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  • 1.
    Adjizian, J.J.
    et al.
    Department of Chemistry, University of Sussex, Falmer, Brighton.
    Latham, Chris
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Briddon, P.R.
    Electrical, Electronic and Computer Engineering, University of Newcastle upon Tyne.
    Heggie, M.I.
    Department of Chemistry, University of Sussex, Falmer, Brighton.
    DFT study of the chemistry of sulfur in graphite, including interactions with defects, edges and folds2013In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 62, p. 256-262Article in journal (Refereed)
    Abstract [en]

    Sulfur has several roles, desirable and undesirable, in graphitization. We perform density functional theory calculations within the local density approximation to define the structures and energetics of sulphur in graphite, including its interactions with point defects and edges, in order to understand its role in the later stages of graphitization. We find sulphur does not cross-link layers, except where there are defects. It reacts very strongly with vacancies in neighbouring layers to form a six coordinate split vacancy structure, analogous to that found in diamond. It is also highly stable at basal edge sites, where, as might be expected, the size and valency of sulfur can be easily accommodated. This suggests a role for sulphur in stabilizing graphene edges, and following from this, we show that sulfur dimers can open, i.e. unzip, folds in graphite rapidly and exothermically.

  • 2.
    Battie, Yann
    et al.
    LCP-A2MC, Université de Lorraine.
    Dossot, Manuel
    Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, Nancy Université, Laboratoire de Chimie Physique et Microbiologie pour l'Environnement, UMR 7564, CNRS–University of Lorraine, LCPME UMR 7564 CNRS-Université de Lorraine.
    Allali, Naoual
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mamane, Victor
    Laboratoire de Synthèse Organométallique et Réactivité, Université Henri Poincaré - Nancy, Laboratoire de Structure et Réactivité des Systèmes Moléculaires Complexes, Nancy Université, SRSMC UMR 7565 CNRS-Université de Lorraine, Faculté des Sciences et Techniques.
    Naciri, Aotmane En
    LCP-A2MC, Université de Lorraine.
    Broch, Laurent
    LCP-A2MC, Université de Lorraine.
    Soldatov, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Mild covalent functionalization of single-walled carbon nanotubes highlighted by spectroscopic ellipsometry2016In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 96, p. 557-564Article in journal (Refereed)
    Abstract [en]

    Single-walled carbon nanotubes (SWCNT) synthesized using the HiPco® process and purified thereafter were submitted to two covalent functionalization processes: i) a mild oxidation in a concentrated HNO3 solution using microwave irradiation and ii) a radical functionalization to graft methoxyphenyl groups. The samples were analyzed by Raman spectroscopy and spectroscopic ellipsometry in the energy window 0.07-4.96 eV. The complex dielectric function was analytically calculated in order to extract the real (εr) and imaginary (εi) parts of this function vs. the incident energy of the light. The ellipsometric data in the infrared part of the spectrum revealed that process i) mainly affected the amorphous carbon deposited on the surface of SWCNTs while process ii) strongly changed the electronic nature of the film due to a charge transfer between methoxyphenyl groups and SWCNTs. These results demonstrate the richness of information that spectroscopic ellipsometry is able to bring about on an entire carbon nanotube ensemble compared to Raman spectroscopy, while not suffering from limitation on their electronic structure and/or aggregate state/presence of surfactants.

  • 3.
    Hedman, Daniel
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Larsson, Andreas
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Length dependent stability of single-walled carbon nanotubes and how it affects their growth2017In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 116, p. 443-447Article in journal (Refereed)
    Abstract [en]

    Using density-functional theory the stability of armchair and zigzag single-walled carbon nanotubes and graphene nanoribbons was investigated. We found that the stability of armchair and zigzag nanotubes has different linear dependence with regard to their length, with switches in the most stable chirality occurring at specific lengths for each nanotube series. We explain these dependencies by competing edge and curvature effects. We have found that within each series armchair nanotubes are the most stable at short lengths, while zigzag nanotubes are the most stable at long lengths. These results shed new insights into why (near) armchair nanotubes are the dominant product from catalytic chemical vapor deposition growth, if templating is not used. Paradoxically, the stability of armchair nanotubes at short lengths favors their growth although zigzag nanotubes are more stable at long lengths, resulting in the production of the least stable nanotubes.

  • 4. Lundin, A.
    et al.
    Soldatov, Alexander
    Sundqvist, B.
    Strongin, R.M.
    Bard, L.
    Fischer, J.E.
    Smith, A.B.
    Compressibility of C61D2 up to 1 GPa in the temperature range 175-345 K1996In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 34, no 9, p. 1119-1121Article in journal (Refereed)
    Abstract [en]

    We have measured the bulk modulus K for C61D2 up to 1 GPa in the temperature range 175-343 K. For face-centered cubic C61D2 above 290 K, we find an anomalously low value for K below about 0.15 GPa, possibly indicating pressure-induced changes in the structure. The (extrapolated) zero-p bulk modulus K(0) decreases with increasing T from 6.7 GPa at 175 K to 5.2 GPa at 343 K. A comparison with hypothetical expanded f.c.c. C60 with the same lattice constant shows that K(0) values are similar, indicating that the main intermolecular interactions are still between molecular bellies, not the sidegroups.

  • 5.
    Savini, G.
    et al.
    Radboud University, Nijmegen.
    Dappe, Y.J.
    Institut de Physique et Chimie des Matériaux, CNRS.
    Öberg, Sven
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Charlier, J-C
    Université Catholique de Louvain.
    Katsnelson, M.I.
    Radboud University, Nijmegen.
    Fasolino, A.
    Radboud University, Nijmegen.
    Bending modes, elastic constants and mechanical stability of graphitic systems2011In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 49, no 1, p. 62-69Article in journal (Refereed)
    Abstract [en]

    The thermodynamic and mechanical properties of graphitic systems are strongly dependent on the shear elastic constant C44. Using state-of-the-art density functional calculations, we provide the first complete determination of their elastic constants and exfoliation energies. We show that stacking misorientations lead to a severe lowering of C44 of at least one order of magnitude. The lower exfoliation energy and the lower C44 (more bending modes) suggest that flakes with random stacking should be easier to exfoliate than the ones with perfect or rhombohedral stacking. We also predict ultralow friction behaviour in turbostratic graphitic systems.

  • 6.
    Stark, A.K.
    et al.
    Luleå tekniska universitet.
    Berglund, L.A.
    Luleå tekniska universitet.
    Tagawa, M.
    Osaka University.
    Ohmae, N.
    Osaka University.
    Effect of atomic oxygen on the mechanical properties of highly graphitized carbon fibers1994In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 32, no 4, p. 641-644Article in journal (Refereed)
    Abstract [en]

    Material degradation is a serious problem for large structural members that operate in low earth orbit for a long time. In order to study how the mechanical properties of the fibers change in this environment, highly graphitized polyacrylonitrile-based high modulus carbon fibers have been exposed to different fluences of atomic oxygen, the dominant atmospheric element in low earth orbit. Tensile tests were performed on these fibers. Young's modulus and tensile strength decreased with increasing exposure to atomic oxygen. Scanning electron microscopy revealed that the surface of the carbon fiber was severely degraded by the atomic oxygen, and this explains the decreases in Young's modulus and tensile strength

  • 7. Sundqvist, B.
    et al.
    Edlund, U.
    Jacobsson, P.
    Johnels, D.
    Jun, J.
    Launois, P.
    Moret, R.
    Persson, P-A
    Soldatov, Alexander
    Wågberg, T.
    Structural and physical properties of pressure polymerized C601998In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 36, no 5-6, p. 657-660Article in journal (Refereed)
    Abstract [en]

    We discuss the structural and dynamic properties of C60 polymerized under low-P, low-T conditions, and suggest that the disordered mixed orthorhombic-tetragonal-rhombohedral phases produced under these conditions arise from nucleation of molecular chains in random directions because of the quasi-free molecular rotation under standard reaction conditions in the fcc phase of C60. Polymerization in He gives results qualitatively different from those obtained in other media.

  • 8.
    Toth, Pal
    et al.
    RISE Energy Technology Center, Piteå; University of Miskolc, Miskolc-Egyetemváros, Hungary.
    Jacobsson, Daniel
    Lund University, Lund.
    Ek, Martin
    Lund University, Lund.
    Wiinikka, Henrik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Energy Science. RISE Energy Technology Center, Piteå.
    Real-time, in situ, atomic scale observation of soot oxidation2019In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 145, p. 149-160Article in journal (Refereed)
    Abstract [en]

    The oxidation of soot is a complex process due to the heterogeneous structure of the material. Several mechanisms have been hypothesized based on ex situ studies, but need confirmation from in situ observation; furthermore, deeper insight is needed to develop and validate structure-dependent reaction mechanisms. In this work, soot oxidation was for the first time observed at atomic scale in situ, in real-time, using a spherical aberration-corrected Environmental Transmission Electron Microscope. The transformation of individual soot particles was followed through from initiation to complete conversion. Observations clearly showed the existence of different burning modes and particle fragmentation previously hypothesized in the literature. Furthermore, transitioning between the modes—affected by temperature and O2 pressure—was unambiguously observed, explaining previous observations regarding structure-dependent and time-varying oxidation rates. A new mode of burning in which oxidation happens rapidly in the bulk phase with the disruption of long-range lamellar order was observed and is suspected to be dominant at practically relevant conditions. The ability to unambiguously relate different burning modes in terms of nanostructure will be of importance for optimizing both soot emission abatement and properties of nanoparticulate carbon products.

  • 9.
    Wu, Jian
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements. State Key Laboratory of Materials-oriented Chemical Engineering, Nanjing Tech University.
    Mu, Liwen
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Zhu, Jiahua
    Intelligent Composites Laboratory, Department of Chemical and Biomolecular Engineering, The University of Akron.
    Feng, Xin
    State Key Laboratory of Materials-Oriented Chemical Engineering, Nanjing Tech University, Nanjing .
    Lu, Xiaohua
    Key Laboratory of Material and Chemical Engineering, Nanjing Tech University, Nanjing .
    Larsson, Roland
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Shi, Yijun
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Synthesis of hollow fullerene-like molybdenum disulfide/reduced graphene oxide nanocomposites with excellent lubricating properties2018In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 134, p. 423-430Article in journal (Refereed)
    Abstract [en]

    In this paper, bubble-on-plate structure is realized on hollow IF-MoS2/reduced graphene oxide (HIF-MoS2/RGO) nanocomposites. HIF-MoS2 nanocages templated with the generated ammonia (NH3) are connected to RGO through the interlayered MoS2. The as-prepared HIF-MoS2/RGO is added into an ionic grease to study the tribological behavior of HIF-MoS2/RGO. For comparison, commercial grade MoS2 nanoparticles, single RGO or HIF-MoS2 or their physical mixture are also studied. Tribological results show that, compared with other additives, HIF-MoS2/RGO nanocomposites have the best anti-wear properties especially under higher load of 3.0 GPa. The wear reduction of HIF-MoS2/RGO reinforced grease under 2.5 GPa and 3.0 GPa reached 67% and 96%, respectively. In addition, HIF-MoS2/RGO reinforced grease achieves much lower and stable friction coefficient (0.079, the value of neat grease is 0.098) under 3.0 GPa. HIF-MoS2/RGO reinforced grease maintains very low friction coefficient and wear up to 4.1 GPa, while the normal MoS2 and RGO show high wear at the pressure up to 3.0 GPa. It is proposed that HIF-MoS2 nanocages on RGO act as rolling balls during friction resulting in better separation of steels.

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