Studies of the temperature dependence of interfacial reaction kinetics have recently been made in experiments on crystal nucleation and growth in undercooled liquid Si, allowing estimation of the apparent activation energy over a fairly wide range in temperature. The activation energy inferred from growth experiments, at temperatures near the equilibrium melting temperature (Tm), is ∮.2eV while nucleation experiments at temperatures near 2Tm/3 indicate a value of 1.09 eV. This discrepancy can be resolved if the interfacial kinetics are described by a Fulcher-Vogel expression rather than an Arrhenius one, consistent with interfacial atomic mobility being free-volume limited. The ideal glass transition temperature indicated by a free-volume analysis is 1040 ± 100 K for liquid Si; however, experimental measurements of the solidification rate for amorphous Si indicate a slightly lower value. © 1992.