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

Mironov, Brindusa E; Freeman, Helen M.; Brown, Andy; Hage, F.; Scott, A. J.; Westwood, Aidan; Costa, Jean-Pierre da; Weisbecker, Patrick; Brydson, Rik

doi:10.1016/j.carbon.2014.11.019

Cited by 66 publications

(61 citation statements)

References 41 publications

(51 reference statements)

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“…With increasing dose and irradiation temperature (PCIB4.0, PCIB6.8 and PCEA6.8), the narrowing of peaks, reduction in I D /I G ratio and a lower wavenumber G peak position, suggest that the higher irradiation temperature (655 C) allows defects to anneal. These results are in line with previous studies [7,9,17,35].…”

Section: Ramansupporting

confidence: 94%

“…It is thought that this is due to the higher irradiation temperatures allowing for slight thermal annealing. In general, the sp 2 values have not reduced as much as those from the room temperature electron irradiation studies in [17], where reductions in sp 2 content of up to 24% (at 0.32 dpa) were observed.…”

Section: Tem/eelscontrasting

confidence: 52%

“…In some cases, the opposite of what is expected is observed; the tortuosity and misorientation decreases with increasing dose for PCIB specimens; potentially an effect of thermal annealing at higher temperatures. Similar lattice image analysis was applied to nuclear grade graphite subject to controlled electron irradiation damage in a previous study by Mironov et al [17]. This demonstrated that the analysis technique can indeed detect subtle changes in the lattice structure.…”

Section: Tem/eelsmentioning

confidence: 71%

“…All electron micrographs were subject to the PyroMaN image analysis technique detailed in DaCosta et al and used on electronirradiated graphite by Mironov et al [17,31]. Since the measurement of fringe length is ultimately limited by the width of the micrograph, TEM images were cropped to be the same size, with approximately the same resolution, ensuring a fair comparison between fringe length values.…”

Section: Tem/eelsmentioning

confidence: 99%

“…The p* and s* peak intensities were analysed following the five Gaussian fitting method used in Refs. [3,17] and data was normalised to 100% sp 2 for HOPG. Using this method, it was possible to derive that virgin PCIB and PCEA exhibited ca.…”

Section: Tem/eelsmentioning

confidence: 99%

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Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Freeman

Mironov

Windes

et al. 2017

Journal of Nuclear Materials

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a b s t r a c tThe neutron irradiation-induced structural changes in nuclear grade graphites PCEA and PCIB were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). The graphite samples were irradiated at the Advanced Test Reactor at the Idaho National Laboratory. Received doses ranged from 1.5 to 6.8 displacements per atom and irradiation temperatures varied between 350 C and 670 C.XRD and Raman measurements provided evidence for irradiation induced crystallite fragmentation, with crystallite sizes reduced by 39e55%. Analysis of TEM images was used to quantify fringe length, tortuosity, and relative misorientation of planes, and indicated that neutron irradiation induced basal plane fragmentation and curvature. EELS was used to quantify the proportion of sp 2 bonding and specimen density; a slight reduction in planar-sp 2 content (due to the buckling basal planes and the introduction of non-six-membered rings) agreed with the observations from TEM.

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Section: Ramansupporting

confidence: 94%

Section: Tem/eelscontrasting

confidence: 52%

Section: Tem/eelsmentioning

confidence: 71%

Section: Tem/eelsmentioning

confidence: 99%

Section: Tem/eelsmentioning

confidence: 99%

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Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Freeman

Mironov

Windes

et al. 2017

Journal of Nuclear Materials

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Unravelling the structural and property changes in graphite under high dose electron beam irradiation

Freeman

Hardcastle

Farbos

et al. 2016

European Microscopy Congress 2016: Proceedings

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Neutron radiation damage is a significant problem for graphite moderated nuclear reactors where graphite serves as both the neutron moderator and a key structural component. Exposure to neutron radiation introduces a variety of chemical and physical property changes, such as a reduction in the thermal conductivity, increase in Young's modulus and dimensional change, creating cracks [1]. Understanding the damage processes experienced by irradiated nuclear graphite over a range of length scales is essential in predicting the lifetime of the material, which influences the overall lifetime of the reactor. In this study, electron irradiation is used as a surrogate for neutron irradiation. A multi‐faceted approach has been applied to transmission electron microscopy (TEM)/ electron energy loss spectroscopy (EELS) data obtained from nuclear grade graphite exposed to the electron beam for differing time periods. This involved deriving initial 3D structural models from a series of 2D TEM images at differing stages of damage, these models were then used to derive theoretical TEM and EELS data which were then in‐turn compared to back to the experimental data from the same sample; finally these models were used to predict mechanical and transport properties relevant to reactor operation. TEM, selected area electron diffraction (SAED) patterns and EEL spectra were collected periodically (along the graphite [100] orientation) during electron beam exposure at 200 kV for 13 minutes (total fluence = 2 × 10 8 e‐nm −2 ). Electron micrographs were subject to 2D image analysis to measure the change in (002) fringe length and tortuosity, following the method outlined in [2]. The EELS series were analysed to extract information about bond length and ratio of non‐planar to planar sp 2 bonded carbon, following the method outlined in [3]. In recent years, a reconstruction procedure has been developed, called image guided atomistic reconstruction (IGAR), that allows large and realistic representations of disordered, yet anisotropic, graphite‐based carbons to be built [4–6], from data inferred from their TEM images (Figure 1). The IGAR procedure was applied to the experimental TEM image series to produce 13 separate models at differing stages of electron beam induced damage. These models provide information about the different atomic environments of the carbon atoms within the structure, e.g. whether they are 2, 3 or 4‐fold, sp 2 bonded or defective. They were used to produce simulated TEM lattice images, which were analysed in the same way as experimental TEM images; the analysis results were then compared. EEL spectra were also calculated from the reconstructed models using the plane wave density functional theory [7,8] (DFT) code CASTEP [9]. These were analysed in the same way as the experimental spectra (Figure 2). Experimental and theoretical data were compared and showed a reasonable correlation (Figures 3 and 4): the proportion of non‐planar to planar sp 2 bonded carbon was observed to increase following a fluence of 2 × 10 8 e‐nm −2 and the C‐C bond length was also observed to increase. These reconstructed models bridge the gap between the primary damage obtained in former molecular dynamics studies which can only cope with short timescales, and the severe damage observed in TEM images and EEL spectra after prolonged exposure to neutrons or electrons.

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EPR Study of Porous Si:C and SiO₂:C Layers

Савченко

Vasin

Muto

et al. 2018

Physica Status Solidi (b)

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Initial porous silicon (por-Si), carbonized porous silicon (por-Si:C), and carbon-incorporated porous silicon oxide (por-SiO 2 :C) layers are studied by electron paramagnetic resonance (EPR) at T ¼ 10-13 K. Scanning transmission electron microscopy and electron energy loss (EEL) spectroscopy show that por-Si:C and por-SiO 2 :C layers have a highly disordered structure with mixing sp 2 and sp 3 C─C bonds. In the por-SiO 2 :C layers, the peak of the oxygen bonded to carbon in the form of hydroxyl groups is found in the EEL spectrum of the C K-edge region. Low-intensity signals of Lorentzian lineshape are detected in the EPR spectrum of por-Si, por-Si:C, por-SiO 2 :C layers. One of them is attributed to the P b0 defect at the Si/SiO 2 interface of nanocrystalline grain and the second to the silicon dangling bonds (SiDB) localized in nanocrystalline Si. The carbonization of por-Si layers and subsequent oxidation of por-Si:C gives rise to the appearance of additional EPR signals of high intensity at g ¼ 2.0035(3) in por-Si:C and at g ¼ 2.0030(3) in por-SiO 2 :C, which are assigned to carbon-related defects (CRD) and carbon clusters, correspondingly. It was found that predominant defect types in por-Si:C and por-SiO 2 :C layers are CRD and carbon clusters, respectively, while the spin concentration of P b0 interface defects and SiDB is low.

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

Cited by 66 publications

References 41 publications

Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Unravelling the structural and property changes in graphite under high dose electron beam irradiation

EPR Study of Porous Si:C and SiO₂:C Layers

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

Cited by 66 publications

References 41 publications

Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

Unravelling the structural and property changes in graphite under high dose electron beam irradiation

EPR Study of Porous Si:C and SiO2:C Layers

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EPR Study of Porous Si:C and SiO₂:C Layers