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Entropy 2014, 16(2), 912-920; doi:10.3390/e16020912
Article

Thermodynamic Analysis of the V-Shaped Area of High Pressure and High Temperature in Cubic Boron Nitride Synthesis with Li3N as a Catalyst

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Received: 4 December 2013 / Revised: 22 January 2014 / Accepted: 7 February 2014 / Published: 14 February 2014
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Abstract

The possibilities of different phase transitions to cBN with Li3N as catalyst at high temperature and high pressure (1600–2200 K, 4.8–6.0 GPa) are analyzed, in the framework of the second law of thermodynamics. The Gibbs free energy (∆G) of three reactions which may happen in the Li3N-BN system: hBN + Li3N→Li3BN2, hBN→cBN, and Li3BN2→cBN + Li3N, is calculated, with the influence of high temperature and high pressure on volume included. We show that ∆G of hBN + Li3N→Li3BN2 and hBN→cBN are between −35~−10 KJ·mol−1 and −25~−19 KJ·mol−1, respectively. However, ∆G of Li3BN2→cBN + Li3N can be positive or negative. The area formed by the positive data is a V-shaped area, which covers the most part of the cBN growing V-shaped area. It confirms that Li3BN2 is stable in the P-T area of cBN synthesis, and cBN is probably transformed directly from hBN. Analysis suggests that Li3BN2 promotes the transition from hBN to cBN.
Keywords: cBN single crystal; high pressure and high temperature; V-shaped area; thermodynamic analysis; Gibbs free energy cBN single crystal; high pressure and high temperature; V-shaped area; thermodynamic analysis; Gibbs free energy
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Xu, B.; Lv, M.-Z.; Yang, H.-M.; Wen, Z.-X. Thermodynamic Analysis of the V-Shaped Area of High Pressure and High Temperature in Cubic Boron Nitride Synthesis with Li3N as a Catalyst. Entropy 2014, 16, 912-920.

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