Containerless Processing Research Articles

MightyLev: An acoustic levitator for high-temperature containerless processing of medium- to high-density materials.

"MightyLev," a new multi-emitter ultrasonic acoustic levitation device capable of extremely stable levitation of materials of density up to at least 11.3g cm-3, is described. The exceptional stability of medium- to high-density samples levitated in MightyLev makes the device highly suitable for chemical and structural analysis using micro-focused spectroscopic and x-ray scattering techniques. In combination with mid-infrared laser heating, MightyLev is capable of levitating metallic and oxide materials during high-temperature cycling and melting above 1500K. Instabilities in particle confinement during heating were investigated by directly visualizing the acoustic field using schlieren imaging. The results reveal jets of hot-air directed along the anti-nodes of the acoustic field. The reaction force on the sample from the jet, coupled with the restoring force of the acoustic trap, generates a parametric lateral oscillation of the sample. This result provides valuable insight for future optimization and wider application of acoustic levitation for high-temperature containerless material processing.

Crucible-less Processing of Ti with TiC Heterogeneous Nucleation Site Particles by Electrostatic Levitation

In this study, the microstructure, hardness, density, viscosity, and surface tension of molten pure Ti with TiC particles were studied via electrostatic levitation experiments, where the electrostatic levitation experiment involved container-less processing, which can suppress heterogeneous nucleation via crucibles. Microstructural observation revealed long needle-shaped α-grains across the whole area in the pure Ti sample. On the other hand, smaller needle-shaped α-grains were found in the samples with TiC particles. However, the detailed microstructural analysis of Ti + 0.7vo l%TiC sample revealed that the fine α-grains observed in the Ti + 0.7vo l%TiC are transformed from single grain of prior β phase. This is because the TiC particles dissolve into the molten Ti during the electrostatic levitation experiment. Instead, Ti–rich TiC precipitates formed by cooling can act as pinning sites rather than heterogeneous nucleation sites, which results in a finer microstructure for the samples with TiC particles during the electrostatic levitation experiment. The density of the samples is linearly related to the temperature, and it decreases with increasing temperature. In addition, a higher density is observed for the samples with TiC particles. Although linear relationships between the surface tension and temperature were found, the addition of TiC particles had no notable effect on the viscosity of the molten pure Ti.

Photoluminescence of Sm3+ and Eu3+ co-doped La2O3–Ga2O3 glasses fabricated by an aerodynamic levitation furnace

A series of transparent (1-y)La2O3–Ga2O3-ySm2O3-xEu2O3 (where x = 0, 0.02, 0.04, 0.06, 0.08, 0.10, 0.12, 0.14, and y = 0, 0.04) were successfully synthesized using a containerless solidification process. Co-doping with Sm3+ and Eu3+ enhanced the energy absorption of Eu3+, notably improving the characteristic emission peak 5D0-7F2 of Eu3+. The peak emission intensity for y = 0.04 was observed at x = 0.08, attributable to the concentration quenching of Eu3+ ions. As the concentration of Eu3+ increased, the energy transfer effect on emission intensity diminished. Attributed to the energy transfer between Sm3+ and Eu3+, Sm3+ may primarily serve as the sensitizer, and Eu3+ as the activator. According to the Dexter theory, which suggests that the interaction between activator ions and their adjacent ions is the primary mechanism of energy transfer and quenching among Eu3+ ions and adjacent ions, an increase in Eu3+ concentration leads to a decrease in the distance between Eu3+ and adjacent ions, strengthening their interaction, and potentially inducing concentration quenching. Furthermore, with an increase in Eu3+ concentration, the CIE chromaticity coordinates for the samples co-doped with Sm3+ and Eu3+ shifted significantly, enhancing the color purity of the emitted light and bringing it closer to the NTSC color standard coordinates (0.67, 0.33).

Non-equilibrium solidification of undercooled Inconel 718

The non-equilibrium solidification of undercooled Inconel 718 melts has been studied in situ on electromagnetically levitated samples by using high-speed video recording and optical pyrometry. Microstructure and phase constitution of solidified samples were analysed by scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron backscatter diffraction and high-energy X-ray diffraction. Due to containerless sample processing experimental data on phase formation, γ-dendrite growth, and microstructural evolution in Inconel 718 were obtained over a wide range of undercooling ΔT between 20 and 289 K. It has been found that the dendrite growth velocity, extracted from high-speed video records, rises exponentially with increasing undercooling at first. At an undercooling of about 150 K, growth slows down drastically. Furthermore, morphology and size of γ-matrix grains essentially depend on ΔT. They alter from coarse equiaxed to coarse columnar at an undercooling of about 60 K, get refined and equiaxed at undercoolings above 150 K, and become larger and elongated again upon reaching an undercooling of about 250 K. The deviation from equilibrium and trapping of solute atoms in γ-dendrites result in a notable reduction of NbC and Laves fraction, the latter apparently disappearing at ΔT larger than 150 K.

Multi-component 20La2O3–20TiO2–20Nb2O5-20(Al2O3/ZrO2)-20(ZrO2/Ta2O5) glasses with ultra-high refractive index and mechanical properties inspired by high-entropy design

The highly refractive glasses with excellent mechanical properties (hardness, Young's modulus, and fracture toughness) are highly desired for the lenses used in small optical devices. In this study, a series of five-primary-component 20La2O3–20TiO2–20Nb2O5-20(Al2O3/ZrO2)-20(ZrO2/Ta2O5) (LTNAZ, LTNAT, LTNZT) glasses were designed by using high-entropy strategy and successfully elaborated through a containerless melting-solidification process. The highest refractive index (nd) of the glasses reach up to 2.25. The maximum vickers hardness (HV), Young's modulus (E), and indentation fracture toughness (KIFT) are 10.74 GPa, 157.5 GPa, and 1.23 MPa m0.5 respectively. The glasses exhibit good glass forming ability with kinetic window (ΔT) ranging from 80 to 116 °C. The excellent comprehensive performances of the glasses are attributed to the high electronic polarizability and dissociation energy, as well as the synergistic effect of multiple components in the high-entropy effect. The glasses will be promising host materials for optical applications such as digital product lenses, endoscopes and mini size lasers.

Viscosity of liquid Ni-based industrial alloys: experiments versus theory

The aim of this review is to succinctly review recent progress in experimental and theoretical investigation of the viscosity of binary and multicomponent Ni–Al-based industrial alloys, summarising the current state of knowledge of the topic. Viscosity data are important for simulation of microstructural evolution during solidification-related processes such as casting. Therefore, to obtain accurate predictions of defect-free microstructure, only reliable input data are required. Based on the synergy between experiment and theory, a review of the literature provides a critical evaluation of temperature- and composition-dependent viscosity data available from existing studies carried out over the last 60 years. The purpose of this review is threefold: to discuss container-based viscometer methods and alternative containerless processing via electromagnetic levitation during parabolic flights and on board the International Space Station; to analyse the viscosity models including their validation; and to refer to the first two points, to interpret the viscosity data.

Evaporation and phase separation of acoustically levitated aqueous two-phase-system drops

As a ground-based experimental method for simulating the containerless state in space, acoustic levitation provides excellent containerless and contact-free conditions for studying droplet dynamics, including droplet evaporation and phase separation. Meanwhile, the nonlinear effects of the acoustic field, such as acoustic radiation pressure and acoustic streaming, bring novel characteristics to the droplet evaporation process and phase separation process. In this work, the evaporation and phase separation of aqueous two-phase-system (ATPS) droplet composed of polyethylene glycol (PEG) and ammonium sulfate (AMS) are investigated by a single-axis acoustic levitator through the combination of image acquisition and processing technique. During the evaporation of the ATPS droplet, the square of its equatorial diameter, <inline-formula><tex-math id="M5">\begin{document}$ {d}^{2} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20230963_M5.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20230963_M5.png"/></alternatives></inline-formula>, decreases linearly with time, and its aspect ratio, <inline-formula><tex-math id="M6">\begin{document}$ \gamma $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20230963_M6.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20230963_M6.png"/></alternatives></inline-formula>, increases linearly with time. The PEG-AMS droplet initially in the single-phase regime can enter into the two-phase regime as the water evaporates, resulting in phase separation. The phase separation of the acoustically levitated PEG-AMS ATPS droplet includes three stages: first, a large number of PEG-rich globules form inside the ATPS droplet, and then these PEG-rich globules collide, coagulate and migrate outward, and finally a horizontal layered structure of the whole droplet comes into being. The evaporation constant, the evolution of the PEG-rich globules and the AMS-rich phase area, are analyzed for ATPS droplets with different initial aspect ratios and different initial compositions. It is concluded that the greater the initial aspect ratio and the smaller the volume fraction of the PEG-rich phase, the faster the evaporation rate of the droplet is; the greater the initial aspect ratio and the lager the volume fraction of the PEG-rich phase, the faster the phase separation is. Numerical simulations show that the acoustically levitated droplets with a large aspect ratio are subjected to greater acoustic radiation pressure on the surface, and that the corresponding sound field is more intense and the acoustic streaming is stronger, which accelerates the evaporation and phase separation of the levitated droplets. These findings contribute to deepening our understanding of the motion characteristics, evaporation dynamics and phase separation of acoustically levitated droplets, and provide a foundation for studying the containerless preparation and processing the materials under acoustic levitation.

Molecular structure of ketoprofen-polyvinylpyrrolidone solid dispersions prepared by different amorphization methods.

Amorphous solid dispersions (ASDs) are a widely studied formulation approach for improving the bioavailability of poorly water-soluble pharmaceuticals. Yet, a complete understanding remains lacking for how specific processing methods may influence ASDs' molecular structure. We prepare ketoprofen/polyvinylpyrrolidone (KTP/PVP) ASDs, ranging from 0-75 wt% KTP, using five different amorphization techniques: melt quenching, rotary evaporation with vacuum drying, spray drying, and acoustic levitation with either a premixed solution or in situ mixing of separate co-sprayed solutions. The co-spray levitation approach enables on-demand compositional changes in a containerless processing environment, while requiring minimal pharmaceutical material (∼1 mg). The structure of all ASDs are then compared using high-energy X-ray total scattering. X-ray pair distribution functions are similar for most ASDs of a given composition (Rx = 0.4-2.5%), which is consistent with them having similar intramolecular structure. More notably, differences in the X-ray structure factors for the various amorphization routes indicate differing extents of molecular mixing, a direct indication of their relative stability against crystallization. Melt quenching, spray drying, and levitation of premixed solutions exhibit some degree of molecular mixing, while the co-sprayed levitation samples have molecular arrangements like those of KTP/PVP physical mixtures. These findings illustrate how X-ray total scattering can be used to benchmark amorphous forms prepared by different techniques.

EFFECTS OF REFRACTIVE INDEX AND ASPECT RATIO ON THE PARTICLE IMAGES IN A LEVITATED DROPLET

A technique using droplets suspended by ultrasound has attracted attention as one of the containerless processing methods. While this can avoid contamination from the container, it is known that ultrasonic levitation creates flow fields inside and outside the droplet. For more precise droplet control, it is desirable to elucidate the internal flow of the droplet, and measurements of the internal flow have been performed using the particle image velocimetry (PIV). The aim of this study is to elucidate the internal flow field behavior by solving optical problems and improving the accuracy of velocity field measurements in levitated droplets. The fluid that is to be investigated is scattered with small tracer particles and illuminated by a laser to capture the flow on a created laser sheet. The curvature distortion is successfully visualized using the PIV approach toward distortion correction using calibration methods. The curvature distortion illustration was performed based on the refractive index and aspect ratio of the simulated droplet in acrylic materials. The fluid flow, affected by droplet curvature and refractive index, has been visualized for both levitated and simulated droplets. The experimental results showed that the droplet curvature can be distorted in two types such as radial and tangential distortions and increase as the refractive index and aspect ratio increases.

Aero acoustic levitation to unveil the solidification of complex oxides: Case study of the system Al2O3–ZrO2

Binary or multi-component phase mixtures are of particular technical importance. Despite the wide field of application of Al2O3 and ZrO2 composites, the literature reveals contradictions about the liquidus region. Containerless processing avoids typical problems of conventional techniques like melt contamination or lack of suitable container materials. Composition ranging from 0–80 mol% ZrO2 were melted and solidified in an aero acoustic levitator. A high-speed camera recorded the crystallization, allowing a direct correlation with the observed microstructures. Due to homogeneous nucleation, all samples exhibited significant undercooling before crystallization. The nucleation temperature of the different compositions roughly followed the slope of the liquidus line. Undercooling, solidification kinetics, and local reheating played a considerable role in microstructure formation. A lamellae eutectic microstructure was created over a large compositional range from 36–48 mol% ZrO2. On the hypoeutectic side, the effect was attributed to solidification within the coupled zone. However, hypereutectic samples also exhibit a zirconia-rich eutectic as well. We assume impaired ZrO2 nucleation or growth favors alumina precipitation from the melt. Aero acoustic levitation proved to be an excellent technique for studying complex high melting oxide systems, enabling a better understanding of their crystallization process.

High‐refraction index glasses with ultra‐high Young's modulus and high hardness fabricated by containerless processing

AbstractHigh‐refractive index glasses with ultra‐high Young's modulus and superior hardness have significant application in optical lenses. Research indicates that high‐entropy glasses, enriched with high dissociation energy and high‐field strength components, enhance the mechanical properties of glass. In this study, we tailored high‐entropy glasses to achieve superior optical and mechanical attributes by optimizing heavy metal oxide components and adjusting the Al2O3 content. The resultant 10RE2O3‐10Gd2O3‐32Al2O3‐36Ta2O5‐12ZrO2 (RE = La, Tm, Lu) glass demonstrates a refractive index of 2.028, a Young's modulus of 186.2 GPa, and a Vickers hardness of 9.18 GPa. The glass was colorless and widely transparent, in the visible‐to‐infrared region from 312.5 to 6674 nm, and the maximum transmittance reach up to 79.3%. These results indicate that the 10RE2O3‐10Gd2O3‐32Al2O3‐36Ta2O5‐12ZrO2 glass would be useful for camera and detector lenses.

Thermodynamic Evaluation of the Surface Tension and Viscosity of Liquid Quaternary Alloys: The Ti-Al-Cr-Nb System

Surface tension and viscosity of complex Ti-based industrial alloys are important for simulation of liquid assisted industrial processes such as casting, joining, crystal growth and infiltration. Modelling of the interface and mass transport during liquid-solid phase transition requires reliable surface tension and viscosity data. Therefore, to obtain accurate predictions of microstructural evolution during solidification related processes, only reliable input data are necessary. In the case of liquid Ti-Al alloys, the experimental difficulties related to high temperature measurements and reactivity of these alloys with supporting materials or containers as well as inevitable presence of oxygen may lead to data gaps including a complete lack of property data. An alternative for container-based methods are containerless processing techniques that offer a significant accuracy improvement and / or make possible to measure temperature and composition dependent thermophysical properties of metallic melts, as in the case of the Ti-Al-Cr-Nb system. Advanced mathematical models and computer simulations, developed in several theoretical frameworks, can be used to compensate the missing data; on the other side, for the validation of theoretical models, the experimental data are used. In the present work, an evaluation of the surface tension and viscosity of liquid Ti-Al-Cr-Nb alloys by means of the predictive models and a comparison to the available experimental data were done. The proposed methodology is a tool to assess the reliability of thermophysical properties data of multicomponent alloy systems.

Parametric analysis of acoustically levitated droplet for potential microgravity application

Acoustic levitation is a versatile technique for the non-contact handling of both solid and liquid samples, yet its potential remains underutilized in container-less processing and lab-on-a-drop application. This study demonstrates the efficient use of acoustically levitated droplets as microgravity simulators on earth similar to clinostat. Using a simple and affordable non-resonant single-axis acoustic levitator called TinyLev, we first investigate the impact of applied voltage and droplet volume on the shape and rotational motion of levitated water droplets. Furthermore, we examine the rotational motion of suspended microparticles within the droplets. Our findings reveal the feasibility of using the levitated droplets as a miniaturized microgravity simulators on earth.

(Invited) The Electrostatic Levitation Furnace Onboard the International Space Station for Container-Less Material Processing and Thermophysical Property Measurements at Extremely High Temperature

Electrostatic levitation is one of the container-less processing methods which utilizes Coulomb force between a charged sample and surrounding electrodes. Contrary to the other methods, electrostatic levitation cannot create a potential minimum, so high-speed feedback position control is necessary. Because of this technical difficulty, development of this method was behind to other methods, such as electromagnetic levitation, or acoustic levitation. Samples can be levitated even in ground. However, to levitate samples against gravity, huge electric field and huge surface charge on the sample are required. This creates some limitations in ground experiments. Firstly, Oxides samples are hard to levitate due to low surface charge. Secondly, experiment in inert gas environment is impossible to prevent electric discharge among electrodes. These limitations can be easily solved in microgravity. Oxides sample cane be levitated and melted. Metals and alloys can be processed in inert gas to suppress evaporation.The electrostatic levitation furnace on the International Space Station (ISS-ELF) developed by Japan Aerospace Exploration Agency, was launched to the ISS in 2015. Then, Installation to the MSPR (multi-purpose Small Payload Rack) was conducted in the next year. Since then, a variety of oxide/ metal samples have been levitated and melted in the facility. The ISS-ELF has a capability to measure thermophysical property of extremely high temperature melts. Density, Surface tension, and viscosity can be measured by this facility. Status of thermophysical property measurements is described in this presentation.

Complete solute trapping of rapidly growing nickel dendrites within liquid Ni72Mo28 hypoeutectic alloy

The rapid dendrite growth in highly undercooled liquid Ni72Mo28 hypoeutectic alloy was accomplished by containerless processing via electromagnetic levitation and drop tube techniques. The (Ni) dendrites achieved a high growth velocity of 26 m/s at the maximum undercooling of 226 K (0.14 TL) under levitated state. Remarkable dendritic structure refinement and Mo solubility extension were observed with the increase in undercooling. For freely falling alloy droplets, the largest undercooling was enhanced to 246 K (0.15 TL), which resulted in thorough solute trapping and almost segregationless solidification. A microstructure transition from columnar dendrite to equiaxed dendrite took place once alloy undercooling exceeded a threshold about 74–79 K. In addition, the Vickers hardness of primary (Ni) dendrite was significantly improved, which was caused by the extension of Mo solubility and microstructure refinement.

Duplex corrosion mechanisms correlated to α/γ phase selection in containerlessly processed Fe-Cr-Ni-Mo alloy

The α/γ phase selection mechanism and corrosion resistance of Fe-21%Cr-12%Ni-5%Mo alloy were investigated by both individual electromagnetic levitation (EML) and EML coupled with falling quench (EML+FQ) techniques. The decomposition of primary δ phase could be partially or completely suppressed in two containerless processing. Both selective and pitting corrosion behaviors were discovered in alloy, which were related to the crystalline orientations and solute distributions of constituent phases. The anti-corrosion property of EML+FQ processed alloy was significantly enhanced with higher corrosion potential of 0 VSCE, lower corrosion current density of 4.1 × 10−7 A/cm2 and lower corrosion rate decreasing over one order of magnitude.

Optical properties and irradiation resistance of novel high-entropy oxide glasses La2O3–TiO2–Nb2O5–WO3–M2O3 (M=B/Ga/In)

A new class of high-entropy oxide glasses 20LaO3/2–20TiO2–20NbO5/2–20WO3–20MO3/2 (M = B/Ga/In) were designed and successfully fabricated by aerodynamic containerless processing. The results show that one can control the properties and increase the functionality of glass by changing the type of M. The Vicker's hardness reaches the highest value of 6.45 GPa for glass M = B. The best thermal stability and the glass forming ability, measured using the glass-transition temperature Tg and the temperature gap ΔT respectively, are found in glass M = In, with Tg = 740 °C and ΔT = 72 °C. The optical properties show that the as-prepared glasses exhibit good transparency and high refractive index. Especially for glass M = In, its transmittance reaches almost 78% from visible to IR region, and the value is nearly unchanged after electron beam irradiation, indicating good irradiation resistance of this high-entropy oxide glass. Furthermore, the glass M = In has the highest refractive index (nd = 2.46) and low wavelength dispersion (νd = 45.6). These results demonstrate that the conceptual design of high-entropy materials is adaptable to high performance oxide glasses, which should be promising host materials for optical applications such as smart phones with digital cameras and endoscopes.

Radiation shielding ability and optical features of La2O3+TiO2+Nb2O5+WO3+X2O3 (X=B, Ga, and In) glass system containing high-entropy oxides

Three high entropy materials (La2O3+TiO2+Nb2O5+WO3+X2O3 coded as LTNWM1, LTNWM2, and LTNWM3 for X = B, Ga, and In) produced by aerodynamic containerless processing were evaluated for optical attributes, and their gamma-radiation absorption abilities were investigated in this report. Optical related parameters such as the molar refractivity (Rm), optical transmission (T), molar polarizability (αm), metallization criterion (M), reflection loss (RL), static (εstatic), and optical (εoptical) dielectric constants were estimated through standard expressions, while photon attenuation parameters were estimated from data from photon transmission simulations in FLUKA code and XCOM software. The attenuation parameters were calculated for a wide energy photon spectrum (15 keV–15 MeV). LTNWM1, LTNWM2, and LTNWM3 had Rm values of 18.94 cm3/mol, 21.45 cm3/mol, and 26.09 cm3/mol respectively. The αm has a value of 7.52 × 10−24 cm3 for LTNWM1, 8.51 × 10−24 cm3 for LTNWM2, and 10.35 × 10−24 cm3 for LTNWM3. The photon shielding parameters evaluated by FLUKA and XCOM are compatible. The mass attenuation coefficient for the glasses was between 0.0338 and 52.8261 cm2/g, 0.0336–58.0237 cm2/g, and 0.0344–52.1560 cm2/g for LTNWM1, LTNWM2 and LTNWM3, respectively. The effective atomic number at 1.5 MeV was 18.718, 20.857, and 22.440 for LTNWM1, LTNWM2, and LTNWM3, respectively. The shielding parameters of the HMOs compared to traditional gamma radiation absorbers are exceptional and highlight the potential of using them as optically transparent gamma-shields.

Revisiting metastable immiscibility in SiO2–Al2O3: Structure and phase separation of supercooled liquids and glasses

AbstractUnderstanding and controlling liquid–liquid phase separation in aluminosilicates is crucial for optimizing glass properties. However, the metastable nature of aluminosilicates’ phase separation has made it difficult to study experimentally, and uncertainty persists regarding the compositional and temperature extents of the miscibility gap. Here, we present new experimental evidence that suggests a consolute temperature between 1440 and 1590°C and endmember compositions of 7 and 62 mol.% Al2O3 for the phase‐separated glasses. Using containerless melt processing, deeply supercooled liquids over the 0–60 mol.% Al2O3 range are probed with in situ small‐ and wide‐angle X‐ray scattering, which simultaneously reveals changes in nanoscale density heterogeneity and atomic structure. Correlations between phase separation and atomic coordination environments are compared for liquids and glasses. Pair distribution function analysis shows mean O–(Si + Al) coordination increases with Al2O3 content and decreases with temperature.

Microscopic structure and dynamics of glass forming Zr2Co melts and the impact of different late transition metals on the melt properties

We studied the short-range order and the atomic dynamics of stable and undercooled binary Zr 2 Co alloy melts as well as their density and viscosity. The containerless processing technique of electrostatic levitation was used to achieve deep undercooling and to avoid contaminations. Static structure factors are determined by combining this technique with neutron and high energy X-ray diffraction. Co self-diffusion coefficients are measured by quasielastic neutron scattering. Our results reveal that the short-range order of the Zr 2 Co melts closely resembles that previously observed for Zr 64 Ni 36 . We consider this as the origin of the very similar melt dynamics of these two alloys at same temperatures. On the other hand, the difference in the structure and dynamics when compared with those of Zr 2 Cu and Zr 2 Pd shows clearly that not only the atomic sizes, but also electronic properties or chemical bonding have an important influence on the melt properties of Zr-based glass forming melts. PACS number(s): 61.20.−p, 61.25.Mv, 66.30.Fq, 61.05.F-, 61.05.cp