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Thermophysical properties of the Al69.1Cu12.8Ag18.1 eutectic liquid alloy are of particular interest for support of self-and inter-diffusion studies. In the presented work, Al69.1Cu12.8Ag18.1-samples were processed contactlessly by electromagnetic levitation under microgravity conditions using the TEMPUS facility. The measurements were performed onboard the Airbus A310 Zero-G in parabolic flight campaigns. The oscillating-drop-method (ODM) was used for measurements of the viscosity via oscillations damping and surface tension via oscillations frequency. These were determined for temperatures in the range of 900–1500 K by analysis of the oscillation spectrum obtained from the electrical impedance. The latter was measured using the Sample Coupling Electronics. An Arrhenius-law η(T) ∝η∞ exp(Eη /RT) was used to fit the temperature-dependent viscosity data. The resulting fit parameters were η∞ = (0.632±0.160) mPas and activation energy of viscous flow Eη = (2.344±0.233) · 104 J/mol. A linear law γ(T) = γl + γT (T - Tm) was fit to the surface tension data yielding γl = (0.9013±0.02625) Nm−1 and γT = −(0.7462±0.2675)·10−4 Nm−1 K−1. The Kozlov-model was applied to determine the enthalphy of mixing as ΔHmix = -(18.576±0.018)kJ/mol.

Force networks play an important role in the stability of configurations when granular material is packed into a container. These networks can redirect part of the weight of grains inside a container to the side walls. We employ monodisperse stress-birefringent spheres to visualize the contact forces in a quasi-2D and a nearly-2D configuration of these spheres in a thin cuboid cell. The packing structures are particularly simple: a hexagonal lattice in the ground state when the cell width is equal to the sphere diameter, and a frustrated, slightly distorted lattice in thicker cells. The force redistribution is substantially changed by this geometrical modification. In both cases, we observe an ‘inverse’ Janssen effect with the pressure decreasing from the top to the bottom of the container when the material is loaded with a weight on top of the vessel.

Journal of physics / Condensed matter 33(26), 264003 (1-12) (2021). doi:10.1088/1361-648X/abf7e1 special issue: "Intense Radiation Sources in Condensed Matter and Materials Physics", Phase formation and evolution was investigated in the CaO–SiO$_2$ system in the range of 70–80 mol% CaO. The samples were container-less processed in an aerodynamic levitation system and crystallization was followed in situ by synchrotron x-ray diffraction at the beamline P21.1 at the German electron synchrotron (DESY). Modification changes of di- and tricalcium silicate were observed and occurred at lower temperatures than under equilibrium conditions. Despite deep sample undercooling, no metastable phase formation was observed within the measurement timescale of 1 s. For the given cooling rates ranging from 300 K s$^{−1}$ to about 1 K s$^{−1}$, no decomposition of tricalcium silicate was observed. No differences in phase evolution were observed between reducing and oxidizing conditions imposed by the levitation gas (Ar and Ar + O$_2$). We demonstrate that this setup has great potential to followcrystallization in refractory oxide liquids in situ. For sub-second primary phase formation faster detection and for polymorph detection adjustments in resolution have to be implemented., Published by IOP Publ., Bristol

A new x-ray isothermal furnace has been developed, suitable for in situ observations of semi-solid processes including the transition from dendritic to globulitic grain morphology and grain coarsening in metallic samples. A homogeneous, isothermal temperature field is achieved using a novel heater concept. The furnace structure is sandwich-like with heating elements positioned in the beam line and parallel to the sample. Planar heat transfer to the sample enables measurements with low cooling rates and a minimized temperature gradient. Cooling rates from 0.1 to 15 K min-1 can be controlled in the temperature range 1170-670 K. The furnace setup is integrable in the existing rotatable laboratory x-ray facility (X-RISE) at the German Aerospace Center (DLR). In this setup, an effective pixel size of 3 mum and a field of view of 8 mm in diameter can be achieved. Preliminary solidification and semi-solid experiments in the hypo-eutectic alloy systems Al-Ge and Al-Cu, inoculated with Al-5Ti-1B grain refiner, are presented. They indicate a very uniform temperature distribution in the sample.

Abstract We discuss recent advances in developing a mode-coupling theory of the glass transition (MCT) of two-dimensional systems of active Brownian particles (ABPs). The theory describes the structural relaxation close to the active glass in terms of transient dynamical density correlation functions. We summarize the equations of motion that have been derived for the collective density-fluctuation dynamics and those for the tagged-particle motion. The latter allow to study the dynamics of both passive and active tracers in both passive and active host systems. In the limit of small wave numbers, they give rise to equations of motion describing the mean-squared displacements (MSDs) of these tracers and hence the long-time diffusion coefficients as a transport coefficient quantifying long-range tracer motion. We specifically discuss the case of a single ABP tracer in a glass-forming passive host suspension, a case that has recently been studied in experiments on colloidal Janus particles. We employ event-driven Brownian dynamics (ED-BD) computer simulations to test the ABP-MCT and find good agreement between the two for the MSD, provided that known errors in MCT already for the passive system (i.e., an overestimation of the glassiness of the system) are accounted for by an empirical mapping of packing fractions and host-system self-propulsion forces. The ED-BD simulation results also compare well to experimental data, although a peculiar non-monotonic mapping of self-propulsion velocities is required. The ABP-MCT predicts a specific self-propulsion dependence of the Stokes–Einstein relation between the long-time diffusion coefficient and the host-system viscosity that matches well the results from simulation. An application of ABP-MCT within the integration-through transients framework to calculate the density-renormalized effective swim velocity of the interacting ABP agrees qualitatively with the ED-BD simulation data at densities close to the glass transition and quantitatively for the full density range only after the mapping of packing fractions employed for the passive system. Graphic abstract

A magnetic thermostat employing soft-ferromagnetic particles and a varying magnetic field has been developed to investigate a homogeneous granular gas system in microgravity. While the thermostat’s mechanism of creating homogeneous distribution of the particles was shown earlier, its characteristics have not been understood well due to limited access to a microgravity environment. Therefore, a parametric study by numerical simulation based on the discrete element method is carried out in this paper to evaluate effects of tunable parameters in the thermostat. The result shows the capability of the system and provides a wide range of options and improvements for future experiments. Moreover, it predicts that the thermostat allows variation of homogeneity and excitation level of the granular gas just by changing the magnetic parameters without using any mechanical means. In addition, the suggested improvement is experimentally implemented and evaluated in a drop tower test.

Journal of materials science 56(13), 8225-8242 (2021). doi:10.1007/s10853-020-05748-3 special issue: "Special Section: High-Temperature Capillarity / Guest Editors: George Kaptay and Philip Nash", Published by Springer Science + Business Media B.V, Dordrecht [u.a.]

Reservoir computing is a very promising approach for the prediction of complex nonlinear dynamical systems. Besides capturing the exact short-term trajectories of nonlinear systems, it has also proved to reproduce its characteristic long-term properties very accurately. However, predictions do not always work equivalently well. It has been shown that both short- and long-term predictions vary significantly among different random realizations of the reservoir. In order to gain an understanding on when reservoir computing works best, we investigate some differential properties of the respective realization of the reservoir in a systematic way. We find that removing nodes that correspond to the largest weights in the output regression matrix reduces outliers and improves overall prediction quality. Moreover, this allows to effectively reduce the network size and, therefore, increase computational efficiency. In addition, we use a nonlinear scaling factor in the hyperbolic tangent of the activation function. This adjusts the response of the activation function to the range of values of the input variables of the nodes. As a consequence, this reduces the number of outliers significantly and increases both the short- and long-term prediction quality for the nonlinear systems investigated in this study. Our results demonstrate that a large optimization potential lies in the systematical refinement of the differential reservoir properties for a given dataset., 11 pages, 8 figures, published in Chaos

A furnace was developed and characterized to allow for safe and controlled gas-loading or degassing of alloys. This oven is able to process samples under varying atmospheres, such as high vacuum or nitrogen containing 10 vol. % deuterium, as well as for pressures up to 800 hPa. Thermal desorption spectroscopy and scanning electron microscopy demonstrate the enhancing effects of high loading-gas concentration, high pressures, high temperatures above liquidus (50-150 K above the liquidus temperature of the cast hypoeutectic aluminum-copper model-alloy), and long holding times (up to 60 min) on the amount of retained gas in the solidified sample. Lack of copper segregation in the casting is confirmed by energy dispersive x-ray diffraction and Rutherford backscattering spectroscopy. It is shown that the facility allows for the controlled generation of distinct amounts of gas pores, down to a nil amount (only shrinkage porosity appearing in the sample).

In a companion paper, we derived analytical expressions for the structure factor of the square-shoulder potential in a perturbative way around the high- and low-temperature regimes. Here, various physical properties of these solutions are derived. In particular, we investigate the large wave number sector, and relate it to the contact values of the pair-correlation function. Then, thermoelastic properties of the square-shoulder fluids are discussed., 25 pages , 16 figures

The European Astronaut Centre (EAC) is currently constructing the European Lunar Exploration Laboratory (LUNA), a large training and operations facility to be located adjacent to EAC at the DLR (German Aerospace Centre) campus in Cologne, Germany. With an estimated representative lunar testbed area of approximately 660 m2, a large volume of lunar regolith simulant material is needed for this purpose. In this study, a basanitic sandy silt from a quarry located in the Siebengebirge Volcanic Field is evaluated as a large-volume source of material. The focus of this project has been to conduct a physical and chemical characterisation of the fine-grained material to be used in LUNA; the European Astronaut Centre lunar regolith simulant 1 (EAC-1 A). The physical characterisation tests undertaken include sphericity, density measurements, cohesion and static angle of repose, with mineralogical investigations via petrographical analysis with optical microscope and SEM, XRF, XRD and DSC measurements. The results of the EAC-1A tests are compared to published data on existing widely used lunar regolith simulants, namely JSC-1A, JSC-2A, NU-LHT-3M, DNA and FJS-1.

We present numerical evidence for an additional discontinuous transition inside the jammed regime for an asymmetric bidisperse granular packing upon compression. This additional transition line separates jammed states with networks of predominantly large particles from jammed networks formed by both large and small particles, and the transition is indicated by a discontinuity in the number of particles contributing to the jammed network. The additional transition line emerges from the curves of jamming transitions and terminates in an end-point where the discontinuity vanishes. The additional line is starting at a size ratio around $\delta = 0.22$ and grows longer for smaller $\delta$. For $\delta \to 0$, the additional transition line approaches a limit that can be derived analytically. The observed jamming scenarios are reminiscent of glass-glass transitions found in colloidal glasses., Comment: 4 pages, 3 figures

In contrast to molecular gases, granular gases are characterized by inelastic collisions and require therefore permanent driving to maintain a constant kinetic energy. The kinetic theory of granular gases describes how the average velocity of the particles decreases after the driving is shut off. Moreover it predicts that the rescaled particle velocity distribution will approach a stationary state with overpopulated high-velocity tails as compared to the Maxwell-Boltzmann distribution. While this fundamental theoretical result was reproduced by numerical simulations, an experimental confirmation is still missing. Using a microgravity experiment which allows the spatially homogeneous excitation of spheres via magnetic fields, we confirm the theoretically predicted exponential decay of the tails of the velocity distribution., Comment: 11 pages, 14 figures

Colloidal hard-sphere suspensions are convenient experimental models to understand soft matter, and also by analogy the structural-relaxation behavior of atomic or small-molecular fluids. We discuss this analogy for the flow and deformation behavior close to the glass transition. Based on a mapping of temperature to effective hard-sphere packing, the stress–strain curves of typical bulk metallic glass formers can be quantitatively compared with those of hard-sphere suspensions. Experiments on colloids give access to the microscopic structure under deformation on a single-particle level, providing insight into the yielding mechanisms that are likely also relevant for metallic glasses. We discuss the influence of higher-order angular signals in connection with non-affine particle rearrangements close to yielding. The results are qualitatively explained on the basis of the mode-coupling theory. We further illustrate the analogy of pre-strain dependence of the linear-elastic moduli using data on PS-PNiPAM suspensions.

Temperature gradients can change the concentration distribution in multicomponent materials. This cross-coupling effect of heat and mass transfer is difficult to measure in liquid alloys. We present a new method using x-ray radiography in combination with a high temperature furnace to measure thermodiffusion in melts time and space resolved. This greatly improves the process control and allows us to determine diffusion and thermodiffusion simultaneously. In a first experiment we demonstrate that in liquid Al_{78.5}Ni_{21.5} the component nickel diffuses to the cold end of the sample with a Soret coefficient on the order of 10^{-3} K^{-1}.

We investigate the spatial structure of dense square-shoulder fluids. To this end we derive analytical perturbative solutions of the Ornstein-Zernike equation in the low- and high-temperature limits as expansions around the known hard sphere solutions. We then discuss the suitability of perturbative approaches in relation to the Ornstein-Zernike equation., 17 pages, 2 figures

Although a resistivity saturation (minimum conductivity) is often observed in disordered metallic solids, such phenomena in the corresponding liquids are not known. Here we report a saturation of the electrical resistivity in ${\mathrm{Zr}}_{64}{\mathrm{Ni}}_{36}$ and ${\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$ liquids above a dynamical crossover temperature for the viscosity (${T}_{A}$). The measurements were made for the levitated liquids under the microgravity conditions of the International Space Station. Based on recent molecular dynamics simulations, the saturation is likely due to the ineffectiveness of electron-phonon scattering above ${T}_{A}$ when the phonon lifetime becomes too short compared to the electron relaxation time. This is different from the conventional resistivity saturation mechanisms in solids.

Metallische Latetnwärmespeicher sind ein vielversprechender Ansatz, den Reichweitenverlust aufgrund der Innenraumheizung von batterieelektrischen PKW und Bus abzuschwächen oder zu verhindern. Im Rahmen eines Vortrags an der HS Karlsruhe wurde eine Übersicht zum Thema gegeben sowie erste Ergebnisse aus dem Projekt "THS-Bus" vorgestellt.

Al-Ti-based alloys are of enormous technical relevance due to their specific properties. For studies in atomic dynamics, surface physics and industrial processing the precise knowledge of the thermophysical properties of the liquid phase is crucial. In the present work, we systematically measure mass density, ρ (g cm−3), and the surface tension, γ (N m−1), as functions of temperature, T, and compositions of binary Al-Ti melts. Electromagnetic levitation in combination with the optical dilatometry method is used for density measurements and the oscillating drop method for surface tension measurements. It is found that, for all compositions, density and surface tension increase linearly upon decreasing temperature in the liquid phase. Within the Al-Ti system, we find the largest values for pure titanium and the smallest for pure aluminum, which amount to ρ(L,Ti) = 4.12 ± 0.04 g cm−3 and γ(L,Ti) = 1.56 ± 0.02 N m−1; and ρ(L,Al) = 2.09 ± 0.01 g cm−3 and γ(L,Al) = 0.87 ± 0.06 N m−1, respectively. The data are analyzed concerning the temperature coefficients, ρ T and γ T, excess molar volume, V E, excess surface tension, γ E, and surface segregation of the surface active component, Al. The results are compared with thermodynamic models. Generally, it is found that Al-Ti is a highly nonideal system.

Many natural and industrial processes rely on constrained transport, such as proteins moving through cells, particles confined in nanocomposite materials or gels, individuals in highly dense collectives and vehicular traffic conditions. These are examples of motion through crowded environments, in which the host matrix may retain some glass-like dynamics. Here we investigate constrained transport in a colloidal model system, in which dilute small spheres move in a slowly rearranging, glassy matrix of large spheres. Using confocal differential dynamic microscopy and simulations, here we discover a critical size asymmetry, at which anomalous collective transport of the small particles appears, manifested as a logarithmic decay of the density autocorrelation functions. We demonstrate that the matrix mobility is central for the observed anomalous behaviour. These results, crucially depending on size-induced dynamic asymmetry, are of relevance for a wide range of phenomena ranging from glassy systems to cell biology., The classical Lorentz gas model is widely used to describe constrained transport, but its assumption of an immobile environment is not applicable to many biological and industrial processes. Here, the authors show that the mobility of the matrix induces anomalous, logarithmic dynamics of the confined particles.

Die Konzeptionierung von neuen Experimenten für die Verwendung auf der Internationalen Raumstation erfordert spezielle Belastungsanalysen der verwendeten Komponenten. Neben der Auslegung in Bezug auf die Verwendung in Schwerelosigkeit und den besonderen Anforderungen des Experimentes selbst, sind diese äußert wichtig um die Experimente auf ihre Beständigkeit während des Transportes zur ISS zu überprüfen. Die Arbeitsgruppe Komplexe Plasmen des Deutschen Zentrums für Luft- und Raumfahrt entwickelt zum Zeitpunkt dieser Arbeit das Ekoplasma Labor, welches der Nachfolger von PK-4 wird. Das Kernstück des Labors ist die Zyflexkammer, in welcher es möglich ist, komplexes Plasma zu erzeugen und in Schwerelosigkeit zu untersuchen. Die vorliegende Bachelorarbeit beschäftigt sich mit der Analyse des in der Zyflexkammer verbauten Antriebs- und Getriebesystems, im weiteren Verlauf als Motionsystem bezeichnet, hinsichtlich dessen Realisierbarkeit, Funktionalität und Belastbarkeit. Es werden Versuche definiert, die die dynamischen Belastungen während des Raketenstarts und Orbitalflugs zu simulieren und es ermöglichen zu überprüfen, ob das Motionsystem auch nach den Belastungen noch funktionstüchtig ist.

A new device for the inductive measurement of electrical resistivity and density of liquid metals and semiconductors is presented. It is integrated in two electromagnetic levitation facilities operating under microgravity. As a result, the completely noninvasive handling and measuring of the metallic melt enables the extension of the accessible sample temperature range far into the undercooled liquid state below the melting point. The microgravity environment permits the undisturbed joining of the containerless inductive sample handling method by the electromagnetic levitation with the inductive sample measurement technique. The following sections explain in detail the basic principles and the technical realization of the whole measurement apparatus and present experimental data showing its high resolution resulting from the combination of microgravity, electromagnetic levitation, and inductive measurement technique.

We review recent progress on a microscopic theoretical approach to describe the nonlinear response of glass-forming colloidal dispersions under strong external forcing leading to homogeneous and inhomogeneous flow. Using mode-coupling theory (MCT), constitutive equations for the rheology of viscoelastic shear-thinning fluids are obtained. These are, in suitably simplified form, employed in continuum fluid dynamics, solved by a hybrid-Lattice Boltzmann (LB) algorithm that was developed to deal with long-lasting memory effects. The combined microscopic theoretical and mesoscopic numerical approach captures a number of phenomena far from equilibrium, including the yielding of metastable states, process-dependent mechanical properties, and inhomogeneous pressure-driven channel flow. published

We study collective modes in a classical system of particles with repulsive inverse-power-law (IPL) interactions in the fluid phase, near the fluid-solid coexistence (IPL melts). The IPL exponent is varied from $n=10$ to $n=100$ to mimic the transition from moderately soft to hard-sphere-like interactions. We compare the longitudinal dispersion relations obtained using molecular dynamic (MD) simulations with those calculated using the quasi-crystalline approximation (QCA) and find that this simple theoretical approach becomes grossly inaccurate for $n\gtrsim 20$. Similarly, conventional expressions for high-frequency (instantaneous) elastic moduli, predicting their divergence as $n$ increases, are meaningless in this regime. Relations of the longitudinal and transverse elastic velocities of the QCA model to the adiabatic sound velocity, measured in MD simulations, are discussed for the regime where QCA is applicable. Two potentially useful freezing indicators for classical particle systems with steep repulsive interactions are discussed., Full text access to the paper using the link: http://rdcu.be/uVRO

Turbulence is one of the last unresolved issues of modern theoretical physics. In conventional experiments on turbulence, the carriers of the interaction are not directly observable. Instead, typically tracer particles are used - a method that might not produce reliable results [1]. Here, we present an experiment performed in the PK-3 Plus Laboratory on board the International Space Station [2] which allows investigating the fundamental particles in turbulence directly. First, the complex plasma cloud was stabilized with an alternating electric field. Once the stabilization was switched off, a heartbeat instability developed, and the microparticles started oscillating radially. We show that the kinetic energy spectra develop a double cascade once the cloud becomes unstable, see Figure 1. This double cascade has been predicted by Kraichnan [3] and Leith [4] for forced two-dimensional turbulence, but has only seldomly been observed in experiments [5]. We also show that the reduced rates of energy and enstrophy transfer can be used to infer the excitation wave number kexc, in good agreement with kexc obtained from the energy spectrum. [1] V. Mathai et al. Phys. Rev. Lett. 117, 024501 (2016). [2] H. M. Thomas et al. New J. Phys. 10, 033036 (2008). [3] R. H. Kraichnan. Phys. Fluids 10, 1417 (1967). [4] C. E. Leith. Phys. Fluids 11, 671 (1968). [5] G. Boffetta and R. E. Ecke. Ann. Rev. Fluid Mech. 44, 427{451 (2012)

The PK-3 Plus laboratory [1, 2] on board the International Space Station is used to study the interaction between metallic spheres and a complex plasma. We show that the spheres significantly affect both the local plasma environment and the microparticles. The spheres charge under the influence of the plasma and repel the microparticles, forming cavities surrounding the spheres. At intermediate distances from the sphere surface, however, the interaction between the microparticles and the spheres is attractive. The spheres affect the plasma fluxes, which can lead to the excitation of dust-acoustic waves near the spheres.

International audience; The Gruneisen parameter is evaluated for three-dimensional Yukawa systems in the strongly coupled regime. A simple analytical expression is derived from the thermodynamic consideration and its structure is analysed in detail. Possible applications are briefly discussed. Published by AIP Publishing.

Thermodynamics of two-dimensional Yukawa (screened Coulomb or Debye-H\"uckel) systems is studied systematically using molecular dynamics (MD) simulations. Simulations cover very broad parameter range spanning from weakly coupled gaseous states to strongly coupled fluid and crystalline states. Important thermodynamic quantities such as internal energy and pressure are obtained and accurate physically motivated fits are proposed. This allows us to put forward simple practical expressions to describe thermodynamic properties of two-dimensional Yukawa systems. For crystals, in addition to numerical simulations, the recently developed shortest-graph interpolation method is applied to describe pair correlations and hence thermodynamic properties. It is shown that the finite-temperature effects can be accounted for by using simple correction of peaks in the pair correlation function. The corresponding correction coefficients are evaluated using MD simulation. The relevance of the obtained results in the context of colloidal systems, complex (dusty) plasmas, ions absorbed to interfaces in electrolytes is pointed out., Comment: 11 pages, 3 figures, 5 tables

We study a complex plasma under microgravity conditions that is first stabilized with an oscillating electric field. Once the stabilization is stopped, the so-called heartbeat instability develops. We study how the kinetic energy spectrum changes during and after the onset of the instability and compare with the double cascade predicted by Kraichnan and Leith for two-dimensional turbulence. The onset of the instability manifests clearly in the ratio of the reduced rates of cascade of energy and enstrophy and in the power-law exponents of the energy spectra., 7 pages, 7 figures

International audience; In this paper, we discuss the relations between the exact shape of interparticle interactions in complex (dusty) plasmas and the dispersion relation of the longitudinal collective mode. Several representative repulsive potentials, predicted previously theoretically, are chosen, and the corresponding dispersion relations are calculated using the quasi-crystalline approximation. Both weakly coupled and strongly coupled regimes are considered. It is shown that the long-wavelength portions of the dispersion curves can be sensitive to the long-range asymptote of the interaction potential. This can be used to discriminate between different interaction mechanisms operational in complex plasmas experimentally. Main requirements are briefly discussed. Published by AIP Publishing.

Granular materials are complex multi-particle ensembles in which macroscopic properties are largely determined by inter-particle interactions between their numerous constituents. In order to understand and to predict their macroscopic physical behavior, it is necessary to analyze the composition and interactions at the level of individual contacts and grains. To do so requires the ability to image individual particles and their local configurations to high precision. A variety of competing and complementary imaging techniques have been developed for that task. In this introductory paper accompanying the Focus Issue, we provide an overview of these imaging methods and discuss their advantages and drawbacks, as well as their limits of application., Comment: Submitted to Review of Scientific Instruments as introduction for: Focus on Imaging Methods in Granular Physics

The goal of this work was to investigate intra-alloy relationships, as they pertain to rapid solidification, which can be applied to computational materials modeling. Those relationships can be utilized to improve the accuracy of predictive modeling by leveraging previous experimental results. With that in mind, Fe–Co samples were prepared with 30–50 at.% cobalt and they were processed via electrostatic levitation (ESL) or electromagnetic levitation (EML). The samples were levitated, melted, and allowed to cool and solidify in a vacuum for ESL testing and under He gas for EML testing. If sufficient undercooling was achieved, the sample solidified via double recalescence. In that event, the metastable δ–phase would grow into the undercooled liquid, and then the stable γ–phase would grow into a combination of the metastable phase and remaining undercooled liquid, or mushy zone. The velocities of the solid phases growing into undercooled liquid were analyzed with current dendrite growth theories. The purpose of the growth velocity analyses was two-fold: 1) Assess the validity of current dendrite theory as it applies to the Fe–Co system. 2) Evaluate the kinetic growth coefficient, μ, assuming a constant kinetic rate parameter, Vo. The results of the analyses indicate that it is reasonable to assume that the kinetic rate parameter, Vo, is constant for a given phase within an alloy system if Δ H f / T m 2 does not vary significantly within the system, or within the composition range of interest. The average growth velocities of the stable phase into the mushy zone, V ¯ γ δ , for the Fe–30, 40, and 50 at.% Co compositions are 1.6, 2.4, and 4.9 m/s, respectively, which scale with the thermal driving forces of the transformations, ΔTγδ, which are 10 K, 24 K, and 40 K, respectively.

Complex microscopic many-body processes are often interpreted in terms of so-called "reaction coordinates," i.e., in terms of the evolution of a small set of coarse-grained observables. A rigorous method to produce the equation of motion of such observables is to use projection operator techniques, which split the dynamics of the observables into a main contribution and a marginal one. The basis of any derivation in this framework is the classical Heisenberg equation for an observable. If the Hamiltonian of the underlying microscopic dynamics and the observable under study do not explicitly depend on time, this equation is obtained by a straightforward derivation. However, the problem is more complicated if one considers Hamiltonians which depend on time explicitly as, e.g., in systems under external driving, or if the observable of interest has an explicit dependence on time. We use an analogy to fluid dynamics to derive the classical Heisenberg picture and then apply a projection operator formalism to derive the nonstationary generalized Langevin equation for a coarse-grained variable. We show, in particular, that the results presented for time-independent Hamiltonians and observables in the study by Meyer, Voigtmann, and Schilling, J. Chem. Phys. 147, 214110 (2017) can be generalized to the time-dependent case.

Die Menge von an einer Oberfläche adsorbiertem Wasser in einer Atmosphäre mit 100% relativer Luftfeuchtigkeit kann um ein vielfaches gesteigert werden, wenn die Oberfläche durch wiederholte Zyklen von Adsorption und Desorption von Wasser vorbehandelt wird. Dies wurde beobachtet an Oberflächen aus Diamant, Titandioxid und Siliziumdioxid bei Temperaturen um 22°C. Mit einer hinreichenden Anzahl dieser Zyklen wird eine schnellere und stärkere Adsorption von Wassermolekülen erreicht, verglichen mit unbehandelten Oberflächen. Dies bedeutet auch einen erhöhten Energieaustausch zwischen der Atmosphäre und der Oberfläche. Durch die Vorbehandlung wurde die Menge des adsorbierten Wassers um mehr als das dreifache erhöht. Der beobachtete Effekt wird erklärt durch eine kleine Menge besonders angeordneter Wassermoleküle, die nach dem Desorptionsprozeß an der Oberfläche verbleibt und die Adsorption von Wasser unterstützen. Der beobachtete Effekt kann dazu genutzt werden die Oberflächen kleiner Partikel sehr wirksam über die Gasphase zu befeuchten.

The processing of semiconductors based on electromagnetic levitation is a challenge, because this kind of materials shows a poor electrical conductivity. Here, we report the results of measurements of the thermophysical properties obtained recently from highly doped semiconductors Si1−xGex under microgravity conditions in the framework of parabola flight campaigns. Due to the limited time of about 20 s of microgravity especially Ge-rich samples with low melting temperatures were investigated. The measurements were performed contactlessly by video techniques with subsequent digital image processing. Linear and volume thermal expansion coefficients were measured hereby from image data. An anomaly of volume changes near the solidus temperature is visible. Viscosity and surface tension were determined by the oscillating drop technique using optic and electronic data. It was observed that the alloying of Si into Ge increases the surface tension of the melts. The viscosity is following an Arrhenius equation and shows a crossover temperature which separates simple liquid at high temperatures from cooperative liquid at low temperatures., Electronic materials: Achieving a better mix Low-gravity environments help to produce a semiconducting alloy with great promise for electronics, shows researchers from Germany. Yuansu Luo from the Georg-August-Universität and co-workers measure the thermal properties of molten silicon–germanium during parabolic flights. Silicon is the dominant material in the electronic industry. Adding germanium, however, creates a semiconductor with even more useful properties. Producing high-quality crystals of this alloy is challenging because gravity separates the two elements when in liquid form. A low-gravity environment could help, but more must be known about the properties of silicon–germanium under such conditions. Luo et al. processed a silicon–germanium melt in an electromagnetic levitation facility in microgravity conditions, analyzed video images to determine its thermal expansion, viscosity, and surface tension and observed an alloying effect and a crossover phenomenon. The results pave the way for more detailed investigations on the International Space Station.

Electromagnetic levitation melting is a containerless processing technique for liquid metals requiring non-contact diagnostic tools. In order to properly perform such experiments, a precise knowledge of the temperaturetime behaviour of the metal sample resulting from the heat Balance between its heating and cooling during the processing is a prerequisite. In two preceding papers we provided the necessary theoretical Background for the inductive heat input by the high frequency magnetic levitation field and the heat loss due to radiation and heat conduction through a surrounding process gas atmosphere and defined the set of experiments needed for obtaining the key parameters of the thermal model. In the present paper we extend the previous work by investigating experimentally the influence of the sample cooling by forced gas convection at high Péclet number in a surrounding Argon gas atmosphere at hand of tests under microgravity.

Die Methode der elektromagnetischen Levitation wurde zum behälterfreien Unterkühlen und Erstarren von reinem Eisen und Eisen-Bor-Legierungen unterschiedlicher Konzentrationen (dendritisches und eutektisches Wachstum) verwendet. Experimente wurden unter verschiedenen konvektiven Bedingungen im Erdlabor, unter reduzierter Schwerkraft bei Parabelflugmissionen, sowie in starken Magnetfeldern durchgeführt, um die Wachstumsgeschwindigkeiten als Funktion der Unterkühlung zu messen. Dabei wurde die Propagation der Erstarrungsfront in situ mit einer Hochgeschwindigkeitskamera beobachtet und erstmals auch unter Verwendung einer Infrarotkamera. Nicht nur die Wachstumskinetik, sondern auch die Morphologie unterliegt dem Einfluss der Konvektion und es konnten erstmals "gebogen" wachsende Dendriten in situ an schwebenden Metallschmelzen beobachtet werden. Zur Analyse der Messdaten wurde ein "Sharp Interface Model" verwendet, mit dem die Messergebnisse quantitativ reproduziert werden konnten.

The relation of self- and interdiffusion in a liquid metal, particularly the influence of cross correlations at low concentrations, is studied experimentally. Accurate interdiffusion data are obtained by a combination of x-ray radiography with the shear-cell method on the ground and on the sounding rocket MAPHEUS under microgravity conditions. Self-diffusion coefficients, measured by quasielastic neutron scattering, increase with decreasing Ni concentration, whereas interdiffusion coefficients are about constant. We show that cross correlations influence interdiffusion even at concentrations as low as 2 at. % Ni. Consequently, Darken's equation is not valid in this case.

We use incoherent quasielastic neutron scattering to study the atomic dynamics of gold in a eutectic Au81Si19 melt. Despite the glass-forming nature of this system, the gold self-diffusivity displays an Arrhenius behavior with a low activation energy characteristic of simple liquids. At high temperatures, long-range transport of gold atoms is well described by hydrodynamic theory with a simple exponential decay of the self-correlation function. On cooling towards the melting temperature, structural relaxation crosses over to a highly stretched exponential behavior. This suggests the onset of a heterogeneous dynamics, even in the equilibrium melt, and is indicative of a very fragile liquid.

Using high energy synchrotron x-ray radiation combined with electrostatic levitation, in situ structural analysis of a bulk metallic glass forming liquid is performed from above the liquidus temperature down to the glass transition. The data indicate a liquid-liquid transition (LLT) in the deeply undercooled state at T/Tg∼1.2 which manifests as a maximum in the heat capacity and an abrupt shift in the first peak position of the total structure factor in the absence of a pronounced density change. Analysis of the corresponding real-space data shows that the LLT involves changes in short- and medium-range order. The structural changes on the length scale of medium-range order imply a fragile-strong transition in agreement with experimental viscosity data.

A system consisting of a high-temperature yttrium-stabilized zirconia (YSZ) based oxygen ion pump and potentiometric sensor enables precise measurement and control of oxygen partial pressure, pO2, at elevated temperatures within 0.2 to 10^-20 bar.

Results of a thermophysical characterization of a Fe-Cr-Mo alloy in the solid and liquid phases are reported. Methods applied include calorimetry, dilatometry; the laser flash technique for thermal diffusivity measurement and ultrasound pulse echo for the measurement of the room temperature sound velocities and elastic constants. Density in the liquid phase and surface tension were measured by optical dilatometry and by the oscillating drop method on electromagnetic levitated specimen. In addition, surface tension and viscosity were measured by the oscillating drop method on board parabolic flights under reduced gravity conditions. The methods applied and results obtained are presented. This work represents a collaborative effort, including round robin measurements in different laboratories for a characterization of the basic thermophysical properties needed for process simulation.

Surface tension data of liquid Al–Cu binary alloys have been measured contactlessly using the technique of electromagnetic levitation. A digital CMOS-camera (400 fps) recorded image sequences of the oscillating liquid sample and surface tensions were determined from analysis of the frequency spectra. Measurements were performed for samples covering the entire range of composition and precise data were obtained in a broad temperature range. It was found that the surface tensions can be described as linear functions of temperature with a negative slope. Moreover, they monotonically decrease with an increase in the aluminium concentration. The observed behaviour with respect to both temperature and concentration is in agreement with thermodynamic model calculations using the subregular solution approximation.

Electromagnetic levitation melting is a containerless processing technique for liquid metals requiring non-contact diagnostic tools. In order to properly perform such experiments, a precise knowledge of the temperature-time behaviour of the metal sample resulting from the heat balance between its heating and cooling during the processing is a prerequisite. In two preceding papers we provided the necessary theoretical background for the inductive heat input by the high frequency magnetic levitation field and the heat loss due to radiation and heat conduction through a surrounding process gas atmosphere and defined the set of experiments needed for obtaining the key parameters of the thermal model. In the present paper we extend the previous work by investigating theoretically and, at hand of further tests under microgravity, experimentally the influence of the sample cooling by forced gas convection at low Péclet number in a surrounding Helium atmosphere.

By means of benchmarking reduced gravity experiments, we have verified the measured viscosity of binary Zr-Ni glass forming liquids utilizing the oscillating drop technique combined with ground-based electrostatic levitation (ESL). Reliable viscosity data can be obtained as long as internal viscous damping of a single oscillation mode of a levitated drop dominates external perturbations. This can be verified by the absence of a sample mass dependence of the results. Hence, ESL is an excellent tool for studying the viscosity of metallic glass forming melts in the range of about 10–250 mPa s, with sample masses below 100 mg. To this end, we show that, for binary Zr-Ni melts, the viscosity is qualitatively controlled by the packing density.

International audience; The collective modes of a familiar two-dimensional one-component-plasma with the repulsive logarithmic interaction between the particles are analysed using the quasi-crystalline approximation (QCA) combined with the molecular dynamic simulation of the equilibrium structural properties. It is found that the dispersion curves in the strongly coupled regime are virtually independent of the coupling strength. Arguments based on the excluded volume consideration for the radial distribution function allow us to derive very simple expressions for the dispersion relations, which show excellent agreement with the exact QCA dispersion over the entire domain of wavelengths. Comparison with the results of the conventional fluid analysis is performed, and the difference is explained. Published by AIP Publishing.

In this paper we present the synthesis and properties of ultra-light and porous cellulose aerogels in different forms: monoliths and fine spun fibers. The cellulose aerogel monoliths and fibers are prepared by dissolving microcrystalline cellulose (0.5-6 wt. %) in a hydrated calciumthiocyanate salt melt-Ca(SCN)2.4H2O at 110oC upon cooling the solution gels around 80°C. Washing the wet gels and regeneration of the cellulose in an ethanol bath followed by drying in an autoclave yields aerogels. The envelope densities of the samples were determined as in the range between 10-140 g/L. The microstructure was viewed with a SEM. The microstructure can be described as an open porous nano-felt with pore size ranging from 10 to 100 nm and fiber diameters of around 10-20 nm. The specific surface area and pore size distribution with nitrogen adsorption were measured with a surface area of 150-230 m2/g. Furthermore compression tests were performed. The mechanical behavior is typical for a porous material: after onset of deformation there is a long plateau at almost constant stress. The aerogels exhibit a Poisson ratio of around zero

The available experimental data for the density and viscosity of liquid cadmium, cobalt, gallium, indium, mercury, silicon, thallium, and zinc have been critically examined with the intention of establishing both a density and a viscosity standard. All experimental data have been categorized into primary and secondary data according to the quality of measurement, the technique employed and the presentation of the data, as specified by a series of criteria. The proposed standard reference correlations for the density of liquid cadmium, cobalt, gallium, indium, silicon, thallium, and zinc are characterized by percent deviations at the 95% confidence level of 0.6, 2.1, 0.4, 0.5, 2.2, 0.9, and 0.7, respectively. In the case of mercury, since density reference values already exist, no further work was carried out. The standard reference correlations for the viscosity of liquid cadmium, cobalt, gallium, indium, mercury, silicon, thallium, and zinc are characterized by percent deviations at the 95% confidence level of 9.4, 14.0, 13.5, 2.1, 7.3, 15.7, 5.1, and 9.3, respectively.