Transient Ostwald ripening and the disagreement between steady-state coarsening theory and experiment

The coarsening of solid-Sn particles in a Pb-Sn liquid has been studied und er microgravity conditions. These experiments permit an unambiguous compari son between theory and experiment to be made. In contrast to steady-state t heories, such as those due to Lifshitz and Slyozov and Wagner, the scaled p article size distributions evolve in samples containing 0.1 and 0.2 volume fractions of solid. Steady state was nor reached even though the average pa rticle radius increased by a factor of three during the experiment. In addi tion, the scaled spatial correlation functions were also found to be time d ependent in samples containing 0.1, 0.2, and 0.3 volume fractions of solid. The size distributions and correlation functions for all coarsening times at the fractions less than or equal to0.3 agree with the predictions of a t heory for transient coarsening. We show that the microstructures have not r eached the steady-stare regime for all volume fractions, are thus not self- similar: and that given our initial experimental conditions the time requir ed to reach steady-state coarsening increases with increasing volume fracti on. In these experiments, and we suspect in others as well, the transients are sufficiently long that steady-state theories cannot adequately describe the evolution of the microstructure. (C) 2001 Acta Materialia Inc. Publish ed by Elsevier Science Ltd. All rights reserved.