Buckle, ruck and tuck: A proposed new model for the response of graphite to neutron irradiation

Abstract

The default theory of radiation damage in graphite invokes Frenkel pair formation as the principal cause of physical property changes. We set out its inadequacies and present two new mechanisms that contribute to a better account for changes in dimension and stored energy. Damage depends on the substrate temperature, undergoing a change at approximately 250 °C. Below this temperature particle radiation imparts a permanent, nano-buckling to the layers. Above it, layers fold, forming what we describe as a ruck and tuck defect. We present first principles and molecular mechanics calculations of energies and structures to support these claims. Necessarily we extend the dislocation theory of layered materials. We cite good experimental evidence for these features from the literature on radiation damage in graphite. © 2011 Elsevier B.V. All rights reserved

The contribution made by lattice vacancies to the Wigner effect in radiation-damaged graphite

“…The measurements of C 44 cited previously find that this occurs above about 200 C, and it was postulated that subsequent accumulation of defects led to the formation of new graphene sheets [63]. In the present model, basal dislocations accumulate in a manner that first creates structures analogous to a ruck in a carpet or sheet of fabric, then fold over completely upon themselves [62]. Hence, the material expands in the c-direction at the expense of the basal dimensions.…”

“…Another model for dimensional change divides the processes that are responsible for it into low-and hightemperature regimes [62].…”

“…The existence of such defects in neutron-irradiated hot-worked pyrolytic graphite has been inferred from measurements of the elastic shear modulus C 44 [63], and it was anticipated that this would generate an enormous strain in heavily damaged material, causing the layers to buckle [64]. It was realised later that if radiation damage caused crinkling or blistering of the sheets, then this would produce an expansion in the prismatic direction [62]. Buckling of graphite layers induced by the presence of defects has even been observed to occur in unirradiated graphite [65].…”

Electron irradiation of nuclear graphite studied by transmission electron microscopy and electron energy loss spectroscopy

“…The bulk properties of damage features have been thoroughly investigated and theoretical models of induced structural changes derived [7].…”

Effects of Displacing Radiation on Graphite Observed Using in situ Transmission Electron Microscopy

“…Heggie et al [7,8], buckling of graphite can occur where one "graphene" sheet is pinned at two points to another sheet of different length or by the interaction of two dislocations of opposite sign in different sheets. Neutron collisions cause basal edge dislocations to pile-up and glide past each other on nearby sheets creating a "ruck and tuck" defect where a "graphene" sheet is buckled.…”