A NEW OSCILLATORY INSTABILITY IN A MUSHY LAYER DURING THE SOLIDIFICATION OF BINARY-ALLOYS

We consider the solidification of a binary alloy in a mushy layer and analyse the linear stability of a quiescent state with specific intere st in identifying an oscillatory convective instability. We employ a n ear-eutectic approximation and consider the limit of large far-field t emperature. These asymptotic limits allow us to examine the dynamics o f the mushy layer in the form of small deviations from the classical c ase of convection in a horizontal porous layer of uniform permeability . We consider also the limit of large Stefan number, which incorporate s a key balance necessary for the existence of the oscillatory instabi lity. The model we consider here contains no double-diffusive effects and no region in which a statically stable density gradient exists. Th e mechanism underlying the oscillatory instability we discover is inst ead associated with a complex interaction between heat transfer, conve ction and solidification.