Effective
Kinetic Phase Diagrams
J. Phys. Chem. B, 109 (30), 14632-14641
Jan H. Los, Marija Matovic
Abstract:
The composition of a solid solution that is growing at conditions well
away from equilibrium is not prescribed by equilibrium thermodynamics,
but is determined kinetically. It depends both on the surface kinetics
and on the transport of mass and heat to and away from the
solidification front. In previous work, we have formulated a model for
the kinetic or nonequilibrium segregation taking place at the
solidification front enabling the construction of kinetic phase
diagrams, which gives the growth composition of a solid solution as a
function of the liquid composition and undercooling at the surface. In
the present work, we extend this model to include both mass and heat
transport, giving rise to effective kinetic phase diagrams. An overview
of the tendencies in the calculated effective kinetic phase diagrams is
given by scanning a large part of the parameter space, covering
different types of materials, including metals, semiconductors, and
molecular systems. We find striking and characteric differences in the
relative contribution of the various processes to the effective
segregation. For molecular mixtures, interfacial undercooling and heat
transport limitation can be expected to be much more important than for
metal and semiconductor mixtures where mass transport limitation is
dominant.