Synthesis of Hexagonal Diamond under Shock Loading Using Single Stage Powder Gun

Abstract:

Hexagonal diamond is considered to be a metastable high-pressure phase of carbon. In previous ab-initio studies, elastic constants of hexagonal diamond were suggested to be higher than those of cubic diamond, which is the stiffest known material. However, the elastic constants of hexagonal diamond have not been investigated experimentally because the size of hexagonal diamond single crystal ever synthesized is not more than 0.5 μm. In this study, we synthesized hexagonal diamond with the size of more than 50 μm in order to measure the elastic constants accurately. Kish graphite powder was used as a starting material and a green compact of kish graphite and copper powder was fabricated as a target. The target was placed into a container made of stainless steel and shock-compressed by a copper projectile accelerated using a single stage powder gun with the velocity of approximately 800 m/s. The estimated shock pressure and temperature were 22 GPa and 1200 °C, respectively. After the shock compression, copper component of the target was dissolved in nitric acid for 24 hours and only carbon component was recovered. A clear (100) peak of hexagonal diamond was observed by a XRD result of the recovered carbon. No peak of cubic diamond was observed. Opaque particles including hexagonal diamond with the size of approximately 100 μm were separated from the graphite and SiO₂ contaminations using heavy-liquid separation method with sodium polytungstate aqueous solution.

• Periodical: Key Engineering Materials (Volume 715)
• Pages: 249-253
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.715.249
• Online since: September 2016
• Authors: Kenichi Tanigaki*, Akihiro Nakahara, Keitaro Horikawa, Hidetoshi Kobayashi
• Keywords: Heavy Liquid Separation, Hexagonal Diamond, Shock Synthesis, Single Stage Powder Gun, X-Ray Diffraction

References

[1] R. E. Hanneman, H. M. Strong, and F. P. Bundy, F. P., Science 155, 995 (1967).

[2] F. P. Bundy and J. S. Kasper, J. Chem. Phys. 46, 3437 (1967).

[3] T. Sekine, M. Akaishi, N. Sekata, J. Mater. Sci. 22, 3615 (1987).

[4] T. Sano, K. Takahashi, O. Sakata, M. Okoshi, N. Inoue, K. F. Kobayashi and A. Hirose, J. Phys.: Conference Series 165 012019 (2009).

DOI: 10.1088/1742-6596/165/1/012019

[5] Z. Pan, H. Sun, Y. Zhang, and C. Chen, Phys. Rev. B 102, 055503 (2009).

[6] S. Q. Wang and H. Q. Ye, J. Phys.: Condens. Matter 15, 5307 (2003).

[7] D. D. Bloomquist, G. E. Duvall, and J. J. Dick, J. Appl. Phys. 50, 4838 (1979).

[8] W. Utsumi and Takehiko Yagi, Science 252, 1542 (1991).