Atomistic Inquiries into the Effect of Hydrogen on Metals

Hydrogen corrosion is significant for systems operating in reducing conditions, including reactor systems, refinery operations, and actinides.  In this talk I will summarize our experience in the application of molecular modeling and atomistic simulation techniques to understanding the interaction of hydrogen with metallic surfaces, the bulk lattice, materials defects, oxides and phase-transformations.  We will present data that show how hydrogen surface activity varies with underlying properties of the metal, as well as with the proximity to coadsorbed impurities, particularly sulfur.  This last aspect is particularly relevant to the concept of hydrogen absorption promoters, that can accelerate hydrogen uptake and embrittlement.  The influence of electrochemical and environmental parameters upon hydrogen surface activity will also be considered using state of the art ab initio models for the solution-metal interface.  Using methods drawn from solid-state physics, hydrogen interactions with stress fields and structural as well as chemical defects in the material have also been evaluated, from which implications can be drawn regarding the role of trap sites in initiating hydrogen coalescence and hydride nucleation.  The application of computational group theory to understanding phase transformations in metal-hydrogen binary systems will also be presented, with the results suggesting that the critical step in the hydriding process is transport and diffusion in the metal.