Aero-acoustic Levitator Research Articles

On occurrence of multiple-site crystallization in undercooled mullite melts

Using a high-speed video, an interesting multiple-site crystallization phenomenon in undercooled mullite oxide is observed in situ in an aero-acoustic levitation apparatus when a laser heating system is incorporated. This crystallization behavior is discussed considering nucleation theory and growth analysis by defining conditions under which multiple-site crystallization can occur.

Direct growth of REBa 2Cu 3O 7-δ (RE=Yb, Er, Y, Dy, Eu, Sm, Nd and Pr) from undercooled melt using aero-acoustic levitator

The authors have previously reported that the NdBa 2Cu 3O 7-δ (Nd123) phase solidifies directly from undercooled melt using an aero-acoustic levitator combined with a CO 2 laser in dry air flow. The reason why the YBa 2Cu 3O 7-δ (Y123) phase never undergoes primary solidification, however, remains unknown. There are systematic differences in the phase diagrams between stoichiometric Y123 and nonstoichiometric Nd123 with respect to the gradient of the liquidus line and the metastable high-temperature phase. In the present study, the containerless solidification of RE123 (RE=Yb, Er, Y, Dy, Eu, Sm, Nd and Pr) was carried out to compare systematically the direct growth of stoichiometric RE123 (sRE123) with that of nonstoichiometric RE123 (nRE123). In sRE123 specimens, the metastable high-temperature phase, the RE 4Ba 3O 9 (RE430) phase, solidified primarily from undercooled melt, while the nRE123 phase solidified primarily in nRE123 specimens. Moreover, in the Cu-enriched RE 3Ba 6Cu 11O x composition, the sRE123 phase solidified directly from the undercooled melt by suppressing the primary solidification of the RE430 phase. The direct growth of RE123, especially Y123, is discussed using the metastable phase diagram proposed on the basis of the experimental results.

Rapid solidification of Y 3Al 5O 12 garnet from hypercooled melt

Containerless solidification of Y 3Al 5O 12 garnet (YAG) was carried out using an aero-acoustic levitator to elucidate the solidification process beyond the hypercooling limit (Δ T hyp). A YAG melt was seeded at different undercoolings by a SiO 2 trigger needle. The apparent plateau after recalescence disappeared at around Δ T=500 K and the post-recalescence temperature ( T post) decreased from the melting point with further increase in undercooling. Δ T hyp of YAG was estimated to be 769 K using the specific heat of liquid that was evaluated by a heat-transfer calculation from the obtained cooling curves. T post decreased before reaching the estimated Δ T hyp. Although this behavior was ascribed to heat extraction by the levitation gas, which suggests that the YAG melt did not solidify adiabatically due to the low thermal conductivity, the maximum undercooling of 1060 K indicates that the YAG melt solidified beyond Δ T hyp. Moreover, the cellular morphology of YAG was observed even beyond Δ T hyp. It can be seen that the cellular morphology is retained since the thermal supersaturation does not reach unity at Δ T hyp due to the large kinetic effect.

Formation of NdBa2Cu3O7−δ amorphous phase by combining aero-acoustic levitation and splat quenching

Small spherical samples (diameter approximately 2 mm) of NdBa2Cu3O7−δ (Nd123) were fully melted in Ar gas flow in an aero-acoustic levitation device and subsequently rapidly cooled by splat quenching. For samples quenched above the liquidus, the microstructual and x-ray-diffraction (XRD) observations suggested the existence of the amorphous phase with small quantities of the BaCuO2 and BaCu2Ox. The high-temperature XRD results indicated that the decomposition of the amorphous phase, probably assisted by atmospheric CO2 and H2O, led to formation of the BaCO3 phase at 400 °C and, subsequently, the Nd123 phase was formed by the solid diffusion above 800 °C. Another set of Nd123 samples was fully melted in O2 gas flow, undercooled while levitated, and then splat quenched at a temperature below the peritectic temperature (TP). These samples possessed a microcrystalline microstructure of the Nd123 phase that was confirmed by XRD. This indicated that the Nd123 phase was solidified directly from the undercooled melt quenched below TP.

Direct Crystallization of Y<SUB><B>3</B></SUB>Fe<SUB><B>5</B></SUB>O<SUB><B>12</B></SUB> Garnet by Containerless Solidification Processing

Yttrium-iron garnet, Y3Fe5O12 (YIG), is formed via the peritectic reaction of YFeO3 (YIP) and liquid phases. The direct growth of YIG from a highly undercooled melt with stoichiometric YIG composition was studied using an aero-acoustic levitator with a CO2 laser heating system. Although a YIG droplet was successfully levitated and undercooled to 1327°C, about 250°C below its peritectic temperature (TP), YIP was primarily solidified in the microstructure of dendritic YIP with interdendritic eutectics of YIP and FeOX. However, when a droplet was quenched after it was undercooled below TP, single phase of YIG without YIP and FeOX was found. The X-ray diffraction pattern as well as microstructure indicated that YIG was solidified directly and congruently from the undercooled melt, bypassing the peritectic reaction.

Containerless Solidification of Peritectic and Eutectic Ceramics Using Aero-Acoustic Levitator

The containerless solidification of Y 3 Al 5 O 12 (YAG) was carried out using an aero-acoustic levitator with a CO 2 laser irradiation system. Pre-sintered specimens with compositions between Al 2 O 3 and YAlO 3 (YAP) were heated above a critical temperature T cl and then cooled down to form YAG. a mixture of YAP+Al 2 O 3 or an amorphous phase, although it has been reported that cooling from temperatures above T cl leads only to the crystallization of YAP-Al 2 O 3 . The metastable eutectic of YAlO 3 and Al 2 O 3 was commonly observed in the composition range from Al 2 O 3 to YAP. The nucleation of YAG was restricted to the composition range of 32.5 to 40.0 mol.% Y 2 O 3 , particularly when the primary YAP or Al 2 O 3 phase was not precipitated. The nucleation temperature of YAG was scattered largely compared with that of the metastable eutectic.

Microstructural control of NdBa 2Cu 3O 7−δ superconducting oxide from highly undercooled melt by containerless processing

Containerless processing of NdBa 2Cu 3O 7− δ (Nd123) superconducting oxide was achieved by combining aero-acoustic levitation with CO 2 laser heating. Nd123 melt was undercooled to 1207 K below the peritectic temperature and congruently solidified. X-ray diffraction peaks of the processed specimen corresponded well with the standard ones of the tetragonal Nd123. The specimen annealed at 573 K in pure oxygen gas showed a high superconductive transition temperature ( T c) of 95.1 K. Moreover, the solidification process with different initial compositions was investigated and discussed; from the undercooled melt with a Cu-poor composition, a small amount of the Nd 4Ba 2Cu 2O 10 phase and the Nd123 phase were directly solidified. T c values of about 94 K were obtained in Cu-poor specimens. On the other hand, the nonstoichiometric phase, Nd 1+ x Ba 2− x Cu 3O 7− δ , was directly solidified from the undercooled melt with a Cu-rich composition. The T c values decreased from 94.6 to 88.2 K with increasing the Cu concentration from that of stoichiometric Nd123.

Measurements of thermophysical properties of liquid metals relevant to Marangoni effects

Restricted accessMoreSectionsView PDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InRedditEmail Cite this article 1998Measurements of thermophysical properties of liquid metals relevant to Marangoni effectsPhil. Trans. R. Soc. A.356845–856http://doi.org/10.1098/rsta.1998.0191SectionRestricted accessMeasurements of thermophysical properties of liquid metals relevant to Marangoni effects Published:15 April 1998https://doi.org/10.1098/rsta.1998.0191AbstractMarangoni convection is caused by a gradient in the surface tension along a free liquid surface. The dimensionless Marangoni number, which controls the strength of this convection, contains additional thermophysical parameters. For liquid metals, these quantities are best measured under containerless conditions using electromagnetic levitation and non–contact diagnostic tools. In microgravity, small electromagnetic fields are sufficient to position a liquid sample. Some experiments can only be performed in such an environment, most others greatly benefit from microgravity and lead to results of higher precision. This paper reports on both terrestrial and microgravity measurements of thermophysical properties of undercooled liquid metals, including specific heat, density, surface tension, viscosity and electrical conductivity. Previous ArticleNext Article VIEW FULL TEXT DOWNLOAD PDF FiguresRelatedReferencesDetailsCited by Ushakov S, Niessen J, Quirinale D, Prieler R, Navrotsky A and Telle R (2021) Measurements of Density of Liquid Oxides with an Aero-Acoustic Levitator, Materials, 10.3390/ma14040822, 14:4, (822) Bachmann B, Siewert E and Schein J (2012) In situ droplet surface tension and viscosity measurements in gas metal arc welding, Journal of Physics D: Applied Physics, 10.1088/0022-3727/45/17/175202, 45:17, (175202), Online publication date: 2-May-2012. LYUBIMOV D, KONOVALOV V, LYUBIMOVA T and EGRY I (2011) Small amplitude shape oscillations of a spherical liquid drop with surface viscosity, Journal of Fluid Mechanics, 10.1017/jfm.2011.76, 677, (204-217), Online publication date: 25-Jun-2011. Moradian A and Mostaghimi J (2008) Measurement of Surface Tension, Viscosity, and Density at High Temperatures by Free-Fall Drop Oscillation, Metallurgical and Materials Transactions B, 10.1007/s11663-007-9120-8, 39:2, (280-290), Online publication date: 1-Apr-2008. Egry I (2003) Surface Tension Measurements in Microgravity and their Relevance to Marangoni Convection, ChemPhysChem, 10.1002/cphc.200390058, 4:4, (329-333), Online publication date: 14-Apr-2003. Priede J and Geroeth G (2000) Spin-up instability of electromagnetically levitated spherical bodies, IEEE Transactions on Magnetics, 10.1109/20.822545, 36:1, (349-353), Online publication date: 1-Jan-2000. This Issue15 April 1998Volume 356Issue 1739Discussion Meeting Issue ‘Marangoni and interfacial phenomena in materials processing’ organized by E. D. Hondros, M. McLean and K. C. Mills Article InformationDOI:https://doi.org/10.1098/rsta.1998.0191Published by:Royal SocietyPrint ISSN:1364-503XOnline ISSN:1471-2962History: Published online15/04/1998Published in print15/04/1998 License: Citations and impact Keywordselectrical conductivityelectromagnetic levitationsurface tensionmicrogravitydensityoscillating drop technique

Growth of Olivine by Aero-Acoustic Levitation: Reproduction of Meteorite Texture

Growth of Olivine by Aero-Acoustic Levitation: Reproduction of Meteorite Texture

Design and Performance of the Aero-Acoustic Levitator

Design and Performance of the Aero-Acoustic Levitator

Aero-acoustic levitation: A method for containerless liquid-phase processing at high temperatures

A method for containerless liquid-phase processing was developed which has practical application in process and property research on virtually any material which is involatile at the melting point. It combines aerodynamic and acoustic forces to support and position the levitated material. The design provides forced convection control of the thermal boundary in the gas surrounding beam-heated specimens, which stabilizes the acoustic forces and allows acoustic positioning necessary to stabilize the aerodynamic levitation forces on molten materials. Beam heating and melting at very high temperatures was achieved. Experiments were conducted on specimens with diameters in the range 0.25–0.4 cm, of density up to 9 g/cm3, at temperatures up to 2700 K, and in oxygen, air, or argon atmospheres. Unique liquid-phase processing results included deep undercooling of aluminum oxide, glass formation at exceptionally small cooling rates, complete melting and undercooling of YBa2Cu3Ox superconductor materials, direct formation of the YBa2Cu3Ox from the liquid phase, and the vaporization of volatile constituents from a low-liquefaction point glass to form a refractory, high melting material. The application of rapid containerless batch processing operations to materials synthesis is discussed.

Formation of tetragonal YBa2Cu3O7−δ from an undercooled melt

Containerless processing of YBa2Cu3O7−δ was performed using an aero-acoustic levitation technique. Upon solidification from the liquid, spheres of size 2.5 mm diameter undercooled and recalesced, forming tetragonal YBa2Cu3O7−δ directly from the melt. Subsequent to solidification processing, these samples were annealed to single phase YBa2Cu3O7−δ with orthorhombic symmetry as indicated by powder XRD, SQUID magnetometer measurements indicate a sharp superconducting transition at approximately 85 K. Magnetic Jc values, calculated using the Bean critical state model, indicate that the spheres can carry critical current densities on the order of 104 A cm−2. Microstructural characterization has been performed on both the as-solidified and annealed spheres.