Initial crystallization kinetics in undercooled droplets

Abstract

In large liquid volumes a variety of residual catalysts can limit the attainable undercooling. With a liquid droplet dispersion an effective nucleant isolation has yielded the largest undercooling for solidification and conditions where the nucleation process is the rate limiting step. Calorimetric measurements provide an effective means to determine the nucleation frequency in droplet samples. Since droplet samples are polydisperse in size, a full kinetics evaluation requires also a consideration of the size distribution which often obeys a log–normal relationship. With this information, the isothermal solidification rate constants may be determined to distinguish between a volume dependent process and a heterogeneous surface area dependent mechanism. An additional study of heterogeneous nucleation kinetics is possible in droplets containing well-defined solid catalyst surfaces in contact with the liquid which undercool to a clear nucleation onset. Suitable two-phase liquid+solid droplet samples may be generated in eutectic and peritectic alloys following thermal cycling and allow for a further analysis of the rate controlling kinetics.