Modeling of the Diffusion of Hydrogen in Porous Graphite

Dynamic Monte-Carlo modeling of hydrogen isotope reactive–diffusive transport in porous graphite

“…These models use rate constants for transport from experiments [9][10][11][12][13]7], some of which still need theoretical explanations. There exists many microscopic models [14][15][16][17] using MD with either empirical potentials or density functional theory and they give an insight into the microscopic mechanisms studied in graphite. It is desirable to use the insights gained from the microscopic models into modeling the transport in the meso-scale and further into the macro-scale in order to understand the physical processes contributing to macroscopic transport.…”

“…We have earlier modeled hydrogen isotope diffusion in pure, crystal graphite using MD at micro-scales (2.5 nm, 10 −10 s) and consistently parametrized the MD results within a KMC scheme [17]. A 3d, porous, granule structure was constructed using statistical distributions for crystallite dimensions and crystallite orientations for a specified micro-void fraction.…”

Modeling of hydrogen isotope exchange from porous graphite

“…In the present work we simulate the physics at meso-scales where a 100 nm × 100 nm × 300 nm sized granule of graphite is taken and Kinetic Monte-Carlo (KMC) is used. In KMC scheme all the thermally activated processes taking place in the system are parametrized in terms of the jump attempt frequency ω j o , the migration energy E j m , and the jump distance L j [4][5][6][7]. The jump distance L j corresponds to the distance jumped by an atom or molecule in a specified direction after overcoming the j th energy barrier with migration energy E j m .…”

“…The model is a hierarchical multi-scale model, wherein simulations at the lower scales or experimental results wherever available are used as inputs to the simulations at higher scales. In other words, the idea is to use the insights gained from the microscopic (up to nanometers) models (MD or ab-initio methods) for modeling the transport at the meso-scale (up to micrometers) and further at the macro-scale (up to cms) in order to understand the physical processes contributing to macroscopic transport [4][5][6][7]. Fig.…”

“…For samples having less internal porosity mixing is very low. Therefore the internal structure of graphite, which affects the diffusion coefficient [4][5][6][7] and consequently molecule formation and atomic re-emission [8,9], plays the most crucial role for the H,D mixing. A new mechanism based on the KMC and SDTrimSP simulation is proposed to explain the experimental data.…”