Low-Frequency Electrical Properties of Polycrystalline Saline Ice and Salt Hydrates

• Published in: The journal of physical chemistry. B Vol. 112; no. 48; pp. 15382 - 15390
• Main Authors: Grimm, Robert E, Stillman, David E, Dec, Steven F, Bullock, Mark A
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 04.12.2008
• Subjects: B: Statistical Mechanics, Thermodynamics, Medium Effects
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp8055366

We measured the 1 mHz−1 MHz electrical properties of ice−hydrate binary systems formed from solutions of NaCl, CaCl2, and MgSO4, with supplementary measurements of HCl. Below the eutectic temperature, electrical parameters are well described by mixing models in which hydrate is always the connected phase. Above the eutectic temperature, a salt concentration threshold of ∼3 mM in the initial solution is required for the unfrozen brine fraction to form interconnected, electrically conductive networks. The dielectric relaxation frequency for saline ice increases with increasing impurity content until Cl− reaches saturation. Because there is insufficient H3O+ for charge balance, salt cations must be accommodated interstitially in the ice. Dielectric relaxations near the ice signature were identified for CaCl2·6H2O and MgSO4·11H2O but not for NaCl·2H2O. Ionic and L-defect concentrations in salt hydrates up to ∼10−4 and 10−3 per H2O molecule, respectively, follow from the electrical properties, Jaccard theory, and the assumption that protonic-defect mobilities are similar to ice. These high defect concentrationsup to a few orders of magnitude greater than saturation values in iceindicate that intrinsic disruption of hydrogen bonding in salt hydrates is common.