Status of the Electrostatic Levitation Furnace (ELF) in the ISS-KIBO

The electrostatic levitation method is a containerless processing technique that utilizes Coulomb force between a charged sample and the surrounding electrodes. The Japan Aerospace Exploration Agency (JAXA) has been developing this technique for more than 20 years. In 2016, JAXA completed the flight model assembly, and the Electrostatic Levitation Furnace (ELF) for the International Space Station (ISS) was launched to the ISS. The ELF is mainly intended to handle oxide melts that are difficult to levitate on the ground based electrostatic levitator due to gravity and due to insufficient charging. ISS-ELF can measure the thermophysical properties (density, surface tension and viscosity) of high temperature melts above 2000 ^°C. The thermophysical properties data of materials at high temperature is useful for the study of liquid states and improvement of numerical simulation by modeling the manufacturing processes using the liquid state. Moreover, the interfacial energy of immiscible melts will be measured by creating a core-shell droplet configuration which otherwise cannot be obtained on the ground due to sedimentation. This paper briefly describes the ELF facility and presents the results of a functional checkout that includes the density measurement of molten alumina.     

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.     

Containerless processing of a lithium disilicate glass

Glasses of Li₂O · 2SiO₂ (LS₂), and LS₂ doped with 0.001 wt% platinum (LS₂ + 0.001 wt% Pt) compositions were melted, cooled and reheated at controlled rates while levitated (containerless) inside an electrostatic levitator (ESL) furnace at the NASA Marshall Space Flight Center. The experiments were conducted in vacuum using spherical, 2.5–3 mm diameter, glass samples. The measured critical cooling rate for glass formation, R _c, for the LS₂ and LS₂ + 0.001 wt% Pt glasses processed at ESL were 14 ± 2 °C/min and 130 ± 5 °C/min, respectively. The values of R _c for the same LS₂ and LS₂ + 0.001 wt% Pt glasses processed in a container were 62 ± 3 °C/min and 162 ± 5 °C/min, respectively. The effective activation energy for crystallization, E, for this LS₂ glass processed without a container at ESL, was higher than that for an identical glass processed in a container. These results suggest that the glass formation tendency for a containerless LS₂ melt is significantly increased compared to an identical melt in contact with a container. The absence of heterogeneous nucleation sites that are inherently present in all melts held in containers is believed to be the reason for the increased glass forming tendency of this containerless melt.     

Noncontact temperature measurement of a falling drop

The 105-m drop tube at the Marshall Space Flight Center has been used in a number of experiments to determine the effects of containerless, microgravity processing on the undercooling and solidification behavior of metals and alloys. These experiments have been limited, however, because direct temperature measurement of the falling drops has not been available. Undercooling and nucleation temperatures are calculated from thermophysical properties based on droplet cooling models. In most cases these properties are not well known, particularly in the undercooled state. This results in a large amount of uncertainty in the determination of nucleation temperatures. If temperature measurement can be accomplished, then the thermal history of the drops could be well documented. This would lead to a better understanding of the thermophysical and thermal radiative properties of undercooled melts. An effort to measure the temperature of a falling drop is under way at Vanderbilt and Marshall Space Flight Center. The technique uses two-color pyrometry and high-speed data acquisition. The approach is presented along with some preliminary data from drop tube experiments. The results from droplet cooling models will be compared with noncontact temperature measurements.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Thermodynamic–kinetic model for the simulation of solidification in binary copper alloys and calculation of thermophysical properties

An earlier developed thermodynamic–kinetic solidification model for binary copper alloys is extended to take into account the formation of the bcc phase via the peritectic transformation and the formation of binary compounds from the fcc phase. Also the eutectic and eutectoid transformations are simulated but only approximately, by modeling the movement of the fcc/eutectic and fcc/eutectoid interfaces due to the diffusion kinetics of the fcc phase only. The new model can handle binary copper alloys containing solutes Ag, Al, Cr, Fe, Mg, Mn, Ni, P, Si, Sn, Te, Ti, Zn and Zr. Depending on the alloy composition, cooling rate and dendrite arm spacing, the model determines the fractions and compositions of the phases (liquid, fcc, bcc, compounds) and calculates thermophysical material properties (enthalpy, specific heat, thermal conductivity, density and liquid viscosity), needed in heat transfer models, from the liquid state down to room temperature. The model is applied to Cu–Sn and Cu–Zn alloys but also to some other binary alloys to show the effect of cooling on the phases formed. Depending on the alloy system, the solidification structures obtained after real cooling processes are shown to be quite different from those estimated from phase diagrams.     

Measurement of thermophysical properties of liquid metallic alloys in a ground- and microgravity based research programme — theThermoLab project

The ThermoLab project is concerned with the measurement of the thermophysical properties of industrial alloys in the liquid phase. The project combines long and short duration microgravity measurements based on containerless processing with an electromagnetic levitation device and a ground based experimental programme using conventional and containerless processing techniques. An overview of the project and representative results from the ground based experimental programme are given. Alloys investigated included Ni-based, Fe-based, a Cu-Sn-Mg alloy and a γ-TiAl alloy.     

超重力下燃烧合成TiB_2-TiC共晶复合陶瓷

采用超重力下燃烧合成技术,制备出TiB2-TiC共晶复合陶瓷。XRD、SEM与EDS结果表明,复合陶瓷主要由大量细小的TiB2片晶均匀分布于TiC基体上的共晶组织构成,而富钛ε碳化物(Ti,Cr)C1-x则断续分布于TiC基体间,同时在基体中还孤立分布着少量的、形态不规则的α-Al2O3晶粒或Al2O3-ZrO2共晶团组织。高温化学反应使所有产物均呈液态,且超重力的引入诱发熔体内部Stocks流,从而获得液态Ti-Cr-C-B与液态氧化物的分层熔体,液态Ti-Cr-C-B在远离平衡态下发生共晶反应生成TiB2-TiC共晶复合陶瓷。性能测试表明,随着B4C+Ti+C在燃烧体系中质量分数增加,TiB2-TiC共晶复合陶瓷相对密度和断裂韧性变化不大,分别为97%~99%与6.5~7.1 MPa.m1/2,而维氏硬度与弯曲强度则逐渐增加,最高可达28.6 GPa与615 MPa。     

Influence of binary additives of compatibilizers on the micro-and macrorheological properties of melts of polypropylene-copolyamide mixtures

We have investigated the influence of binary additives of compatibilizers copolymer of ethylene with vinyl acetate/siloxane liquid on the rheological properties of melts and the processes of structure formation in polypropylene-copolyamide mixtures. It has been shown that there exists an optimal ratio of compatibilizers at which the maximum influence of additives on the process of specific fiber formation shows up. The mechanism of their action is connected with an increase in the length of the interphase layer, a decrease in the surface tension, and an increase in the lifetime of the liquid jet. The use of compatibilizers influences the viscosity of melts only slightly, and the capability of four-component compositions to be processed markedly increases. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 4, pp. 737–743, July–August, 2008.     

Unidirectionally cooled eutectic and eutectoidal composites of Al-Cu alloy

Al-Cu alloys having eutectic (Al-17·3 at.% Cu) or eutectoid (Cu-24 at.% Al) compositions were allowed to solidify unidirectionally. These two alloys were cooled from an elevated temperature in order to observe the microstructural characteristics. The freezing rate for obtaining a parallel and ordered structure is naturally much faster in eutectic than in eutectoid alloys although both the reaction temperatures are about the same (eutectic temperature =548, eutectoid temperature =565° C). The difference in the solidification rate is due to the diffusion rates of each atomic species in the liquid and the solid states. Similar defects were observed in both the specimens and their mechanisms of formation will be considered.     

Structure of liquid cadmium-antimony alloys

The structure of liquid Cd-Sb alloys was determined with the help of the Kumar-Samarin technique of centrifuging liquid metals. Alloys containing 7, 29, 50, 57 and 79 at. % Sb were examined in the range 350 to 650° C. It shows that (i) all alloys except in the vicinity of equi-atomic composition, consist of a colloidal dispersion of compound clusters in a random monatomic matrix, and (ii) the cluster size depends on composition with minima occurring at the two eutectic compositions. The volume fraction of clusters and their heat of formation were determined. The composition of the compound cluster was deduced as Cd₄₀Sb₃₀. Concentration gradient was not established in the equi-atomic alloy during centrifuging. The investigation shows that residual structure can exist far into the liquid state and is not confined to liquids of stoichiometric compound compositions.     

Microstructural Evolution of Rapidly Solidified Co-Mo and Ni-Mo Eutectic Alloys

Droplets of Co-37.6 wt pct Mo and Ni-47.7 wt pct Mo eutectic alloys were rapidly solidified during containerless processing in a 3 m drop tube. A kind of anomalous eutectic appears in these two eutectic alloys when undercooling is beyond 56 and 61 K, respectively. The two eutectic phases in anomalous eutectic were observed to grow in dendrite manner. The formation of anomalous eutectic is ascribed to the cooperative dendrite growth of the two independently nucleated eutectic phases. Current dendrite and eutectic growth theories are applied to describe the observed processes.     

Physico-mechanical properties of naphthalene–acenaphthene eutectic system by different modes of solidification

Anisotropic crystal growth kinetics from compositional melts encompassing the entire naphthalene–acenaphthene eutectic system, evidentially, evinces the dislocation mechanism. Rheological properties of eutectic phase melts at different temperatures explore the occurrence of molecular interactions emanating molecular clusters, rich in one phase or the other, in the eutectic melt. Microscopic studies confirm the crystalline faceted–faceted structure of the naphthalene–acenaphthene eutectic system. Implicit in the present work is the concept of strength–growth relationship that follows an identical form of the Weibull probability distribution curve. The curve exhibits two cut-off points corresponding to a lower strength limit in the slow and fast growth regions, and an upper strength limit in the moderate growth region. Relational essence between microstructural parameters essentially structuring morphology and excess thermodynamic functions implicitly governing molten state of the naphthalene–acenaphthene eutectic system is extracted.     

Thermophysical Properties of γ-Titanium Aluminide: The European IMPRESS Project

In the framework of its 6th Framework Programme, the European Union funds the Integrated Project IMPRESS, related to industrial applications of Ti–Al and Ni–Al alloys. One central task of this project is the precise determination of the relevant thermophysical properties of selected alloys for both the solid and liquid phases. The properties to be measured include thermal data such as heat of fusion, specific heat, and thermal conductivity, as well as thermophysical and transport properties such as density, surface tension, and viscosity. In addition to conventional high-temperature equipment, containerless methods are used. This article introduces the IMPRESS project, and discusses the first results obtained to date.     

Formation and magnetic properties of Fe-B-Si metallic glasses

The equilibrium solidification behaviour of Fe-rich Fe-B-Si alloys has been characterized in terms of primary and secondary crystallization, and correlated to metallic glass formation and properties. A eutectic trough extends from the binary eutectic on the Fe-B edge of the ternary composition diagram toward the binary eutectic on the Fe-Si edge. Metallic glass forming compositions closely follow the path of the eutectic trough, extending from the Fe-B edge to compositions containing approximately 20 at% Si. The relative ease of glass formation and the thermal stability of the glassy state are maximized at compositions along the eutectic trough. The magnetic coercive forces of both as-cast and annealed metallic glasses are minimized along the eutectic trough.     

Influence of eutectic mixture as a multi-component system in the improvement of physicomechanical and pharmacokinetic properties of diacerein

A multi-component system of diacerein (DIA) with 2, 4 – dihydroxybenzoic acid (DHA) as coformer at various molar compositions was formulated to simultaneously improve solubility, compressibility and bioavailability of DIA by applying acetone assistant grinding technique. Various evaluation parameters pertaining to measure physicomechanical properties were conducted. Thermal analysis revealed a ‘V’-shaped binary phase diagram along with single melting event as a possibility of eutectic formation between drug and coformer. It was further confirmed PXRD and FT-IR. Equidimensional shape with platy nature of eutectic material was observed in SEM images imparting its better flow and compressibility. Solubility and dissolution study showed 2 and 1.8 folds enhancement respectively compared to pure DIA and control batch. Pharmacokinetic study proved 2.1 times higher bioavailability in case of prepared eutectic compared to DIA along with its stable nature. Hence, the multi-component system can become a potential way for the improvement of material characteristics.     

采用无容器凝固技术研究过冷熔体热物理性质

深过冷是获得特殊性能亚稳材料的一种非常重要的手段,采用无容器凝固技术可以在较低的冷却速度下实现并保持较长时间熔体的深过冷,使过冷熔体热物理性质参数的测量成为可能.介绍了电磁悬浮、助熔剂处理等几种常用的无容器凝固技术,阐述了它们在测量过冷熔体比热容等热物理性质方面的应用,同时综述了过冷状态下熔体比热容等热物理性质的研究现状,并展望了今后的发展趋势.     

Thermophysical and Acoustic Liquid Properties in the Framework of the Cluster Theory

A relation for the distribution function of clusters in a liquid, earlier proposed by the authors, allows one to find the number of particles in a cluster and its dependence on state parameters and to find the frequencies of IR-spectra of organic liquids. The authors have improved the method of finding the number of particles contained in a cluster. The proposed modification of the cluster theory allows one to estimate the energy of clusters, to reveal features of their structure, and to calculate the basic thermophysical properties of liquids, such as the difference of isobaric and isochoric heat capacities, the dynamic viscosity, and other properties. The authors have determined the cluster component of full absorption of ultrasonic waves, the cluster relaxation time, and the dimer formation energy for liquid noble gases and organic liquids. The comparison of the obtained results with experimental data demonstrates the reasonableness of the proposed model for prediction of thermophysical and acoustic properties of liquids.     

Two-melt separation in supercooled Cu-Co alloys solidifying in a drop-tube

The microstructure of Cu-Co alloys solidified by a free-fall containerless solidification was investigated using scanning electron microscopy. Spherical Cu-Co drops of about 3 mm diameter were solidified in an evacuated 105 m long drop-tube. The microstructures were compared with those obtained by an electromagnetic levitation technique. It was found that the falling drops were at the liquid + solid state at the moment of impact on the floor. Upon bumping on to the floor the drop splits into many fragments, which finally solidify in the form of flakes upon retouching the tube floor. The microstructure depends mainly on the solid fraction in the flake, and on its temperature at the moment of impact. Supercoolings up to 0.2T_M could be achieved within the drop-tube, causing separation of the liquid into two melts. Under certain conditions the microstructure reveals the occurrence of discarded spheres, suggesting that cooling below a certain temperature (T _misc) will cause mixing of the two melts into one liquid. Interpretation of the observed microstructures is based on the current understanding of rapid solidification mechanisms.     

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.