydrogen affects these damage processes. Void growth is governed by dislocations that nucleate at the void surface to transport mass away from the void as well as dislocations arriving at the void from the lattice exterior to deposit vacancies and accommodate void-surface expansion. Hydrogen can retard void growth when large local hydrogen concentrations impede dislocation nucleation and propagation at the void surface. The formation of hydrogen gas molecules in the void interior does not necessarily aid void growth. Pressure in small voids may be mitigated by the mutual interaction of hydrogen molecules and the interaction of molecules with the void surface.
A Model for Calculating Substrate Curvature During Coalescence of PT Islands on an Amorphous Substrate
Authors: Phillips M. A. , Ramaswamy V. , Clemens B. M. , Nix W. D.
Published: April 2011

Previous work using in-situ curvature measurement has shown a correlation between stress and microstructure during the early stages of thin film growth. The model presented here can be used to predict the curvature change of the substrate during part of this growth process. Curvature, and thus film stress, is measured in-situ during growth of sputter-deposited Pt on amorphous substrates. The average film stress is observed to be slightly compressive initially, followed by a change towards a tensile maximum, after which the stress becomes compressive again. Plan view TEM micrographs of Pt films of thicknesses up to 35 Å show the evolution of microstructure from isolated islands to a coalesced film. This evidence suggests that the tensile regime is due to island coalescence. The model calculates the curvature induced in a substrate during the tensile excursion associated with island coalescence, where discontinuous islands are modeled as a series of cracks in an otherwise continuous film. Quantitative measurements of island size and areal fraction covered are extracted from the TEM micrographs and used to predict the curvature during coalescence. The predicted stresses are shown to compare favorably with the measured stresses.
Influence of Grain Boundary Structure on Liquid Metal Penetration Behavior
Authors: Ren Liping , Bahr D.F. , Hoagland R.G.
Published: April 2011

The penetration of Ga along Al grain boundaries under stress-free conditions is investigated in the present study. In-situ SEM observations indicate that the penetration rate of Ga along Al grain boundaries at room temperature ranged from 6.4 to 9.2 μm/s, which is similar to the rate of diffusion in the liquid state. For a specific high energy grain boundary, the grain boundary misorientation is determined from the TEM diffraction Kikuchi pattern, and a molecular statics simulation method was employed to investigate grain boundary structure. A comparison of the structure of this high energy boundary is made with the Σ11(131)[101] tilt grain boundary that is not penetrated by Ga in the absence of the applied stress. The results indicate that the grain boundary plane void structure in the high energy grain boundary may provide void channels for Ga monolayer penetration. In addition, penetration behavior investigated under different length scales supports this model.
The Cellular Automaton Simulation of Microstructural Evolution During Deformation Processing of Metals
Authors: Davies Chris H.J.
Published: April 2011

The computer simulation of the evolution of microstructure during deformation processing is a desirable but elusive goal. In order to be effective, models must be tied to deformation parameters (temperature, strain rate, strain), and grain size distributions and recrystallisation kinetics must be predicted with high accuracy if the evolution of microstructure is to be tracked through several passes. This paper examines the cellular automaton (CA) simulation technique which has the potential to enable the modeller to accomplish these goals.

Aspects of the CA approach examined are the three dimensional representation of microstructure and its evolution and the incorporation of texture representation into simulations.Also investigated will be the limitations of the technique, in terms of the error that can be expected when different boundary conditions are imposed on a simulation.

Although at a rudimentary stage of investigation, the interfacing of CA simulations to deformation simulations (eg, finite element) will be examined. The paper concludes with a discussion of the challenges facing the implementation of CA simulations in industrial process models.
Transmission Electron Microscopy Study of Gold-Coated Iron Core-Shell and Au/Fe/Au Onion-Like Nanoparticles Synthesized using Reverse Micelles
Authors: Zhou W.L. , Carpenter E.E. , Sims J. , Kumbhar A. , O'Connor C.J.
Published: April 2011

Gold-coated iron core-shell structure and Au/Fe/Au onion-like nanoparticles synthesized using reverse micelles were characterized by transmission electron microscopy (TEM). The average nanoparticle size of the core-shell structure is about 8 nm, with about 6 nm diameter core and 2 nm shell. The gold shell structure can be resolved from both high resolution electron microscopy (HREM) image and energy dispersive X-ray spectrum (EDS). Even though the gold and iron electron diffraction rings overlap a little bit, they can still be identified due to the slight mismatch of the diffraction rings. The Au/Fe/Au onion-like nanoparticles were also observed. The nanoparticles were formed with about 6 nm diameter gold core, 1 nm iron interlayer and 2 nm gold shell. The shell structure coated on the core appeared unhomogeneous, however, in both cases the iron core and interlayer iron shell stay air-stable.
Nanocomposites in the Systems Fe1−xO-Fe3O4 and MgO-MgFe2O4 Produced by Mechanical Alloying
Authors: Huerta A. , Calderon H. A. , Yee-Madeira H. , Umemoto M. , Tsuchiya K.
Published: April 2011

Wtastite-magnetite and magnesia-magnesioferrite nanocrystalline ceramics have been prepared by mechanical milling and spark plasma sintering. As-milled powders have a nanocrystal-line structure in both systems. Low energy milling gives rise to an increasingly higher volume fraction of wfistite as a function of milling time in the Fe1−xO-Fe3O4 system. Similar results are obtained in the MgO-MgFe2O4 system with increasingly larger amounts of MgFe2O4 produced by milling. Composites of magnetic particles (Fe3O4 or MgFe2O4) in a nonconductive matrix (FeO or MgO, respectively) are found in the sintered samples. Measurement of magnetic properties can be used to determine conclusively the nature of the developed phases and the effect of grain size.
Steady State Phase Diagram of Cu-Ag Under Ball Milling: An XRD and APFIM Study
Authors: Wu F. , Bellon P. , Melmed A.J. , Lusby T.A.
Published: April 2011

The nature of the steady state reached during ball milling of CuxAg1−x powders (x=35 to 75) is studied as a function of the milling temperature (85K≤T≤503K). The characterization of the powders is performed by using x-ray diffraction, differential calorimetry and atom probe field ion microscopy. A steady-state phase diagram is built. Three-phase coexistence is shown to generally take place at intermediate milling temperatures. Atom probe data reveals that the solid solution stabilized by low milling temperature is nearly random, where as milling at elevated temperatures results in the decomposition of the elements at a lengthscale of 20∼30 nm.
Synthesis and Characterization of CdSe/CdS Core-Shell and CdSe/CdS Composites
Authors: Malika M. Azad , O'Brien Paul , Revaprasaduac N.
Published: April 2011

Highly mono-dispersed CdSe/CdS core-shell and CdSe/CdS composites have been prepared by a novel route involving thermolysis in TOPO using Cd(Se2CNMe(nHex))2 and Cd(S2CNMe(nHex))2. The absorption band edge (652 nm, 1.90 eV) of the CdSe-CdS core-shell structure is red shifted (22 nm, 0.0 17 eV) as compared to the CdSe nanoparticles (630 nm, 1.96 eV) whereas the absorption spectrum of the CdSe-CdS composites shows the absorption band edge at (584 nm, 2.12 eV), blue shifted (46 nm, 0.037 eV) as expected. Photoluminescence (PL, λex = 400 nm) of both the core-shell (622 nm) and the composites (588 nm) show values close to band edge emission. A sharper emission maximum with a considerable increase of intensity is observed for core-shell structure as compared to that of CdSe whereas the composite showed a broader emission maximum. The TEM images of the CdSe/CdS core-shell nanoparticles show crystalline, spherical particles with the average size of 53 Å (±7 %), a increase of 8 Å than the average size of CdSe (45 Å) nanoparticles, with a narrow size distribution. The High Resolution Transmission Electron Microscopy (HRTEM) showed lattice spacing intermediate between those for CdSe and CdS as is observed by Selected Area Electron Diffraction (SAED) and X-ray patterns (hexagonal phase). As expected no interface can be observed by HRTEM between CdSe core and CdS shell. The TEM image of the CdSe-CdS composites show particles with an average size of 48.7 Å (±10%).
Effect of Vapor Pressure of H2O on the Formation of Nano-Crystalline TiO2 Ultrafine Powders
Authors: Lee K. R. , Kim S. J. , Song J. S. , Park S.
Published: April 2011

Mono-dispersed TiO2 ultrafme particles with diameters 40-400nm were obtained from aqueous TiOCl2 solution with 0.67M Ti4+ concentration prepared diluting TiCl4 by homogeneous precipitation process in the ranges of 17-230°C. With the spontaneous hydrolysis of TiOCl2, which means the natural decrease of pH value in the aqueous solution, all mono-dispersed precipitates were crystallized with the anatase or rutile TiO2 phase. TiO2 precipitate with the pure rutile phase was fully formed at the temperatures below 65 °C, not involving the evaporation of H2O, and above 155 °C, which were available by suppressing it. TiO2 precipitate with rutile phase including a small amount of the anatase phase started to be formed in the intermediate temperatures above 70 °C showing the full formation of the anatase above 95 °C under the free evaporation of H2O. However, in the case of completely suppressing H2O evaporation at the temperatures above 70°C, TiO2 precipitate with anatase phase was fully transformed into the precipitate with the rutile phase by the vapor pressure of H2O. Therefore, the formation of TiO2 precipitates with the rutile phase around room temperature would be caused due to the existence of the capillary pressure between the agglomerated needle-shaped particles or the ultrafme clusters, together with the slow reaction rate.
CVD of Carbide Multi-Phased Coatings
Authors: Versprille K.E. , Ji Hua Xia , Amato-Wierda C.C. , Ramsey P.J. , Wierda D.A.
Published: April 2011

TiC and Ti-W-C films have been produced by chemical vapor deposition (CVD). A fractional factorial design was used to study the effects of deposition temperature, C:Ti input, H:Ti input, reactor pressure, and total mass flow on TiC film composition. Statistical models were developed for both titanium at.% and C:Ti in the film. It was found that the most significant affect on titanium at.% was the interaction of temperature, pressure and total mass flow. The most important affect on the C:Ti in the deposited film was the interaction C:Ti input, H:Ti, and total mass flow. Ti-W-C films have been deposited at 1050°C at various (TiCl4+W(CO)6)/CH4 inlet ratios ranging from 0.53 to 1.01. The characterization of the films revealed that the changes in deposition rate, crystallinity, film orientation, and morphology of various Ti-W-C compositions were affected by (TiCl4+W(CO)6)/CH4 inlet ratios.
Fiber Reinforced Epoxy Resin Composite Materials Using Carboxylate-Alumoxanes as Cross-Linking Agents
Authors: Vogelson Cullen T. , Koide Yoshihiro , Barrona Andrew R.
Published: April 2011

Chemically functionalized alumina nanoparticles (carboxylate-alumoxanes) are used as the inorganic component of a new class of inorganic-organic hybrid materials. Lysine- or para- hydroxybenzoic acid-derivatized alumoxanes are readily prepared from the reaction of boehmite, [Al(O)(OH)]n, with the appropriate carboxylic acid. The peripheral organic hydroxides and amines of these carboxylate-alumoxanes either react directly with epoxide resins, such as the diglycidyl ether of bisphenol-A (DER 332), to form a hybrid material, or in the presence of an organic resin and hardener system to form a composite material. SEM and AFM show a uniform distribution of alumina nanoparticles within the resin matrix. The properties and cure times of the alumoxane hybrid and composite materials are distinct from both the pure resins and from a physical blend of the resins with traditional ceramic fillers. A significant increase in thermal stability and tensile strength is observed for both the hybrid and composite resin systems. In addition, both carbon fiber and carbon/Kevlar® matting have been successfully incorporated into the hybrid resin systems resulting in further property improvements.
Proton Conducting Organic/Inorganic Nanocomposite Polymer Electrolytic Membrane Synthesized by Sol-Gel Process
Authors: Honma I. , Nomura S. , Nakajima H.
Published: April 2011

In this paper, new synthetic routes have been investigated for the preparation of Organic/inorganic nanocomposite polymer membranes consisting of SiO2 /PTMO(polytetramethylene oxide) hybrids and novel proton conducting materials. These materials have been synthesized through sol-gel processes in flexible, ductile, free-standing thin membrane form. The hybrid membrane has been found to be thermally stable up to 160 C and possesses proton conductivities of approximately 10−4 S/cm from a room temperature to 160 C.
Modified Sol-Gel Synthesis of Vanadium Oxide Nanocomposites Containing Surfactant Ions
Authors: Dobley Arthur , Zavalij Peter Y. , Whittingham M. Stanley
Published: April 2011

Recently, there has been much interest in creating new layered transition metal oxides. Vanadium oxides may be used as sorbents, catalysts, and cathodes in lithium batteries. The modified sol-gel technique allows for some control towards the final structure of the compound. Using this technique, a new layered vanadium oxide compound - I, containing the surfactant dodecylphosphate, has been synthesized. After the removal of the organic ligand a new compound - II is formed which might be hexagonal. The compounds were analyzed using XRD, TGA, SEM, and NMR. VO2PO3(OH)C12H25(H2O)n is the general formula of the layered product I with a layer spacing of about 40 angstroms. II appears to be hexagonal with a = 43Å. The synthesis, composition, and structure of these compounds are discussed.
Electroluminescence Devices with CdS and CdS:Mn Nanoparticles and Polymer Blends
Authors: Brugger Ch. , Tasch S. , Lal M. , Prasad P.N. , Leising G.
Published: April 2011

We have investigated the photophysical properties of surface capped CdS and CdS:Mn nanoparticles in the form of spin coated thin films of the pure nanoparticles and nanoparticle -polymer blends. The organic capping reagent was p-thiocresol. Electroluminescence (EL) devices were fabricated and characterized by their current/voltage characteristics and EL emission performance. This is to our knowledge the first report on Mn doped CdS nanoparticles applied in EL devices with a single layer device structure (ITO/CdS:Mn/Al). Photoluminescence (PL) and PL excitation measurements were performed on CdS:Mn nanoparticles in pyridine dispersion and on thin films. The PL excitation spectrum shows a narrow peak at 390nm. Excitation at this wavelength yields a broad PL spectrum spanning from about 450 to 700nm, which is dominated by a strong emission band at 585nm. This emission is attributed to transitions involving Mn levels in previous works. The EL emission peak is shifted to the red compared to the PL emission spectra. The characteristics and performance of these new types of EL devices will be presented and discussed.
Synthesis of Passivated Metal Nanoparticles
Authors: Green Mark , O'Brien Paul
Published: April 2011

Here we report the synthesis of organically passivated nanoparticles of gold, chromium and nickel. The routes involve the reduction of a metal precursor in various Lewis base solvents, which appear to affect the final nanoparticle morphology. The preparation of highly monodispersed samples can lead to the potential for further manipulation of dots into ordered 2D and 3D arrays. These colloidal thin films and crystals have potential application in magnetic data storage devices.
Features of Fracture Surface and Grain Boundary Structure of Boride/Nitride Materials
Authors: Andrievski R.A. , Kalinnikov G.V. , Shtansky D.V.
Published: April 2011

Nanostructured bulks and films of TiB2, TiN, AIN, Ti(B,N), and (Ti,Al)N prepared by high pressure sintering and nonreactive magnetron sputtering accordingly. Fracture surfaces and structure of grain boundaries have been investigated by high-resolution scanning and transmission electron microscopy as well as by atomic force microscopy. The revealing of transgranular fracture, homogeneous and inhomogeneous deformation, and the availability of dislocations and amorphous phases in structure are discussed.