Diamond formation from methane hydrate under the internal conditions of giant icy planets

At a Glance

Metadata	Details
Publication Date	2021-04-14
Journal	Scientific Reports
Authors	Hirokazu Kadobayashi, Satoka Ohnishi, Hiroaki Ohfuji, Yoshitaka Yamamoto, Michihiro Muraoka
Institutions	Rissho University, Yazaki (Japan)
Citations	21
Analysis	Full AI Review Included

Technical Documentation & Analysis: Diamond Formation Under Planetary Conditions

Executive Summary

This research successfully demonstrates the formation of diamond from methane hydrate (C-O-H system) under High-Pressure High-Temperature (HPHT) conditions relevant to the interiors of giant icy planets (Uranus and Neptune). The findings significantly advance planetary science and validate the extreme performance requirements for diamond materials in high-pressure research.

Core Achievement: First experimental demonstration of diamond formation from methane hydrate (a homogeneous water-methane sample) in the C-O-H system.
Conditions: Diamond synthesis achieved under static HPHT conditions ranging from 13 GPa to 45 GPa and temperatures up to 3800 K using a CO₂ Laser-Heated Diamond Anvil Cell (LHDAC).
Milder Synthesis: The presence of water in the C-O-H system resulted in diamond formation at substantially milder conditions (T > 1600 K) compared to previous C-H system studies (T > 2000 K).
Product Morphology: The recovered product was nanocrystalline diamond (NCD) with grain sizes ranging from 50 nm to 350 nm.
Planetary Relevance: The observed formation conditions overlap with the predicted isentropes of Uranus and Neptune, suggesting that diamond precipitation occurs in the upper icy mantles of these planets.
Material Validation: The experiment relied on high-quality, optically transparent diamond anvils capable of withstanding extreme thermal gradients and pressures up to 45 GPa while allowing in-situ synchrotron XRD and Raman analysis.

Technical Specifications

Hard data extracted from the HPHT experiments demonstrating diamond formation.

Parameter	Value	Unit	Context
Maximum Pressure Achieved	45.0	GPa	CO₂-LHDAC experiment maximum.
Maximum Temperature Achieved	3800	K	CO₂-LHDAC experiment maximum.
Diamond Formation Pressure Range	13 - 45	GPa	Conditions where diamond was observed in the C-O-H system.
Minimum Diamond Formation Temperature	> 1600	K	Temperature threshold for rapid formation in the C-O-H system.
Starting Material	Methane Hydrate (MH-I)	N/A	Homogeneous water-methane composition.
Diamond Grain Size (Recovered)	50 - 350	nm	Size range of nanocrystalline diamond particles observed via FE-SEM.
Diamond Raman Peak	1331	cm^-1	Characteristic peak observed in recovered HPHT products.
DAC Anvil Culet Sizes Used	300 or 450	µm	Used depending on target pressure requirements.
Heating Duration (Typical)	10 - 120	min	Static heating time provided sufficient reaction kinetics.

Key Methodologies

The experiment utilized a sophisticated combination of HPHT synthesis and advanced in-situ characterization techniques.

Starting Material Preparation: Methane Hydrate Phase I (MH-I) was synthesized via the conventional ice-gas interface reaction method (8 MPa, 269 K) to ensure a homogeneous water-methane starting composition.
Sample Loading: Powdered MH-I (2-3 µm grain size) and ruby pressure markers (2-5 µm) were loaded into a Rhenium foil gasket (~50 µm thickness) within a symmetric Diamond Anvil Cell (DAC).
HPHT Generation: Samples were pressurized to target GPa levels and heated using a CO₂ laser system (LHDAC). The laser focal point was approximately 50 µm in diameter.
Temperature Determination: Temperatures were determined by measuring the thermal radiation spectra emitted from the heated area (10-12 µm diameter) and fitting the data to the grey-body radiation formula.
In-Situ Phase Analysis (XRD): Synchrotron X-ray Diffraction (XRD) measurements were conducted at SPring-8 (BL10XU) using monochromatic X-rays (0.04150 nm wavelength) to identify phases (MH-III, Ice VII, Diamond) during heating.
In-Situ Chemical Analysis (Raman): Raman spectroscopy (473 nm semiconductor laser) was used to monitor C-H and H-H vibration modes, confirming the dissociation of methane and the formation of heavier hydrocarbons and hydrogen-related materials.
Ex-Situ Microstructure Analysis: Recovered samples were analyzed using Field-Emission Scanning Electron Microscopy (FE-SEM) to confirm the octahedral shape and size of the resulting diamond nanoparticles.

6CCVD Solutions & Capabilities

6CCVD provides the high-performance MPCVD diamond materials and precision engineering services necessary to replicate, extend, and industrialize research conducted under extreme HPHT conditions, such as those simulating planetary interiors.

Applicable Materials for HPHT Research

To replicate the LHDAC experiments described, researchers require diamond materials optimized for extreme pressure, temperature, and optical transparency.

Research Requirement	6CCVD Material Recommendation	Technical Rationale
Diamond Anvil Material	Optical Grade Single Crystal Diamond (SCD)	Essential for high-pressure stability (up to 45 GPa) and superior optical transparency required for CO₂ laser heating and in-situ analysis (XRD, Raman).
High-Purity Substrates	SCD Substrates (up to 10 mm thickness)	Provides the robust foundation necessary for large-volume DAC experiments or specialized multi-anvil systems.
Nanocrystalline Diamond (NCD) Applications	High-Quality Polycrystalline Diamond (PCD)	While the paper synthesized NCD, 6CCVD supplies large-area PCD wafers (up to 125 mm) for industrial applications derived from NCD research (e.g., wear parts, thermal management).

Customization Potential & Precision Engineering

The success of LHDAC experiments hinges on the precision of the diamond anvils, particularly the culet geometry and surface finish.

Custom Dimensions and Shaping: 6CCVD specializes in providing custom SCD plates and wafers in thicknesses from 0.1 µm to 500 µm. We offer precision laser cutting and shaping services to meet exact culet size requirements (e.g., 300 µm or 450 µm) and complex geometries for specialized DAC designs.
Ultra-Precision Polishing: For LHDAC applications where optical quality is paramount for temperature measurement and laser coupling, 6CCVD guarantees an ultra-smooth surface finish:
- SCD Polishing: Surface roughness Ra < 1 nm.
- PCD Polishing (Inch-size): Surface roughness Ra < 5 nm.
Advanced Metalization Services: For future experiments requiring integrated electrical measurements (e.g., monitoring conductivity changes during phase transitions) or resistive heating elements, 6CCVD offers in-house metalization capabilities, including Au, Pt, Pd, Ti, W, and Cu deposition.

Engineering Support

6CCVD’s in-house team of PhD material scientists and engineers provides authoritative support for complex HPHT and planetary simulation projects.

Material Selection: We assist researchers in selecting the optimal diamond grade (SCD purity, PCD grain size) and orientation for specific pressure ranges and laser wavelengths (e.g., CO₂ laser compatibility).
Design Consultation: Our team can consult on material specifications necessary to extend this research, such as developing anvils for higher pressure regimes (> 100 GPa) or integrating advanced sensing layers.
Logistics: We ensure reliable, global shipping (DDU default, DDP available) of critical diamond components directly to international research facilities and synchrotron beamlines.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

Tech Support

Original Source

DOI: https://doi.org/10.1038/s41598-021-87638-5