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

Entropy

Bin Xu¹  Mei-Zhe Lv²  Hong-Mei Yang² 

[1] School of Materials Science and Engineering, Shandong Jianzhu University, Jinan 250101, China;

关键词: cBN single crystal;    high pressure and high temperature;    V-shaped area;    thermodynamic analysis;    Gibbs free energy;   

DOI  :  10.3390/e16020912

来源: mdpi

【 摘 要 】

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 (ΔG) 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 ΔG of hBN + Li₃N→Li₃BN₂ and hBN→cBN are between −35∼−10 KJ·mol⁻¹ and −25∼−19 KJ·mol⁻¹, respectively. However, ΔG 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.

【 授权许可】

CC BY   
© 2014 by the authors; licensee MDPI, Basel, Switzerland