Hydrogen grain-boundary diffusion in nano-crystalline Mg-films - experimental and theoretical study

• Applicant: Professorin Dr. Astrid Pundt
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 213953861

Grain boundary (GB) diffusion of hydrogen differs strongly from that of substitutional elements: while GB diffusion of substitutional elements is about three orders of magnitude faster than bulk diffusion, GB diffusion of interstitial hydrogen is slower or similar to hydrogen bulk diffusion. This was proven by Mütschele and Kirchheim in 1986 for nano-crystalline Pd for low hydrogen concentrations. Moreover, different isotherms of nano-crystalline Pd-H can be easily explained under the assumption that GBs do not transform into a hydride phase but keep their amorphous-like properties. In this project we plan to stress the idea that GBs mainly keep their properties over the full concentration range leading to the result that GB diffusion at high concentrations should be similar to that measured at low concentrations. This is of special interest for alloys transforming into extra-stable hydrides with low bulk diffusivity, because GBs could act as pathways for hydrogen diffusion. Microstructure and the stress state could be optimized for fastest diffusivity. Mg transfers into a stable Mg-dihydride phase with extremely low bulk diffusivity. Mg is, further, of special interest for mobile storage applications because of its high gravimetric storage density. With the proposed studies we hope to link basic research on the idea of GBs acting as pathways for hydrogen diffusion with promising new aspects for the design of nano-crystalline, faster kinetics hydrogen storage materials.

• DFG Programme: Research Grants