Linear growth rates of ice crystals grown from the vapor phase

Abstract

Measurements of the linear growth rates of individual basal and prism faces of ice grown on a substrate were made as functions of temperature, excess vapor pressure, and partial pressure of air. The crystals grown in an environment of pure water vapor appear relatively featureless and flat, but still exhibit well-defined specular faces, indicating a domination of surface kinetic effects. Addition of air to the system decreases the growth in proportion to the diffusivity of water vapor in air, so it appears that the effects of the environment are separable from the surface kinetic processes. Steps were observed on both the basal and prism faces and are an important feature of the growth mechanism. Trains of macroscopic steps were observed being “shunned” in an area packed by etch pits and initially inhibited faces were seen to assume the same linear growth velocity as overtaking adjoining faces. The temperature dependences of the linear growth rates of basal and prism faces are remarkable with local maxima and minima which are consistent with the observed alternation with temperature of the primary habit. The temperature trends are not readily explained, but they are correlated with previously measured values of the velocity and interaction distance of steps on the basal face. This correlation and the other observations of this study are consistent with a growth mechanism based on spiral steps arising from emergent screw dislocations.