Energy released at high temperature by irradiated graphite

Rappeneau, J.; Taupin, Jean‐Luc; Grehier, J

doi:10.1016/0008-6223(66)90016-9

Cited by 15 publications

(4 citation statements)

References 6 publications

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“…Not all the stored energy is released at once in a typical annealing process, since defects with significant concentrations interact and form aggregates, clusters and voids 34 . Due to defect aggregation, multiple energy release steps are commonly observed experimentally (for example, in irradiated graphite 35 ) rather than just one energy release event. To release all the stored energy at once, the defect aggregation problem would need to be addressed.…”

Section: Discussionmentioning

confidence: 99%

Using defects to store energy in materials – a computational study

Bernardi

2017

Sci Rep

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Energy storage occurs in a variety of physical and chemical processes. In particular, defects in materials can be regarded as energy storage units since they are long-lived and require energy to be formed. Here, we investigate energy storage in non-equilibrium populations of materials defects, such as those generated by bombardment or irradiation. We first estimate upper limits and trends for energy storage using defects. First-principles calculations are then employed to compute the stored energy in the most promising elemental materials, including tungsten, silicon, graphite, diamond and graphene, for point defects such as vacancies, interstitials and Frenkel pairs. We find that defect concentrations achievable experimentally (~0.1–1 at.%) can store large energies per volume and weight, up to ~5 MJ/L and 1.5 MJ/kg for covalent materials. Engineering challenges and proof-of-concept devices for storing and releasing energy with defects are discussed. Our work demonstrates the potential of storing energy using defects in materials.

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Section: Discussionmentioning

confidence: 99%

Using defects to store energy in materials – a computational study

Bernardi

2017

Sci Rep

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“…Thus the activation energy E becomes a function of the remaining, and newly formed, lattice defects and annealing temperature leading to a reduced annealing rate as the temperature increases. This behaviour is typical of the release of stored energy in which the rate of release reduces significantly above 200°C and only starts to increase again at temperatures in excess of 1200°C, as discussed by Rapenaux et al [4]. Thus the form and solution of Eq.…”

Section: Thermal Annealing Of Defects In Graphitementioning

confidence: 86%

“…This investigation examined the determination of doses and temperatures of experiments conducted in Dounreay fast reactor (DFR) by comparing dimensional and thermal conductivity changes in PGA graphite irradiated in DFR or DIDO (Figs. [3][4][5][6]. At temperatures of 350°C and below, data that applied the equivalent temperature conversion (using an activation energy E of 1.2 eV) showed improved agreement over the data that did not use the conversion.…”

Section: Experimental Evidencementioning

confidence: 98%

The origins and use of the equivalent temperature concept

Eason¹,

Hall

Heys

et al. 2008

Journal of Nuclear Materials

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“…The uncertainty is estimated by taking account of the differences in the irradiation fluence and temperature. 82 This corresponds to formation energy for a C 2 molecule and two single vacancies = 16.7 Ϯ 3.0 eV. ͑26͒ When two single interstitial atoms combine to form an interstitial C 2 molecule, the sum of the difference between their respective self-energies and the binding energy of C 2 molecule is released.…”

Section: E Stored Energy and Formation Energy Of A Frenkel Pairmentioning

confidence: 99%

Increase in specific heat and possible hindered rotation of interstitialC2molecules in neutron-irradiated graphite

Iwata

Watanabe

2010

Phys. Rev. B

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Irradiation-induced increase in the low-temperature specific heat has been measured in the temperature range of 1.9-43 K in graphite neutron-irradiated to 1.4ϫ 10 20 n / cm 2 ͑E Ͼ 1 MeV͒ around 333 K. The increase of the lattice specific heat is interpreted as due to the hindered rotation of interstitial C 2 molecules in the periodic potential of V͑͒ = ͑V 0 / 2͒͑1 + cos 2͒, where is the angle of rotation and V 0 is 0.040 eV. The first-excited rotational level is 0.0058 eV above the ground state and the rotational frequency is 1.39ϫ 10 12 s −1 . This result shows that C 2 molecules do not form covalent bonds with atoms in the surrounding graphite layers. It is in marked contrast with the result of recent first-principles theoretical calculations that interstitial atoms form strong covalent bonds with atoms in the graphite layers. The concentration of C 2 molecules is estimated to be f = 1.16%. The hole concentration, deduced from the electronic specific heat and the SWMcC band model, suggests that one single vacancy creates one hole and the single vacancy concentration is 2f. Since the measurement of the lattice specific heat gave the concentration of the defects directly, we could evaluate some physical properties for a unit concentration of the defects. The volume changes by a single interstitial atom, an interstitial C 2 molecule, and a single vacancy are deduced to be 2.6Ϯ 0.3, 9.3Ϯ 1.4, and −0.46Ϯ 0.07 atomic volumes, respectively. The formation energy of a Frenkel pair is estimated to be 12.6Ϯ 2.5 eV. The phonon scattering with a reciprocal relaxation time proportional to 1.5 , where is the angular frequency of phonons, is attributed to the scattering of phonons by the disklike strain around interstitial C 2 molecule clusters. A broad dip in the a-axis thermal conductivity observed below room temperature is attributed to the resonance scattering of phonons by the hindered rotation of interstitial C 2 molecules as well as by the vibration of these molecules as rigid units. The positron lifetime of 350 ps is suggested to be the lifetime of positrons trapped in an open space on the periphery of the interstitial clusters of C 2 molecules. The well-known Wigner energy is stored mainly as interstitial C 2 molecules and single vacancies.

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Energy released at high temperature by irradiated graphite

Cited by 15 publications

References 6 publications

Using defects to store energy in materials – a computational study

Using defects to store energy in materials – a computational study

The origins and use of the equivalent temperature concept

Increase in specific heat and possible hindered rotation of interstitialC2molecules in neutron-irradiated graphite

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