bluuebunny/crossref_metadata_2025_split huggingface dataset:
Different Solvent Free Synthetic Routes to Organic/Inorganic Hybrid Materials
Authors: Kaddami H. , Gerard J. F. , Pascault J. P. 
Published: April 2011

ABSTRACTThe 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

ABSTRACTDendrimer 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

ABSTRACTA 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

ABSTRACTThe 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

ABSTRACTThermosets 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

ABSTRACTFirst-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

ABSTRACTEmerge 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

ABSTRACTThe 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

ABSTRACTQuad-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

ABSTRACTIn 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

ABSTRACTUltrathin 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

ABSTRACTA 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

AbstractThis 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractRecent 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

AbstractIn 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

AbstractTypical 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.