Showing papers on "Phase (matter) published in 1993"
TL;DR: In this article, the properties of a new family of metallic alloys which exhibit excellent glass forming ability are reported, where the critical cooling rate to retain the glassy phase is of the order of 10 K/s or less.
Abstract: We report on the properties of one example of a new family of metallic alloys which exhibit excellent glass forming ability. The critical cooling rate to retain the glassy phase is of the order of 10 K/s or less. Large samples in the form of rods ranging up to 14 mm in diameter have been prepared by casting in silica containers. The undercooled liquid alloy has been studied over a wide range of temperatures between the glass transition temperature and the thermodynamic melting point of the equilibrium crystalline alloy using scanning calorimetry. Crystallization of the material has been studied. Some characteristic properties of the new material are presented. The origins of exceptional glass forming ability of these new alloys are discussed.
2,305 citations
Book•
01 Jan 1993
2,081 citations
13 May 1993
TL;DR: The phase of condensed matter known as spin glasses has become a vital and productive area of research as mentioned in this paper, and experiment has suggested unusual effects which have brought the theoretical study of the spin glass Problem Onto The Same Footing As The Experimental Study.
Abstract: The phase of condensed matter known as spin glasses has become a vital and productive area of research. Historically, experiment has suggested unusual effects which have brought the theoretical study of the spin Glass Problem Onto The Same Footing As The Experimental Study. Experiments in the late 1960s on magnetic alloys presented interesting effe
1,746 citations
TL;DR: In this article, a simple phase field model for one component melt growth is presented, which includes anisotropy in a certain form, and the formation of various dendritic patterns can be shown by a series of numerical simulations of this model.
1,131 citations
TL;DR: In this article, the first observation of cholesteric blue phases in chiral anisotropic polymer networks was reported, in which two-component mixtures of a chiral and a non-chiral diacrylate were photopolymerized at constant temperature.
Abstract: We report the first observation of cholesteric blue phases in chiral anisotropic polymer networks. In two-component mixtures of a chiral and a non-chiral diacrylate, we observed typical textures of BPI, BPII and BPIII phases. By photopolymerization of these materials at constant temperature we obtained blue phase networks. After polymerization, the blue phases were stored, which enabled us to further study them without any temperature control.
1,008 citations
31 Aug 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the formation of a special grain boundary phase, i.e., a thin near-boundary layer with high dynamic activity of atoms, has been found, leading to the manifestation of promising new elastic, strength, superplastic, damping and magnetic properties of UFG materials.
Abstract: Strain-heat methods of obtaining ultrafine-grained (UFG) metallic materials with grain sizes as small as 20 nm and peculiarities of their structure are considered. It is shown that intercrystalline boundaries are the main element of the structure of UFG materials and that they are typically in a non-equilibrium state. The formation of a special grain boundary phase, i.e. a thin near-boundary layer with high dynamic activity of atoms, has been found. This unusual structure leads to the manifestation of promising new elastic, strength, superplastic, damping and magnetic properties of UFG materials.
918 citations
TL;DR: The phase behavior of the triblock copolymers dissolved in water has been studied using SANS as discussed by the authors, and the structural properties have been studied as a function of polymer concentration and temperature.
Abstract: The phase behavior of the triblock copolymers dissolved in water has been studied using SANS. The structural properties have been studied as a function of polymer concentration and temperature. At low temperature (T ≤ 15°C) and low polymer concentrations the unimers are fully dissolved Gaussian chains with radius R g =17 A. Close to ambient temperature, the hydrophobic nature of PPO causes aggregation of the polymers into spherical micelles with core sizes of the order of 40-50 A, somewhat temperature dependent. The concentration of micelles increased roughly linearly with temperature, until either a saturation is reached,where all the polymers are part of a micelle, or the volume density of micelles is so high that they lock into a crystalline structure of hard spheres
669 citations
TL;DR: In this article, the structure of Li1−xNiO2 is studied as Li is electrochemically deintercalated from LiNiO 2 with in situ X-ray diffraction methods.
622 citations
TL;DR: In this paper, the phase transformation mechanisms and the resulting microstructures of excimer laser-induced crystallization of amorphous Si films on SiO2 were investigated, and it was shown that the process can be characterized into two major regimes, based on the dependence of the grain size and the melt duration as a function of the incident energy density.
Abstract: We have investigated the phase transformation mechanisms and the resulting microstructures of excimer laser‐induced crystallization of amorphous Si films on SiO2. It is shown that the process can be characterized into two major regimes, based on the dependence of the grain size and the melt duration as a function of the incident energy density. It is found that at the transition between the two regimes, exceedingly large grain‐sized polycrystalline films can be obtained. We call this the super lateral growth phenomenon, and propose a model based on liquid‐phase regrowth from the residual solid seeds when near‐complete melting of the Si film occurs.
561 citations
TL;DR: In this article, it was shown that there is a strong tendency for dilute holes in an antiferromagnet to phase separate, leading to high-temperature superconductivity.
Abstract: There is a strong tendency for dilute holes in an antiferromagnet to phase separate. (This is a generic feature of doping into a commensurate correlated insulating state.) We review the general and model-specific theoretical arguments that support this conclusion for neutral holes. In the presence of long-range Coulomb interactions, there is frustrated phase separation leading to large-amplitude, low-energy fluctuations in the hole density at intermediate length scales, provided the dielectric constant is sufficiently large. We describe extensive experimental evidence showing that such “clumping” of the holes is an important feature of the cuprate superconductors. We also summarize theoretical results which suggest that frustrated phase separation may account for the anomalous properties of the normal state and give rise to high-temperature superconductivity.
506 citations
TL;DR: In this paper, double-headed surfactants with a short spacer were used to control amphiphile self-aggregation in aqueous solution, and microstructures formed by these dimeric surfactant with m = 12 and s = 2,3 or 4 were investigated with transmission electron microscopy.
Abstract: SURFACTANT molecules in water form organized assemblies of various shapes, such as micelles and bilayer lamellae, which are of interest as analogues of biological structures, as model systems for studying complex phase behaviour and because of their technological importance, for example to the food and paint industries. The polar head groups are usually arranged randomly at the surface of these assemblies. We have studied the effect on the microstructure of these assemblies of imposing constraints on the head-group spacing. We investigate the structures formed by 'double-headed' surfactants in which two quaternary ammonium species (CmH2m+1N+(CH3)2) are linked at the level of the head groups by a hydrocarbon spacer (CsH2s). Here we report the microstructures formed by these dimeric surfactants with m = 12 and s = 2,3 or 4 in aqueous solution, by rapidly cooling the micellar solutions and investigating the vitrified structures with transmission electron microscopy. The surfactants with a short spacer (s = 2,3) form long, thread-like and entangled micelles even at low concentrations, whereas the corresponding monomeric ammonium surfactants can form only spherical micelles. The dimeric surfactants with s = 4 form spheroidal micelles. Thus short spacers (which impose reduced head-group separation) appear to promote lower spontaneous curvature in the assemblies. This approach may afford a new way to control amphiphile self-aggregation.
TL;DR: In this article, Monte Carlo simulations of the phase diagrams of straight-chain alkanes with unbranched carbon chains as long as C48 up to the vicinity of the liquid-vapour critical points are presented.
Abstract: ALTHOUGH the liquid–gas phase equilibria of simple fluids have been studied extensively since the seminal work of van der Waals, the properties of fluids with more complex molecular structures, such as polymers, present a less tractable problem both theoretically and experimentally. The phase behaviour of hydrocarbons is of particular importance for the petrochemical industry. But despite significant experimental and theoretical efforts, the phase diagrams of the straight-chain alkanes longer than decane (C10) are known only partially, and even qualitative aspects such as the chain-length dependence of the critical properties are poorly understood. Until recently it was considered impossible to estimate the critical properties of such complex fluids using computer simulations. Here we report Monte Carlo simulations of the phase diagrams of alkanes with unbranched carbon chains as long as C48, up to the vicinity of the liquid–vapour critical points. Our calculations show that, in contrast to the traditional view, the critical density of the long-chain alkanes decreases rather than increases with carbon number. This work indicates that simulations can be used as an 'engineering tool' to estimate properties that are not readily accessible experimentally.
TL;DR: In this paper, a detailed x-ray scattering study on the rotator phases of normal alkanes is presented, and a new tilted rotator phase is characterized and the temperature and chain length dependence of the distortion, tilt, and azimuthal order parameters are determined.
Abstract: We present results of a detailed x‐ray scattering study on the rotator phases of normal alkanes: CH3–(CH2)n−2–CH3 (20≤n≤33). We have characterized a new tilted rotator phase and determined the temperature and chain length dependence of the distortion, tilt, and azimuthal order parameters which characterize the time‐space averaged structures of the five rotator phases. We have shown that there is no strong even–odd chain length effect on the phase diagram within the rotator phases and have shown the continuity of that phase diagram in the 26‐27 carbon vicinity.
TL;DR: The phase behavior and aggregate morphology of mixtures of the oppositely charged surfactants cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) are explored with cryotransmission electron microscopy, quasielastic light scattering, and surface tensiometry as mentioned in this paper.
Abstract: The phase behavior and aggregate morphology of mixtures of the oppositely charged surfactants cetyltrimethylammonium bromide (CTAB) and sodium octyl sulfate (SOS) are explored with cryotransmission electron microscopy, quasielastic light scattering, and surface tensiometry. Differences in the lengths of the two hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phases), and vesicles form spontaneously over a wide range of compositions in both CTAB-rich and SOS-rich solutions. Bilayer properties of the vesicles depend on the ratio of CTAB to SOS, with CTAB-rich bilayers stiffer than SOS-rich ones. We observe two modes of microstructural transition between micelles and vesicles. The first transition, between rodlike micelles and vesicles, is first order, and so there is macroscopic phase separation. This transition occurs in CTAB-rich solutions and in SOS-rich solutions at higher surfactant concentrations. In the second transition mode, mixtures...
TL;DR: In this article, a 1 wt. % polystyrene in toluene solution into CO2 through a 100-μm nozzle is formed with diameters from 0.1 to 20 μm.
Abstract: Polymer microspheres and fibers are formed with a versatile new process, precipitation with a compressed fluid antisolvent. By spraying a 1 wt. % polystyrene in toluene solution into CO2 through a 100-μm nozzle, microspheres are formed with diameters from 0.1 to 20 μm as the CO2 density decreases from 0.86 to 0.13 g/cm3. The uniform submicron spheres produced at high CO2 density are due in part to the rapid atomization produced by the large intertial and low interfacial forces. Fibers, with and without microporosity, are obtained at higher polymer concentrations where viscous forces stabilize the jet. The effect of CO2 density and temperature on the size, morphology and porosity of the resulting polymeric materials is explained in terms of the phase behavior, spray characteristics, and the depression in the glass transition temperature.
TL;DR: In this paper, the authors reported direct evidence of a unit mesh containing more than one hydrocarbon chain at the surface of a self-assembled monolayer of long-chain n−alkanethiols.
Abstract: We report direct evidence of a unit mesh containing more than one hydrocarbon chain at the surface of a self‐assembled monolayer of long‐chain n‐alkanethiols. Our helium diffraction measurements for a monolayer of n‐octadecanethiol on Au(111) are consistent with a rectangular primitive unit mesh of dimensions 8.68×10.02 A containing four crystallographically distinct hydrocarbon chains. This packing arrangement can also be described as a c(4×2) superlattice with respect to the fundamental simple hexagonal [(√3×√3)R30°] array of lattice parameter 5.01 A previously observed for monolayers of other n‐alkanethiols on gold. No temperature‐dependent phase behavior is observed in the temperature range where surface diffraction is measurable (30–100 K) and cycling up to temperatures as high as 50 °C caused no observable change in the diffraction. It is proposed that this larger unit mesh is the result of a patterned arrangement of rotations of the hydrocarbon chains about their molecular axes. This patterned arrangement must be different than the herringbone structure expected by simple analogy to bulk n‐alkanes.
TL;DR: The method of matched asymptotic expansions is used to recover the appropriate anisotropic form of the Gibbs-Thomson equation in the sharp-interface limit in which the width of the diffuse interface is thin compared to its local radius of curvature.
Abstract: The inclusion of anisotropic surface free energy and anisotropic linear interface kinetics in phase-field models is studied for the solidification of a pure material. The formulation is described for a two-dimensional system with a smooth crystal-melt interface and for a surface free energy that varies smoothly with orientation, in which case a quite general dependence of the surface free energy and kinetic coefficient on orientation can be treated; it is assumed that the anisotropy is mild enough that missing orientations do not occur. The method of matched asymptotic expansions is used to recover the appropriate anisotropic form of the Gibbs-Thomson equation in the sharp-interface limit in which the width of the diffuse interface is thin compared to its local radius of curvature. It is found that the surface free energy and the thickness of the diffuse interface have the same anisotropy, whereas the kinetic coefficient has an anisotropy characterized by the product of the interface thickness with the intrinsic mobility of the phase field.
TL;DR: A symmetry conserving method which allows for efficient structural searches and optimizations in spaces with preselected symmetry groups and is used to investigate MgSiO[sub 3], a perovskite, the marjor Earth-forming mineral phase which exists particularly in the lower mantle.
Abstract: We report the development of an ab initio constant pressure extended molecular dynamics method with variable cell shape. This is a symmetry conserving method which allows for efficient structural searches and optimizations in spaces with preselected symmetry groups. We have used it to investigate ${\mathrm{MgSiO}}_{3}$, a perovskite, the marjor Earth-forming mineral phase which exists particularly in the lower mantle. We predict its structural behavior up to pressures which exceed the highest values reached in this region.
TL;DR: In this article, the interaction of oxygen with Al(111) was studied by scanning tunneling microscopy (STM) images, where for moderate tunnel currents and independent of the bias voltage the former are imaged as depressions, while the latter appear as protrusions.
Abstract: The interaction of oxygen with Al(111) was studied by scanning tunneling microscopy (STM). Chemisorbed oxygen and surface oxides can be distinguished in STM images, where for moderate tunnel currents and independent of the bias voltage the former are imaged as depressions, while the latter appear as protrusions. An absolute coverage scale was established by counting O adatoms. The initial sticking coefficient is determined to so=0.005. Upon chemisorption at 300 K the O adlayer is characterized by randomly distributed, immobile, individual O adatoms and, for higher coverages, by small (1×1) O islands which consist of few adatoms only. From the random distribution of the thermalized O adatoms at low coverages a mobile atomic precursor species is concluded to exist, which results from an internal energy transfer during dissociative adsorption. These ‘‘hot adatoms’’ ‘‘fly apart’’ by at least 80 A, before their excess energy is dissipated. A model is derived which explains the unusual island nucleation scheme by trapping of the hot adatoms at already thermalized oxygen atoms. Oxidation starts long before saturation of the (1×1) O adlayer, at coverages around ΘO≂0.2. For a wide coverage range bare and Oad covered surfaces coexist with the surface oxide phase. Upon further oxygen uptake both chemisorbed and oxide phase grow in coverage. Oxide nucleation takes place at the interface of Oad islands and bare surface, with a slight preference for nucleation at upper terrace step edges.Further oxide formation progresses by nucleation of additional oxide grains rather than by growth of existing ones, until the surface is filled up with a layer of small oxide particles of about 20 A in diameter. At very large exposures up to 5×105 L they cover the entire surface as a relatively smooth, amorphous layer of aluminum oxide. The difference in Al atom density between Al metal and surface oxide is accommodated by short range processes, with no indication for any long range Al mass transport. Based on our data we discuss a simpler two step model for the interaction of oxygen with Al(111), without making use of an additional subsurface oxygen species. The complex spectroscopic data for the O/Al(111) system are rationalized by the wide coexistence range of bare and Oad covered surface with surface oxide and by differences in the electronic and vibronic properties of the surface atoms depending on the number of neighboring O adatoms in the small Oad islands.
TL;DR: In this paper, the authors identify three significant aspects of defect accumulation behavior under cascade damage conditions: (a) evolution of cavity microstructure in a spatially heterogeneous and segregated fashion, (b) high swelling rates at very low doses when the dislocation density is negligibly low and (c) enhanced vacancy accumulation in the vicinity of grain or subgrain boundaries.
Journal Article•
TL;DR: In this article, it was shown that the previously unreacted asphaltene was the fraction with the highest rate of thermal reaction but with the least extend of reaction, leading to the preferential conversion of the most associated asphatene to coke.
Abstract: Coke formation during the thermolysis of petroleum residua is postulated to occur by a mechanism that involve the liquid-liquid phase separation of reacted asphaltene to form a phase that is been in abstractable hydrogen. This mechanism provide the basis of a model that quantitatively describe the kinetics for the thermolysis of ColD Lake vacuum residuum and its deasphalted oil in a open fuse reactor at 400°C. The previously unreacted asphaltene were found to be the fraction with the highest rate of thermal reaction but with the least extend of reaction. Further evidence of the liquid-liquid phase separation was the observation of spherical particle of liquid crystalline coke and the preferential conversion of the most associated asphatene to coke
TL;DR: In this article, a high transport critical current density, J c, in Ag-sheathed Bi-2223 superconducting tapes had been obtained using the oxide powder-in-tube technique.
Abstract: A high transport critical current density, J c , in Ag-sheathed Bi-2223 superconducting tapes had been obtained using the oxide powder-in-tube technique. At 77 K and self-field, the highest J c value of 69 000 A/cm 2 was measured for tapes of 80 μm thickness ( I c =35 A), while the largest critical current, I c , reached 74 A for tapes of 150 μm thickness ( J c =61 000 A/cm 2 ). A detailed investigation of the processing parameters has been carried out on the phase content and particle size of the starting powders, and on the sintering treatment and mechanical deformation of the tapes.
TL;DR: In this paper, the effects of process variables such as concentration of displacement agent, flow-rate and gradient slope on HPMC separations in the ion exchange, hydrophobic interaction and reversed phase modes were studied using model protein mixtures.
TL;DR: The comparison of different particle types shows that backscattering is a sensitive indicator for the identification of types of ice-crystal, and the effects of particle concavity on the scattering signature are discussed in detail.
Abstract: The single-scattering phase functions of polyhedral-shaped ice particles are calculated by means of geometric optics and the diffraction theory. Particle orientation is assumed to be random in space. Particle shapes are taken both from ice-crystal classifications and from in situ measurements. The effects of particle concavity on the scattering signature are discussed in detail. A common feature is the pronounced forward-scattering peak, as well as different halo peaks that are due to a minimum deviation at corresponding ice prisms. An unusual halo phenomena, which results from a minimum deviation in a double-prism configuration, is found and verified. The comparison of different particle types shows that backscattering is a sensitive indicator for the identification of types of ice-crystal. Aggregate particles, like bullet rosettes, basically show the scattering characteristics of their individual components.
TL;DR: In this article, the micellization and phase equilibria in aqueous solutions of cationic quaternary ammonium bromide surfactants were investigated as a function of alkyl chain length, electrolyte concentration, and temperature.
Abstract: The micellization and phase equilibria in aqueous solutions of cationic quaternary ammonium bromide surfactants of the type alkyltrimethyl-, -ethyl-, -propy-, -butyl-, and -pentylammonium bromide have been investigated as a function of alkyl chain length, electrolyte concentration, and temperature. A large isotropic (micellar) phase is observed in triethyl- and tripropylammonium surfactants, which demixes into two conjugate phase on warming in the case of the alkyltributylammonium bromides. Liquid-liquid phase separation is also observed for tetradecyltripentylammonium bromide. Critical micelle concentrations are found to decrease with increasing hydrophobicity of the surfactant ion, but the free energy of micellization of tetradecyltributylammonium bromide is the same as that of tetradecyltrimethylammonium bromide over a range of temperatures
TL;DR: The dependence of solute retention (k′) on mobile phase composition (%B) for binary-solvent mixtures A-B is reviewed and compared with various empirical and theoretical equations that have been proposed for this relationship as discussed by the authors.
TL;DR: In this article, a computer simulation technique based on a microscopic kinetic model including the elastic strain effect is developed, which can be efficiently used for understanding, interpreting and predicting structural evolutions in real alloys.
Abstract: Morphological evolutions controlled by a transformation-induced elastic strain during a solid state precipitation are systematically investigated using a prototype binary alloy as a model system. A computer simulation technique based on a microscopic kinetic model including the elastic strain effect is developed. Without any a priori assumptions concerning shapes, concentration profiles and mutual positions of new phase particles, various types of coherent two-phase morphologies such as basket-weave structures, sandwich-like multi-domain structures, precipitate macrolattices and GP zones are predicted. A wide variety of interesting strain-induced kinetic phenomena are observed during development of the above microstructures, including selective and anisotropic growth, reverse coarsening, particle translational motion, particle shape transition and splitting. In spite of all simplifications of the model, most of the simulation results are confirmed by experimental observations in various alloy systems, indicating that this kinetic model can be efficiently used for understanding, interpreting and predicting structural evolutions in real alloys.
TL;DR: In this article, a group additivity method is described which provides heat capacity estimates of the condensed phase, and the standard error of estimation using this approach on this data base is 19.5 and 26.9 J/mole K (solids).
Abstract: A group additivity method is described which provides heat capacity estimates of the condensed phase. The data base consists of 810 liquids and 446 solids. Group values for carbon in various common substitution and hybridization states and for 47 functional groups are provided. The standard error of estimation using this approach on this data base is 19.5 (liquids) and 26.9 J/ (mole K) (solids). This can be compared to typical experimental uncertainties of 8.12 and 23,4 J/ (mole K) associated with these measurements, respectively. Experimental uncertainties were estimated from the numerical differences obtained for a given substance from multiple independent literature reports.
TL;DR: A model in which the dispersive interactions can be varied independently from the dipolar (magnetic) interactions is considered, showing that a minimum amount of dispersive energy is required to observe liquid-vapor coexistence.
Abstract: We report computer simulations of the phase behavior of dipolar (ferro-) fluids. We consider a model in which the dispersive interactions can be varied independently from the dipolar (magnetic) interactions. The simulation results show that a minimum amount of dispersive energy is required to observe liquid-vapor coexistence. If the dispersive energy is below this threshold, as for example in the dipolar hard-sphere fluid, the system forms chains of dipoles aligning nose to tail. Our simulations did not give any evidence that these ``polymerlike'' systems phase separate into a liquid and vapor phase.
TL;DR: The phase equilibria of the sodium dodecyl sulfate (SDS)-didodecyldimethylammonium bromide (DDAB)-water system have been studied by water deuteron NMR and polarizing microscopy methods at 40 o C as mentioned in this paper.
Abstract: The phase equilibria of the sodium dodecyl sulfate (SDS)-didodecyldimethylammonium bromide (DDAB)-water system have been studied by water deuteron NMR and polarizing microscopy methods at 40 o C. 1 H NMR relaxation, PGSE FT-NMR self-diffusion, and dynamic light scattering are used to study aggregate structures of isotropic phases. A pseudoternary representation of the four-component phase diagram contains a large number of regions of homogeneous solutions and liquid crystalline phases, as well as multiphase regions. Isotropic solution regions contain SDS-rich micellar aggregates or (spontaneously forming) vesicles, rich in either surfactant; the vesicles form at very high dilution (<0.1% surfactant)