Can clathrates heterogeneously nucleate ice?

Area of Science:

• Materials Science
• Physical Chemistry
• Geophysics

Background:

• Methane hydrates exhibit anomalous self-preservation at ambient pressure when stored at 240–270 K.
• This preservation is attributed to an ice coating preventing gas loss, but the ice nucleation mechanism remains unclear.

Purpose of the Study:

• Investigate ice nucleation mechanisms on decomposing clathrate hydrates.
• Determine if nucleation is heterogeneous (clathrate/vapor or clathrate/liquid interfaces) or homogeneous (supercooled water).

Main Methods:

• Molecular simulations
• Thermodynamic analysis
• Nucleation theory
• Contact angle measurements

Main Results:

• Clathrates do not heterogeneously nucleate ice.
• Ice nucleation occurs homogeneously due to cooling at the clathrate/liquid interface.
• Weak epitaxy observed between sII clathrate (111) face and ice planes.
• Interfacial free energy of the most favorable ice-clathrate interface determined as 59 ± 5 mJ/m².

Conclusions:

• Homogeneous nucleation is the dominant mechanism for ice formation on decomposing methane hydrates.
• Understanding this mechanism is crucial for managing gas hydrate stability and storage.
• Results provide insights into gas clathrate formation at ice/vapor interfaces.