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Homogeneous freezing nucleation occurs in supercooled liquid water by the formation of critical-sized ice embryos. Molecular Dynamics simulations were performed 'sowing' a solid embryo into liquid and monitoring the subsequent system evolution. The size of critical ice embryos and the activation energy barrier associated with the incorporation of molecules into the germ were estimated using the TIP5P-E water model for three different temperatures: 237, 240 and 244 K. The results show how MD simulations provide reliable outcomes for the study of both parameters. [ABSTRACT FROM AUTHOR]

Bulk metallic glass (BMG) samples are amalgamated by high-energy ball milling using the general formula (Ni75Cr15Si10)100−xTix (labelled as NCSTx, where x = 0,4, 8 and 12 at.%). The crystallinity and phase attribution properties of nickel (Ni), chromium (Cr), silicon (Si) and titanium (Ti) are scrutinized using the XRD analysis. The trend related to glass-forming ability (ΔT) and the GFA parameter (γ) is NCST8 > NCST12 > NCST4 > NCST0, which confirms that NCST8 sample shows superior glass-forming ability. The reduced glass transition temperature (Trg) for all the present BMG systems is greater than 0.5, which offers its good thermal stability and glass-forming ability (GFA). Corrosion studies suggested that a sample, having dynamic nature towards corrosion resistance and potential (Ec) (NCST8, (Ni75Cr15Si10)92Ti8), exhibits relatively lower values of both ic (4.7 × 10−4 A/cm2) and ip (0.0079 A/cm2), as recommended in potentio-dynamic findings. [ABSTRACT FROM AUTHOR]

The thermophysical properties of refractory MoNbReTaW high-entropy alloy in both supercooled liquid and high-temperature solid states were explored by an electrostatic levitation technique. The maximum supercooling attains 504 K, and the hypercooling limit is derived as 571 K. The liquid density at liquidus temperature is measured to be 13.3 g cm−3, which increases linearly with decreasing temperature at a slope of 6.83 × 10−4 g cm−3 K−1. The liquid alloy exhibits 5.3% relative volume shrinkage during crystallization. The thermal expansion coefficient of liquid and solid alloy at liquidus temperature are determined as 5.0 × 10−5 K−1 and 3.6 ×10−5 K−1, respectively. The liquid specific heat at liquidus temperature is found to be 38.2 J mol−1 K−1, and basically displays a linear decreasing tendency with temperature. According to the calculated enthalpy of fusion 24.7 kJ mol−1 and measured specific heats, the temperature-dependent entropy and Gibbs free energy difference between supercooled liquid and crystalline solid are obtained. [ABSTRACT FROM AUTHOR]

Cold start has been realized as an important issue for PEMFC in its global commercialization. As is well-known, the conventional "channel-rib" type flow field will surely lead to several problems, such as water accumulation under the rib, resulting in slow water removal and serious ice blockage in the pores. In recent years, with the fast development of metal foam materials, metal foam has been recognized as a promising alternative replacement of the conventional "channel-rib" type flow field. In this study, a cold start model of PEMFC is established under sub-zero temperature. The coupled transport processes of heat, mass and charge in PEMFC under various subzero temperatures and startup modes are simulated. The results show that ice formation is slower in the PEMFC with metal foam as cathode flow field in cold start process, due to the superior performance of metal foam in water removal and uniform distribution of gas supply. However, the excellent thermal conductivity of metal foam could also result in faster heat loss from PEMFC. Furthermore, ice formation is highly dependent on the supercooled water transfer behavior, though small amount of supercooled water is maintained in the cell. This work aims to provide a systematic analysis for the cold start behavior of PEMFC with metal foam flow field. [ABSTRACT FROM AUTHOR]

Polycyclic aromatic hydrocarbons (PAHs) in contaminated waterbodies can cause serious pollution to the adjacent atmosphere through volatilization. Gas–particle partitioning of PAHs controls the atmospheric concentrations of these pollutants. PAH levels in gaseous and particulate air samples were investigated near two polluted lagoons along the eastern coast of the Red Sea. Gas chromatography–mass spectrometry was used to analyze nine priority parent PAHs and nine methylated PAHs. Total gaseous and particulate PAHs ranged from 12.2 to 397.5 ng m−3, with an average of 125.6 ± 117.3 ng m−3, which was nearly 10-fold higher than that found in a previous study. Particulate PAHs (ranging from 0.04 to 16.32 ng m−3, with an average of 2.56 ± 1.71 ng m−3) contributed to less than 20% of the total atmospheric PAHs. Applied diagnostic indices showed that gasoline emissions were the main sources of PAHs in the lagoons' atmosphere. Multiparameter statistical analyses indicated that wind speed strongly affected the distribution of atmospheric PAHs. The average PAH gas–particle partitioning coefficient was 0.49 m3 µg−1 (ranging from 2.1 × 10−8 to 51.23 m3 µg−1) and was significantly correlated with supercooled liquid vapor pressure. In addition to the effects of meteorological parameters and vehicle exhausts in the study area, the discharge of wastewater in the lagoons elevated PAH levels in the surrounding atmosphere. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are often used to study the structures and dynamics of ionic liquids. Here, we have simulated three ionic liquids, trihexyl(tetradecyl)-phosphonium chloride [P66614][Cl], 1-butyl-3-methylimidazolium acecate [BMIm][Oac] and 1-ethyl-3-methylimidazolium dicyanamide, [EMIm][DCA] in a comparison of two force fields, GAFF and CL&PFF. In most cases, the resulting theoretical densities agree with experimental values within a 2% error. Diffusive properties were characterised by mean squared displacements to show the significant effect of the alkyl chain on the movement of the [P66614] cation. Activation energies of diffusion were calculated from linear Arrhenius plots which agree with previous studies. Simulations of the dynamical behaviour show retention of short and medium-range structure of the ionic liquids with temperature. However, although with increasing temperature more high energy local configurations become accessible, they are observed less frequently as energy barriers are more easily overcome, resulting in more ordered time-averaged structures. [ABSTRACT FROM AUTHOR]

The paper provides an overview of existing models of the liquid metals structure, as well as the structural changes in their melts as a result of thermal treatment. The most important, in our opinion, are various versions of the quasicrystal model. The model is leant on the assumption that the melt consists of clusters and disordered space. The clusters as atomic micro-groups inherit the short-range order of the atomic structure from the solid state. Increasing the temperature of the melt and/or the holding time under isobaric conditions leads to polymorphic transformations of the short-range order. As a result, a new structure with smaller radii of atomic micro-groups, a lower lattice parameter and coordination number, and a more uniform distribution of elements is formed. The structural changes of the melts are irreversible and have a significant effect on crystallization and the formation of the structure and properties of the solid metal. [ABSTRACT FROM AUTHOR]

Solidification is an important issue that needs to be addressed when modelling supercooled large droplets (SLD) impacting aircraft surfaces. This work develops a 3D triple-phase smoothed particle hydrodynamics (SPH) solver that can simultaneously simulate SLD impingement and solidification on cold surfaces by solving the Euler equations for fluid dynamics, the energy equation for heat transfer, and a latent heat model for phase changes. The solver is validated against a Stefan problem in which a liquid is cooled and solidified by a cold boundary, and against a still droplet freezing on a cold plate. It is then applied to droplets impacting on cold surfaces at aeronautical speeds, analysing the freezing time and ice particle distributions as the droplet velocity and impact angle are varied. This is an important step towards a macroscopic numerical model of SLD post-impact behaviour for in-flight icing simulations. [ABSTRACT FROM AUTHOR]

In this study, we present a novel fixed-grid interface-tracking method using finite volume method to simulate multidimensional rapid solidification (RS) of under-cooled pure metal. The discretized advection equation for solid fraction function is solved using the THINC/WLIC method, which is a VOF method. The governing equations for fluid flow are solved numerically using pressure-velocity coupling SIMPLE algorithm in a 2-D model with incompressible Newtonian fluid. The energy equation is modeled using an enthalpy-based formulation. The nonequilibrium solidification kinetics, interface tracking, undercooling, nucleation, heat transfer, and movement of liquid are included in the presented RS model. [ABSTRACT FROM AUTHOR]

We performed all-atom molecular dynamics simulations for bulk cyclohexane and analysed the short- and medium-range structures in supercooled and glassy states by using the Voronoi tessellation technique. From the analyses of both the potential energy of the system and the radial distribution function of molecules, cyclohexane was found to be vitrified as the temperature decreased. Furthermore, the icosahedral-like local structures are dominant at all temperatures and grow in a supercooled liquid, whereas the face-centred cubic structures do not grow when the temperature decreases. It was also ascertained that the icosahedral-like structure is more dominant than the full-icosahedral one. The network of the distorted icosahedron spreads throughout the system at low temperatures. Our simulation demonstrates the stability of the icosahedral local structure even in a non-spherical molecule such as cyclohexane. [ABSTRACT FROM AUTHOR]

We provide a detailed derivation of the mode-coupling equations for a colloidal liquid confined by two parallel smooth walls. We introduce irreducible memory kernels for the different relaxation channels thereby extending the projection operator technique to colloidal liquids in slit geometry. Investigating both the collective dynamics as well as the tagged-particle motion, we prove that the mode-coupling functional assumes the same form as in the Newtonian case corroborating the universality of the glass-transition singularity with respect to the microscopic dynamics. [ABSTRACT FROM AUTHOR]

In this paper, we present a molecular dynamics study of the glass transition for a soft-core primitive model for ionic liquids, in which cations are fully flexible chains of tangent soft spherical monomers, being the positively charged monomer at one of the ends of the chain, and anions as charged soft spheres. We have monitored transport coefficients such as the self-diffusion coefficients and the shear viscosity, as well as correlation functions such as the mean-square displacement, the self-intermediate scattering function, and probes of heterogeneous dynamics such as the van Hove distribution function and the four-points susceptibility. The analysis of these properties indicates that, for a given pressure, the glass transition shows a weak temperature dependence on the cation length, occurring first for short-chain than for long-chain ionic liquids. [ABSTRACT FROM AUTHOR]

Here we report on the temperature dependence of the anomalous behaviour of water in terms of (i) its growth in tetrahedral structures, (ii) instantaneous spatial correlations from small angle x-ray scattering (SAXS) data, (iii) estimates of thermodynamic response functions of isothermal compressibility and (iv) thermal expansion coefficient. Water's thermal expansion coefficient is estimated for the first time at supercooled conditions from liquid water's structure factor. We used previously published data from classical force-fields of TIP4P/2005 and iAMOEBA to compare experimental data with molecular dynamics simulations and observe that these force-fields underestimate water's anomalous behaviour but perform better upon increasing pressure. We demonstrate that the molecular dynamics simulations can describe better the temperature dependent anomalous behaviour of ambient pressure water if simulated at 1 kbar. The deviation in anomalous fluctuations in the simulations is not restricted to ≈228 K but extends all the way to ambient temperatures. [ABSTRACT FROM AUTHOR]

Heat capacity of several liquids which demonstrate anomalous behaviour is studied. It is shown that isochoric heat capacity of these liquids shows anomalously high values which is related to smooth structural crossover in these liquids. This phenomenon can be used for qualitative explanation of high heat capacity of water and some other substances. [ABSTRACT FROM AUTHOR]

We review the effect of water anomalies on the properties of low-temperature water. When supercooled, liquids dynamical properties change drastically. Supercooled liquids undergo an at least exponential decrease of their diffusion coefficient when temperature decreases while their structure merely does not change. We discuss how that still unexplained change of dynamical properties at low temperatures affects water differently from other liquids and what can be deduced from it. [ABSTRACT FROM AUTHOR]

The shear viscosity of liquid cobalt at the pressure p = 1.5 bar and at the temperatures corresponding to equilibrium liquid and supercooled liquid states is measured experimentally and evaluated by means of molecular dynamics simulations. Further, the shear viscosity is also calculated within the microscopic theoretical model. Comparison of our experimental, simulation and theoretical results with other available data allows one to examine the issue about the correct temperature dependence of the shear viscosity of liquid cobalt. A strong correlation between the viscosity and the configuration entropy of liquid cobalt over the considered temperature range is found, which can be taken into account by the Rosenfeld’s model. [ABSTRACT FROM AUTHOR]

A generalised scaling relationship of the imaginary part of the dielectric permittivity as well as of the real part of the dielectric permittivity is presented. The proposed scaling of the dielectric response has been successfully applied to main relaxation processes in various supercooled isotropic liquid phases and supercooled plastic-crystal phases in several glass-forming liquids as glycerol, propylene carbonate, 3-fluoroaniline, ethanol, cyclooctanol and cyanocyclohexane. Existence of the excess wing, the resolved secondary relaxation (β-relaxation) or both the processes was identified for some of these materials. It is demonstrated that behaviour of the resolved β-relaxation and the excess wing strictly depends on the parameters of the main relaxation process. This implies that the main relaxation process and the secondary one are not independent. [ABSTRACT FROM AUTHOR]

A simple and highly reproducible procedure was established for the study of orthorhombic paracetamol crystallization kinetics, comprising melting, quench-cooling of the melt and scanning the formed glass by DSC at different heating rates. Results were analyzed on the basis of the mean as well as local values of the Avrami exponent,n, the energy of activation, as well as the Šesták–Berggren two-parameter autocatalytic kinetic model. The mean value of the Avrami kinetic exponent,n, ranged between 3 and 5, indicating deviation from the nucleation and growth mechanism underlying the Johnson–Mehl, Avrami–Kolmogorov (JMAK) model. To verify the extent of the deviation, local values of the Avrami exponent as a function of the volume fraction transformed were calculated. Inspection of the local exponent values indicates that the crystallization mechanism changes over time, possibly reflecting the uncertainty of crystallization onset, instability of nucleation due to an autocatalytic effect of the crystalline phase, and growth anisotropy due to impingement of spherulites in the last stages of crystallization. The apparent energy of activation,Ea, has a rather low mean value, close to 81 kJ/mol, which is in agreement with the observed instability of glassy-state paracetamol. Isoconversional methods revealed thatEatends to decrease with the volume fraction transformed, possibly because of the different energy demands of nucleation and growth. The exponents of the Šesták–Berggren two-parameter model showed that the crystallized fraction influences the process, confirming the complexity of the crystallization mechanism. [ABSTRACT FROM PUBLISHER]

We discuss a potential energy landscape (PEL) approach to calculate the characteristically sluggish viscous behaviour of supercooled liquids. This phenomenon is central to the theoretical understanding of the liquid-to-glass transition, a long-standing challenge in non-equilibrium statistical mechanics of amorphous states of matter. Experimentally, the shear viscosity of supercooled glass-forming liquids shows strong variations with the quench temperature. In particular, two types of behaviour are observed, Arrhenius and highly super-Arrhenius. Conceptually, the molecular description of the structural and dynamical processes underpinning the viscosity behaviour has become a topic of interest because of general implications for the kinetics of slow relaxation in the glassy state. We regard the supercooled liquid as an assembly of interacting particles undergoing thermal fluctuations such that the system evolves in space and time by crossing a series of potential energy barriers. To find these barriers and their corresponding atomic configurations, we apply an energy landscape sampling algorithm that maps out the evolution trajectories in the form of alternating sequences of local energy minima and saddle points. The energy sequences and the atomic coordinates constitute a body of atomic-scale data which we then process using two distinct methods. One is based on an effective activation barrier extracted from the transition-state pathway data, and the other is based on the linear response theory of statistical mechanics. The former is heuristic by being more physically transparent, while the latter is theoretically more rigorous. Through these two complementary calculations, an understanding of the temperature variations of shear viscosities of supercooled liquids, as well as the nature of fragile and strong behaviour of the glass transition, emerges. Our calculation provides a molecular-level account of the viscosities of supercooled liquids in a unified and consistent manner without invoking ad hoc assumptions. Relative to the nature of the glass transition, the usefulness of the PEL perspective is demonstrated, along with the concept of crossover between strong and fragile behaviour. In terms of advancing atomistic simulation capability, we believe the time-scale limitations of traditional molecular dynamics may be significantly extended through the use of metadynamics algorithms for sampling transition-state pathways. [ABSTRACT FROM AUTHOR]

When liquids are cooled below their melting temperatureTm, sometimes they do not solidify immediately but remain in supercooled state up to temperatures far below the melting point. Under certain conditions, they can solidify into the form of amorphous solids without crystallizing. A supercooled liquid and a amorphous solid are metastable phases, which are not completely understood in terms of structural arrangement and thermodynamic behaviour. But by far the most interesting feature is the glass transition which is the manifestation of a true thermodynamic transition and a dynamic event since a dramatic dynamic arrest intervenes. A unified theory of supercooled liquids and glass transition does not yet exist and, more specifically, the link between the sharp increase of the relaxation time and the correlation length is a question still largely open. This article presents in the most elementary manner a brief overview of this delicate issue. [ABSTRACT FROM AUTHOR]

Recent computational studies have reported evidence of a metastable liquid–liquid phase transition (LLPT) in molecular models of water under deeply supercooled conditions. A competing hypothesis suggests, however, that non-equilibrium artefacts associated with coarsening of the stable crystal phase have been mistaken for an LLPT in these models. Such artefacts are posited to arise due to a separation of time scales in which density fluctuations in the supercooled liquid relax orders of magnitude faster than those associated with bond-orientational order. Here, we use molecular simulation to investigate the relaxation of density and bond-orientational fluctuations in three molecular models of water (ST2, TIP5P and TIP4P/2005) in the vicinity of their reported LLPT. For each model, we find that density is the slowly relaxing variable under such conditions. We also observe similar behaviour in the coarse-grained mW model of water. Our findings, therefore, challenge the key physical assumption underlying the competing hypothesis. [ABSTRACT FROM AUTHOR]

Size effects play an important role in structural phase transitions, melting transitions, in martensitic materials, glass transitions, etc. Very often the question arises, whether a measured size effect originates from the geometrical confinement itself, or if it appears due to the interaction with the limiting surface. Using dynamic mechanical analysis (DMA) technique we have studied various microphase segregated polymers, molecular glass forming liquids and supercooled water confined in nanoporous silica as well as in biological tissues. Here we show on some selected examples that DMA measurements can be used to study relaxation processes in detail and to disentangle in favourable cases pure pore size effects from effects that are induced by the confining surface. [ABSTRACT FROM AUTHOR]

Recent experimental results suggest that metallic liquids universally exhibit a high-temperature dynamical crossover, which is correlated with the glass transition temperature (). We demonstrate, using molecular dynamics results for, that this temperature,, is linked with cooperative atomic rearrangements that produce domains of connected icosahedra. Supercooling to a new characteristic temperature,, is shown to produce higher order cooperative rearrangements amongst connected icosahedra, which manifests as the formation of large Zr-rich connected domains that possess macroscopic proportions of the liquid’s icosahedra. This coincides with the decoupling of atomic diffusivities, large-scale domain fluctuations and the onset of glassy dynamics in the liquid. These extensive domains then abruptly stabilise aboveand eventually percolate before the glass is formed. All characteristic temperatures (,and) are thus connected by successive manifestations of the structural cooperativity that begins at. [ABSTRACT FROM AUTHOR]

We present a new generalized scaling relationship accounting both for the real and imaginary parts of the complex permittivity data. The generalized scaling procedure has been successfully used for various relaxation processes in liquid crystals (4-bromobenzylidene-4′-pentyloxyaniline, 4-bromobenzylidene-4′-hexyloxyaniline, 4′-butyl-4-(2-methylbutoxy)-azoxybenzene, 4-ethyl-4′-octylazoxybenzene), and in glass-forming liquids (glycerol, propylene carbonate, salol, cresolphthalein-dimethylether). As it is shown, one obtains common master-curve for liquid-like phases (isotropic liquid, cholesteric, nematic, smectic A), solid-like phases (smectic B, conformationally disorder crystal) and supercooled liquid phase. [ABSTRACT FROM PUBLISHER]

Stochastic-Beta-Relaxation provides a characterisation of the glass crossover in discontinuous Spin-Glasses and supercoooled liquid. Notably it can be derived through a rigorous computation from a dynamical Landau theory. In this paper, I will discuss the precise meaning of this connection in a language that does not require familiarity with statistical field theory. I will discuss finite-size corrections in mean-field Spin-Glass models and loop corrections in finite-dimensional models that are both described by the dynamical Landau theory considered. Then I will argue that the same Landau theory can be associated to supercooled liquid described by Mode-Coupling Theory invoking a physical principle of time-scale invariance. [ABSTRACT FROM PUBLISHER]

These early investigations led John and colleagues to pioneer research into how water molecules are ordered around ions in aqueous solutions- a major step forward in chemical physics. The death of John Enderby on August 3, 2021 saw the loss to neutron science of one of its leading protagonists. John was a brilliant communicator and motivator who inspired many with their careers in neutron scattering. [Extracted from the article]

Deeply supercooled water exhibits complex dynamics with large density fluctuations, ice coarsening and characteristic time scales extending from picoseconds to milliseconds. Here, we discuss implications of these time scales as they pertain to two-phase coexistence and to molecular simulations of supercooled water. Specifically, we argue that it is possible to discount liquid–liquid criticality because the time scales imply that correlation lengths for such behaviour would be bounded by no more than a few nanometres. Similarly, it is possible to discount two-liquid coexistence because the time scales imply a bounded interfacial free energy that cannot grow in proportion to a macroscopic surface area. From time scales alone, therefore, we see that coexisting domains of differing density in supercooled water can be no more than nanoscale transient fluctuations. [ABSTRACT FROM PUBLISHER]

We have improved the non-equilibrium molecular dynamics measurement for the longitudinal wave (LW) velocity (the speed of sound) and have applied it to a model system in 2D and 3D. The LW velocity at temperature of the glass or supercooled liquid state reaches the range ofin the 2D system andin the 3D system, with a gradual increase with increasing temperature under the isochoric and adiabatic conditions. In our previous paper [4] we analysed that the cooperative motion in intermediate time and length scales propagates with a speed depending on temperature and found that its dependency is opposed to that of the LWs. It suggests that the cooperative motion spreads over the system in a different way of sound. [ABSTRACT FROM AUTHOR]

The random first-order transition theory of the structural glass transition is reviewed in a pedagogical fashion. The rigidity that emerges in crystals and glassy liquids is of the same fundamental origin. In both cases, it corresponds with a breaking of the translational symmetry; analogies with freezing transitions in spin systems can also be made. The common aspect of these seemingly distinct phenomena is a spontaneous emergence of the molecular field, a venerable and well-understood concept. In crucial distinction from periodic crystallisation, the free energy landscape of a glassy liquid is vastly degenerate, which gives rise to new length and time scales while rendering the emergence of rigidity gradual. We obviate the standard notion that to be mechanically stable a structure must be essentially unique; instead, we show that bulk degeneracy is perfectly allowed but should not exceed a certain value. The present microscopic description thus explains both crystallisation and the emergence of the landscape regime followed by vitrification in a unified, thermodynamics-rooted fashion. The article contains a self-contained exposition of the basics of the classical density functional theory and liquid theory, which are subsequently used to quantitatively estimate, without using adjustable parameters, the key attributes of glassy liquids, viz., the relaxation barriers, glass transition temperature, and cooperativity size. These results are then used to quantitatively discuss many diverse glassy phenomena, including the intrinsic connection between the excess liquid entropy and relaxation rates, the non-Arrhenius temperature dependence ofα-relaxation, the dynamic heterogeneity, violations of the fluctuation-dissipation theorem, glass ageing and rejuvenation, rheological and mechanical anomalies, super-stable glasses, enhanced crystallisation near the glass transition, the excess heat capacity and phonon scattering at cryogenic temperatures, the Boson peak and plateau in thermal conductivity, and the puzzling midgap electronic states in amorphous chalcogenides. [ABSTRACT FROM AUTHOR]

The isothermal crystallization kinetics of 4-n-pentyl-4–cyanobiphenyl (5CB) has been studied with Differential Scanning Calorimetry (DSC) and Dielectric Relaxation Spectroscopy (DRS). 5CB is a well characterized material which makes it ideal for a dielectric and thermal comparative study. The effect that isothermal crystallization exerts on the behavior of relaxation processes α and δ by cooling the isotropic liquid below the nematic phase or through the process of cold crystallization by heating it from the supercooled state is explored by comparing the DRS and DSC. Furthermore, by employing the Avrami equation, we compare the ability to probe the crystallization with each technique. [ABSTRACT FROM AUTHOR]

Copyright 2014 American Association for Aerosol Research [ABSTRACT FROM AUTHOR]

The effects of pressure treatment at room temperature on the microstructure and corrosion resistance in seawater solution of the as spun RE65Co25Al10 (RE = Ce, La, Pr, Sm and Gd) metallic glass ribbons have been investigated using X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and electrochemical workstation. The results indicate that the pressure treatment causes the changes of microstructure, which results in the variation of the glass transition temperature and supercooled liquid region of the RE65Co25Al10 metallic glass. The RE65Co25Al10 metallic glass treated by pressure in 16 kN exhibits low self-corrosion current density and distinct passive region, indicating the higher seawater corrosion resistance. However, the corrosion resistance of the RE65Co25Al10 metallic glass becomes poor with increasing pressure to 30 kN. The discussion of the corrosion mechanism has been made based upon the structural relaxation and bonding force of the matrix elements and oxygen during the electrochemical corrosion process. [ABSTRACT FROM AUTHOR]

Bulk metallic glass (BMG) alloys have been known to show superior formability under a Newtonian viscous mode in a supercooled liquid region (SLR). Crystalline phases generated by a high-temperature forming process have a negative effect on the formability of the BMG alloys by the rapid increase of viscosity for an amorphous matrix. A constitutive model considering dynamic crystallization and a viscous flow for high-temperature deformation behavior of the Ti-based BMG was used for n estimation of the formability, and was verified to apply to the forming process in an SLR. The experimental formability of the Ti-based BMG has been found to be in good agreement with the finite element analyses results based on the constitutive model, and thus enable one to apply to the other forming processes conducted in an SLR. [ABSTRACT FROM AUTHOR]

Götze took intense interest in experiments aimed at determining the range of applicability of MCT and covered this topic in several reviews. The most striking confirmation of MCT came from colloidal systems; the photon correlation data by Peter Pusey and William Van Megen and the discovery of different arrest mechanism in short-range attractive colloids gave Götze great satisfaction. Wolfgang Götze, theoretical physicist, died on October 20, 2021, at age 84 in Munich. [Extracted from the article]

The interfacial friction behaviour of Zr35Ti30Be26.75Cu8.25metallic glass during micro-extrusion was investigated at various strain rates and temperatures in the supercooled liquid region. A friction mechanism map that distributes adhesion regime, furrow regime and mechanical engagement regime was constructed. These regimes respectively correspond to Newtonian flow, non-Newtonian flow and inhomogeneous flow by comparing with the typical deformation map. The correlation between flow characteristics and interfacial friction behaviour is well analysed by combining the viscosity theory with the finite-element simulations. [ABSTRACT FROM AUTHOR]

The surface tension and specific heat of liquid Ni-5%Cu-5%Fe-5%Co-5%Sn-5%Ge hexabasic alloy were measured over a broad range of temperature. The maximum undercooling obtained in the experiments is 363 K (0.22 TL). The surface tension value is determined as 1.460 N m−1at the liquidus temperature of 1652 K, while its temperature coefficient is –6.361 ×  10− 4N m−1 K−1. The specific heat value is determined to be 41.49 ± 1.210 J mol−1 K−1in the temperature range from 1289 to 1850 K. The dendritic growth velocity of α-Ni solid solution phase within the liquid alloy was measured as a function of undercooling, which attains 25.4 m s−1at the undercooling of 358 K. The rapid dendritic growth results in the significant solute trapping of all the five solutes. The lattice constant of α-Ni solid solution phase is found to increase with the extent of solute trapping. A microstructural morphology transition occurs from well-branched dendrites into equiaxed grains with the rise of undercooling. [ABSTRACT FROM AUTHOR]

We carried out the formulation set-up and thermodynamics as well as morphological characterization of two systems: an aqueous-based formulation and an organic-solvent-based formulation with tert-butanol (TBA) at eutectic composition (20% TBA + water 80% by mass) containing ibuprofen as the model pharmaceutical active component. The goal was to carry out the optimization of a soft freeze-drying cycle for heat-sensitive drugs. The organic-based ibuprofen formulation had a glass transition temperature significantly higher compared to that of the aqueous-based ibuprofen formulation, which allowed much higher sublimation temperatures for these systems in comparison with the pure water-based ibuprofen formulations. The morphological study of the frozen organic-based formulation showed unexpected behavior in comparison with previous literature data reported for water-based formulations. For the same freezing rates, the mean diameters of the solvent crystals of organic-based formulations were much larger than that of ice crystals of aqueous-based formulation, which led to a freeze-dried matrix of higher permeability. In contrast to what was observed with the aqueous-based formulations, the freezing rates, in the range of classical industrial values investigated, had no significant effect on the supercooling of the liquid ibuprofen formulations tested as well as on the nucleation temperatures and on the morphology of the organic solvent crystals. All these singular characteristics, with lower sublimation enthalpies and higher equilibrium vapor pressure values previously measured with the same formulations in our laboratory, explain the large reduction of sublimation times observed during the soft freeze-drying processes for heat-sensitive drugs with organic (TBA)-based formulations. [ABSTRACT FROM PUBLISHER]

The concept ‘relaxativity’ is proposed to describe the degree of dielectric relaxor in relaxor ferroelectrics, like the ‘fragility’ in supercooled liquid in describing glass forming ability during vitrification process. The calculated results of Pb(Mg1/3Nb2/3)O3-PbTiO3relaxors and BaTiO3-BaZrO3relaxors exhibit good coincidences with the intervals between their dielectric peak temperatures. The larger relaxativity is corresponding to larger configurational entropy and smaller spatial correlation length, or stronger local interactions for a relaxor. [ABSTRACT FROM PUBLISHER]

experimental study was carried out to investigate the freezing characteristics of supercooled water droplets impacting on solid surfaces. Each water droplei was supercooled on the inside surface of a water-repellent guideway in a cooled air environment and then blasted horizontally by a jet of pressurized cooled air to impact on the vertical surface of a test block. The deformation and freezing of the droplets were ob-served using a high-speed camera. The droplets were frozen under varying conditions of air temperature, surface temperature, impact velocity and droplet volume. The results indicated that the freezing behavior of a droplet was strongly affected by the condition of the solid surface. Further, the results revealed that the supercooling solidification process consisted of two steps with two greatly different time scales. Finally, it was shown that the freezing behavior of an ice layer was affected by the presence of a liquid-like thin film. [ABSTRACT FROM AUTHOR]

Using experimental data for the structure factor S(q) of supercooled liquid silicon, and amorphous and supercooled liquid cobalt, we have calculated and compared the Fourier transform c(q) of the Ornstein–Zernike direct correlation function for these two systems. Differences of c(q) between Si and Co are ascribed to the different atomic coordination and packing, high in Co due to typical metallic bonding, and lower in Si due to more directional bonding. Also, in contrast to previous expectations, differences are found between the direct correlation function of amorphous and supercooled liquid cobalt. [ABSTRACT FROM PUBLISHER]

We consider the relationship between the excess entropy and anomalies of water. We investigate by molecular dynamics simulations the thermodynamic region of supercooled water and a supercooled aqueous solution with NaCl at a salt concentration of 0.67 mol kg−1. The TIP4P potential model displays, as already established, in pure water and in solution a phase diagram with a liquid–liquid critical point. We explore how the two-body excess entropy calculated from the radial distribution functions is an indicator of density and structural anomalies of supercooled liquid water, both in the pure system and in the NaCl(aq). The two-body excess entropy shows a peculiar behaviour associated with the density anomaly and structural changes in water as revealed by the radial distribution functions. The signature of a change in the structural relaxation of water from fragile to strong is also found by examining the behaviour of the excess entropy at decreasing temperature. [ABSTRACT FROM AUTHOR]

The specific heat Cp is analyzed using the experimental data at various temperatures in the solid phase of cholesteryl myristate according to a power-law formula for the rapidly and slowly cooled solid in the stability limit. We also analyze the temperature dependence of the Cp using the experimental data for the supercooled solid phase of p-azoxyanisole in the stability limit and the stability temperatures are determined for both cholesteryl myristate and p-azoxyanisole. Our results show that the method of analysis given here is adequate to describe the observed behaviour of the Cp at low temperatures in the solid phase. [ABSTRACT FROM AUTHOR]

The acoustic sound velocity of water in the supercooled regime shows peculiar behaviour. According to the available data, the sound velocity displays complex behaviour below -15°C, where anomalous frequency dispersion phenomena seem to appear and need to be understood. In particular, lower-frequency data at a few tens of KHz show levelling-off of the sound velocity value below -25°C, with a possible minimum around -30°C. Other data at higher frequencies, around 1 GHz, in comparison with the low-frequency data, could instead suggest the existence of a 'negative dispersion'; yet other high-frequency data show normal dispersion behaviour. To gain new insight into this topic, we made measurements of the acoustic sound velocity in bulk water in the liquid and supercooled phase down to -29°C by means of a heterodyne detected transient grating (TG) experiment at an unexplored frequency value around 100 MHz. [ABSTRACT FROM AUTHOR]

We present a Raman scattering study of B2O3 as a function of temperature. Measurements have been done from liquid helium temperature up to the supercooled liquid state. We found that the shift in the boson peak could be completely ascribed to the temperature induced elastic medium transformation and we do not need the introduction of other mechanisms. Furthermore we show also in this system that the boson peak spectral shape is invariant. [ABSTRACT FROM AUTHOR]

A brief review is presented of the situation concerning the dielectric hole burning technique applied to supercooled (molecular) liquids. Some of the problems related to recently obtained results are discussed. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations were performed of the structural changes occurring through the liquid-glass transition in Cu-Zr alloys. The total scattering functions (TSF), and their associated primary diffuse scattering peak positions (Kp), heights (Kh) and full-widths at half maximum (KFWHM) were used as metrics to compare the simulations to high-energy X-ray scattering data. The residuals of difference between the model and experimental TSFs are ∼0.03 for the liquids and about 0.07 for the glasses. Over the compositional range studied, Zr1-xCux (0.1 ≤ x ≤ 0.9), Kp, Kh and KFWHM show a strong dependence on composition and temperature. The simulation and experimental data correlate well between each other. MD simulation revealed that the Cu-Zr bonds undergo the largest changes during cooling of the liquid, whereas the Cu-Cu bonds change the least. Changes in the partial-pair correlations are more readily seen in the second and third shells. The Voronoi polyhedra (VP) in glasses are dominated by only a few select types that are compositionally dependent. The relative concentrations of the dominant VPs rapidly change in their relative proportion in the deeply undercooled liquid. The experimentally determined region of best glass formability, xCu ∼ 65%, shows the largest temperature dependent changes for the deeply undercooled liquid in the MD simulation. This region also exhibits very strong temperature dependence for the diffusivity and the total energy of the system. These data point to a strong topological change in the best glass-forming alloys and a concurrent change in the VP chemistry in the deeply undercooled liquid. [ABSTRACT FROM AUTHOR]

We review the spectroscopic techniques and scattering experiments used to probe the structure of water, and their interpretation using empirical and ab initio models, over the last 5 years. We show that all available scientific evidence overwhelmingly favors the view of classifying water near ambient conditions as a uniform, continuous tetrahedral liquid. While there are controversial issues in our understanding of water in the supercooled state, in confinement, at interfaces, or in solution, there is no real controversy in what is understood as regards bulk liquid water under ambient conditions. [ABSTRACT FROM AUTHOR]

Application of an electric or magnetic field can significantly affect the freezing characteristics of water. A DC electric field will tend to induce ice nucleation at a lower degree of supercooling, and there is evidence to show that an AC electric field delays the onset of ice nucleation. Industrial research has shown that a magnetic field can be used to delay nucleation and to induce small, unclustered ice. Smaller ice crystals are essential in the preservation of the structure or bioavailability of frozen materials, particularly biological or food products. On the other hand, larger ice crystals facilitate faster freeze drying because it results in less vapor mass transfer resistance. The end part of this review introduces another application of magnetic field in the form of magnetocaloric freezers. This technology is a potential alternative to heat pump drying for commercial freezing and refrigeration. [ABSTRACT FROM AUTHOR]

Chathoth and coworkers (Phys. Rev. Lett. 101, 037801 (2008)) have reported examples of multicomponent glass-forming metallic liquids in which the packing fraction appears to be a dominant parameter. Here, we first summarise, for 15 pure liquid metals, properties of the Ornstein-Zernike direct correlation function c(r) which provide a necessary, though not sufficient, condition for hard-sphere-like (HS) liquid behaviour. Returning to multicomponent melts, NiNb and NiNbSn systems have been studied by Chathoth and coworkers. Pure Ni, according to c(r) data near melting, satisfies the necessary condition for HS behaviour, while Sn certainly does not. But the Sn concentration is low in the metallic glass-forming liquid NiNbSn investigated by Chathoth and coworkers. Suitable experimental diffraction data to obtain c(r) in pure liquid Nb seems not to be available presently. Finally, a brief discussion is given of atomic transport in supercooled multicomponent metallic liquids, the status of the Stokes-Einstein relation being one focus. [ABSTRACT FROM AUTHOR]

Glassy phases which have insulating character exist for a variety of monatomic species. By contrast, until recently, it has been possible to make bulk metallic glasses (BMG) by vitrification only for multicomponent systems. After a relatively brief summary on supercooling of a few molecular liquids, we review some of the recently reported results on molecular assemblies of the series N, P, As and amorphous Si and Ge. Based on these results, we suggest that the transition metals with their directional bonding might be suitable candidates for the production of BMG by vitrification. [ABSTRACT FROM AUTHOR]