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

Abstract

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/m 2 was calculated.

Low‐temperature‐SEM study of dihedral angles in the ice‐I/sulfuric acid partially molten system

“…The dihedral angle in the three‐phase system is significantly smaller than that of the binary, with the former showing complete wetting of grain boundaries (corresponding to a dihedral angle of 0°) displayed in Figure 5 and in the bottom half of Figure 4. The complete wetting of grains on the outside of spherules (in equilibrium with vapour) is identical to what has been observed in the H 2 O–NaCl system (Blackford et al ., 2007).…”

“…Liquid solution with a bulk composition of 0.5 mol L −1 (4.67wt%H 2 SO 4 ) was prepared by mixing semi‐concentrated sulfuric acid with distilled water at room temperature within a fume hood. Following the protocol of Blackford et al . (2007), the liquid was misted with a simple plant sprayer into a mortar filled with liquid nitrogen (LN; T =–196 °C) creating droplets with diameters between 50 and 200 μm that were then crushed with a pestle.…”

Morphology of ice wear from rubber–ice friction tests and its dependence on temperature and sliding velocity

“…The ice was frozen from tap water, which contains salts. At −5 • C these salts result in some liquid both in the ice and on the surface of the ice [19]. This means that we have lubricating liquid without the requirement for frictional heating.…”

“…Natural ice and snow contain impurities such as salts [18], and roads in winter may be deliberately salted. The influence of salts on friction depends on the composition, amount, and morphology within the ice [19], and the effect they have at particular temperatures. For example, the eutectic temperature for NaCl-H 2 O is −21 • C at equilibrium.…”

The Morphology of Ice and Liquid Brine in the Environmental SEM: A Study of the Freezing Methods

“…Thus, we can also assume, based on current and previous observations (Krausko et al,731 2014; Blackford et al, 2007), that the impurities will be contained primarily inside ice spheres prepared 732 by solution nebulization into LN. Experimental procedures essentially identical with our method for 733 the preparation of ice spheres were described by Kurkova et al (2011); however, these authors 734…”