Irradiation-induced amorphization of graphite: A dislocation accumulation model

Niwase, Keisuke

doi:10.1080/09500830210137416

Cited by 36 publications

(50 citation statements)

References 17 publications

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“…However, despite this, very few in-depth microstructural studies have been conducted on irradiated graphite [10,11,12,13,14,15,16,17]. The majority of those that have been performed have employed highresolution transmission electron microscopy (HRTEM) to examine irradiation-induced defect formations [15,16] and micro-crack evolution [18] in various nuclear graphite grades.…”

Section: Introductionmentioning

confidence: 99%

“…Both the techniques are well established, non-destructive, have a practical significance and provide information on the bulk properties of polycrystalline materials averaged over the whole sample volume (~1 μm below the top layer) [19,20]. Only a handful of literature is available that focuses on characterising the change in crystal dimensions and lattice parameters from the diffraction and spectroscopic data obtained via XRD and Raman spectroscopy, respectively [10,11,12,13,14,21]. Tuinstra and Koenig (1970) Cançado et al (2006) and Lu et al (2001), for example, have both performed systematic X-ray diffraction and Raman studies on graphitised samples [10,22,23].…”

Section: Introductionmentioning

confidence: 99%

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An understanding of lattice strain, defects and disorder in nuclear graphite

Krishna¹,

Wade²,

Jones³

et al. 2017

Carbon

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In this study, microstructural parameters, such as lattice dimension, micro-strain and dislocation density, of different neutron-irradiated graphite grades have been evaluated using the diffraction profiles of X-ray diffraction (XRD) and the scattering profiles of Raman spectroscopy. Using Gen-IV candidate graphite samples (grade PCEA, GrafTech), subjected to neutron irradiation at 900°C to 6.6 and 10.2 dpa, and graphite samples of similar grain size and microstructure taken from the core of the British Experimental Pile Zero reactor, which have been irradiated at 100-120 °C to 1.60 dpa, an investigation on the effect of irradiation dose and temperature on the aforementioned microstructural parameters is

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

An understanding of lattice strain, defects and disorder in nuclear graphite

Krishna¹,

Wade²,

Jones³

et al. 2017

Carbon

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show abstract

“…Upon annealing, the atoms aggregate into new graphene sheets between existing ones, taking the form of interstitial prismatic dislocation loops, while vacancies coalesce into lines which collapse, causing shrinkage in the basal plane [30,31]. Thus, the response of graphite to damaging radiation involves the creation and accumulation of non-basal edge dislocation dipoles, and causes progressive reduction in long-range order [32,33]. Details of the processes that are believed to occur have been captured by high-resolution transmission electron microscopy experiments showing the nucleation of prismatic dislocation loops [34].…”

Section: Introductionmentioning

confidence: 99%

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

Latham

Heggie

Alatalo

et al. 2013

J. Phys.: Condens. Matter

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Models for radiation damage in graphite are reviewed and compared, leading to a re-examination of the contribution made by vacancies to annealing processes. A method based on density functional theory, using large supercells with orthorhombic and hexagonal symmetry, is employed to calculate properties and behaviour of lattice vacancies and displacement defects. It is concluded that annihilation of intimate Frenkel defects marks the onset of recovery in electrical resistivity, which occurs when the temperature exceeds about 160 K. Migration of isolated monovacancies is estimated to have an activation energy of E a ≈ 1.1 eV. Coalescence into divacancy defects occurs in several stages, with different barriers at each stage, depending on the path. The formation of pairs ultimately yields up to 8.9 eV energy, which is nearly 1.0 eV more than the formation energy for an isolated monovacancy. Processes resulting in vacancy coalescence and annihilation appear to be responsible for the main Wigner energy release peak in radiation-damaged graphite, occurring at about 475 K.

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“…However, theoretical calculations for such energies are consistently higher (1.2 -2 eV) [9,17,29]. It has been proposed that these discrepancies are due to a simplified interpretation of the indirect experimental results, in particular the effect of shear on the derived migration energies not being accounted for [9,17,30].…”

Section: Discussionmentioning

confidence: 83%

Thermal annealing of nuclear graphite during in-situ electron irradiation

Freeman

Scott

Brydson

2017

Carbon

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We have investigated the in-situ electron irradiation of nuclear graphite within a 200 kV transmission electron microscope at temperatures between 83 K and 473 K. For each temperature, nuclear grade Pile Grade A graphite specimens were subject to a fluence of ca. 10 22 electrons cm -2 , and transmission electron micrographs and selected area diffraction patterns were collected during electron beam exposure. By considering a critical fluence, at which the graphite (002) d-spacing increased by 10%, a temperature threshold for damage has been determined. Below ca. 420 K, electron irradiation caused significant net structural damage: fragmenting basal planes and producing a tortuous nanotexture. Above this temperature the effects of thermal annealing became more prevalent, maintaining the structure even at much higher fluences. We have derived activation energies for the annealing processes operative in these two temperature regimes and, via a comparison with theoretical predictions have, for the first time, associated these with specific recovery processes.

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Irradiation-induced amorphization of graphite: A dislocation accumulation model

Cited by 36 publications

References 17 publications

An understanding of lattice strain, defects and disorder in nuclear graphite

An understanding of lattice strain, defects and disorder in nuclear graphite

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

Thermal annealing of nuclear graphite during in-situ electron irradiation

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