Diamond formation kinetics in shock-compressed C─H─O samples recorded by small-angle x-ray scattering and x-ray...

Area of Science:

• Planetary Science
• Materials Science
• High-Pressure Physics

Background:

• Ice giants like Uranus and Neptune experience extreme conditions leading to unique chemical and structural changes.
• Previous experiments observed diamond precipitation in pure carbon-hydrogen systems and superionic water in pure H2O systems.

Purpose of the Study:

• To investigate the chemical and structural transitions in a stoichiometric mixture of carbon and water under extreme conditions.
• To understand the role of oxygen in diamond formation and superionic water structures within ice giants.
• To explore a novel method for producing nanodiamonds.

Main Methods:

• Shock-compressing polyethylene terephthalate (PET) plastics to simulate planetary interior conditions.
• Utilizing in situ X-ray probing, including X-ray diffraction and small-angle X-ray scattering.
• Analyzing the kinetics of the carbon-water reaction under high pressure and temperature.

Main Results:

• Observed diamond formation at pressures between 72-125 GPa and temperatures of 3500-6000 K.
• Evidence of carbon and water demixing, suggesting oxygen enhances diamond precipitation.
• Confirmed the potential for forming superionic water structures.
• Demonstrated a method for producing nanodiamonds via laser-driven shock compression of PET plastics.

Conclusions:

• Oxygen plays a crucial role in enhancing diamond precipitation within ice giants, potentially influencing the formation of superionic water.
• The findings provide insights into the internal chemistry and structure of ice giants and their magnetic fields.
• Laser-driven shock compression of PET plastics offers a viable route for synthesizing nanodiamonds.