Mesoscopic structure features in synthetic graphite
journal contributionposted on 26.02.2018, 09:32 by Benjamin Maerz, Kenny Jolley, Thomas James Marrow, Zhaoxia Zhou, Malcolm Heggie, Roger Smith, Houzheng Wu
The mesocopic structure features in the coke fillers and binding carbon regions of a synthetic graphite grade have been examined by high resolution transmission electron microscopy (TEM) and Raman spectroscopy. Within the fillers, the three-dimensional structure is composed of crystal laminae with the basal plane dimensions (La) of hundreds nanometres, and thicknesses (Lc) of tens of nanometres. These laminae have a nearly perfect graphite structure with almost parallel c-axes, but their a-b planes are orientated randomly to form a “crazy paving” structure. A similar structure exists in the binding carbon regions, with a smaller La. Significantly bent laminae are widely seen in quinoline insoluble inclusions and the graphite regions developed around them. The La values measured by TEM are consistent with estimates from the intensity ratios of the D to G Raman peak in these regions. Atomistic modelling finds that the lowest energy interfaces in the crazy paving structure comprise 5, 6 and 7 member carbon rings. The bent laminae tend to maintain the 6 member rings, but are strained elastically. We suggest that a 7 member carbon ring leaves a cavity representing an arm-chair graphite edge contributing to the Raman spectra D peak.
This work was supported the EPSRC Advanced Materials for Nuclear Fission programme under UNIGRAF: Understanding and Improving Graphite for Nuclear Fission (grant number EP/M018822/1, EP/M018598/1, EP/M018679/1). The EPSRC grant, EP/K040375/1, for the ‘South of England Analytical Electron Microscope’ is also gratefully acknowledged.