[MIS23-P05] Growth of ice crystals via quasi-liquid layers: Effect of nitric acid gas
Keywords:Ice, quasi-liquid layer, nitric acid gas, optical microscopy
Ice is one of the most abundant crystals on the earth, and hence the molecular-level understanding of ice crystal surfaces holds the key to unlocking the secrets of a number of fields. We and Olympus Engineering Co., Ltd. have developed laser confocal microscopy combined with differential interference contrast microscopy (LCM-DIM), by which we succeeded in the direct visualization of 0.37-nm-thick elementary steps on ice for the first time [1]. In addition, we could also visualize the quasi-liquid layers (QLLs) on ice crystal surfaces [2], which are covered with thin liquid layers even below the melting point (0°C). The direct observations of QLLs under nitrogen gas revealed the appearance temperatures and partial pressure of water vapor [3,4]. On the other hand, we also found that even trace acidic gas induced the stability of QLLs. In this study, we chose HNO3 as a model atmospheric gas, and directly observed the QLLs on ice basal faces by advanced optical microscopy[5].
Irrespective of the presence/absence of the HNO3 gas, the pure-QLLs and HNO3-QLLs appeared with increasing temperature and disappeared with decreasing temperature. The shape of pure-/HNO3-QLLs showed spherical dome and the contact angle of them on the ice basal face was ~1°. Although the appearance/disappearance temperatures of the pure-QLLs were not so different (-1.9 and -2.2 °C, respectively), there was the large thermal hysteresis between the appearance and disappearance temperatures of HNO3-QLL (-1.8 and -6.4 °C, respectively). The result suggests that the disappearance mechanisms of the pure-/HNO3-QLLs were different. Our previous paper indicated that the pure-QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. On the other hand, we found that the HNO3-QLLs are not composed of pure water, but rather of aqueous HNO3 solutions, and also that the HNO3-QLL and the ice crystal were in equilibrium.
When the HNO3-QLL and the ice crystals were in equilibrium, we suddenly reduced the temperature, which meant that the systems fell out of equilibrium and the HNO3-QLL became supercooled. At this time, we observed that a macrosteps appeared along the periphery of the HNO3-QLL. Such growth behavior is well known as the vapor−liquid−solid (VLS) growth mechanism, which usually causes the growth of whisker crystals.
Recently, we studied the effects of hydrogen chloride gas on the behavior of QLLs (HCl-QLLs) on ice basal faces [6,7]. We found that the HCl-QLLs were also aqueous hydrochloric acid solution, and that the temperature and HCl concentration of the HCl-QLLs were also very close to those of a liquidus line: these results were similar to those found in this study. However, the growth of ice started preferentially from droplet–ice–vapor contact lines, thereby causing the HCl-QLLs to become embedded within ice crystals without freezing[7]: no VLS growth occurred contrary to the case of the HNO3-QLLs. We will present more detail of the difference between the roles of pure-/HNO3-/HCl-QLLs while ice growth and evaporation.
[1] Sazaki et al. (2010) PNAS 107, 19702.
[2] Sazaki et al. (2012) PNAS 109, 1052.
[3] Asakawa et al. (2015) PNAS 113, 1749.
[4] Murata et al. (2016) PNAS 113, E6741.
[5] Nagashima et al. (2020) Crystals 10, 72.
[6] Nagashima et al. (2016) Cryst. Growth Des. 16, 2225.
[7] Nagashima et al. (2018) Cryst. Growth Des. 18, 4117.
The details of this study are shown in our paper [5]. We will present this study from other viewpoints in "A-AS07 Atmospheric Chemistry" and “A-CC39 Glaciology” sessions.
Irrespective of the presence/absence of the HNO3 gas, the pure-QLLs and HNO3-QLLs appeared with increasing temperature and disappeared with decreasing temperature. The shape of pure-/HNO3-QLLs showed spherical dome and the contact angle of them on the ice basal face was ~1°. Although the appearance/disappearance temperatures of the pure-QLLs were not so different (-1.9 and -2.2 °C, respectively), there was the large thermal hysteresis between the appearance and disappearance temperatures of HNO3-QLL (-1.8 and -6.4 °C, respectively). The result suggests that the disappearance mechanisms of the pure-/HNO3-QLLs were different. Our previous paper indicated that the pure-QLLs are kinetically formed, not by the melting of ice surfaces, but by the deposition of supersaturated water vapor on ice surfaces. On the other hand, we found that the HNO3-QLLs are not composed of pure water, but rather of aqueous HNO3 solutions, and also that the HNO3-QLL and the ice crystal were in equilibrium.
When the HNO3-QLL and the ice crystals were in equilibrium, we suddenly reduced the temperature, which meant that the systems fell out of equilibrium and the HNO3-QLL became supercooled. At this time, we observed that a macrosteps appeared along the periphery of the HNO3-QLL. Such growth behavior is well known as the vapor−liquid−solid (VLS) growth mechanism, which usually causes the growth of whisker crystals.
Recently, we studied the effects of hydrogen chloride gas on the behavior of QLLs (HCl-QLLs) on ice basal faces [6,7]. We found that the HCl-QLLs were also aqueous hydrochloric acid solution, and that the temperature and HCl concentration of the HCl-QLLs were also very close to those of a liquidus line: these results were similar to those found in this study. However, the growth of ice started preferentially from droplet–ice–vapor contact lines, thereby causing the HCl-QLLs to become embedded within ice crystals without freezing[7]: no VLS growth occurred contrary to the case of the HNO3-QLLs. We will present more detail of the difference between the roles of pure-/HNO3-/HCl-QLLs while ice growth and evaporation.
[1] Sazaki et al. (2010) PNAS 107, 19702.
[2] Sazaki et al. (2012) PNAS 109, 1052.
[3] Asakawa et al. (2015) PNAS 113, 1749.
[4] Murata et al. (2016) PNAS 113, E6741.
[5] Nagashima et al. (2020) Crystals 10, 72.
[6] Nagashima et al. (2016) Cryst. Growth Des. 16, 2225.
[7] Nagashima et al. (2018) Cryst. Growth Des. 18, 4117.
The details of this study are shown in our paper [5]. We will present this study from other viewpoints in "A-AS07 Atmospheric Chemistry" and “A-CC39 Glaciology” sessions.