Crystallization of silicon dioxide and compositional evolution of the Earth’s core

At a Glance

Metadata	Details
Publication Date	2017-02-21
Journal	Nature
Authors	Kei Hirose, G. Morard, Ryosuke Sinmyo, Koichiro Umemoto, J. W. Hernlund
Institutions	Sorbonne Université, Centre National de la Recherche Scientifique
Citations	227
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Extreme Geophysics

Executive Summary

This research utilizes Laser-Heated Diamond Anvil Cells (LH-DAC) to simulate the extreme pressure and temperature conditions of the Earth’s core, demonstrating the crystallization behavior of silicon dioxide (SiO₂) from liquid iron alloys. This work highlights the critical role of high-quality Single Crystal Diamond (SCD) in advancing high-pressure geophysics.

Core Achievement: Demonstrated that liquid Fe-Si-O alloy crystallizes solid SiO₂ at uppermost core pressures (133-194 GPa) and temperatures (up to 4,560 K).
Geophysical Impact: The wide liquidus field of SiO₂ suggests that the early Earth’s core crystallized SiO₂, releasing sufficient compositional buoyancy to power the geodynamo from the Hadean eon.
Methodology: Experiments relied on high-strength diamond anvils (90 µm to 300 µm culets) combined with spectro-radiometric laser heating and advanced electron microscopy (FE-EPMA, EDX).
Material Requirement: The success of the LH-DAC technique hinges on the mechanical integrity and optical purity of the diamond anvils used to contain the sample under multi-megabar pressures.
6CCVD Value Proposition: 6CCVD provides the necessary Optical Grade SCD materials, custom-fabricated to precise culet dimensions and ultra-low surface roughness (Ra < 1 nm), essential for reliable, high-fidelity HPHT research.

Technical Specifications

The following hard data points were extracted from the experimental results and methodology sections, demonstrating the extreme conditions required for this research:

Parameter	Value	Unit	Context
Maximum Pressure Achieved	194	GPa	Run 5 (Highest pressure experiment)
Maximum Temperature Achieved	4,560	K	Run 5 (Highest temperature experiment)
Typical Liquid/Solid Boundary T	3,860 - 3,990	K	Estimated temperature at 142-145 GPa
Diamond Anvil Culet Sizes Used	90, 120, 300	µm	Required for generating core pressures
Heating Duration	3 - 5	s	Limited duration to avoid complex melting textures
Laser Spot Diameter	~20	µm	Area of flat energy distribution for heating
Starting Material Thickness	5 - 8	µm	Fe-Si-O alloy coating thickness
Starting Material Grain Size	< 5	nm	Ultrafine-grained metal and oxide homogeneity
Pressure Uncertainty	±10	%	Overall experimental pressure error
Temperature Uncertainty	±3	%	Spectro-radiometric temperature error

Key Methodologies

The experiment successfully simulated core conditions using a highly controlled, multi-stage process centered on the Laser-Heated Diamond Anvil Cell (LH-DAC):

Starting Material Synthesis: Fe-Si-O alloys (5-8 µm thickness) were synthesized via magnetron cathodic sputtering in reactive mode under vacuum (10^-6 mbar), yielding ultrafine-grained material (<5 nm) with high chemical homogeneity.
DAC Assembly: Samples were loaded into pre-indented Rhenium (Re) gaskets. High-purity SCD anvils with specific culet sizes (90 µm, 120 µm, 300 µm) were used, often insulated by Al₂O₃ layers.
High P/T Generation: Samples were compressed to target pressures (52-194 GPa). Heating was performed from both sides using 100-W single-mode Yb fiber lasers for short durations (3-5 s) to achieve temperatures up to 4,560 K.
Temperature Profiling: Radial temperature distributions were measured using the spectro-radiometric method to accurately estimate the temperature at the liquid/solid SiO₂ boundary.
Pressure Calibration: Pressures were measured at room temperature after heating based on the Raman shift of the diamond culet and corrected for thermal pressure effects.
Post-Experiment Characterization: Recovered samples were cross-sectioned using a focused Ga ion beam (FEI Versa 3D DualBeam) and analyzed for chemical composition and texture using Field-Emission Electron Microprobe (FE-EPMA) and Energy-Dispersive X-ray (EDX) analysis.

6CCVD Solutions & Capabilities

The successful execution of high-pressure geophysics experiments, particularly those involving LH-DACs, relies entirely on the quality and precision of the diamond anvils. 6CCVD is uniquely positioned to supply the materials and customization services required to replicate and extend this research on planetary core dynamics.

Applicable Materials

To achieve and maintain pressures up to 194 GPa and temperatures exceeding 4,500 K, the following 6CCVD materials are required:

Optical Grade Single Crystal Diamond (SCD): Essential for DAC anvils. Our SCD material offers superior mechanical strength, high thermal stability, and extremely low birefringence, ensuring reliable pressure generation and optimal optical access for laser heating and spectro-radiometry.
High-Purity SCD Substrates: Available in thicknesses from 0.1 µm up to 500 µm for use as specialized windows, insulation layers, or backing plates in complex HPHT assemblies.

Customization Potential

The research explicitly required custom culet dimensions (90 µm, 120 µm, 300 µm) and high surface quality. 6CCVD’s advanced fabrication capabilities directly address these needs:

Research Requirement	6CCVD Custom Capability	Technical Specification
Precision Culet Geometry	Custom laser cutting and shaping services.	Plates/wafers up to 125 mm (PCD) or custom SCD dimensions.
Ultra-Low Surface Roughness	Advanced mechanical and chemical polishing.	Ra < 1 nm (SCD); Ra < 5 nm (Inch-size PCD).
Metalization for Heating/Sensors	In-house thin-film deposition capability.	Custom metalization layers (Au, Pt, Pd, Ti, W, Cu) for electrodes or resistive heating elements (e.g., in BDD).
Boron Doping (BDD)	Custom doping levels available.	Boron-Doped Diamond (BDD) for integrated resistive heating elements or high-pressure electrical conductivity measurements.

Engineering Support

Replicating the complex Fe-Si-O phase relations at core conditions demands precise material specifications. 6CCVD’s in-house PhD team provides expert consultation to optimize material selection for similar high-pressure geophysics projects:

Material Selection: Assistance in choosing the optimal SCD grade and crystal orientation for maximum strength and minimal failure risk at multi-megabar pressures.
Design Optimization: Support for designing custom diamond components, including specific culet angles and dimensions, to maximize pressure generation efficiency and experimental longevity.
Global Logistics: Global shipping (DDU default, DDP available) ensures rapid delivery of critical components to research facilities worldwide.

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/nature21367