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Ice and cryosalt formation in saline microporous clay gels
Umeå University, Faculty of Science and Technology, Department of Chemistry.
Umeå University, Faculty of Science and Technology, Department of Plant Physiology. (Umeå Core Facility for Electron Microscopy)
Umeå University, Faculty of Science and Technology, Department of Chemistry.
2018 (English)In: ACS Earth and Space Chemistry, ISSN 2472-3452, Vol. 2, no 4, p. 314-319Article in journal (Refereed) Published
Abstract [en]

Hydrated clay minerals that are common to Earth’s atmosphere and terrestrial and aquatic environments can form gels that host saline solutions. Using cryogenic electron microscopy and vibration spectroscopy, we show that saline gels of montmorillonite frozen at < −90 °C host elongated hexagonal ice (Ih) microcrystals embedded in a network of honeycomb micropores. Freezing segregates salts into walls of aggregated clay nanoparticles sharing face-to-face contacts. Above ∼ −50 °C, clay gels that are sufficiently dense (≫10 g/L) and flexible (Na-exchanged montmorillonite) also host the cryosalt mineral hydrohalite (NaCl·2H2O), either co-existing or entirely replacing Ih in the gels. Hydrohalite does not form in gels of low-density (<10 g/L) or rigid (Ca-exchange montmorillonite) clay particles. These results suggest that hydrohalite forms in expandable clay gels that are sufficiently dense and flexible to retain saline solutions within their walls, possibly through interparticle capillary and hydration forces. These forces effectively oppose water diffusion to growing ice microcrystals within micropores, thus prolonging the lifetime of hydrohalite within these hydrated clay gels. Our findings tie the fate of ice and cryosalt nucleation and growth to the water-retention capability of expandable clay gels.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018. Vol. 2, no 4, p. 314-319
Keywords [en]
montmorillonite, hydrohalite, ice, vibration spectroscopy, cryo-SEM
National Category
Geosciences, Multidisciplinary
Research subject
Physical Chemistry
Identifiers
URN: urn:nbn:se:umu:diva-145727DOI: 10.1021/acsearthspacechem.7b00134ISI: 000430896000003Scopus ID: 2-s2.0-85045729913OAI: oai:DiVA.org:umu-145727DiVA, id: diva2:1190804
Funder
Swedish Research Council, 2016-03808Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-09-25Bibliographically approved
In thesis
1. Thin water and ice films on minerals: a molecular level study
Open this publication in new window or tab >>Thin water and ice films on minerals: a molecular level study
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Minerals in Earth’s crust and suspended in the atmosphere form water or ice films as thin as a few nanometers to as thick as a few micrometers, and beyond. Mineral-bound water and ice films in terrestrial systems (e.g. vadose zones, permafrosts) can impact the bio(geo)chemistry of nutrients and contaminants, water cycling, as well as possible land-air exchanges in terrestrial environments. In the atmosphere, films are tied to clouds and rain formation, and can influence the absorption and scattering of solar radiation of dust mineral aerosols. Water films are, at the same time, of interest to technology. They are even of interest in the study of asteroids, comets, and planet Mars. Still, their formation on the various types of minerals common to the environment is misunderstood.

The aim of this thesis is to gain fundamental insight on the roles that minerals play on forming and stabilising thin water and ice films. This work is separated in two parts, with Part A associated with Papers I-II, and Part B with Papers III-V of the appendix of this thesis.

In Part A of this work (Papers I-II), water loadings and vibrational signatures of thin water films were collected on 21 different minerals (metal oxides, silicates, carbonates) relevant to terrestrial environments, atmosphere and perhaps outer-space. Measurements were made on minerals of varied (i) composition, (ii) structure, (iii) morphology, (iv) particle size and (v) surface roughness. Loadings, measured by a microgravimetric Dynamic Vapour Sorption technique, were of a few monolayers in sub-micrometer-sized particles but of several hundreds to thousands of water layers in micrometer-sized particles (Paper I). This was seen in the Fourier Transform Infrared (FTIR) spectra of sub-micrometer-sized particles with different hydrogen bonding environments than liquid water. Micrometer-sized particles formed liquid-like films regardless of the mineral. Similar observations were made in the spectra of the thinnest water films remaining on these minerals after long periods of sublimation of ice overcoatings at sub-freezing temperatures (Paper II).

In Part B of this work (Papers III-V), focus on the expandable clay mineral montmorillonite was made to study (i) intercalated water, (ii) ice and cryosalt formation inside microporous gels, and (iii) its interactions with intercalated CO2.  FTIR extracted spectral components reflecting interlayer hydration states of ~0W, 1W and 2W monolayers of water (Paper III). Thermal dehydration/dehydroxylation experiments showed that the driest forms of montmorillonite strongly retained low levels of crystalline water in its structure.  FTIR also showed that frozen wet gels of montmorillonite form ice and the cryosalt mineral hydrohalite. Ice was seen in rigid gels and aggregated compact particles, as well as low particle density with low salt content. In contrast, concentrated (>> 10 g/L) saline gels host hydrohalite, probably between and/or near aggregated clay particle walls. Field-Emission Cryogenic Scanning Electron Microscopy showed that ice microcrystals form in micropores of the gels (Paper IV). Finally, release rates of CO2 trapped in interlayers of montmorillonite, monitored by FTIR spectroscopy, were larger in the presence of 1-2W. The activation energy of CO2 release from~0W montmorillonite (34 kJ/mol) is comparable to other mineral surfaces. This study highlights that the most stabilised CO2 occur in of dry and cold conditions.

This thesis will hopefully serve as a springboard for further work exploring the chemistry and physics of water and ice films at minerals surfaces. It should contribute to improve our understanding of the geochemistry of Earth’s soils, processes in the atmosphere, and even of space chemistry.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2018. p. 67
Keywords
water, ice, cryosalt, minerals, rocks, atmosphere, Dynamic Vapour Sorption, FTIR, cryo-FESEM
National Category
Physical Chemistry Geosciences, Multidisciplinary Inorganic Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:umu:diva-145836 (URN)978-91-7601-868-2 (ISBN)
Public defence
2018-04-13, Stora hörsalen KB.E3.03, KBC-Huset, Umeå, 09:30 (English)
Opponent
Supervisors
Available from: 2018-03-23 Created: 2018-03-19 Last updated: 2018-06-09Bibliographically approved

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Yeşilbaş, MerveLee, Cheng ChooBoily, Jean-François

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