Density functional and dislocation theory of graphite related to nuclear materials

Sheehan, Glen (2013) Density functional and dislocation theory of graphite related to nuclear materials. Doctoral thesis (PhD), University of Sussex.

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Abstract

This thesis concerns the physicochemical understanding of radiation damage in
graphite. It is structured in two parts, the first being a foundation of elastic
and bonding properties in graphite and its intercalation compound with Bromine.
The second builds on this with dislocation theory to analyse dimensional change
and stored elastic energy. Part 1: Density functional theory (DFT) in the local
density approximation (LDA) has been used to study the elastic properties of
hexagonal graphite and of Bromine intercalated graphite. The second and third
order elastic constants of graphite have been calculated ab initio. The internal
strain has been considered and the results include partial and total elastic constant
results. The nature of the interlayer binding energy has been studied using DFT
with LDA. The London dispersion forces have been applied to the DFT results
using a simple Lennard-Jones type model. The results of this study are in good
agreement with other theoretical and experimental studies. The zero point energy
has also been calculated and its effects applied to the interlayer energy and the
related elastic constant C33 . This constant has also been calculated for stage-1 and
stage-2 Bromine-intercalated graphite in order to aid interpretation of intercalation
experiments which try to emulate with Br intercalation, the c-axis dimensional
change that occurs from radiation damage. Part 2: A two dimensional dislocation
model has been written based on both basal and prismatic dislocations. The
model elucidates the stress fields arising from irradiation damage in graphite in
either the standard damage model based on prismatic loops or the newly proposed
model based on basal dislocations. It illustrates the different physical processes
underlying dimensional change and should enable it to be quantified. The energy
of the stress fields is calculated and found to be comparable to stored energies
measured for graphite irradiated below 250oC.

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: 31 May 2013 05:57
Last Modified: 08 Sep 2015 15:02
URI: http://sro.sussex.ac.uk/id/eprint/44683

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