ASA 125th Meeting Ottawa 1993 May

4aPA6. Undercooling and solidification of acoustically levitated molten drops.

Kenichi Ohsaka

Eugene H. Trinh

Jet Propulsion Lab., California Inst. of Technol., M/S 183-401, 4800 Oak Grove Dr., Pasadena, CA 91109

Undercooling of a liquid prior to the nucleation of a solid is necessary for producing novel microstructures including metastable phases that are not formed by conventional solidification processes. Because containerless techniques such as acoustic levitation are capable of achieving a high undercooling level of liquids, they are under consideration as possible techniques for material processing on Earth and in space. For an application of acoustic levitation on Earth, however, there is a strong concern that ultrasound may prematurely initiate the nucleation of the solid and prevent further undercooling in experiments designed for the study of solidification in the deeply undercooled liquid. An experiment using a model material with a single axis levitation system shows an effect of ultrasound as the occasional nucleation of the solid at low undercooling levels. This premature nucleation may be explained by thermodynamic considerations which predict an increase in effective undercooling of the liquid upon the collapse of cavities. [Work supported by NASA.]