Modelling of hydrogen release from functional materials via cellular automaton

In the present work, Cellular Automaton (CA) model of the hydrogen transport through a metallic material is constructed. The model consists of three parts such that, desorption, surface-bulk interaction and bulk diffusion model. In the conventional approach, bulk diffusion is expressed by a diffusion equation and the surface processes are included into the boundary condition. For transient analysis of hydrogen release, it is necessary to implement the surface processes more precise than just a boundary condition. The surface can be treated as completely a different system from the bulk without loosing the interfacial relationship of each medium by the use of CA model. The model is constructed in compliance with thermally-activated processes. The model is used to simulate the transition state of the hydrogen transport between the bulk and the vacuum through the surface. For the first time, a backward diffusion toward the bulk from downstream side surface is seen. It is deduced that such a phenomenon is caused by accumulation of hydrogen at the surface since desorption is limited by surface migration at early transient stage. Such behaviour has not seen by the conventional model since the surface is treated as just a boundary condition for the bulk diffusion equation. It is also deduced that the advantage of this CA model is the suitability for the transient analysis.