Structure and Thermophysical Properties of Molten BaGe Using Electrostatic Levitation Technique

BaGe alloys with two compositions near their eutectic point form open framework structures called the clathrate structure. These BaGe compounds with the clathrate structure can be made by rapid solidification from their liquid state. However, the formation mechanism of the clathrate structure has not been clarified due to lack of information on their liquid-state structure and properties. Since BaGe alloy melts have very high reactivity, it is difficult to measure the thermophysical properties of them by ordinary methods using a container. Therefore, a containerless technique must be used to measure the thermophysical properties of BaGe melts. Using the electrostatic levitation (ESL) technique as a containerless technique, the thermophysical properties (density, surface tension, and viscosity) of BaGe melts around the eutectic composition were measured in order to clarify the formation mechanism of the clathrate structure, and also the structure of them was observed by using the high-energy X-ray diffraction method combined with ESL. From experimental results, it was observed that the short-range order based on the clathrate structure exists even in the liquid state at the clathrate-forming compositions.     

Measurement of Density and Structural Short-Range Order of Levitated Liquid Metals

The determination of thermophysical properties and structure of undercooled metallic melts must be accomplished by contactless methods due to the high reactivity of the material. It has been shown that electromagnetic levitation provides high-purity conditions to allow deep undercooling. The density and thermal expansion of a levitated drop can be derived from volume measurements using a charge-coupled device (CCD) camera and a digital image processing system. Combining levitation with extended x-ray absorption fine structure (EXAFS) spectroscopy leads to the possibility of studying the local structure of the liquid in a wide temperature range including the deeply undercooled regime.     

Viscosity,thermal conductivity,and surface tension of high-temperature melts

High-temperature melts are substances which are solids at room temperature and liquids at high temperatures. They include liquid metals, molten salts, and other melts such as molten semiconductor materials. Although they show scientifically interesting behavior and have industrially important characteristics, the thermophysical properties of these substances at high temperature are not sufficiently known due to experimental difficulties. Many melts show strong chemical activity and therefore are corrosive to materials of container and sensors. Applicable sensors are limited also because of the high temperature and the electrical conductivity of melts. In this paper the present status of available data for the viscosity, the thermal conductivity, and the surface tension of high-temperature melts is reviewed. Limited experimental information is available and these properties are difficult to predict theoretically. The transport properties are important for predicting heat transfer and flow patterns. For the prediction of the behavior of melts under microgravity condition, the temperature dependence of the surface tension plays a major role.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Electrostatic Levitation Research and Development at JAXA: Past and Present Activities in Thermophysics

This paper reviews the past and present research and development activities in the field of electrostatic levitation at the Japan Aerospace Exploration Agency (JAXA). Particular emphasis is given on the important innovations of sub-millimeter sample handling, launch levitation initiation, aero-electrostatic hybrid levitation, multi-beam heating geometry, electrode design, and ultraviolet (UV) imaging. A summary of the thermophysical properties of refractory materials measured in their liquid states, above and below their melting point, as well as preliminary results of samples solidified from deep supercooled states are also reported. Paper presented at the Seventh International Workshop on Subsecond Thermophysics, October 6–8, 2004, Orléans, France.     

Ground-based thermophysical property measurements of supercooled and liquid platinum-group metals by electrostatic levitation

In this study, thermophysical properties of several metals of the platinum group (Pd, Rh, Ru, Ir) were found using the unique capabilities (sample stability, imaging) of a vacuum electrostatic levitation furnace developed by the Japan Aerospace Exploration Agency. Over temperature ranges covering the liquid and the supercooled phases, the density was measured and the isobaric heat capacity was estimated. The enthalpy and the entropy of fusion were also calculated.     

Speed of Sound and Some Thermodynamic Properties of Liquid Methylcyclopentane and Butylcyclohexane in a Wide Range of Pressure

Ultrasonic velocity measurements were performed on liquid methylcyclopentane and butylcyclohexane at pressures from atmospheric up to 150 MPa in the temperature range from 293 to 373 K using a pulse echo technique operating at 3 MHz. The data were used to evaluate various thermophysical properties such as density, and isentropic and isothermal compressibilities up to 150 MPa with the help of additional density measurements.     

Microsecond Laser Polarimetry for Emissivity Measurements on Liquid Metals at High Temperatures—Application to Tantalum

The aim of this work was to determine accurate and reliable thermophysical properties of liquid tantalum from melting up to temperatures of 5000 K. Temperature measurements on pulse-heated liquid metal samples reported by different authors have always been performed under the assumption of a constant emissivity over the whole liquid range because of the lack of data for liquid metals. The uncertainty in temperature measurement is reduced in this work by the direct measurement of emissivity during the experiments. The emissivity measurements are performed by linking a laser polarimetry technique with the established method for performing high speed measurements on liquid tantalum samples at high temperatures during microsecond pulse-heating experiments. A set of improved thermophysical properties for liquid tantalum, such as temperature dependences of normal spectral emissivity at 684.5 nm, heat capacity, enthalpy, electrical resistivity, thermal diffusivity, and thermal conductivity, was obtained.     

基于气动悬浮激光加热技术YAG熔体高温热物理性能评测

钇铝石榴石Y₃Al₅O₁₂(Yttrium Aluminum Garnet, 简记为YAG)材料具有优异的光、热和电学性能, 引起了广泛关注。但高熔点和冷却过程中复杂的相选择机制, 使YAG熔体特别是熔点以下过冷区内的热物理性能参数获得困难。利用自主搭建的气动悬浮无容器激光加热装置, 基于受迫振动和光学描影等原理, 在1750~2650 K宽达900 K的温区内, 评测了YAG熔体的黏度、表面张力和密度。研究表明, 与Al₂O₃熔体相比, YAG熔体密度具有更高的温度敏感性, 具有高约1倍的平均线膨胀系数; 不同于表面张力随温度变化不敏感的Al₂O₃熔体, YAG熔体的表面张力随温度升高产生略微降低; 与Al₂O₃熔体的黏温关系相比, 在熔点以下的过冷区内发现YAG熔体具有更陡峭的黏温变化趋势。     

Temperature dependence of viscosity and density of the melts of quasibinary systems formed by copper chalcogenides

The temperature and concentration dependence of the kinematic viscosity and density of melts of quasi-binary systems formed of copper chalcogenides is investigated. The temperature dependence of the investigated properties is analyzed on the basis of the activated complex theory and of the fundamental equation of A.I. Bachinskii. It is shown that the postmelting effect is observed in all of the investigated melts, which is associated with the structural changes occurring on heating the melts. These changes consist in the transformation of a structurally inhomogeneous liquid into a homogeneous Newtonian liquid due to the thermal decay of clusters. It is also shown that the concentration dependence of viscosity exhibits a smooth behavior, and that of density exhibits a strictly additive behavior, which favors intermolecular interaction. The notions of this interaction follow from the treatment of the diagrams of state of appropriate quasi-binary systems and thermodynamic analysis.     

Pressure Dependence of the Thermophysical Properties of n-Pentadecane and n-Heptadecane

The speed of sound in liquid n-pentadecane and n-heptadecane was measured using a pulse technique operating at 3 MHz. The measurements were carried out at pressures up to 150 MPa in the temperature range from 293 to 383 K. The experimental results have been used to evaluate various thermophysical properties such as density and isentropic and isothermal compressibilities up to 150 MPa with the help of additional density and heat capacity data at atmospheric pressure.     

Top loading cryogen-free apparatus for low temperature thermophysical properties measurement

The thermophysical properties of matter, especially properties at low temperature, are extremely important for engineering and materials science. Traditional liquid helium based cryostats are in many cases no longer affordable to operate due to the high liquid helium cost. This paper describes the design and test results of a cryogen-free cryostat, based on a GM cryocooler, with 50 mm diameter top loading sample facilities for thermophysical properties measurement at low temperature. The sample temperature range is tuned between 2.6 K and 300 K and it can be continuously controlled with a high resolution. Moreover, the modular sample holder can be adapted to multiple properties measurement.     

Thermophysical Properties of W–Re Alloys Above the Melting Region

In earlier experiments we have studied pure elements with a fast pulse heating technique to obtain thermophysical properties of the liquid state. We report here results for thermophysical properties such as specific heat and dependences among enthalpy, electrical resistivity, and temperature, for four W–Re alloys (3.95, 21.03, 23.84, and 30.82 at % of Re) in a wide temperature range covering solid and liquid states. Thermal conductivity is calculated using the Wiedemann–Franz law for the liquid alloy, as.well as data for thermal diffusivity for the beginning of the liquid phase. Additionally, data for the entire temperature range studied have been analyzed in comparison with those of the constituent elements, tungsten and rhenium, since both metals have been studied previously with the same experimental technique. Such information is of interest in the field of metallurgy since W–Re alloys of low Re content in the region of mutual component solubility in the solid state are widely used as thermocouple materials for the purposes of high-temperature thermometry.     

Thermophysical Properties of Molten Yttrium Measured by Non-contact Techniques

Understanding the nature and behavior of liquid metals requires accurate values of their physical properties (e.g., density, surface tension, viscosity). However, maintaining samples of matter in their liquid phases, in particular under supercooled conditions, is a great challenge when dealing with refractory metals. This is due mainly to their high melting temperatures (e.g., 3,695 K for W), their high vapor pressure, and the risk of melt contamination with a support or crucibles. Electrostatic levitation, laser heating in vacuum, and non-contact characterization techniques circumvented these difficulties and allowed the determination of the properties of several metals in their liquid state, above their melting temperature as well as in their supercooled phase. In this work, several thermophysical properties were successfully measured with an electrostatic levitation furnace under vacuum conditions. For the first time, density and viscosity data of yttrium were reported over large temperature intervals in the liquid phase. Over the 1,560 to 2,100 K temperature span, the density can be expressed as $\rho (T)=4.15\times 10^3-0.21\, (T - T_{\rm m})$ (kg·m^???3) with T _m = 1,796 K, yielding a volume expansion coefficient of 5.1 × 10^???5 K^???1. In addition, the surface tension can be expressed as $\sigma \left( T \right)=8.04\times 10^2-0.05\,(T - T_{\rm m})$ (mN·m^???1) and the viscosity as $\eta \left( T \right)=0.00287\,\exp \left[ {{1.1\times 10^5} \mathord{\left/ {\vphantom {{1.1\times 10^5} {\left( {\mbox{RT}} \right)}}} \right. \kern-0em} {\left( {\mbox{RT}} \right)}} \right]$ mPa·s over the 1,830 to 2,070 K interval. The results, in particular those for viscosity, suggest that performing similar experiments in microgravity could improve the accuracy of the measurements.     

Measurement of density,sound velocity,surface tension,and viscosity of freely suspended supercooled liquids

Noncontact methods have been implemented in conjunction with levitation techniques to carry out the measurement of the macroscopic properties of liquids significantly cooled below their nominal melting point. Free suspension of the sample and remote methods allow the deep excursion into the metastable liquid state and the determination of its thermophysical properties. We used this approach to investigate common substances such as water,v-terphenyl. succinonitrile, as well as higher temperature melts such as molten indium, aluminum, and other metals. Although these techniques have thus far involved ultrasonic, eletromagnetic, and more recently electrostatic levitation, we restrict our attention to ultrasonic methods in this paper. The resulting magnitude of maximum thermal supercooling achieved has ranged between 10% and 15% of the absolute temperature of the melting point for the materials mentioned above. The methods for measuring the physical properties have been mostly novel approaches, and the typical accuracy achieved has not yet matched the standard equivalent techniques involving contained samples and invasive probing. They are currently being refined, however, as the levitation techniques become more widespread and as we gain a better understanding of the physics of levitated liquid samples.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–34, 1994, Boulder, Colorado, U.S.A.     

Surface Tension and Viscosity of Quasicrystal-Forming Ti–Zr–Ni Alloys

Recent X-ray scattering measurements show that icosahedral short-range order in Ti–Zr–Ni alloys is responsible for a change in phase selection from the stable C14 Laves phase to the quasicrystalline icosahedral phase, and that icosahedral short-range order increases at deeper undercoolings. This change in short-range order should be reflected in changes in the thermophysical properties of the melt. The surface tension and viscosity of quasicrystal-forming Ti–Zr–Ni alloys were measured over a range of temperature, including both stable and undercooled liquids, by an electrostatic levitation (ESL) technique. ESL is a containerless technique which allows processing of samples without contact, greatly reducing contamination and increasing access to the metastable undercooled liquid. The measured viscosity is typical of glass-forming alloys of similar composition to the quasicrystal-forming alloys studied here; however, the surface tension shows an anomaly at deep undercoolings.     

Thermophysical properties of solid and liquid beryllium

A submillisecond resistive heating technique under high pressure (0.12 GPa) has been used to measure selected thermophysical properties of both solid and liquid beryllium. Data have been obtained between room temperature and 2900 K. Results on enthalpy, volume expansion, electrical resistivity, and sound velocity measurements are presented.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Thermophysical properties of rhenium

Experimental investigations of the thermophysical properties of rhenium at high temperatures (above 2000 K) are scarce and quite recent. Using an isobaric expansion technique, we performed new measurements up to 7000 K under 0.12GPa argon pressure and report here enthalpy, density, temperature, and electrical resistivity data for both solid and liquid states. Agreement is good with other pulse heating results obtained on this refractory metal (T _m =3453 K), except in the volume increase at melting.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria.     

Binary and Ternary Mixtures of Biopolymers and Water: Viscosity,Refractive Index,and Density

Biopolymers have been the focus of intense research because of their wide applicability. The thermophysical properties of solutions containing biopolymers have fundamental importance for engineering calculations, as well as for thermal load calculations, energy expenditure, and development of new products. In this work, the thermophysical properties of binary and ternary solutions of carboxymethylcellulose and/or high methoxylation pectin and water at different temperatures have been investigated taking into consideration different biopolymer concentrations. The experimental data related to the thermophysical properties were correlated to obtain empirical models that can describe the temperature–concentration combined effect on the density, refractive index, and dynamic viscosity. From data obtained from the experiments, the density, refractive index, and dynamic viscosity increase with increasing biopolymer concentration and decrease with increasing temperature. The polynomial models showed a good fit to the experimental data and high correlation coefficients (\(R^{2}\ge \) 0.98) for each studied system.     

The density of alloys of tin—lead system in the solid and liquid states

The method of gamma-raying the samples by a narrow beam of gamma radiation for cesium-137 isotope is used to investigate the density of five liquid alloys of a tin—lead system (17.64, 25.35, 25.61, 26.07, and 33.88 at.% Pb) in the temperature range from 293 to 1040 K with an error of 0.20–0.25%. Approximation dependences are obtained for the density of melts of investigated alloys, and our data are compared with the results of other authors. Procedural aspects of the investigation of the density of binary and multicomponent melts are treated, which are associated with the emergence of gradients of concentration of the components in the gravity field. Tables are compiled of the temperature dependences of the thermal properties of pure tin and lead from zero to 1600–1950 K. It is demonstrated that the density of the solid and liquid phases of tin—lead system in the investigated concentration range may be calculated in an additive approximation with an error of 0.1–0.3% or less.     

Measurement of thermophysical properties of lead by a submicrosecond pulse-heating method in the range 2000–5000 K

A submicrosecond ohmic pulse-heating technique with heating rates of more than 10⁹K· s^–1 allows the determination of such thermophysical properties as heat capacity and the mutual dependences among enthalpy, electrical resistivity, temperature, and volume up to superheated liquid states for lead. Also, an estimation of the critical point data is given from investigations at elevated static pressures.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.