THE EFFECTS OF CONVECTION ON OSTWALD RIPENING IN SOLID LIQUID-MIXTURES

The effects of convection on Ostwald ripening in solid-liquid mixtures have been studied using a Sn-Pb alloy over a wide range of volume fraction solid. The convection was induced by a slow rotation of a disk shaped sample with the axis of rotation perpendicular to the gravity vector. At low volume fractions of solid the experiments show that convection can alter the exponent of the temporal power law for the average intercept length from its classical value of 1/3 to 0.37. For intermediate volume fractions of solid the temporal exponent is 1/3, but the amplitude of the temporal power law for the average particle radius dcpends on the rate of rotation. At very high volume fractions of solid, where a stable skeletal structure was present, rotation had no effect on the kinetics of the ripening process. A theoretical analysis of Ostwald ripening in the low Peclet number limit was undertaken in an effort to understand the experimental results. The analysis showed that temporal power law solutions to the equations describing ripening do not exist when the particles move in the fluid with either a constant velocity or according to Stokes law. However, if the magnitude of the fluid flow scales with time in the proper way, temporal power law solutions can be found which are qualitatively consistent with the experiments.