Rapid Solidification: Growth Kinetics

Abstract

Crystal growth from the melt involves two processes occurring in series: (a) the "interface reaction," which incorporates atoms into lattice sites in the growing crystal, and (b) the long-range transport of rejected species and latent heat from the solid-liquid interface. The classical equations of continuum heat and mass transport that govern step (b) have been understood for a long time, although in many situations their solutions remain a challenge; however, the kinetics of the interface reaction, step (a), have been elucidated only very recently. Rapid growth during solidification is generally brought about by one of two methods. One mehtod is rapid quenching of the liquid, which means extracting heat from it through a steep temperature gradient. This necessitates that the sample be thin in at least one dimension so heat from the center can flow out quickly. The other method is to undercool a liquid by a large amount below the equilibrium melting temperature prior to solid nucleation. Nucleation is followed by a period of very rapid growth, which terminates when the latent heat liberated raises the sample temperature to near the equilibrium temperature.