THE EFFECT OF HEAT CURRENTS ON THE STABILITY OF THE LIQUID SOLID INTERFACE

Rapid changing of the temperature of a liquid in equilibrium with its solid can lead to instabilities of the interface in two ways: the change in pressure, induced by a temperature change at the interface, leads to a uniaxial stress which can cause a Grinfeld instability at the capillary wavelength; a temperature gradient is set up which modifies the effective gravity at the interface. When the effective gravity becomes negative, the interface is unstable at very long wavelengths. For a superfluid, such as He-4, the situation is more complex. If we ignore surface dissipation, there is still a small critical temperature gradient across the solid above which the interface is unstable. However surface dissipation - in particular the growth resistance - pushes the instability to huge temperature gradients, ones which cannot be realised experimentally. The only instability that can be seen is caused by uniaxial stress.