Thermal expansion coefficients of graphite crystals

Morgan, W.C.

doi:10.1016/0008-6223(72)90011-5

Cited by 113 publications

(55 citation statements)

References 17 publications

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“…Below room temperature, we find good agreement with the experimental in-plane coefficients of thermal expansion, 16,80 not surprising considering the agreement in the specific heat at this temperature observed previously. From 300 to 100 K, the X6 potential overestimates the thermal expansion coefficient by 40%, although convergence is observed at higher temperatures.…”

Section: Lattice Parameters and Thermal Expansionsupporting

confidence: 91%

Quantum mechanics based force field for carbon (QMFF-Cx) validated to reproduce the mechanical and thermodynamics properties of graphite

Pascal

Karasawa

Goddard

2010

The Journal of Chemical Physics

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As assemblies of graphene sheets, carbon nanotubes, and fullerenes become components of new nanotechnologies, it is important to be able to predict the structures and properties of these systems. A problem has been that the level of quantum mechanics practical for such systems ͑density functional theory at the PBE level͒ cannot describe the London dispersion forces responsible for interaction of the graphene planes ͑thus graphite falls apart into graphene sheets͒. To provide a basis for describing these London interactions, we derive the quantum mechanics based force field for carbon ͑QMFF-Cx͒ by fitting to results from density functional theory calculations at the M06-2X level, which demonstrates accuracies for a broad class of molecules at short and medium range intermolecular distances. We carried out calculations on the dehydrogenated coronene ͑C24͒ dimer, emphasizing two geometries: parallel-displaced X ͑close to the observed structure in graphite crystal͒ and PD-Y ͑the lowest energy transition state for sliding graphene sheets with respect to each other͒. A third, eclipsed geometry is calculated to be much higher in energy. The QMFF-Cx force field leads to accurate predictions of available experimental mechanical and thermodynamics data of graphite ͑lattice vibrations, elastic constants, Poisson ratios, lattice modes, phonon dispersion curves, specific heat, and thermal expansion͒. This validates the use of M06-2X as a practical method for development of new first principles based generations of QMFF force fields.

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Section: Lattice Parameters and Thermal Expansionsupporting

confidence: 91%

Quantum mechanics based force field for carbon (QMFF-Cx) validated to reproduce the mechanical and thermodynamics properties of graphite

Pascal

Karasawa

Goddard

2010

The Journal of Chemical Physics

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“…This leads to a ''hexagonal'' lattice constant in the (111) plane of 0.2528 nm for nickel and 0.2533 nm for c-Ni(Al). Comparison of these values with the lattice constant of the graphite basal plane, which has a value of 0.24608 nm at 650°C [38], hints at a smaller misfit for pure nickel. While the changes in lattice parameters are only small, the solubility of carbon increases significantly from 0.01 wt% for pure nickel [39] to 1.1 wt% for Ni 2.5Al at 700°C: Schuster et al [40] reported a solubility of at least 5 at.% C in a 90 at.% Ni and 5 at.% Al mixture at 700°C.…”

Section: Dusting Kinetics and Morphologiesmentioning

confidence: 86%

Metal Dusting of Nickel–Aluminium Alloys

2009

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Alloys of c-Ni(Al), c-c 0 Ni(Al)-Ni 3 Al, c 0 -Ni 3 Al and b-NiAl were exposed in 1 h cycles to a carbon-supersaturated CO-H 2 -H 2 O gas mixture (a C = 36.7, p O 2 = 2.83 9 10 -26 atm) at 650°C and an overall pressure of 1 atm. It was found that all alloys except b-NiAl had been attacked by metal dusting, leaving a layered structure of nickel particles, graphite and catalytically grown nano-sized carbon filaments as the corrosion product. Carbon uptake and metal wastage rates were slowed with increasing aluminium content for the single-phase alloys. However, the c-c 0 two phase alloy had the overall highest metal loss rate. Surface morphologies reflected uniform attack for the c and c-c 0 alloys, whereas on c 0 a pitting type of attack was observed. Amorphous alumina formation was identified on the surface of the c 0 and b alloys, and is thought to be the major factor providing protection against dusting attack.

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“…Before performing AIMD simulations DFT simulations on the unit-cell were performed to predict the 0 K lattice parameters, summarized in Tables 1 and 2 for beryllium and graphite respectively. Subsequently, the lattice parameters of the supercell at each temperature were determined from these 0 K parameters using the experimental thermal expansion coefficients [14,15]. Initially the supercell was equilibrated using AIMD at the simulation temperature for 1000 time-steps of 1fs using a canonical thermodynamic ensemble (NVT).…”

Section: Calculation Of Phonon Density Of Statesmentioning

confidence: 99%

Thermal neutron scattering law calculations using ab initio molecular dynamics

Wormald

Hawari

2017

EPJ Web Conf.

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Abstract. In recent years, methods for the calculation of the thermal scattering law (i.e. S(α, β), where α and β are dimensionless momentum and energy transfer variables, respectively) were developed based on ab initio lattice dynamics (AILD) and/or classical molecular dynamics (CMD). While these methods are now mature and efficient, further advancement in the application of such atomistic techniques is possible using ab initio molecular dynamics (AIMD) methods. In this case, temperature effects are inherently included in the calculation, e.g. phonon density of states (DOS), while using ab initio force fields that eliminate the need for parameterized semi-empirical force fields. In this work, AIMD simulations were performed to predict the phonon spectra as a function of temperature for beryllium and graphite, which are representative nuclear reactor moderator and reflector materials. Subsequently, the calculated phonon spectra were utilized to predict S(α, β) using the LEAPR module of the NJOY code. The AIMD models of beryllium and graphite were 5 × 5 × 5 crystal unit cells (250 atoms and 500 atoms respectively). Electronic structure calculations for the prediction of Hellman-Feynman forces were performed using density functional theory with a GGA exchange correlation functional and corresponding core electron pseudopotentials. AIMD simulations of 1000-10,000 time-steps were performed with the canonical ensemble (NVT thermostat) for several temperatures between 300 K and 900 K. The phonon DOS were calculated as the power spectrum of the AIMD predicted velocity autocorrelation functions. The resulting AIMD phonon DOS and corresponding inelastic thermal neutron scattering cross sections at 300 K, where anharmonic effects are expected to be small, were found to be in reasonable agreement with the results generated using traditional AILD. This illustrated the validity of the AIMD approach. However, since the impact of the temperature on the phonon DOS (e.g. broadening of spectral peaks) was observed in AIMD analysis, this technique may be envisioned as the approach for deriving the needed atomistic data for thermal scattering law calculations under realistic temperature and structural conditions for a given material.

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Thermal expansion coefficients of graphite crystals

Abstract: Graphite crystal expansions were derived as a function of temperature using the theoretical relationships of ~i ley(' ); the resultant 1 equations provide reasonable f i t s t o the measured l a t t i c e expansion . I data over the temperature range 300' t o 3000°K.

Cited by 113 publications

References 17 publications

Quantum mechanics based force field for carbon (QMFF-Cx) validated to reproduce the mechanical and thermodynamics properties of graphite

Quantum mechanics based force field for carbon (QMFF-Cx) validated to reproduce the mechanical and thermodynamics properties of graphite

Metal Dusting of Nickel–Aluminium Alloys

Thermal neutron scattering law calculations using ab initio molecular dynamics

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