COARSENING OF LIQUID AL-PB DISPERSIONS UNDER REDUCED GRAVITY CONDITIONS

In the multifurnace assembly (MFA) of the free-flying satellite EURECA , experiments were performed with molten Al-Pb alloys to investigate O stwald ripening of liquid-liquid dispersions under diffusive condition s free from any sedimentation effect. Al-Pb alloys with very low volum e fractions of dispersed phase (0.75 and 1.1 vol.%) were processed by annealing cylindrical samples within the liquid miscibility gap at 107 3 K for 1, 5 and 20 h. The initial droplet size distribution was cente red around 0.5 mu m diameter. After the annealing treatments in the MF A a coarsening of the droplets to sizes around 5-10 mu m was observed. The droplets were, however; not evenly distributed in the samples. Th ere was some drift which can be attributed to Marangoni motion caused by small temperature gradients (0.5-3 K cm(-1)) during the annealing t reatment and also the heating and cooling periods. The microstructural observations agree with similar results obtained in Spacelab 1 with Z n-Pb alloys. The coarsening is a superposition of diffusional Ostwald ripening and coagulation of droplets by Marangoni motion and discussed with a model based on population dynamics.