BUBBLE BEHAVIOR DURING SOLIDIFICATION IN LOW GRAVITY

The trapping and behavior of gas bubbles were studied during low-gravity solidification of carbon tetrabromide, a transparent metal-model material. The experiment was performed during a NASA-sponsored sounding rocket flight and involved gradient freeze solidification of a gas-saturated melt. Gas bubbles were evolved at the solid-liquid interface during the low-gravity interval. No large-scale thermal migration of bubbles, bubble pushing by the solid-liquid interface, or bubble detachment from the interface were observed during the low-gravity experiment. A unique bubble motion-fluid flow event occurred in one specimen: a large bubble moved downward and caused some circulation of the melt. The gas bubbles that were trapped by the solid in commercial purity material formed voids that had a cylindrical shape, in contrast to the spherical shape that had been observed in a prior low-gravity experiment. These shapes were not influenced by the gravity level (10-4 g0 vs g0), but were dependent upon the initial temperature gradient. In higher purity material, however, the shape of the voids changed from cylindrical in Ig to spherical in low gravity. © 1979 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.