Abstract
Real-time observation of the melting and solidification of the system PbBri-PbCh under microgravity was successfully performed using a sounding rocket. An analysis of the solid-liquid interface shape, liquid flow and growth stability provides basic data concerning crystal growth from a melt. he interface shape is convex towards the melt during melting and becomes almost flat upon solidification, which agrees well with the results of a computational thermal analysis. The liquid flow observed during melting had a velocity between 0.2 mm/ s and 1.5 mm/ s. This is much higher than expected and is most likely due to Marangoni convection. Although PbBr 2 melt is capable of wetting with the quartz, traces of microscopic free surface areas during solidification are observed on the grown crystal surface. The microscopic free surface is the origin of Marangoni convection. Observation of the Marangoni flow in the liquid wettable to an ampoule wall is the first time and is of much interest. The experimentally determined critical G/ R for stable growth is 3.3 K·h/ cm2, which agrees well with 2.7 K· h/ cm2 derived numerically using the physical properities of the PbBri-PbCh system.
