Modelling extended efects in neutron irradiated graphite

Boone, James (2013) Modelling extended efects in neutron irradiated graphite. Doctoral thesis (PhD), University of Sussex.

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This thesis is a contribution towards modelling extended defects in nuclear graphite. Programmatic tools have been created which allow the implementation of displacement fields for basal and prismatic dislocations in graphite using the anisotropic elastic equations. These dislocation displacements have also been used to accommodate other defects which may be represented using dislocation formalisms. Structures such as prismatic loops, dislocation dipoles, folds, surface ridges and turbostratic graphite have been created for the purpose of generating structures for modelling.

We have investigated the X-ray diffraction simulations resulting from the various structures containing defects and compared these directly with experimental results from samples of neutron irradiated graphite. We have shown that some of the line defects, such as the ruck and tuck fold, reproduce characteristic diffraction phenomena as seen in the literature, providing evidence for the existence of such defects in the relevant temperature range. Powder diffraction patterns also show diffraction peaks at small angles, in line with what is expected from long range disorder. With the use of molecular modelling software with interatomic potentials, we have shown that the spiro interstitial defect, which binds adjacent layers, may not be a sufficient barrier to prevent the glide of partial basal dislocations past one another, especially when the shear constant for graphite is reduced by the presence of disregistry or stacking faults. In addition, we have shown that basal dislocations with large Burgers vectors (superedge dislocations) give rise to delamination across the glide plane, whereas a 90° partial basal dislocation does not.

Finally we treat graphene as a continuum membrane, performing calculations of the formation energy due to free bending, and compared the results for the nanotube with Density Fucntional Theory (DFT) calculations with good agreement. As such, the same method has been applied to other, more exotic structures for layer deformations, such as a buckles, folds and a wave packet like structure representing a local ripple in a layer, thought to occur when dislocation motion is inhibited and in-plane strain is relieved as out-of-plane deformations.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QD Chemistry > QD0146 Inorganic chemistry
Depositing User: Library Cataloguing
Date Deposited: 07 Nov 2013 11:52
Last Modified: 17 Sep 2015 12:18

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