Nano-polycrystalline diamond synthesized through the decomposition of stearic acid

ABSTRACT

Here we report a novel route for synthesizing nano-polycrystalline diamond (NPD) using stearic acid (C₁₈H₃₆O₂) as a starting material under high pressure and high temperature. The obtained NPD shows a transparent dark-yellowish color similar to the standard NPD synthesized from graphite and consists of extremely fine diamond grains (∼10 nm). The temperature required for the present synthesis of pure transparent NPD is as low as 1000°C at 13 and 17 GPa, which is surprisingly lower than that for conventional NPD synthesis (1800–2000°C). The amorphous-like, extremely poorly crystalline graphite produced by the thermal decomposition of stearic acid likely provides preferential nucleation sites for diamond and significantly lower the activation energy. The removal of volatile components such as H₂O generated through the decomposition from the system is a key to obtain pore-free transparent NPD. Magnesite, MgCO₃ and periclase, MgO can be used as an efficient H₂O remover through the hydration reaction.

KEYWORDS:

• Nano-polycrystalline diamond
• stearic acid
• multi-anvil apparatus
• high pressure and high temperature
• transmission electron microscopy

Acknowledgements

The authors thank S. Kakizawa and K. Litasov for their technical assistance in performing high pressure experiments using multi-anvil apparatus. We also appreciate M. Nishi, H. Hirai, H. Kadobayashi and T. Inoue for their valuable comments and advice while developing the experimental setup. We thank two anonymous reviewers for their valuable comments and suggestions.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study is partly supported by Advanced Research Unit Program for Materials Science under Ultra-High Pressure of Ehime University.