Abstract
The structure of brine films in grain boundaries of halite has been the subject of much controversy over the past 20 years; although a number of innovative methods have been developed to study these structures, much is still unknown and fundamental information is missing. In this study, we investigated different methods of plunge-freezing to vitrify the brine fill of grain boundaries for natural salt polycrystal. This was followed by a preliminary study of the 3D morphology of a vitrified grain boundary in a natural rock salt sample with a focused ion beam (FIB) excavation system. We have shown that brine-filled grain boundaries in rock salt can be efficiently well frozen when dimensions are less than about 1 mm. Coupled with an ion beam tool, cryo-SEM allows 3D observation of the well-frozen grain boundaries in large volumes and high resolution. Initial results of brine-filled natural halite grain boundaries show non-faceted crystal-brine interfaces and unexpectedly low dihedral angles at room temperature and pressure.