Directional solidification of faceting material in a centrifuge

In situ observation of directional solidification of salol was carried out at a centrifuge acceleration of 10 G (G = 9.81 m/s²). Growth rate, temperature distribution and flow pattern in front of the solid-liquid interface could be simultaneously measured and visualized using a microscopic interferometer and thermocouples. The specimens were transparent, faceting organic compounds, which develop cellular arrays. These materials of commercial grade were purified by several zone-refining cycles on a laboratory scale and were enclosed in quartz glass cells. The solidification were controlled by the imposed temperature gradient in the cell and cooling rate at the both side of the cell. The growth direction was adjusted to opposite to the acceleration vector. We found appearance of a local recalescence region in front of the growing surface not only under 1 G but 10 G. The uniformity of the recalescence region along the interface seemed to be defined by the flow induced by the centrifuge acceleration. We considered the non-uniform temperature distribution ahead of the interface as one of the driving forces of the interface breakdown.