Modelling of the diffusion of hydrogen in porous graphite
The graphite used in fusion devices as first wall material is porous and consists of granules and voids [1,2]. The 1-10mu m granules are further composed of graphitic micro-crystallites (5-10nm), which are separated by micro-voids. Understanding the hydrogen transport and trapping in such granules is an important aspect of understanding the effect of a realistic graphite structure on hydrogen recycling and hydrocarbon formation in graphite. We use Kinetic Monte Carlo (KMC) to study the diffusion of hydrogen in a typical granule of graphite. We use molecular dynamics (MD) to obtain the jump attempt frequency omega (o) and the migration energy E(m) of interstitial graphite which are inputs to the KMC. A consistent parameterization of MD within KMC is presented. The diffusion shows a non-Arrhenius behaviour, which can be explained with two types of different jump processes within the graphite crystal. The porous granule structure is constructed using statistical distributions for the crystallite dimensions and for crystallite orientations at a given porosity. The hydrogen trapping at inter-crystallite micro-voids are modelled by assuming that a fraction of the hydrogen atom flux transiting through the micro-void is trapped. We present a parametric study of the diffusion and trapping of hydrogen within the granule for various trapping fractions at the inter-crystallite micro-voids.
Bibliographic Reference: An article published in: Physica Scripta Online Vol. T108, 85-89, 2004
Availability: This article can be accessed online by subscribers, and can be ordered online by non-subscribers, at: http://www.physica.org/
Record Number: 200417640 / Last updated on: 2004-07-12
Original language: en
Available languages: en