Vibrational Stirring in Bridgman Crystal Growth: Low-Frequency Vibrations to Control Fluid Flow

This PhD thesis examines a promising stirring technique called coupled vibrational stirring (CVS) with the aim of quantifying its effects so that it could be applied to the Bridgman growth of technologically important materials. CVS generated flows were directly studied using a physical modeling system containing water/glycerin. Sodium nitrate was chosen as a model growth system due to its transparent melt and solid. Lead magnesium niobate¿lead titanate (PMNT) was chosen as a third system because of its application for high performance solid state transducers and actuators. One of the most important results obtained was the discovery of an axial velocity gradient decreasing from the fluid surface. The velocity profile and corresponding depth of fluid motion were found to be easily tuned by changing the vibrational frequency. When a control system was used to hold a constant fluid velocity near the growth interface during crystal growth, good quality crystals were produced. By adjusting the fluid flow rate near the growth interface, the interface shape could be controlled at high growth rates in the sodium nitrate system.