Flows before the solidification front in transparent model systems

The processes which determine the structure during solidification of a material occur in a small area ahead of the growth front. The boundaries of this area are determined by the flow in the melt and, in addition, by the morphology and growth rate of the solidification front. Interaction effects between the flow in the melt and the solidification front can be described by characteristic quantities. The type of interactions involved can be utilized to affect the morphology and, therefore, the structure which is formed. Processes occurring before and during solidification can be directly observed with the aid of transparent model systems. It is also possible to determine the velocity, temperature, and density distributions by means of a noncontact approach. Processes not related to convection can be separately explored by eliminating convection on the basis of a conduction of experiments in Spacelab. Similarity relations make it feasible to derive conditions for metal systems. The considered investigation provides, thus, a contribution to 'solidification technology'.