Containerless Processing Research Articles

Fabrication of Barium Titanate Based Ferroelectrics by Containerless Processing

Lead-free ferroelectric materials are desired in our lives owing to the environmental problem, and are anticipated to replace conventional ferroelectrics such as Pb(Zr,Ti)O3(PZT) ceramics. Many researchers have attempted to develop lead-free ceramics whose ferroelectric properties would surpass those of PZT ceramics. Recently, it has been reported that oxygen-deficient hexagonal-BaTiO3which is metastable state of perovskite-BaTiO3exhibits giant dielectric constants over the wide temperature range. Such a metastable material has capability as a lead-free dielectric material with high performance. The containerless processing has an advantage over the other conventional methods in synthesizing metastable materials. It can suppress heterogeneous nucleation from the container wall, and produce the undercooled state below the solidification point of the metastable phase, which is lower than that of the stable phase. The purpose of this study is to synthesize barium titanate based ferroelectrics by the containerless processing as lead-free metastable materials. We developed the aerodynamic levitation furnace which enables us to levitate and melt a sample about 1-3 mm in diameter in containerless condition. Figure 1 shows a schematic view of the aerodynamic levitation furnace. The samples are levitated by the gas jet nozzle, and are melted using the CO2laser radiation. The metastable crystals of the barium titanate based ferroelectrics were fabricated by the aerodynamic levitation furnace. The crystal structure is demonstrated by analyzing high energy synchrotron radiation powder diffraction data. We discuss the prospects of the ferroelectricity on the basis of the determined crystal structure.

Atomic dynamics in binary Zr-Cu liquids

We studied Cu self-dynamics and liquid density of Zr66.7Cu33.3, Zr35.5Cu64.5, Zr36Cu64, and Zr38.2Cu61.8 liquids using a combination of containerless processing techniques and quasielastic neutron scattering. We show that the composition dependence of the Cu self-dynamics is qualitatively controlled by the liquid packing density. It is hence monotonic within a narrow composition range and not sensitive to small composition variations. Similarly, replacing Cu by Ni results in a slower atomic dynamics in the Zr-Ni liquids, as a consequence of the more dense packing. This is in contrast to the strong composition dependence of the glass-forming behaviour, and the better glass-forming ability of the Zr-Cu over Zr-Ni alloys, which usually favours sluggish liquid dynamics. Thus, in the Zr-Cu case, the glass-forming ability is not directly correlated with liquid dynamics and packing density.

Non-Equilibrium Solidification of Undercooled Metallic Melts

If a liquid is undercooled below its equilibrium melting temperature an excess Gibbs free energy is created. This gives access to solidification of metastable solids under non-equilibrium conditions. In the present work, techniques of containerless processing are applied. Electromagnetic and electrostatic levitation enable to freely suspend a liquid drop of a few millimeters in diameter. Heterogeneous nucleation on container walls is completely avoided leading to large undercoolings. The freely suspended drop is accessible for direct observation of rapid solidification under conditions far away from equilibrium by applying proper diagnostic means. Nucleation of metastable crystalline phases is monitored by X-ray diffraction using synchrotron radiation during non-equilibrium solidification. While nucleation preselects the crystallographic phase, subsequent crystal growth controls the microstructure evolution. Metastable microstructures are obtained from deeply undercooled melts as supersaturated solid solutions, disordered superlattice structures of intermetallics. Nucleation and crystal growth take place by heat and mass transport. Comparative experiments in reduced gravity allow for investigations on how forced convection can be used to alter the transport processes and design materials by using undercooling and convection as process parameters.

Structural aspects of glass-formation in Ni-Nb melts

We report on investigations of the static structure factors of glass-forming Ni59.5Nb40.5 alloy melts by combination of the containerless processing technique of electrostatic levitation with neutron diffraction. By application of the isotopic substitution method, the full set of partial structure factors was determined. The short-range order in liquid Ni59.5Nb40.5 is characterized by a large nearest neighbor coordination number of ZNN = 14.3 and a chemical short-range order with an affinity for the formation of heterogeneous Nb-Ni nearest neighbors. The structure factors observed here in the liquid state closely resemble those reported for amorphous Nb-Ni solids. The comparison with earlier results on the short-range structure in Zr-based glass-forming melts suggests that a large local density of packing, chemical order, and structural frustration are, amongst others, common structural properties of these metallic glass-forming systems, which favor glass-formation.

Thermal and optical properties of La_2O_3-Nb_2O_5 high refractive index glasses

(100−x)La2O3-xNb2O5 glasses with high refractive indices (>2.1) and low wavelength dispersion were prepared by containerless processing. All the glasses were colorless and transparent in the visible region. The glass forming region was divided into two regions: a high-La2O3-content (39 ≤ x ≤ 42) region and a high-Nb2O5-content (60 ≤ x ≤ 75) region. The dependence of the physical properties on the composition for these two types of glasses was different, implying that the high-La2O3-content glasses (La glasses) and high-Nb2O5-content glasses (Nb glasses) were intrinsically different. A large difference in the molar volumes of the two types of glasses indicated that the Nb glasses were more densely packed than the La glasses. Furthermore, the oxygen polarizabilities estimated from the molar volumes and refractive indices were greater than 2.43 A3 for the La glasses, while those for the Nb glasses decreased from 2.43 A3 with decreasing x. The large oxygen polarizabilities, as compared to those of conventional optical glasses, indicate a particularly high degree of ionic character for the component elements in the glasses. These results suggest that both the La and Nb glasses are desirable materials for high-valued optics, such as lenses with high power and high resolution as well as wide viewing angles used for a digital camera in a smartphone.

Containerless Processing in the Study of Metastable Solids from Undercooled Melts

An undercooled melt possesses an enhanced free enthalpy that enables to crystallize metastable solids in competition with their stable counterparts. Crystal nucleation selects the crystallographic phase whereas the growth dynamics controls microstructure evolution. We apply containerless processing such as electromagnetic and electrostatic levitation to containerlesss undercool and solidify metallic melts. Heterogeneous nucleation on container-walls is completely avoided leading to large undercooling with the extra benefit that the freely suspended drop is direct accessible for in situ observation of crystallization far away from equilibrium. Results of investigations of maximum undercoolability on pure zirconium are presented showing the limit of maximum undercoolability set by the onset of homogeneous nucleation. Rapid dendrite growth is measured as a function of undercooling by a high-speed camera and analysed within extended theories of non-equilibrium solidification. In such both supersaturated solid solutions and disordered superlattice structure of intermetallics are formed at high growth velocities. A sharp interface theory of dendrite growth is capable to describe the non-equilibrium solidification phenomena during rapid crystallization of deeply undercooled melts.

Generation Mechanism of Horizontal Holding Force of an Acoustically Levitated Droplet

Container-less processing could prevent the heterogeneous nucleation and contamination due to the container wall. Acoustic levitation is expected to be used in the field of the analytical chemistry and manufacturing new materials. Thus, it is important to understand the non-linear behavior of an acoustically levitated droplet. The purpose of the study is to experimentally investigate the interfacial behavior and translational motion of an acoustically levitated droplet. In this study, translation of the droplet with the different reflectors was recorded by high speed video camera and estimated quantitatively. As a result, it is shown that translational amplitude of droplet with concave reflector was drastically smaller than that with flat type because of the lower sound pressure gradient around the levitated droplet.

無容器浮遊法による超高屈折率ガラスの開発

TiO2 – based and Nb2O5 – based glasses without any network former oxides were prepared by containerless processing. The glasses exhibit excellent optical properties such as high refractive index with low wavelength dispersion, and transparency in visible light. It was indicated that the high refractive index is caused by unusual dense state of highly ionic constituent elements. Structural analyses revealed that the dense packed structure is realized because oxygen coordination numbers of cations are rather larger than those of conventional oxide glasses and the cation-oxygen polyhedra are connected to each other not only by corner-sharing but also edge – or face sharing. These results raise the possibility that novel higher refractive index with lower wavelength dispersion glasses, which contain highly ionic heavy elements at the lower left in the periodic table, may be synthesized.

Increase of the blue upconversion emission in Tm3 +/Yb3 + co-doped titanate glass–ceramics

Tm3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glass–ceramics with intense blue emission have been fabricated by containerless processing in an aerodynamic levitation furnace, following by heat treatment at different temperatures in the air. The intensity of blue upconversion luminescence increases two times compared with the precursor glass after a heat treatment process at 890°C. Blue and red emissions centered at 476nm and 650nm owing to the Tm3+ transitions 1G4→3H6 and 1G4→3F4 are achieved under the excitation of 980nm at room temperature. The upconversion luminescence is based on a two-photon process by the cooperative sensitization which transfers energy from Yb3+ to Tm3+. Furthermore, Tm3+ and Yb3+ ions are enriched in nanoparticles which disperse in glass matrixes. Dense lattice fields and strong partitions of nanocrystals reduce energy losses caused by mutual interactions among rare earth ions to obtain strong upconversion luminescence. The presented intense blue emission of Tm3+/Yb3+ co-doped La2O3–TiO2–ZrO2 glass–ceramics shows potential promising perspective in the optical materials.

Phase selection and microstructure formation in undercooled Co–61.8 at.% Si melts under various containerless processing conditions

The hypoeutectic composition Co–61.8at.% Si was undercooled and solidified using electromagnetic levitation, electromagnetic levitation under a static magnetic field, electrostatic levitation and glass-fluxing. The samples generally showed two thermal events, either separated or continuous depending on undercooling. In situ monitoring of the two thermal events with a high-speed camera revealed a sudden decrease of dendritic growth velocities of primary phases at a critical undercooling of 88K. Scanning electron microscopy studies of the solidified samples showed that the CoSi compound and the CoSi2 compound nucleate as the primary phase for low and high undercoolings, respectively. The microstructure of the samples depends not only on undercooling, but also on the onset temperature or delay time of the second thermal event. Melt convection has no effect on the primary phase selection in undercooled melts, but it has a significant effect on the delay time and therefore on microstructure formation of the samples for high undercoolings.

Correlated process of phase separation and microstructure evolution of ternary Co-Cu-Pb alloy

The phase separation and rapid solidification of liquid ternary Co45Cu42Pb13 immiscible alloy have been investigated under both bulk undercooling and containerless processing conditions. The undercooled bulk alloy is solidified as a vertical two-layer structure, whereas the containerlessly solidified alloy droplet is characterized by core-shell structures. The dendritic growth velocity of primary α(Co) phase shows a power-law relation to undercooling and achieves a maximum of 1.52 m/s at the undercooling of 112 K. The Pb content is always enriched in Cu-rich zone and depleted in Co-rich zone. Numerical analyses indicate that the Stokes motion, solutal Marangoni convection, thermal Marangoni convection, and interfacial energy play the main roles in the correlated process of macrosegregation evolution and microstructure formation.

Complex phase separation of ternary Co–Cu–Pb alloy under containerless processing condition

The macrosegregation and solidification processes of ternary Co43Cu40Pb17 alloy have been investigated under the containerless processing condition in drop tube. The addition of Pb element is found to be quite effective to promote the phase separation of Co–Cu alloy, resulting in a macroscopic segregation pattern in ternary Co43Cu40Pb17 alloy. The rapidly solidified alloy droplets are characterized by core–shell structures due to the combined effects of reduced gravity and containerless state during free fall. When the droplet diameter is smaller than 450μm, a kind of three-layer core/shell structure is formed, which consists of a Co-rich core, a Cu-rich intermediate layer and a Pb-rich surface shell. EDS analyses show that the Pb solute has a stronger affinity with Cu-rich liquid and a repulsive interaction with Co-rich liquid. The solidification process of Co43Cu40Pb17 ternary alloy involves two successive phase separation events, a subsequent peritectic transformation and a final monotectic transformation.

Containerless processing for preparation of akermanite bioceramic spheres with homogeneous structure, tailored bioactivity and degradation.

Bioceramic spheres have been widely studied for bone/dental filler materials. Conventional methods, such as alginate cross-linking, microemulsion and spray drying, have distinct disadvantages for preparing pure bioceramic spheres with controllable size, bioactivity and degradation. In this study, a containerless processing method, for the first time, was applied to prepare bioceramic spheres for potential bone/dental filling applications. Akermanite (Ca2MgSi2O7, AKT) glass spheres were firstly prepared by a unique containerless processing method. Then, the as-prepared AKT glass spheres were heat-treated at varied temperatures. Furthermore, the effect of heat treatment on the phase transition, surface microstructure, apatite mineralization and ionic dissolution production of AKT spheres has been systematically studied. The interaction of MC3T3 cells with AKT spheres was further studied by investigating cell attachment, proliferation and alkaline phosphate (ALP) activity. The results show that containerless processing is a quite effective method to prepare homogeneous AKT glass spheres with controllable size. Heat-treatment promotes the phase transition from amorphous, semi-crystalline to fully crystalline AKT spheres. Thus, AKT spheres with controllable crystallinity were successfully prepared by combining containerless processing and heat treatment. The as-prepared AKT glass spheres induced apatite mineralization after soaking in simulated body fluids (SBF) for 7 days; however, AKT spheres treated at 800 °C suppressed apatite mineralization in SBF. Interestingly, AKT spheres treated at 1000 or 1350 °C had distinct apatite mineralization, indicating that the bioactivity of the AKT spheres can be regulated by modulating the heat-treatment-induced crystallinity. Further study has shown that the ionic dissolution production of the containerless-processed AKT spheres can be tailored by controlling the heat-treatment temperatures. The prepared crystalline AKT spheres supported the attachment, spreading, growth and early differentiation of MC3T3 cells, and significantly stimulated the proliferation of MC3T3. Therefore, the containerless-processed AKT spheres may be a unique bone/dental filler material due to their homogeneous structure, controllable size, bioactivity and ionic degradation, as well as their excellent cytocompatibility.

20809 超音波浮遊液滴の相変化過程における伝熱流動特性(086-3【熱流体工学のフロンティア(3)】)

Container-less processing using levitation technique could prevent heterogeneous nucleation and contamination from container wall. Acoustic levitation is expected to be used for analytical chemistry and manufacturing new materials. Thus,It is important to gather the knowledge about acoustically levitated droplet. The purpose of this study is to investigate the heat transfer and flow characteristic of an acoustically levitated droplet. The following results were obtained from experiments. Evaporation process of levitated droplet was observed. Surface temperature lowers after levitation and volume decreases while levitation. External flow was observed and differs by water and ethanol. Toroidal vortex near the ethanol droplet interface was observed. By measuring temperature,temperature distribution near the droplet surface was found. Finally, heat transfer coefficient was estimated and it was higher than the existing experimental formula.

VISCOSITY MEASUREMENT USING BREAKUP OF A LEVITATED DROPLET BY ROTATION

Thermophysical property measurement without container is used for high-temperature molten material. A microgravity environment is useful in order to achieve a containerless condition, and the levitation technique can also be used for containerless processing even on the ground. The purpose of this study is to establish a new measurement technique to measure viscosity in the moderate viscous range, which has no conventional measurement methods. In this study, a droplet is levitated by electrostatic force and induced to rotate. The dynamic behavior of the levitated droplet shape is observed, and the viscosity measurement is obtained by using breakup of the levitated droplet depending on the viscosity.

Back Cover: Phys. Status Solidi C 12/2012

physica status solidi cVolume 9, Issue 12 Back CoverFree Access Back Cover: Phys. Status Solidi C 12/2012 First published: 14 December 2012 https://doi.org/10.1002/pssc.201290022AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract Containerless processing is a suitable technique for vitrification of materials with low glass-forming ability, because it suppresses inhomogeneous nucleation from the container wall and promotes deep undercooling in molten materials. Therefore, materials even without a network former oxide can be vitrified using containerless processing. In their paper on pp. 2424–2427, Atsunobu Masuno et al. report the glass formation in the LaO3/2–TiO2–MOx ternary system (M = Ga, Y, Gd, Hf, W, Zn, Ge, Nb, Ta, Bi, and Ba) by an aerodynamic levitation furnace. These TiO2-based glasses exhibit a high refractive index around 2.3 and low wavelength dispersion with a large Abbe number over 20. It was found that the substitution of GdO3/2 for LaO3/2 components was most effective for the increase of the Abbe number with keeping a high refractive index. These results are useful for glass composition design toward future innovative optical applications in the visible region. The illustration shows schematically an aerodynamic levitation furnace, surrounded by a series of pictures of the cooling and glass formation process of the levitated titanate melt. Volume9, Issue12Special Issue: Fifth International Conference on Optical, Optoelectronic and Photonic Materials and Applications (ICOOPMA12), see further papers in Phys. Status Solidi A 209, No. 12 (2012)December 2012 RelatedInformation

Does an icosahedral short-range order prevail in glass-forming Zr-Cu melts?

We report on investigations of the static structure factors of glass-forming Zr-Cu alloy melts by combination of the containerless processing technique of electrostatic levitation with diffraction of neutron and synchrotron radiation. The partial Bhatia-Thornton structure factors SNN and SNC were determined from the two total structure factors. While it is widely assumed in literature that the good glass-forming ability of Zr-Cu is related to an icosahedral short-range order prevailing in the melt, our partial structure factors demonstrate that the liquid Zr-Cu is not characterized by a dominant icosahedral short-range order.

Glass‐forming region and high refractive index of TiO2‐based glasses prepared by containerless processing

AbstractTiO2‐based high‐refractive‐index glasses without any network former oxides were fabricated by containerless processing in an aerodynamic levitation furnace. The glass‐forming region of a BaO‐LaO3/2‐TiO2 ternary system was determined. Moreover, the glass transition and crystallization temperatures of a (La1−xBax)4Ti9O24 glass system and a LaO3/2‐TiO2‐M Ox ternary system (M = Ga, Y, Gd, Hf, W, Zn Ge, Nb, Ta, Bi, and Ba) were obtained. Finally, the refractive index dispersion of LaO3/2‐TiO2‐M Ox (M = Ga, W, and Gd) was also investigated. The results indicate that these glasses are promising materials for future optical applications in the visible region. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transparent and High Refractive Index La2O3–WO3 Glass Prepared Using Containerless Processing

Transparent and high refractive index 0.2La2O3·0.8WO3 glass was prepared in bulk form using containerless processing. The glass transition temperature, crystallization onset temperature, and melting temperature were 553°C, 594°C, and 1043°C, respectively. The glass was colorless and widely transparent, in the visible to infrared region, indicating that the valence state of the W ion was 6. The refractive index was 2 in the visible range, and the Abbe number estimated from the Drude–Voigt relationship was 24. These results indicate that the La2O3–WO3 glass would be useful for optical applications in the visible to infrared region.

Nucleation and Thermophysical Properties of Glass-Forming Liquids

The intimate links among structure, nucleation, and thermophysical properties are demonstrated from a few select experiments on high-melting-temperature metallic alloy liquids, made possible by containerless processing techniques. To complement the ground-based studies, future experiments on the International Space Station using a new electromagnetic levitation facility developed by the European Space Agency are discussed. The knowledge obtained from these studies is expected to deepen the understanding of supercooled liquid properties, elucidate their role in nucleation and glass formation, and test and develop more advanced theories of nucleation. All of these are expected to improve liquid phase processing techniques for crystalline and amorphous materials so that better functional properties may be achieved.