Pressure-mediated effects on thermal dendrites

We subjected succinonitrile dendrites growing under steady-state conditions to a rapid change in thermal driving force through a step-change in pressure. This change in pressure caused a corresponding change in the equilibrium melting temperature due to the Clapeyron effect, and a shift in the temperature field due to an adiabatic temperature change in both the solid and its melt. The new thermal conditions caused the dendrites to transition from wellcharacterized initial steady states to states appropriate for the new operating conditions. The initial and final states are clearly discernable, but the onset of the change in tip radius lags behind the change in tip velocity even though the total transition times appear to be similar. During the transition, a fast growing, small dendrite emerges out of the tip of a slow growing, large dendrite. Lastly, the pressure changes appear to destabilize the interface, which leads to the initiation of a dominant side branch. This work constitutes evidence that pressure changes quantifiably change growth behavior and can be used as a perturbation to influence interfacial morphology in a well-characterized free dendritic growth system. This hints at how such a mechanism may be used to control growth microstructures. r 2005 Elsevier B.V. All rights reserved. PACS: 68.70.+w; 81.30.Fb; 64.70.Dv