Observation of a Brine Layer on an Ice Surface with an Environmental Scanning Electron Microscope at Higher Pressures and Temperatures

Krausko, Ján; Runštuk, Jiří; Neděla, Vilém; Klán, Petr; Heger, Dominik

doi:10.1021/la500334e

Cited by 49 publications

(49 citation statements)

References 57 publications

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“…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).…”

Section: Ffs At a High Temperature: Brine Fingers Formationmentioning

confidence: 99%

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

Yang

Neděla²,

Runštuk³

et al. 2017

Atmos. Chem. Phys.

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Abstract. An environmental scanning electron microscope (ESEM) was used for the first time to obtain well-resolved images, in both temporal and spatial dimensions, of labprepared frost flowers (FFs) under evaporation within the chamber temperature range from −5 to −18 • C and pressures above 500 Pa. Our scanning shows temperature-dependent NaCl speciation: the brine covering the ice was observed at all conditions, whereas the NaCl crystals were formed at temperatures below −10 • C as the brine oversaturation was achieved. Finger-like ice structures covered by the brine, with a diameter of several micrometres and length of tens to 100 µm, are exposed to the ambient air. The brine-covered fingers are highly flexible and cohesive. The exposure of the liquid brine on the micrometric fingers indicates a significant increase in the brine surface area compared to that of the flat ice surface at high temperatures; the NaCl crystals formed can become sites of heterogeneous reactivity at lower temperatures. There is no evidence that, without external forces, salty FFs could automatically fall apart to create a number of sub-particles at the scale of micrometres as the exposed brine fingers seem cohesive and hard to break in the middle. The fingers tend to combine together to form large spheres and then join back to the mother body, eventually forming a large chunk of salt after complete dehydration. The present microscopic observation rationalizes several previously unexplained observations, namely, that FFs are not a direct source of sea-salt aerosols and that saline ice crystals under evaporation could accelerate the heterogeneous reactions of bromine liberation.

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Section: Ffs At a High Temperature: Brine Fingers Formationmentioning

confidence: 99%

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

Yang

Neděla²,

Runštuk³

et al. 2017

Atmos. Chem. Phys.

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“…The technology has now been widely used in biological research1112, food study13, and material synthesis14. ESEM has been used to observe ice surface structures15, and ice growth behaviour1617. Surface ablation of ice crystal facets have also been observed below −30 °C16.…”

mentioning

confidence: 99%

“…Surface ablation of ice crystal facets have also been observed below −30 °C16. However, most previous studies on ice with ESEM have been performed below 0.1 Pa and at temperatures much lower than 0 °C15, which only allow in situ observation of vapour-liquid-solid transitions in low melting temperature systems (e.g. the partially molten sulfuric system)18, but are unable to study the vapour-liquid-ice system of pure water.…”

mentioning

confidence: 99%

Abnormal gas-liquid-solid phase transition behaviour of water observed with in situ environmental SEM

Chen

Shu

Chen

2017

Sci Rep

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Gas-liquid-solid phase transition behaviour of water is studied with environmental scanning electron microscopy for the first time. Abnormal phenomena are observed. At a fixed pressure of 450 Pa, with the temperature set to −7 °C, direct desublimation happens, and ice grows continuously along the substrate surface. At 550 Pa, although ice is the stable phase according to the phase diagram, metastable liquid droplets first nucleate and grow to ~100–200 μm sizes. Ice crystals nucleate within the large sized droplets, grow up and fill up the droplets. Later, the ice crystals grow continuously through desublimation. At 600 Pa, the metastable liquid grows quickly, with some ice nuclei floating in it, and the liquid-solid coexistence state exists for a long time. By lowering the vapour pressure and/or increasing the substrate temperature, ice sublimates into vapour phase, and especially, the remaining ice forms a porous structure due to preferential sublimation in the concave regions, which can be explained with surface tension effect. Interestingly, although it should be forbidden for ice to transform into liquid phase when the temperature is well below 0 °C, liquid like droplets form during the ice sublimation process, which is attributed to the surface tension effect and the quasiliquid layers.

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“…Such a slow freezing apparently caused rejection of the solute solution into the veins and on the surface of a polycrystalline ice matrix along with a substantial increase of the perchloric acid local concentration. Based on the reported linear dependence of the uranyl luminescence lifetime on the perchloric ion concentration, we estimate that the final perchlorate concentration was 1.5 M, see Fig.1b white areas [3]. Figure 1c shows an ESEM image of the ice sample prepared by freezing of pure water under atmospheric pressure inside the specimen chamber.…”

Section: +mentioning

confidence: 94%

“…Our ESEM and fluorescence analyses thus provided unequivocal evidence that freezing of the uranyl salt aq solutions causes rejection of a solute solution to the ice grain boundaries to form a more concentrated brine layer at temperatures above the eutectic temperature, regardless of the rate and method of freezing (at 270 or 77 K). However, uranyl ion speciation was largely dependent on the experimental conditions [3]. Acknowledgments go the grants [4].…”

Section: +mentioning

confidence: 99%

Morphological and Chemical Analysis of Impurities in Ice Using the Environmental Scanning Electron Microscopy and Fluorescence Spectroscopy

Neděla¹,

Runštuk²,

Krausko

et al. 2015

Microsc Microanal

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Accumulated and concentrated impurities can be stored in natural ice or snow. They are found to be rejected from the freezing solution to the ice grain boundaries, free ice surfaces or liquid/brine inclusions. Information about compartmentation and phase speciation in ice is thus essential for the assessment of their fate. The location of impurities and their interactions with the water molecules of ice, still not sufficiently clarified, must be studied at low temperatures because thawing smears the information out. When the impurities keep their location while the surrounding ice sublimes, a 3D morphology of the ice boundaries is revealed. Environmental scanning electron microscopy (ESEM) is one of the few methods allowing direct observation of ice bulk sample with location and compartmentation impurities in dynamically changing conditions of relatively high pressure of gas and stable temperature of cooled sample holder.For this work, aqueous (aq) samples were frozen under atmospheric pressure on a silicon plate cooled by the Peltier stage. The initial sample holder temperature was above -1 °C, and a droplet of pure water or the uranyl nitrate solution placed on it was frozen. A uranyl nitrate solution (0.01 M) acidified by perchloric acid to pH = 1 was used because hydrolysis of UO 2 2+ is suppressed, and only a single species (i.e., a hydrated uranyl ion) is present under these conditions. ESEM AQUASEM II equipped with a YAG:Ce 3+ BSEs detector, an ionization detector of SEs, a special hydration system and a Peltier cooled stage were used [1]. The pressures between 400-700 Pa, 50% water-vapor saturation, and the temperatures above 250 K were utilized in the experiments. The phenomena of etching and subsequent stripping of impurities are largely suppressed at these conditions. In order to get information about the phase speciation of the uranyl ion and its microenvironment in the ice samples, the corresponding frozen aq solutions were subjected to a luminescence analysis. Crystalline uranyl nitrate hexahydrate provided a luminescence emission spectrum with the emission band maxima located at 488, 509, 533, 559, and 587 nm at 293 K (Fig. 1a). A hydrated uranyl ion in a solution exhibited one additional band at 473 nm besides those observed in the emission spectrum of a crystal. The luminescence lifetime of crystalline uranyl nitrate is known to depend considerably on the degree of its hydration. Uranyl perchlorate was prepared from solid uranyl nitrate by repeated cycles of dissolution in perchloric acid (70%) and evaporation. The luminescence lifetime of uranyl perchlorate crystals was found to be (283 ± 10) μs. In addition, the dependence of the uranyl ion luminescence lifetime on the perchloric acid concentration has been reported to be nearly linear at the concentrations between 0.3 and 10 M (0.1 M aq HClO 4 : τ = 2 μs; 11 M aq HClO 4 : τ = 65 μs) [2]. We utilized the linear regression equation to estimate the perchloric acid concentration in the brine.In this work, the mono-exponential lifetime of uranyl a...

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Observation of a Brine Layer on an Ice Surface with an Environmental Scanning Electron Microscope at Higher Pressures and Temperatures

Cited by 49 publications

References 57 publications

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

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

Abnormal gas-liquid-solid phase transition behaviour of water observed with in situ environmental SEM

Morphological and Chemical Analysis of Impurities in Ice Using the Environmental Scanning Electron Microscopy and Fluorescence Spectroscopy

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