bluuebunny/crossref_metadata_2025_split huggingface dataset:
Combustion Synthesis of Ni-Ti-X Shape Memory Alloys
Authors: Moore John J. , Yi Ru Chun 
Published: March 2011

AbstractCombustion synthesis is an energetically favorable new method of producing Ni-Ti series shape memory alloys (SMA′s). The ΔH°f,,298/Cp298ratio plays a key role, especially if a liquid product is required. Solidified TiNi SMA's were hot rolled into plates exhibiting the shape memory effect. Ms transition temperatures can be controlled from -78 to 460°C by substituting Fe or Pd for Ni.
Residual Stress, Adhesion and Crystallization of Ion-Sputtered and Ibed Processed NiTi Films
Authors: Walles B. , Chang L. , Grummon D. S. 
Published: March 2011

AbstractWhen conventional sputtering is used to deposit nickel-titanium thin films at temperatures below ∼623 - 723 Kelvins, the resultant structures are amorphous and the films must be annealed to form the requisite B2 parent ordering. This invites complications related to interface diffusion and chemical reaction with components of the substrate. For the present work, thin films of near-equiatomic NiTi were prepared on potassium chloride, (100) single-crystal silicon, and Si3N4 passivated silicon substrates by ion sputtering and by ion beam enhanced deposition (IBED). We have investigated residual stress levels produced by these processes, evaluated substrate adhesion levels, and explored the crystallization behavior of NiTi films grown under conditions of concurrent low-energy inert gas ion bombardment. Residual stresses of ionsputtered and IBED films were measured using profilometric techniques. Film crystallization behavior was studied by transmission electron microscopy of as-deposited films. Films produced by unassisted ion sputtering showed compressive residual stresses in the as-deposited amorphous state, which became highly tensile after annealing, leading to spontaneous cracking and delamination. Preliminary results from IBED experiments showed a reduction in the asdeposited stress, and improved adhesion. Under certain conditions, ion enhancement of the deposition process promoted film crystallization during deposition at moderate substrate temperature, producing a dispersion of extremely fine particles, indexed as Ni3Ti.
Structure and Properties of Rapidly Solidified Nitinol Materials
Authors: Wu K. H. 
Published: March 2011

AbstractTi50-(Pd(x)-Ni(50-x)) alloys were prepared with Pd ranging from 18 at% to 22%. Both hot-rolled strips and melt-spun ribbons were fabricated. Heat treatments from 400°C to 1000éC were evaluated. It was found that the meltspun ribbons demonstrated much higher transformation temperatures than those of as-cast materials. However, the hot-rolled strips failed to display a shape memory effect, as well as those ribbons with 18 at.% and 20% Pd.
Characterization of the Phase Transformations in the Shape Memory Alloy Ni-36 at.% Al
Authors: Horton J.A. , George E.P. , Sparks C.J. , Kao M.Y. , Cavin O.B. , Thoma P. 
Published: March 2011

AbstractA survey by differential scanning calorimetry (DSC) and recovery during heating of indentations on a series of nickel-aluminum alloys showed that the Ni-36 at.% Al composition has the best potential for a recoverable shape memory effect at temperatures above 100°C. The phase transformations were studied by high temperature transmission electron microscopy (TEM) and by high temperature x-ray diffraction (HTXRD). Quenching from 1200°C resulted in a single phase, fully martensitic structure. The initial quenched-in martensites were found by both TEM and X-ray diffraction to consist of primarily a body centered tetragonal (bct) phase with some body centered orthorhombic (bco) phase present. On the first heating cycle, DSC showed an endothermic peak at 121°C and an exothermic peak at 289°C, and upon cooling a martensite exothermic peak at 115° C. Upon subsequent cycles the 289°C peak disappeared. High temperature X-ray diffraction, with a heating rate of 2°C/min, showed the expected transformation of bct phase to B2 between 100 and 200°C, however the bco phase remained intact. At 400 to 450°C the B2 phase transformed to Ni2Al and Ni5Al3. During TEM heating experiments a dislocation-free martensite transformed reversibly to B2 at temperatures less than 150°C. At higher temperatures (nearly 600°C) 1/3, 1/3, 1/3 reflections from an ω-like phase formed. Upon cooling, the 1/3, 1/3, 1/3 reflections disappeared and a more complicated martensite resulted. Boron additions suppressed intergranular fracture and, as expected, resulted in no ductility improvements. Boron additions and/or hot extrusion encouraged the formation of a superordered bct structure with 1/2, 1/2, 0 reflections.
Deformation of Shape-Memory Materials
Authors: James Richard D. 
Published: March 2011

AbstractWe present an overview of a theory of martensitic transformations developed by J. M. Ball and the author, and additional related results by Bhattacharya, Chu and Collins and Luskin and Kinderlehrer. This theory is in a form that is amenable to detailed numerical computations of microstructure. We describe the energy minimizing microstructures of a single crystal under applied displacements and under detailed dead loading. The relation of the theory to the crystallographic theory of martensite is presented.A consequence of the theory is the sensitivity of the patterns of microstructure to the precise lattice parameters. In the case of the wedge-like microstructure studied by Bhattacharya, it is found that this microstructure is only possible as a coherent, energy minimizing microstructure if very restrictive conditions on the lattice parameters are satisfied. Materials that exhibit the wedge satisfy this relation closely. The analysis suggests that optimal shape-memory behavior may be related to relations of this type.The theory has a relation to the work of Khachaturyan, Roitburd and Shatalov. We compare and contrast the two approaches. We present results that suggest that any approach based on the kinematics of linear elasticity will make serious quantitative errors in the prediction of microstructure.
Time-Resolved X-Ray Diffraction from Liquid Crystalliine Systems: Thermotropic Phase Transitions and the Effect of Applied Electric Fields
Authors: Mcnamee Scott G. , Galli G. , Ober C. K. 
Published: March 2011

AbstractTime resolved X-ray diffraction from thermotropic liquid crystalline (LC) materials has been studied in conjunction with standard LC characterization techniques to investigate phase transitions and alignment due to applied electric fields. A more detailed understanding of the kinetics of the interaction between LC systems and applied fields is being sought. Both the effect of electric fields on the inter-molecular structure and the orientation parameter have been evaluated as a function of temperature for LC model compounds. These results are compared to observations of these mesogens in applied electric fields using optical microscopy. Materials of interest include low molar mass distyrylbenzene mesogens which exhibit both nematic and smectic mesophases. Results of investigations of thermotropic polymers will be discussed.
Predictions of Static and Dynamic Properties of Liquid Crystalline and Polymeric Systems in Electric Fields
Authors: Dowell F. 
Published: March 2011

AbstractPredictions of static and dynamic properties from a unified molecular statistical mechanics theory for complex fluids in static electric fields are summarized. Included are thermodynamic, molecular ordering, and transport properties. In this new theory, the effects of an electric field Ee on the dipole moments and bond polarizabilities of tile molecules have been added to an eaxlier successful theory for complex organic molecules in condensed phases. Included are liquid crystalline (LC) and polymeric systems (including the first interlocking polymers).
Simiple Shear Flow of a Non-Aligning Nematic
Authors: Han W. H. , Rey A. D. 
Published: March 2011

AbstractThis paper presents a nonlinear numerical analysis of the orientational instabilites, textures, and flow patterns of a characteristic rod-like nematic liquid crystal in steady simple shear flow. The parameter vector V=(λ,E) is given by the reactive parameter (λ) and the Ericksen number (E). There are two stationary solutions: in-plane(IP) and out-of-shear-plane(OP), according to whether the average orientation lies in or out of the plane of shear. For a given λ the in-plane stationary solutions may undergo a continuous transition (second order) to two dissipatively equivalent OP solutions when E=Eo or a discontinuous transition (first order) to a highly distorted IP solution when E=Ei. The continuous transition at E=Eo is a supercritical (pitchfork) bifurcation and the discontinuous transition at E=Ei is a limit point instability. Nonlinear numerical analysis shows that for the studied liquid crystal Eo < Ei. The orientation phase diagram for stable stationary solutions therefore consist of a region of OP solutions separated from a region of IP solutions by the curve Vo = (λ,Eo), describing a set of continuous supercritical bifurcations. These stable OP solutions are characterzied by the absence of sharp splay and bend deformations and by the presence of complex secondary flows arising from the three dimensional orientation. Presented results also include the dependence of the three dimensional texture, primary and secondary velocity fields on E.
Kinetics of Shear Induced Micellar Association
Authors: Dewalt L. E. , Ou-Yang H. D. , Kim M. W. , Liu S-N , Pine D. , Dixon P. , Peiffer D. G. 
Published: March 2011

AbstractRheological measurements have been used to study the kinetics of shear induced association for rod-shape micelles formed by mixtures of ADHAB and salicylic-sodium salt. Pronounced hysteresis and large fluctuations were found in the stress-shear rate diagram. We investigate the association and dissociation mechanism through stress quench experiments where viscosity measurements study the system relaxation. The association process was found to be a single exponential with a relaxation time of about 1 minute, whereas the dissociation process was much slower and was non-exponential. In the semidilute regime, the critical shear rates increase with concentration, contradictory with existing theories.
Characterization of Pmma Gel Spheres and Shear Induced Microstructure
Authors: Paulin S. E. , Ackersons Bruce J. , Wolfe M. S. 
Published: March 2011

AbstractPolymethylmethacrylate (PMMA) particles are suspended without additional free polymer in benzyl alcohol, where they swell to nearly three times their dry radius. The single particle properties are examined by static and dynamic light scattering measurements, as well as by intrinsic viscosity measurements. A colloidal liquid/crystal phase diagram is determined as a function of effective volume fraction determined from the intrinsic viscosity. The samples are subjected to oscillatory shear flows to determine the influence of flow on the particle microstructure. A nonequilibrium phase diagram is constructed indicating a correlation between spontaneous ordering at equilibrium and shear induced ordering. These results are compared with previous work done for hard PMMA sphere suspensions.
Theory of Defects in Condensed Phases of Langmuir Monolayers
Authors: Selinger Jonathan V. 
Published: March 2011

AbstractRecent fluorescence-microscopy experiments have observed two types of defects—star defects and striped textures-in the liquid—condensed phases of Langmuir monolayers. These defects can be understood through a continuum elastic theory. This theory predicts both splay stripes, which are driven by the asymmetry between molecular heads and tails, and bend stripes, which are driven by a spontaneous breaking of chiral symmetry in the monolayer. These predictions are compared with experimental observations.
Butterfly Patterns: an Anomaly Common to the Neutron Scattering Spectra of Elongated Rubbers, Melts and Gels:
Authors: Bastide J. , Boue F. , Oeser R. , Mendes E. , Zielinski F. , Buzier M. , Lartigue C. , Lindner P. 
Published: March 2011

AbstractA totally unexpected phenomenon has been observed for the first time a few years ago when studying, by small angle neutron scattering, rubbery networks containing a small proportion of uncrosslinked labelled (deuterated) chains [1].When such a system is elongated, the scattered intensity strongly increases with the extension ratio λ for q vectors parallel to the stretching direction (and for low q values). Conversely, in the direction perpendicular to the elongation axis, the scattered intensity slightly decreases at low q for small extension ratios and then remains approximately constant when λ is further increased. The changes which are observed occur therefore in a direction opposite to the “conventional” one, i.e. that corresponding to chains effectively linked by at least two chemical junctions to the network and thus oriented on an average along the direction of stretching.
Physical-Chemistry Parameters of SiO2 Monoliths Processed Via Sol - Gel
Authors: Elias A. M. , Elias M. E. , Nunes M. M 
Published: March 2011

AbstractHigh quality glasses may be prepared from liquid precursors, via sol - geL Starting materials and variable control determine the final characteristics of silica monoliths for optical fiber preforms, prepared via sol - gel, as we have found in previous studies. The rate of hydrolysis. and condensation reactions, as wcU as the time required for densification of a gel, is dependent on water/alkoxide ratio, pH and the presence of drying control chemical additives. The physical and optical properties of the preforms are also determined by the specific conditions of the sol - gel processing.In this study we present an additional analysis of pH effects on the kdnetics, before and during the material syneresis. The effect of CO2 as a contaminant, is also considered. Samples are prepared from hydrolysis of tetrametoxysane in methanol - water mixtures, in the presence of a - picoline. At 20°C, the initial values of pH range between 8 and 6 and show an exponential decrease as the hydrolytic polymensation proceeds, tending to acidic or more acidic values. These steps also are followed by TEM and SEM and are correlated with the sort of aggregates formed in the material along the percolation process. Optical properties of the preforms are interpreted in terms of the clusters formed from those aggregates.Details on instrumental monitoring of [H+] along the alcogelation process are discussed.
Two-Dimensional Melting of Magnetic Bubble Arrays: A Continuous Hexatic-To-Liquid Transition
Authors: Seshadri R. , Westervelt R. M. 
Published: March 2011

AbstractArrays of two-dimensional magnetic bubbles in thin garnet films undergo a hexatic-toliquid transition as a function of bubble density controlled by an applied spatially uniform dc bias magnetic field that opposes the magnetization in the bubbles. The phase transition is driven by topological point defects. The bubbles are observed directly using optical microscopy and digital imaging techniques. In the presence of a linear gradient in the dc bias magnetic field the hexatic-to-liquid transition occurs spatially in the direction of the gradient. As the system goes from hexatic to liquid, a continuous decrease in bubble density accompanied by a continuous disordering of the array is observed along the gradient direction. This continuous disordering persists even after the system is allowed to equilibrate for very long periods of time, indicating that the hexatic-to-liquid transition is continuous at equilibrium. Dynamics of topological defects observed in the gradient field correspond to those observed in the uniform field.
Surface Evolution of Copolymer thin Films as Revealed by Atomic Force Microscopy
Authors: Coulon G. , Collin B. , Chatenay D. , Ausserre D. 
Published: March 2011

AbstractAtomic Force Microscopy has been used to study the early stage evolution of the free surface of annealed symmetric poly(styrene-b-n-butylmethacrylate) diblock copolymer thin films. As the lamellar ordering propagates through the film thickness, Islands or holes are formed on the free surface. It Is shown that, depending on the Initial film thickness, I.e. on the fraction of the film surface occupied by the islands (or holes) In the ordered state, the existence or non-existence of spatial correlations characterizes the ordering kinetics of both islands and holes. However, the limit between these two regimes is not the same in the two cases : in the case of holes, spatial correlations occur for a higher value of the surface coverage than In the case of islands.
The Volume Fraction Profile of Terminally Adsorbed Polymers
Authors: Composto R. J. , Mansfield T. , Beaucage G. , Stein R. S. , Iyengar D. R. , Carthy T. J. Mc , Satija S. K. , Ankner J. F. , Majkrzak C. F. 
Published: March 2011

AbstractWe have used neutron reflectivity to measure the concentration profile of carboxylic acid-terminated polystyrene at the liquid/solid interface. Two isotopic systems were studied: (1) deuterated polystyrene (DPS) in cyclohexane and (2) polystyrene (PS) in deuterated cyclohexane. Although measured at 24°C (a poor solvent condition), the high grafting density of PS tethered chains causes the chains to weakly stretch to 3-5 times its unperturbed dimension. Although of similar molecular weight, the height of the DPS layer is about 50% higher than that of the PS. In both systems, the volume fraction of polymer near the wall is ∼ 0.60. For the DPS system, reflectivity profiles can be simulated using a parabolic profile with a depletion layer at the silicon-liquid interface. However, in the PS system, no depletion is observed. Here, the shape. of the PS concentration profile is parabolic with a rounded tail.
Static and Hydrodynamic Dimensions of Flexible Polyions in Solutions
Authors: Mattoussi Hedi , O'donohue Steve , Karasz Frank E. 
Published: March 2011

AbstractThe variation of the radius of gyration RG and the hydrodynamic size RH are followed as the ionic strength of the medium is monitored for a flexible polyelectrolyte compound in solutions. In addition, a comparison between the thermodynamical and hydrodynamical interaction parameters is given for the present system.
Structural Relaxations in the GHz Frequency Range in Glass Forming Silicate Melts
Authors: Masnik John E. , Kieffer J. , Bass J.D. 
Published: March 2011

AbstractThe Brillouin light scattering technique is used for the investigation of structural relaxations in glass-forming liquids at high temperatures. From the analysis of the line shapes of Rayleigh and Brillouin peaks, the friction coefficients, which are associated with the atomic scale mechanisms of the structural relaxations in these systems, are determined. Results for a series of K2O-SiO2 compositions, which were chosen as model substances, are reported. As a function of temperature, maxima in the Brillouin line widths were observed, which reflect resonant conditions of molecular scale structural motions, where the relaxation time is of the order of the reciprocal Brillouin frequency shift. Due to thermal activation of the component mobilities, different relaxation mechanisms couple at different temperatures. Typically, at least one strongly absorbing regime is observed in between the glass transition and the equilibrium melting temperatures. The prominence of this regime decreases with increasing silica concentration. The friction coefficients approach the hydrodynamic viscosity in the high temperature limit, when the relaxation times become short in comparison with the time scale of the Brillouin shift.
Structure and Dynamics of the Ferrosmectic Phase
Authors: Fabre Pascale 
Published: March 2011

AbstractWe have elaborated a system -that we call a ferrosmectic- which contains magnetic particles included in a lamellar phase. Because of the presence of the confined particles, this phase exhibits specific features that are revealed by submitting it to a magnetic field as well as by neutrons or quasi-elastic light scattering experiments. We present here a review of the different properties of this ferrosmectic phase.
The Rotator Phases of the Normal Alkanes
Authors: Sirota E. B. , King H.E. , Singer D.M. , Shao H. 
Published: March 2011

AbstractWe present results of an x-ray scattering study on the rotator phases of normal alkanes: CH2-(CH3)n-CH2 (20 ≤ ≤ 33). We have characterized a new tilted rotator phase and measured the distortion and tilt order parameters in all 5 rotator phases. We have shown that there is no strong even-odd chain effect within the rotator phases.
X-Ray Diffraction Studies of Tubules Formed from a Diacetylenic Phosphocholine Lipid
Authors: Thomas B. , Safinya C. R. , Plano R.J. , Clark N. A. , Ratna B.R. , Shashidar R. 
Published: March 2011

AbstractThe diacetylenic phosphocholine lipid 1,2-bis(10, 12-tricosadiyonol)-sn-glycerol- 3-phosphocholine forms, upon cooling below the chain melting temperature, hollow cylindrical structures known as ‘tubules’. These tubules are approximately one micron in diameter and may range from tens to hundreds of microns in length. We have carried out x-ray diffraction studies of tubules (1) in 75/25 ethanol/water by volume and (2) in a dessicated state. We present results which show marked differences in the nature of both the in-plane and inter-layer correlations associated with the wrapped multilayer structure of the tubules in the two states.
Ba2YCu3O7−x Thin Films with Jc>105 A/cm2 at 77 K Prepared by Metalorganic Deposition at Reduced Oxygen Pressure
Authors: Hallock Robert B. , Rhine W.E. , Jolly M.S. , Cima MIchael J. 
Published: March 2011

ABSTRACTSuperconducting Ba2YCu3O7-x films 0.1-0.2 gim thick were prepared by spin coating a methanol solution of Ba, Y and Cu acrylates on (100)LaAlO3 and firing to 800°C in a total pressure of 1 mm O2. X-ray diffraction showed that these films were epitaxial with the c-axis normal to the substrate. Zero resistance was achieved above 90 K and transport DC critical current densities as high as 125,000 A/cm2 were measured at 77 K in zero applied field.
Sol Gel Derived Aluminum Nitride Thin Films Via the Nitridation of Alumina
Authors: Russell M.W. , Giannelis E.P. 
Published: March 2011

ABSTRACTCrystalline aluminum nitride thin films (∼ 1200 Å) were prepared via nitridation of amorphous aluminum oxide and characterized by XRD, SEM, TEM, oxygen resonance, Auger depth-profile analysis and ellipsometry. Precursor chemistry, heating rate, nitridation temperature and nitridation time were varied to explore the competition between densification, crystallization and nitridation. Oxygen content in the films decreased with increasing nitriding temperature or nitriding time. Heating rate was determined to have minimal effect on the oxygen content for the parameters evaluated. A modified Kissinger analysis of DTA data for the crystallization of α-Al2O3 yielded an effective activation energy of ∼104 kcal/mol.
A Novel Route to Silocon Based Ceramic Coatings on Carbon Substrates
Authors: Macinnes Andrew N. , Barron Andrew R. 
Published: March 2011

ABSTRACTCarbon fiber tows have been impregnated by ethanolic solutions of organo-silicon chlorides, and fired at temperatures up to 900°C to form silicon based coatings. Fired tows were subsequently examined by X-ray photoelectron spectroscopy and scanning electron microscopy to characterize the coated material. A uniform silicon oxycarbide is formed at temperatures upwards of 400°C, which provides an oxidation barrier in carbon fiber reinforced metals.