Visualization of convective flow in liquid metals

Segregation in compound electronic materials and advanced structural alloys is one of the prime foci in materials research. A radioscopic technique was developed to visualize density fields in opaque metallic melts. Beginning with pure element melts, the technique was refined to study alloys. With the pure monocomponent gallium every experiment delivered results that are in line with current theories. When alloying the gallium with indium, the experiments showed under specific conditions serious discrepancies with theory, such as a threshold for onset of convection in natural convection situations. This threshold is linked to an observation of a substantial gravitational segregation of indium in the melt which is, for currently unknown reasons, more than predicted by thermodynamic theory. Further, thermosolutal convection, which is also expected in the alloyed melts, does not develop according to predictions in salt solutions. In conclusion, the experiments have revealed several deficiencies in current theoretical treatments of liquid metal convection with solidification which emphasize the crucial need for experiments to validate analytical and numerical models