Measurement of surface tension in an atmosphere with controlled oxygen partial pressure under microgravity using a parabolic flight
Abstract
Use of a levitation technique is an elegant way to determine thermophysical properties of high temperature melts, because this containerless technique can avoid contamination from a container and assures measurement in a wide temperature range including superheated and undercooled conditions. In particular, electromagnetic levitation is suitable for electrically conductive materials, such as molten metals, alloys and semiconductors. For surface tension measurement, the Rayleigh equation can be applicable only under microgravity condition [1]. However, when this technique is applied on earth, the l = 2 mode frequency is split into five frequencies, because a droplet is deformed from a spherical shape into an egg shape due to gravitational force and the Lorentz force. Surface tension must be calculated taking account of correction term [2]. Therefore, measurement under microgravity is required to minimize uncertainty. Furthermore, surface tension is sensitive to oxygen partial pressure of an ambient atmosphere. However, there has been less report on surface tension measurement under microgravity in an atmosphere with controlled oxygen partial pressure. We are going to measure surface tension of high temperature metallic melts under microgravity using a parabolic flight of a jet aircraft, the Gulf Stream II, operated by Diamond Air Service in Japan. In September of 2007, through parabolic flight experiments we confirmed that droplets of Cu and Ag were successfully levitated using a newly designed coil under the 1G and 10-2G conditions. Droplets were also assured to be levitated in the pull-up period (1.5G); we can melt samples before entering microgravity condition, so that we can use 20 second microgravity only for measurement. On earth, surface tension of molten silicon was successfully measured using electromagnetic levitation in an ambient atmosphere with various oxygen partial pressures; surface tension of molten silicon showed a marked dependence of oxygen partial pressure. Oxygen partial pressure control system has been designed and installed within an electromagnetic levitation facility for parabolic flight experiments. References [1] Lord Rayleigh: Proc. Royal Soc. London, 29, 71 (1879). [2] D. L. Cummings and D. A. Blackburn: J. Fluid Mech. 224, 395 (1991).
- Publication:
-
37th COSPAR Scientific Assembly
- Pub Date:
- 2008
- Bibcode:
- 2008cosp...37.1232H