Surface Transition on Ice Induced by the Formation of a Grain Boundary

Abstract

Interfaces between individual ice crystals, usually referred to as grain boundaries, play an important part in many processes in nature. Grain boundary properties are, for example, governing the sintering processes in snow and ice which transform a snowpack into a glacier. In the case of snow sintering, it has been assumed that there are no variations in surface roughness and surface melting, when considering the ice-air interface of an individual crystal. In contrast to that assumption, the present work suggests that there is an increased probability of molecular surface disorder in the vicinity of a grain boundary. The conclusion is based on the first detailed visualization of the formation of an ice grain boundary. The visualization is enabled by studying ice crystals growing into contact, at temperatures between −20°C and −15°C and pressures of 1–2 Torr, using Environmental Scanning Electron Microscopy. It is observed that the formation of a grain boundary induces a surface transition on the facets in contact. The transition does not propagate across facet edges. The surface transition is interpreted as the spreading of crystal dislocations away from the grain boundary. The observation constitutes a qualitatively new finding, and can potentially increase the understanding of specific processes in nature where ice grain boundaries are involved.

Mesoscopic surface roughness of ice crystals pervasive across a wide range of ice crystal conditions

“…These data have also confirmed the idea that surface roughness can be enhanced in proximity to a grain boundary between two neighboring crystals (e.g., Pedersen et al, 2011). In Fig.…”

“…It is possible that this effect might enhance roughness in aggregates of ice particles or in cloud regions with high collision frequencies, both of which have been found to be particularly common near deep convection regions, which have also been associated with satellite retrievals indicative of severe particle roughening (Cole et al, 2014). Blackford (2007) and Pedersen et al (2011) also point out that the microstructure of ice along grain boundaries can play an important role in advancing the understanding of the mechanical properties of snowpacks that are susceptible to avalanche, as well as the dynamics of glaciers. Figure 2 shows a four-panel plot of a growing hexagonal ice crystal starting at 762× magnification in Fig.…”

“…In addition to passive satellite measurements of cirrus ice microphysics, it is also likely that ice scattering functions assumed in radar and lidar imaging of cirrus and mixed-phase cloud properties would be affected (Sun et al, 2011). Because satellite observations, aircraft measurements, and modeling of cirrus and mixed-phase clouds have often been at odds (Baran, 2012;Garrett and Gerber, 2003;Gierens et al, 2003;Kramer et al, 2009;Harrington et al, 2009;Jensen et al, 2009;McFarquhar et al, 2007;Peter et al, 2006;Connolly et al, 2007), potential artifacts of surface roughness on both satellite retrievals and modeling of ice microphysics must be carefully evaluated.…”

Variation of ice crystal size, shape, and asymmetry parameter in tops of tropical deep convective clouds

“…However, the retrieved distortion parameter shows a substantial decrease with cloud top temperature. Recent laboratory studies using scanning electron microscope imagery indicate that surface roughness on ice crystals is prevalent over all investigated conditions and that the surface roughness structures vary with temperature and humidity, although this variation has not been quantified [Pfalzgraff et al, 2010;Pedersen et al, 2011;Neshyba et al, 2013;Magee et al, 2014]. Since the crystal distortion parameter retrieved using our approach is a proxy for crystal surface roughness, our results may indicate that crystal roughness increases with decreasing temperature.…”

Probing Molecular Solids with Low-Energy Ions

“…The properties, surface structure, and reactions of ice have been studied in significant detail because of their importance to several chemical and physical processes that occur at low temperatures (90,91), as well as their catalytic role in polar stratospheric clouds in the depletion of the ozone layer (1)(2)(3)92) and their relevance in chemistry in the interstellar medium (25,(93)(94)(95). Ice surfaces prepared at low temperatures offer a unique environment in which to investigate various chemical and physical processes, such as diffusion (21), cluster formation (40,41), phase transition (96,97), chemical reaction, hydrogen/deuterium exchange (98)(99)(100)(101)(102)(103)(104)(105)(106), interactions with small molecules (46), and adsorption (26,30). All these phenomena can be promoted and/or identified with hyperthermal energy (1-100-eV) ion collisions.…”