Supercooled Range Research Articles

Densities of Au-X (X = Cu, Ni and Pd) binary melts and thermodynamic correlations

Our group has previously investigated the correlations between the excess volumes, thermodynamic functions and phase diagrams of binary alloy melts, and the present study focused on binary Au-X (X = Cu, Pd and Ni) alloy melts. The Au-Cu and Au-Pd systems have intermetallic compounds with order–disorder transitions. The densities of these alloy melts were determined with small uncertainties using a combination of an electromagnetic levitation technique and a static magnetic field. The densities of these melts varied linearly with temperature, including those temperatures within the supercooled range. These results are discussed herein within a thermodynamic framework based on the correlation between excess volume (VE) and excess Gibbs energy (GE). The data obtained in this work confirmed that binary alloy systems having an order–disorder transition, such as the Au-Cu and Au-Pd systems, belonged to the group defined by VE ≥ 0 and GE < 0. The effect of composition on VE was examined with regard to cluster formation in the liquids. The Au-Ni system was shown to possess a miscibility gap in the solid solution and the corresponding melts had positive VE and positive GE values.

Evaluation of Mass Accommodation Coefficients of Water over a Wide Temperature Range and Determination of Diffusion Coefficient of Water in Nitrogen

Diffusion coefficient of water in nitrogen (Dvg) is a critical thermophysical parameter. However, the widely used empirical parametrizations of Dvg are only applicable in the temperature range from 273 K to 373 K. In the supercooled range, the reported experimental values of Dvg is sparse, and Dvg varies with temperature in a way different from the empirical equations and the recently reported first-principles calculation. In this paper, Dvg values at given temperatures, including in the supercooled range, were determined using the evaporation kinetics of individual water droplets in nitrogen flow under well-controlled conditions. The KVH model capable of describing the rapid evaporation/condensation process of an individual water droplet was utilized, and the thermophysical/kinetic parameters were evaluated carefully. Through reviewing the literature values of mass accommodation coefficient (αM) for ice, ice with liquid-like layer, supercooled water, normal water, and hot water, it is observed that the Slogistic1 function presented by OriginPro® could describe the temperature dependence of αM well. Then, the radius vs. time curve of an individual water droplet was predicted from the KVH model by varying Dvg and then compared with the experimental curve recorded by the Electrodynamic Balance. The trial value of Dvg corresponding to the best agreement was treated as its experimental value. By reviewing and regression fitting of all available experimental data, an improved expression of Dvg is proposed. The accuracy is evaluated to be ± 4 % in the temperature range of 248 K to 600 K.

Correlation between configurational entropy, excess entropy, and ion dynamics in imidazolium-based ionic liquids: Test of the Adam–Gibbs model

The Adam-Gibbs (AG) model, linking thermodynamics with molecular dynamics of glass-forming liquids, plays a crucial role in the studies of the glass transition phenomenon. We employ this approach to investigate the relationship between ion dynamics and thermodynamics in three imidazolium-based ionic liquids in the current work. We show that the AG relation, -log10σdc ∝ (TSc)-1 (where σdc, T, and Sc denote the dc-conductivity, absolute temperature, and configurational entropy, respectively), does not work when the whole supercooled liquid state is considered. Meanwhile, a linear relationship between -log10σdc and (TSe)-1 (where Se denotes the excess entropy) was observed in the entire supercooled range. On the other hand, the generalized AG model log10σdc ∝ (TSc α)-1 with an additional free parameter α successfully describes the relation between σdc and Sc. The determined α values being less than unity indicate that the configurational entropy is insufficient to govern the ion dynamics. Meanwhile, we found a systematical decrease in α with the elongation of the alkyl chain attached to the imidazolium ring.

Comparative study of crystallization process in metallic melts using ab initio molecular dynamics simulations

The crystallization process of liquid metals is studied using ab initio molecular dynamics simulations. The evolution of short-range order during quenching in Pb and Zn liquids is compared with body-centered cubic (bcc) Nb and V, and hexagonal closed-packed (hcp) Mg. We found that the fraction and type of the short-range order depends on the system under consideration, in which the icosahedral symmetry seems to dominate in the body-centered cubic metals. Although the local atomic structures in stable liquids are similar, liquid hcp-like Zn, bcc-like Nb and V can be deeply supercooled far below its melting point before crystallization while the supercooled temperature range in liquid Pb is limited. Further investigations into the nucleation process reveal the process of polymorph selection. In the body-centered cubic systems, the polymorph selection occurs in the supercooled state before the nucleation is initiated, while in the closed-packed systems it starts at the time of onset of crystallization. Atoms with bcc-like lattices in all studied supercooled liquids are always detected before the polymorph selection. It is also found that the bond orientational ordering is strongly correlated with the crystallization process in supercooled Zn and Pb liquids.

Temperature dependence of the vapor pressure and evaporation coefficient of supercooled water

We report measurements of the vapor pressure of water over the supercooled temperature range 248 to 273 K derived from evaporation kinetics measurements of single water droplets. Accurate measurements of the relative humidity of the surrounding gas phase are derived from comparative and sequential measurements of the evaporation kinetics of droplets containing sodium chloride. The temperature dependence of the vapor pressure of supercooled water is shown to conform closely to the parameterization provided by Murphy and Koop (2005) once the uncertainties in experimental and thermophysical parameters are accounted for by ensuring an accurate representation of evaporation rates at temperatures above 273 K. Further, from a sensitivity analysis of all of the data over the full temperature range from 248 to 293 K, we can conclude that the evaporation coefficient of water, and thus the mass accommodation coefficient, is greater than, or equal to, 0.5.

Liquid structure and temperature invariance of sound velocity in supercooled Bi melt

Structural rearrangement of liquid Bi in the vicinity of the melting point has been proposed due to the unique temperature invariant sound velocity observed above the melting temperature, the low symmetry of Bi in the solid phase and the necessity of overheating to achieve supercooling. The existence of this structural rearrangement is examined by measurements on supercooled Bi. The sound velocity of liquid Bi was measured into the supercooled region to high accuracy and it was found to be invariant over a temperature range of ∼60°, from 35° above the melting point to ∼25° into the supercooled region. The structural origin of this phenomenon was explored by neutron diffraction structural measurements in the supercooled temperature range. These measurements indicate a continuous modification of the short range order in the melt. The structure of the liquid is analyzed within a quasi-crystalline model and is found to evolve continuously, similar to other known liquid pnictide systems. The results are discussed in the context of two competing hypotheses proposed to explain properties of liquid Bi near the melting: (i) liquid bismuth undergoes a structural rearrangement slightly above melting and (ii) liquid Bi exhibits a broad maximum in the sound velocity located incidentally at the melting temperature.

Aerodynamic levitator furnace for measuring thermophysical properties of refractory liquids

The development of novel contactless aerodynamic laser heated levitation techniques is reported that enable thermophysical properties of refractory liquids to be measured in situ in the solid, liquid, and supercooled liquid state and demonstrated here for alumina. Starting with polished crystalline ruby spheres, we show how, by accurately measuring the changing radius, the known density in the solid state can be reproduced from room temperature to the melting point at 2323 K. Once molten, by coupling the floating liquid drop to acoustic oscillations via the levitating gas, the mechanical resonance and damping of the liquid can be measured precisely with high-speed high-resolution shadow cast imaging. The resonance frequency relates to the surface tension, the decay constant to the viscosity, and the ellipsoidal size and shape of the levitating drop to the density. This unique instrumentation enables these related thermophysical properties to be recorded in situ over the entire liquid and supercooled range of alumina, from the boiling point at 3240 K, until spontaneous crystallization occurs around 1860 K, almost 500 below the melting point. We believe that the utility that this unique instrumentation provides will be applicable to studying these important properties in many other high temperature liquids.

Crystallization during Bending of a Pd-Based Metallic Glass Detected by X-Ray Microscopy

Without the availability of slip systems and dislocation glide as in crystalline materials, metallic glasses resist irreversible deformation to elastic strains of 2% or more before undergoing heterogeneous plastic flow via the formation of shear bands. Observation of crystallite formation under compressive load was previously obtained by transmission electron microscopy. In this Letter, we present results of nondestructive x-ray diffraction microprofiling of the section of a bent glassy Pd40Cu30Ni10P20 ribbon in transmission using a synchrotron microbeam. Crystallization was clearly detected but only on the compression side of the neutral fiber. The experimental results and crystal nucleation frequency analysis are consistent with massive nucleation in shear bands forming under compressive stress but mainly for metallic glasses that show a large supercooled liquid temperature range ΔT=T(x)-T(g) between glass transition at T(g) and crystallization at T(x). The phenomenon is sensitively dependent on the volume change that accompanies crystallization in the supercooled liquid temperature range where the much larger liquid-state thermal expansion coefficient significantly increases the specific volume difference between the liquid and crystalline states. The results are also consistent with the many reports of extensive strain to fracture of metallic glasses under compressive load but not under tension.

Nanoimprinting of Metallic Glass for Periodic Nano-Hole Structures with Dies Fabricated by FIB-CVD and RIE

Metallic glasses are amorphous structured materials exhibiting perfect Newtonian viscous flow in the supercooled liquid temperature range and superior nanoformability under low stress. These properties make metallic glasses ideal materials for nanoimprinting, which is a promising high-throughput, low-cost method of mass producing micro- and nanodevices. For this study, we fabricated SiO2/Si dies having periodic nanodot structures with dot pitches of 50 nm and 40 nm by focused ion beam (FIB) assisted chemical vapor deposition (CVD), and reactive ion etching (RIE). We successfully nanoimprinted Pt-based metallic glass using these dies. The periodic nanohole structures were accurately imprinted due to the optimization of the loading and unloading thermal cycle conditions in the nanoimprinting process with the flattened and thinned metallic glass specimen. The results demonstrate the excellent capability of metallic glass as a nanoimprintable material for fabricating nanodevices such as patterned media. [doi:10.2320/matertrans.M2010241]

Surface tension-driven shape-recovery of micro/nanometer-scale surface features in a Pt 57.5Ni 5.3Cu 14.7P 22.5 metallic glass in the supercooled liquid region: A numerical modeling capability

Recent experiments in the literature show that micro/nano-scale features imprinted in a Pt-based metallic glass, Pt 57.5Ni 5.3Cu 14.7P 22.5, using thermoplastic forming at a temperature above its glass transition temperature, may be erased by subsequent annealing at a slightly higher temperature in the supercooled liquid region ( Kumar and Schroers, 2008). The mechanism of shape-recovery is believed to be surface tension-driven viscous flow of the metallic glass. We have developed an elastic–viscoplastic constitutive theory for metallic glasses in the supercooled liquid temperature range at low strain rates, and we have used existing experimental data in the literature for Pt 57.5Ni 5.3Cu 14.7P 22.5 ( Harmon et al., 2007) to estimate the material parameters appearing in our constitutive equations. We have implemented our constitutive model for the bulk response of the glass in a finite element program, and we have also developed a numerical scheme for calculating surface curvatures and incorporating surface tension effects in finite element simulations. By carrying out full three-dimensional finite-element simulations of the shape-recovery experiments of Kumar and Schroers (2008), and using the independently determined material parameters for the bulk glass, we estimate the surface tension of Pt 57.5Ni 5.3Cu 14.7P 22.5 at the temperature at which the shape-recovery experiments were conducted. Finally, with the material parameters for the underlying elastic–viscoplastic bulk response as well as a value for the surface tension of the Pt-based metallic glass fixed, we validate our simulation capability by comparing predictions from our numerical simulations of shape-recovery experiments of Berkovich nanoindents, against corresponding recent experimental results of Packard et al. (2009) who reported shape-recovery data of nanoindents on the same Pt-based metallic glass.

Nature of the glassy transition in simulations of the ferromagnetic plaquette Ising model

The homogeneous plaquette Ising model in two and three dimensions is investigated by means of Monte Carlo simulations. By introducing a suitable order parameter for the two-dimensional lattice, and the finite-size scaling of the corresponding fourth-order cumulant, it is found that, consistent with the previous theoretical indications, the model in two dimensions is disordered at finite temperature and exhibits a zero-temperature phase transition characteristic of the one-dimensional Ising model with an essential (exponential) singularity of the order-parameter susceptibility as opposed to a Curie-law (power-law) divergence. In three dimensions, however, the model is believed to have a first-order phase transition at Tc approximately 3.6 screened by strong metastability leading to a so-called "glassy transition" at T approximately 3.4 when subjected to slow cooling. By computing the configurational entropy Sc identical withS(liquid)-S(crystal) in the supercooled temperature range via thermodynamic integration of the internal energy results, the Kauzmann temperature defined as that temperature where the extrapolated configurational entropy Sc(T) vanishes, is estimated to be TK approximately 3.18 . By finding ways to estimate the equilibration time of the supercooled liquid and the nucleation time of the stable crystal droplets, it is shown that T approximately 3.4 is indeed the limit of stability or the effective spinodal temperature Tsp, at which the two time-scales associated with the quasiequilibration of the supercooled liquid, taueq, and the nucleation of the stable crystal droplets, taunuc, cross one another, with the former rising above the latter such that the supercooled liquid state becomes physically irrelevant below Tsp approximately 3.4 and the impending entropy crisis at TK approximately 3.18 (<Tsp) is thus avoided. Hence, what is sometimes called "glassy temperature," is really a kinetic spinodal temperature that may be regarded as the remnant of the mean-field spinodal.

Classical and Quantum Gibbs Free Energies and Phase Behavior of Water Using Simulation and Cell Theory

A method to calculate the classical and quantum free energy of a liquid from a computer simulation by using cell theory [J. Chem. Phys. 2007, 126, 064504] is tested for liquid water and ice Ih against experiment as a function of temperature. This fast and efficient method reproduces reasonably well the experimental values of entropy, enthalpy, and free energy of a liquid across the supercooled, stable, and superheated range of temperatures considered. There are small differences between classical and quantum results of water at 298 K, necessitating a small correction term to reproduce water's enthalpy of vaporisation. Only at higher temperatures is entropy underestimated by up to 9 J K(-1) mol(-1) as verified by thermodynamic integration calculations. Satisfactory agreement for ice, however, is only obtained by using the quantum formulation. Even then, at higher temperatures, the entropies exceed experiment by up to 15 J K(-1) mol(-1). Further insight into the quantum nature of water is provided by inspecting the temperature dependence of the frequencies. The harmonic approximation is further supported by the harmonic force and torque distributions and the very similar entropies obtained from the force and torque variances. All these results suggest that the single molecule harmonic oscillator approximation for water, although not exact, provides a rapid, insightful, and useful means to evaluate the thermodynamic properties of water from a computer simulation in a way that can account for the quantization of water's energy levels.

Crystallization of Amorphous Al&lt;sub&gt;85&lt;/sub&gt;Ce&lt;sub&gt;5&lt;/sub&gt;Ni&lt;sub&gt;10&lt;/sub&gt; Ribbon

In the present work the crystallization process of an aluminum-based amorphous metal have been investigated. Rapidly quenched Al85Ce5Ni10 ribbon has been produced by melt-spinning. The amorphous structure evolution during heating has been studied by a combination of X-ray diffraction (XRD) and differential scanning calorimetry (DSC). Thermograms obtained in continuous heating regime reveal a glass transition, Tg, resulting in a supercooled liquid temperature range of ∼16°C. Multiple crystallization events were observed by isothermal annealing of the as-quenched melt-spun ribbon at temperatures below Tg; precipitation of a metastable phase in the amorphous matrix has been observed. Further heating at increasing temperatures resulted in complete crystallization with α-Al and intermetallic compounds. Kinetics analyses indicate that crystallization occurs though nucleation and three-dimensional growth.

Superplastic nanoforming of optical components of Pt-based metallic glass

Metallic glasses are useful for fabricating nanodevices due to their viscosity and homogeneity on nanometer scales. In this study, we developed optical components of metallic glasses by superplastic nanoforming. Metallic glasses exhibit Newtonian viscous flow in a supercooled temperature range between the glass transition temperature and the crystallization temperature. This study used Pt-based metallic glass with a glass transition temperature of 502 K. This material was applied to reflective interference optical components, and a diffraction grating (1 μm interval) and a hologram were fabricated by superplastic nanoforming. Dies were made by Ni-electroforming, with master models fabricated by photolithography of the interference pattern. The working temperature of Pt-based metallic glass was 540 K under a compressive stress of 10 MPa. The results demonstrated the advantages of the superplastic nanoforming technique on metallic glass and for mass production of optical components.

EFFECT OF HOT ISOSTATIC PRESSING ON MECHANICAL PROPERTIES OF Fe41Cr15Mo14C15B6Y2Co7 BMG

Fe -based bulk amorphous rods of 3 mm in diameter and a composition of Fe 41 Cr 15 Mo 14 C 15 B 6 Y 2 Co 7 were produced by copper mold casting. The as-cast amorphous rods contain a small (2%) fraction of pores. To close the pores, samples cut from the amorphous rods were hot isostatically pressed (hipped) at 863 K, which is in the supercooled liquid temperature range between the glass transition temperature and the crystallization temperature of the amorphous phase, and under a pressure of 200 Mpa. Microstructure examination of the hipped samples shows that hipping results in an increase of the density of the samples from 7.9 g/cm3 to 8.0 g/cm3, and a decrease of the porosity level from 2% to 1%, and that a very small fraction of unknown crystalline phase form. As a result of these microstructure change caused by hipping, the average room temperature compressive fracture strength of the bulk metallic glass (BMG) decrease from 3500 Mpa to 3000 MPa, while the strain to fracture changes little from 1.5% to 1.4%. The mechanisms of the effect of hipping on microstructure and mechanical properties of the Fe -based BMG are discussed.

Electron transport behaviour and soft magnetic properties of bulk amorphous Fe72Si4B20Nb4 alloy

The crystallization behaviour, electrical resistivity, magnetic and mechanical properties of as-quenched bulk amorphous Fe72Si4B20Nb4 alloy was investigated. The alloy, prepared in the form of rods by a copper mould casting technique, revealed an amorphous structure as observed from x-ray diffractometry. Differential scanning calorimetry and thermal variation of electrical resistivity measurements showed distinct glass transition temperature, Tg occurring 50–60 K below the crystallization onset (TX). Such a wide supercooled range was also attributed to the highly reduced glass transition temperature, Trg which was in the range of 0.56–0.58 found to be prevalent in good glass forming alloys. The alloy also showed a non-linear decrease in stability time at different temperatures between Tg and TX. The bulk amorphous alloy exhibited a drastic decrease in electrical resistivity around the glass transition temperature which was attributed to high electron propagation due to enhanced stress relaxation as result of a decrease in viscosity. The material exhibited superior soft magnetic properties with a coercivity value of 212 mOe, which is fairly low with respect to reported bulk amorphous alloys. The amorphous alloy also showed saturation induction of 12 kG and a moderate Curie temperature of 595 K. The as-quenched bulk amorphous alloy exhibited a high mechanical hardness of 1250 HV (Vickers). The superior soft magnetic properties coupled with high mechanical hardness opens up the scope for bulk amorphous Fe–Si–B systems with Nb incorporation.

2719 金属ガラス-Siハイブリッド構造による圧力センサ用ダイアフラムの開発(S33-2 材料の超精密加工とマイクロ/ナノ加工の動向(2),S33 材料の超精密加工とマイクロ/ナノ加工の動向)

We designed and fabricated a diaphragm for hybrid structured pressure sensor of metallic glass and (100) Si. Metallic glasses are known to be homogeneous and isotropic in nanometer scales and they exhibit high strength, low elastic coefficient, large elastic strain and superior material functions such as corrosion resistance at a room temperature. This material also exhibits Newtonian viscous flow in the supercooled liquid temperature range between the glass transition and the crystallization temperature. In this study, we developed a sputtering target and deposited Zr-based metallic glass film on the (100) Si substrate by RF magnetron sputtering technique. By successive silicon process such as lithography and anisotropic etching, a hybrid structure of metallic glass and (100) Si has been fabricated. These fabrication processes demonstrate the advantages of metallic glasses and a technique for producing hybrid structured MEMS devices.

How the Liquid-Liquid Transition Affects Hydrophobic Hydration in Deeply Supercooled Water

We determine the phase diagram of liquid supercooled water by extensive computer simulations using the TIP5P-E model. We find that the transformation of water into a low density liquid in the supercooled range strongly enhances the solubility of hydrophobic particles. The transformation of water into a tetrahedrally structured liquid is accompanied by a minimum in the hydration entropy and enthalpy. The corresponding change in sign of the solvation heat capacity indicates a loss of one characteristic signature of hydrophobic hydration. The observed behavior is found to be qualitatively in accordance with the predictions of the information theory model of Garde et al.

Comparison of Raman spectroscopic methods for the determination of supercooled and liquid water temperature

AbstractRaman spectroscopy provides an efficient method for non‐contact determination of liquid water temperature with high spatial resolution. It can be also used for remote in situ determination of subsurface water temperature. The method is based on temperature‐dependent changes of the molecular OH stretching band in the Raman spectra of liquid water. These in turn are attributed to a decrease in intermolecular hydrogen‐bonding interactions with increase in temperature. Here, the results of an experimental study employing three different approaches in the determination of temperature from recorded OH stretching band in the Raman spectra of liquid and supercooled water are presented and discussed. The first two methods are based on deconvolution of the spectral band into Gaussian components whose intensities and associated specific spectral markers are temperature dependent, and the third approach is based on Raman difference spectroscopy (RDS). The presented measurements were conducted on distilled and deionized supercooled and liquid water in the temperature range between −12.5 and +32.5 °C. The results are compared in terms of linearity of response, sensitivity and accuracy. It is shown that the method based on RDS even in the supercooled temperature range provides better accuracy (the standard deviation from the true temperature is ±0.4 K) and linearity in temperature determination than more complicated methods based on Gaussian deconvolution of the OH stretching band. Copyright © 2005 John Wiley &amp; Sons, Ltd.

2123 金属ガラスの超塑性鍛造によるマイクロインダクターの開発(S29-1 マイクロ/ナノ加工の動向と可能性(1),S29 マイクロ/ナノ加工の動向と可能性)

We designed and fabricated a micro-inductor that may be used for hybrid electric circuits such as those in a mobile phone. The component was fabricated by superplastic die-forging of Pt-based metallic glass. This material exhibits Newtonian viscous flow in the supercooled liquid temperature range between the glass transition and the crystallization point. The working temperature was 543K, so a polyimide film was selected as a die material due to its good mechanical properties at elevated temperatures and its precision machinability. The die was fabricated with an excimer laser micro-machining system using the image-projection method. Laser ablation machining was carried out using a photomask in the shape of the micro-inductor. The photomask was fabricated using a lithography system. Superplastic die-forging of the metallic glass was carried out using this die, and micro-structures of the micro-inductor were easily fabricated. These fabrication processes demonstrate the advantages of metallic glasses and superplastic microforming techniques for mass producing micro/nano machine parts or devices.