Vibrational Stirring in Bridgman Crystal Growth

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.

Autorentext
Kevin Zawilski graduated from Bucknell University in 1998 with a BS in Chemical Engineering. He received a MS and PhD in Materials Science from Stanford University in 2000 and 2004 respectively. He has been an author 15+ technical publications and is currently working in the field of crystal growth and materials development for IR lasers.

Klappentext
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.