Pressure-amorphized cubic structure II clathrate hydrate: crystallization in slow motion.

Area of Science:

• Materials Science
• Physical Chemistry
• Crystallography

Background:

• Producing amorphous aqueous solutions is challenging, with existing methods yielding thermally labile samples.
• Aqueous tetrahydrofuran (THF) hydrate typically crystallizes above 110 K, limiting its applications.
• Previous pressure-induced amorphization protocols for THF hydrate leave crystalline remnants, reducing stability.

Purpose of the Study:

• To develop a novel protocol for producing highly crystallization-resistant amorphous THF hydrate.
• To investigate the influence of crystalline remnants on the thermal stability of amorphous THF hydrate.
• To characterize the early stages of crystallization in amorphous THF hydrate.

Main Methods:

• A modified pressure-induced amorphization protocol involving higher pressures (1.8 GPa) and annealing temperatures (180 K).
• Powder X-ray diffraction (PXRD) to analyze structural changes and crystallization kinetics.
• Thermal analysis to assess the stability of the amorphous samples.

Main Results:

• The new protocol successfully produced amorphous THF hydrate with significantly enhanced crystallization resistance.
• Amorphous THF hydrate produced by the new method remained stable at temperatures up to 150 K, unlike previous samples.
• Elimination of crystalline remnants through optimized pressure and annealing conditions was identified as key to improved stability.
• PXRD studies revealed that the characteristic cage structure of crystalline hydrate develops even at the initial stages of crystallization.

Conclusions:

• A robust method for synthesizing purely amorphous THF hydrate has been established.
• The presence of crystalline remnants critically impacts the thermal stability of amorphous hydrates.
• Understanding nucleation and crystal growth in amorphous systems is crucial for developing stable amorphous materials.