Levitation methods for structural and dynamical studies of liquids at high temperatures

Abstract

Abstract. In recent years, levitation methods have been increasingly used to study the atomic structure and dynamics of high-temperature liquids, in particular metallic melts. These methods provide a containerless and, consequently, high-purity sample environment. No corrections for signals due to a crucible need to be made, and deep undercoolings of the liquid become possible, reducing the effect of thermal fluctuations. On the other hand, the sample position and, hence, the scattering geometry is not fixed and the free sample surface exhibits capillary waves. Nevertheless, the combination of levitation techniques with x-ray or neutron sources has proven to be possible and successfull. This paper reviews the progress made in this field during the last 10 years or so. It discusses the different levitation techniques: aerodynamic, electromagnetic, electrostatic, as well as the applied spectroscopic techniques: x-ray and neutron diffraction, x-ray absorption and quasi-elastic neutron diffraction. Some recent results are also highlighted.

Calculation of absorption and secondary scattering of X-rays by spherical amorphous materials in an asymmetric transmission geometry

“…below the equilibrium melting temperature). Recently, these levitation techniques have been used for laboratory X-ray, synchrotron and neutron scattering studies of these supercooled liquids (Masaki et al, 2007;Egry & Holland-Moritz, 2011;Gangopadhyay et al, 2005;Mauro & Kelton, 2011;Krishnan et al, 1997;Aoki et al, 2003). Owing to surface-tension effects, the liquids are nearly spherical in shape.…”

Change in atomic coordination in a heavily deformed metallic glass

“…In liquids, thermal expansion due to temperature increase is caused by an increase in the equilibrium concentration of vacancies accompanied by a decrease in coordination number rather than by an increase in nearest neighbour distance. [41][42][43][44] For example, the coordination number of Ni in liquid Ni increases from 11.2 to 12.3 when the temperature decreases from 1905 K to 1435 K while changes in interatomic distance in liquid Ni are small compared to those in crystalline Ni at similar temperature increments. 44 Moreover, in molten Si where the bonds have a more covalent character than in pure metals an increase in Z from 4.9 at 1893 K to 6.1 at 1403 K was observed while changes in interatomic distance were again small.…”

“…[41][42][43][44] For example, the coordination number of Ni in liquid Ni increases from 11.2 to 12.3 when the temperature decreases from 1905 K to 1435 K while changes in interatomic distance in liquid Ni are small compared to those in crystalline Ni at similar temperature increments. 44 Moreover, in molten Si where the bonds have a more covalent character than in pure metals an increase in Z from 4.9 at 1893 K to 6.1 at 1403 K was observed while changes in interatomic distance were again small. 45 We therefore conclude that the decrease in Z from %6 to %5 in Al 85 Ni 10 La 5 during ball-milling results either from an increase in the shear band temperature by several hundred K, thus notably exceeding the glass transition temperature, or by plastic deformation at sufficiently low temperatures that do not allow for structural relaxation.…”

Aerodynamic levitation, supercooled liquids and glass formation

“…Containerless methods (also called levitation or contactless processing) represent an appealing solution to long-standing problems in materials processing [1][2][3]. Chemical reactions between a container and its contents can lead to contamination of both components.…”