Pulsation of a liquid excited by a fast-moving crystallization front with segregation of surface active impurities

A new mechanism is described which produces short-wave patterns in a freezing metal melt that contains surface active impurities. The main feature of the process is a periodic accumulation of the impurity atoms in sharp crests of a rake wave, which forms due to segregation of the impurity atoms ahead of the crystallization front, and which moves with the same velocity. The local rise of the concentration of the impurity increases the chemocapillary surface forces, whereby “excitations” are emitted in opposite directions into the melt. These excitations interact with the crystallization front and produce ripples on a solidifying surface. The model was used to explain ripples in solidified melts produced by short laser pulses in Au and Al films.