Synthesis of nano-polycrystalline diamond from glassy carbon at pressures up to 25 GPa

ABSTRACT

Nano-polycrystalline diamond (NPD) with various grain sizes has been synthesized from glassy carbon at pressures 15–25 GPa and temperatures 1700–2300°C using multianvil apparatus. The minimum temperature for the synthesis of pure NPD, below which a small amount of compressed graphite was formed, significantly increased with pressure from ∼1700°C at 15 GPa to ∼1900°C at 25 GPa. The NPD having grain sizes less than ∼50 nm was synthesized at temperatures below ∼2000°C at 15 GPa and ∼2300°C at 25 GPa, above which significant grain growth was observed. The grain size of NPD decreases with increasing pressure and decreasing temperature, and the pure NPD with grain sizes less than 10 nm is obtained in a limited temperature range around 1800–2000°C, depending on pressure. The pure NPD from glassy carbon is highly transparent and exhibits a granular nano-texture, whose grain size is tunable by selecting adequate pressure and temperature conditions.

KEYWORDS:

• Nano-polycrystalline diamond
• glassy carbon
• grain size of NPD
• ultrahigh pressure synthesis
• multianvil apparatus

Acknowledgements

We thank Takeshi Arimoto, Takeshi Sakai, Masayuki Nishi, Yoshio Kono, and Takehiko Yagi for discussion.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The present study was supported by the Grand-in-Aid for Scientific Research on Innovative Areas (No.15H5829) to T. I., and also by the Project in the Joint-Usage/Research Center, Premier Research Institute for Ultrahigh-pressure Sciences (PRIUS), of Ehime University.