Graphite to Diamond: Origin for Kinetics Selectivity
添加于 2017/2/24 10:46:41 182次阅读 | 0次推荐 | 5个评论
Under mild static compression (15 GPa), graphite preferentially turns into hexagonal diamond, not cubic diamond, the selectivity of which is against thermodynamics. Here we, via novel potential energy surface global exploration, report seven types low energy intermediate structures at the atomic level that are key to the kinetics of graphite to diamond solid phase transition. On the basis of quantitative kinetics data, we show that hexagonal diamond has a facile initial nucleation mechanism inside graphite matrix and faster propagation kinetics owing to the presence of three coherent graphite/hexagonal diamond interfaces, forming coherent nuclei in graphite matrix. By contrast, for the lack of coherent nucleus core, the growth of cubic diamond is at least 40 times slower and its growth is inevitably mixing with that of hexagonal diamond.
Yao-Ping Xie, Xiao-Jie Zhang, Zhi-Pan Liu
J. Am. Chem. Soc.
Publication Date (Web): February 6, 2017 第139卷 第7期 2545–2548 页
化学科学 » 无机化学 » 无机材料化学
Graphite, cubic diamond, hexagonal diamond
Researchers have finally answered a question that has eluded scientists for years: when exposed to moderately high pressures, why does graphite turn into hexagonal diamond (also called lonsdaleite) and not the more familiar cubic diamond, as predicted by theory?
The answer largely comes down to a matter of speed—or in chemistry terms, the reaction kinetics. Using a brand new type of simulation, the researchers identified the lowest-energy pathways in the graphite-to-diamond transition and found that the transition to hexagonal diamond is about 40 times faster than the transition to cubic diamond. Even when cubic diamond does begin to form, a large amount of hexagonal diamond is still mixed in.
The researchers, Yao-Ping Xie, Xiao-Jie Zhang, and Zhi-Pan Liu at Fudan University and Shanghai University in Shanghai, China, have published their study on the new simulations of the graphite-to-diamond transition in a recent issue of the Journal of the American Chemical Society.