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

Abstract

SummaryThe transport and mechanical properties of partially molten materials are influenced by the wetting behaviour of the melt with respect to the crystalline solid. The equilibrium microstructure of an ice + melt system was examined using low-temperature scanning electron microscopy. The samples were prepared by spraying a liquid solution of H 2 O-H 2 SO 4 into liquid nitrogen and packing the frozen particulates into aluminium capsules. Samples were then sintered at -35• C or -55• C (above the eutectic temperature, T E = -62 • C) for various durations and were quenched in liquid nitrogen to capture the equilibrium microstructure. This paper reports the first quantitative measurements of dihedral angle in this system. The measured median dihedral angle between the solid and vitrified melt is approximately 26 ± 2• at -35 • C and increases slightly as temperature decreases and approaches the solidus (32 ± 3• at -55 • C).

Evaporating brine from frost flowers with electron microscopy and implications for atmospheric chemistry and sea-salt aerosol formation

“…In contrast, the dynamics of freezing forces the solutes to segregate and form the veins of freeze-concentrated solutions engulfed by the ice (Blackford, 2007;Cheng et al, 2010;McCarthy et al, 2013;Bogdan et al, 2014;Krausko et al, 2014). The solutes in the freeze-concentrated solution, here probably in the surface layer only, experience not only an increased concentration (Heger et al, 2005;Kania et al, 2014;Krausko et al, 2015a) but also a changed pH (Heger et al, 2006;Krausková et al, 2016;Papadimitriou et al, 2016;Rérolle et al, 2016) and polarity (Heger and Klan, 2007).…”

The Effects of H2SO4 on the Mechanical Behavior and Microstructural Evolution of Polycrystalline Ice

“…Subsequently, Fukazawa et al () showed via Raman spectroscopy the presence of peaks (981 cm −1 ) at triple junctions in ice cores collected from Antarctica. In other more recent work from C. McCarthy et al (), high‐resolution low‐temperature scanning electron microscopy was used to study the effects of 4.67 wt % H 2 SO 4 doping on the interfacial energies between sintered ice grains at −35°C. In the study, it was found that an equilibrium solid‐melt microstructure of ice and aqueous H 2 SO 4 forms after sintering and that the solid‐liquid equilibrium dihedral angle was found to be approximately 30°.…”

“…In the study, it was found that an equilibrium solid‐melt microstructure of ice and aqueous H 2 SO 4 forms after sintering and that the solid‐liquid equilibrium dihedral angle was found to be approximately 30°. As given in equation , the position of the melt with respect to the grains is given by a force balance of the interfacial energies, where γ ss and γ SL are the interfacial energies of the solid‐solid interface and solid‐liquid interface, respectively, and θ is the solid‐liquid dihedral angle subtended at the at the corner of a fluid filled pore (C. McCarthy et al, ; Nye & Frank, ). …”

“…When θ > 60°, surface energy dictates that melt is trapped in isolated pockets at triple junctions, whereas for θ < 60°, the equilibrium position of the melt has been found to be in triple junction tubes or veins. At θ = 0°, the solid‐liquid surface increases to a maximum to minimize the surface energy, thus fully wetting the grain boundaries (C. McCarthy et al, ; Nye & Frank, ; Waff & Bulau, ). Based on the H 2 O‐H 2 SO 4 phase diagram (Beyer et al, ; Maynard‐Casely et al, ; C. McCarthy et al, ; Zeleznik, ), these findings are significant in that the eutectic temperature and composition for the H 2 O‐H 2 SO 4 system, −62°C and 35.6 wt %, respectively, would not be expected to be found anywhere on Earth.…”

“…At θ = 0°, the solid‐liquid surface increases to a maximum to minimize the surface energy, thus fully wetting the grain boundaries (C. McCarthy et al, ; Nye & Frank, ; Waff & Bulau, ). Based on the H 2 O‐H 2 SO 4 phase diagram (Beyer et al, ; Maynard‐Casely et al, ; C. McCarthy et al, ; Zeleznik, ), these findings are significant in that the eutectic temperature and composition for the H 2 O‐H 2 SO 4 system, −62°C and 35.6 wt %, respectively, would not be expected to be found anywhere on Earth. Therefore, some margin of aqueous sulfuric acid would be expected to be present within laboratory‐prepared specimens of H 2 SO 4 ‐doped specimens of polycrystalline ice as well.…”