Segregation and morphological instability due to double-diffusive convection in rotational directional solidification

Through computer simulation and direct observation of the freezing interface during directional solidification of succinonotrile (SCN) containing acetone on a rotating table, the effect of double-diffusive flows caused by gravitational and centrifugal forces on solute transport and morphological instability is investigated. Without rotation, the concave interface caused by solidification-induced buoyant convection resulted in local solute accumulation at the center of the interface. This led to pit formation and accelerated morphological breakdown. At medium rotation rate, the convection near the interface was suppressed, but the fast buildup of the solute caused much larger interface deformation and earlier morphological breakdown. However, if the rotation rate was high enough, the flow direction near the interface could be reversed, and solute accumulation slowed down. Pit formation was eliminated as well.