Department of Engineering Sciences, Uppsala University, Uppsala, Sweden.
PLoS One. 2011;6(9):e24373. doi: 10.1371/journal.pone.0024373. Epub 2011 Sep 7.
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.
个体冰晶之间的界面，通常称为晶界，在自然界的许多过程中起着重要的作用。例如，晶界性质控制着雪和冰的烧结过程，这些过程将雪层转化为冰川。在考虑单个冰晶的冰-气界面时，人们认为表面粗糙度和表面融化没有变化。与这一假设相反，目前的工作表明，在晶界附近，分子表面无序的可能性增加。这一结论是基于首次详细观察到的冰晶界的形成。通过在 -20°C 至 -15°C 的温度和 1-2 托的压力下使用环境扫描电子显微镜研究冰晶接触生长，实现了可视化。观察到晶界的形成诱导了接触面的表面转变。这种转变不会穿过面边缘传播。表面转变被解释为晶体位错从晶界处的扩展。这一观察结果构成了一个定性的新发现，有可能提高对涉及冰晶界的自然特定过程的理解。
