The Transient Evolution of Flow Due to the Excitation Pulse in Oscillating Drop Experiments in Microgravity Electromagnetic Levitation

In oscillating drop experiments, surface oscillations in a molten sample are captured and analyzed to determine the surface tension and viscosity of a melt without the need to contact the liquid sample. In electromagnetic levitation, surface oscillations are initiated using an excitation pulse in the electromagnetic field. The variation in the electromagnetic force field drives rapid acceleration in the melt while also changing the flow pattern. During the quasi-static flow conditions prior to the excitation pulse, the flow displays a “positioner-dominated” flow pattern with 4 recirculation loops in the sample hemisphere. However, the accelerating flow of the excitation pulse transitions into a “heater-dominated flow” pattern in which there are only 2 recirculation loops in the sample hemisphere. Following the excitation pulse, the flow rapidly slows and quickly returns to the conditions present before the excitation pulse. For many combinations of parameters, the transition in the flow pattern results in a very complicated variation in velocity with time; that variation is the topic of this paper

Demonstration of the effect of stirring on nucleation from experiments on the International Space Station using the ISS-EML facility

The effect of fluid flow on crystal nucleation in supercooled liquids is not well understood. The variable density and temperature gradients in the liquid make it difficult to study this under terrestrial gravity conditions. Nucleation experiments were therefore made in a microgravity environment using the Electromagnetic Levitation Facility on the International Space Station on a bulk glass-forming Zr57Cu15.4Ni12.6Al10Nb5 (Vit106), as well as Cu50Zr50 and the quasicrystal-forming Ti39.5Zr39.5Ni21 liquids. The maximum supercooling temperatures for each alloy were measured as a function of controlled stirring by applying various combinations of radio-frequency positioner and heater voltages to the water-cooled copper coils. The flow patterns were simulated from the known parameters for the coil and the levitated samples. The maximum nucleation temperatures increased systematically with increased fluid flow in the liquids for Vit106, but stayed nearly unchanged for the other two. These results are consistent with the predictions from the Coupled-Flux model for nucleation

Dynamic nucleation in sub-critically undercooled melts during electromagnetic levitation

By classical nucleation theory, sub-critically undercooled melts in electromagnetic levitation are expected to be very stable for extended periods of time. While electromagnetic levitation experiments are typically consistent with classical nucleation theory, there have been several historical instances including experiments on zirconium during the MSL-1 campaign and during the IML-2 experiments where the molten sample solidified at sub-critical undercoolings. While different electromagnetic levitation conditions were present in these anomalous nucleation events, both sets of anomalous nucleation events were attributed to dynamic nucleation. The work presented here investigates more recent experiments in the International Space Station Electromagnetic Levitation facility in which both sets of anomalous nucleation events were replicated and further investigated. The conditions of the MSL-1 solidification events were replicated in the ISS-EML using a pure zirconium sample held in isothermal conditions between 45 °C and 290 °C below the melting temperature. The sample successfully solidified in 18 of these experiments in less than 600 s where classical nucleation theory predicts the melt to remain liquid for very long periods of time. The IML-2 result, was replicated in the ISS-EML in which a Zr64Ni36 sample was used to demonstrate pulse-triggered nucleation events. During these experiments, the excitation pulse triggered solidification in the sample which was held between 59.5 °C and 64.5 °C below the melting temperature. Again, classical nucleation predicts that under these conditions the sample will remain molten. The results of both sets of experiments are consistent with dynamic nucleation theory in which nucleation events are affected by the flow conditions within the drop

Confirmation of Anomalous Nucleation in Zirconium

Pure, low-oxygen zirconium samples have been observed to nucleate a solid phase under conditions during which the sample was expected to remain liquid. This phenomenon was first seen during Spacelab Mission MSL-1R (materials science laboratory) experiments and has since also been observed in the International Space Station (ISS) electromagnetic levitation (EML) facility on a different sample. Current work has been able to replicate these anomalous solidification events under a range of conditions in the ISS MSL-EML facility. The solidification events are not well explained by classical homogeneous or heterogeneous nucleation. The current theory is that collapsing voids in the melt create a local region of high pressure that results in local material being deeply undercooled and a strong driving force for solidification

Pyrolytische Rohstoffrueckgewinnung

SIGLEDEGerman

Pyrolytische Rohstoffrueckgewinnung Abschlussbericht. Abschlussdatum: Oktober 1980

AC 6072 enth. Anhang: Begleitendes Messprogramm zur pyrolytischen Rohstoffrueckgewinnung. 132 S.SIGLETechnische Informationsbibliothek Hannover: RN 2598 (81-017) + AC 6072 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman