Graphite/diamond transformation mechanism under the action of an iron-based catalyst. Issue 13 (11th November 2022)

• Record Type: Journal Article
• Authors: Wang, Junpu; Tian, Yi; Su, Yuzhu; Xiang, Xiaojun; Zhou, Li; Huang, Mengyang; Zhang, Lu; He, Duanwei
• Is Part Of: CrystEngComm. Volume 25:Issue 13(2023)
• Page Start: 1884
• Page End: 1893
• Publication Date: 2022-11-11
• Subjects: Crystals -- Periodicals; Crystal growth -- Periodicals; Crystallography -- Periodicals; Cristaux -- Périodiques; Cristaux -- Croissance -- Périodiques; Cristallographie -- Périodiques; 548
• DOI: 10.1039/d2ce01202b
• Languages: English
• ISSNs: 1466-8033

Abstract

Abstract : Transformation of graphite to diamond in Fe–Ni–C eutectic melt. Abstract : Although it has been nearly 70 years since iron-based catalysts were used to synthesize diamond from graphite at high pressure and high temperature (HPHT), the graphite to diamond transformation mechanism in this process is still a mystery. It is found that the formation of a eutectic melt between carbon and an iron-based catalyst plays a critical role in the graphite to diamond transformation at HPHT. In this work, the eutectic temperature of Fe–Ni–C (diamond and graphite) was determined using the in situ high-pressure temperature measurement (HPTM) and the high-pressure differential thermal analysis (HPDTA) method up to 8 GPa in a large-volume cubic press. The experimental results of XRD, Raman, SEM and XPS indicate that the transformation of graphite to diamond occurs in the Fe–Ni–C eutectic melt: the C–C bonds in graphite are broken in the eutectic melt, and the free carbon atoms in the melt form sp 3 bond states in the thermodynamically stable region of diamond. In this process, the role of iron-based catalysts is to reduce the environmental conditions, in which the C–C bonds in graphite are destroyed, and to make the carbon atoms that are separated from the sp 2 bond state form the sp 3 bond state in the diamond P–T phase stable region.