Microstructural evolution in sintered ice particles containing NaCl observed by low-temperature scanning electron microscope

Ice particles containing NaCl were made by spraying 0.043 M salt solution into liquid nitrogen. The ice particles were packed into capsules and annealed at -8 °C for 168 h and -25 °C for 20 h. This material can be considered as a model material for sintered snow containing impurities. The capsules were fractured open inside the low-temperature scanning electron microscope, which minimized the artefacts caused by cryofixation. The morphology of the sintered structure was observed with low-temperature scanning electron microscope. The microstructure of the sintered material consists of ice grains with a liquid meniscus containing NaCl between the grains. This structure is similar to the equilibrium morphology of water-filled veins in polycrystalline ice and liquid phase sintered metallic materials. The combined effect of the surface energies between the solid, liquid, and vapour governs the morphology of the microstructure. A dihedral angle where the brine intersects a grain boundary in ice of 8.0 ± 2.6°, and a contact angle for brine on ice at the interface with vapour of 5.0 ± 1.3° were measured, for samples quenched from -8 °C. Using the dihedral angle measurement, a surface energy value for ice-brine of 32.6 ± 0.1 mJ/m2 was calculated.