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Pressure-induced transformations in LiCl-H2O at 77 K
G N Ruiz1, L E Bove, H R Corti
1Instituto de Química Física de los Materiales, Medio Ambiente y Energía (INQUIMAE-CONICET), Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Pabellón II, Ciudad Universitaria, (1428), Buenos Aires, Argentina.
Physical Chemistry Chemical Physics : PCCP
|July 30, 2014
Summary
This study reveals how salt concentration affects amorphous ice. At low salt, ice transforms to high-density amorphous ice (HDA) and then low-density amorphous ice (LDA). At higher salt, LDA forms directly, influenced by the salt itself.
Area of Science:
- Physical Chemistry
- Materials Science
- Geophysics
Background:
- High-density amorphous ice (HDA) properties in salt solutions are understudied due to crystallization challenges.
- Investigating HDA in aqueous solutions requires methods to prevent ice crystallization during cooling under pressure.
Purpose of the Study:
- To investigate the transformation behavior of aqueous LiCl solutions under pressure at low temperatures.
- To understand the influence of varying LiCl concentrations on the formation and properties of amorphous ice phases.
Main Methods:
- Pressurization of quenched aqueous LiCl solutions (mole fraction x < 0.25) at 77 K using a piston-cylinder apparatus.
- In situ dilatometry under high pressure and ex situ characterization using powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) after pressure release.
Main Results:
- Two distinct regimes were identified based on LiCl mole fraction (x), with a transition around x = 0.12.
- At x < 0.12, samples behaved similarly to pure water, forming hexagonal ice (Ih) and undergoing pressure-induced amorphization to HDA (>1 GPa).
- At x > 0.12, hexagonal ice formation ceased; low-density amorphous ice (LDA) formed directly, and phenomena were dominated by the salt, including glassy LiCl solutions and potential glassy hydrates.
Conclusions:
- The study demonstrates a critical salt concentration (x ≈ 0.12) dictating the amorphous ice formation pathway.
- Below this threshold, water transforms to HDA and then LDA, with segregated glassy LiCl acting as a spectator. Above it, LDA forms directly, influenced by the salt's glassy state.
- These findings offer insights into the behavior of water in complex systems, relevant to cryobiology, geology, and planetary science.
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