Article Cite This: ACS Earth Space Chem. XXXX, XXX, XXX−XXX
Ice and Cryosalt Formation in Saline Microporous Clay Gels Merve Yeşilbaş,† Cheng Choo Lee,‡ and Jean-François Boily*,† †
Department of Chemistry and ‡Umeå Core Facility for Electron Microscopy, Umeå University, SE-901 87 Umeå, Sweden S Supporting Information *
ABSTRACT: 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 (
