Low-frequency electrical properties of ice-silicate mixtures

Area of Science:

• Geophysics
• Materials Science
• Physical Chemistry

Background:

• Understanding subfreezing interactions in silicate-saline water mixtures is crucial for various earth science and engineering applications.
• The role of adsorbed unfrozen water at low temperatures significantly impacts bulk electrical properties.
• Previous studies have often simplified the complex interplay between mineral surfaces, water, ice, and salts.

Purpose of the Study:

• To investigate the low-frequency electrical properties of silicate-saline water mixtures across wide temperature and frequency ranges.
• To elucidate the synoptic effects of adsorbed unfrozen water on electrical conductivity and dielectric permittivity.
• To determine the influence of pore size, mineralogy, and salt content on subfreezing electrical behavior.

Main Methods:

• Electrical property measurements (DC conductivity, dielectric permittivity) over broad temperature and frequency ranges.
• Nuclear magnetic resonance (NMR) to quantify adsorbed water content.
• Controlled preparation of silicate-H2O-salt mixtures with varying grain sizes and mineralogies.
• Application of Archie's law and power-law mixing models for data interpretation.

Main Results:

• DC conductivity in sand-salt-H2O follows Archie's law, with brine or salt hydrate as the conductive phase.
• In fine-grained materials (< few micrometers), DC conductivity is governed by surrounding ice due to disconnected brine/hydrate channels.
• High conductivity in montmorillonite-H2O is linked to proton mobility in interlayer adsorbed water.
• Ice content in sand mixtures was accurately determined using dielectric permittivity and a power-law mixing model.
• Five distinct dielectric relaxations related to water were identified, including ice, adsorbed water, and interfacial polarization effects.

Conclusions:

• Subfreezing electrical properties are strongly influenced by the state and location of water (adsorbed, brine, ice, hydrate).
• Proton mobility in adsorbed water layers, particularly in acidic conditions near silicate surfaces, plays a key role in interfacial polarization.
• The electrical behavior of these mixtures is complex and depends on a combination of factors including pore structure, mineralogy, and salt concentration.