(Lecture) Local structure and cyclic durability of BCC alloys
date:2019-12-04 pageviews:36

Speaker: Dr. Kouji Sakaki(National Institute of Advanced Industrial Science and Technology, Japan)

Time:  16:30, Dec. 4th, 2019

Venue: Room on the 3rd Floor, Building B5, University Town Campus

Abstract: Hydrogen would be clean energy and be expected to be utilized as a gas fuel (so-called Power to gas system) if it is produced by using renewable energy. For this purpose, hydrogen storage method with compact, safe and easy operation is required. Since most of hydrogen storage alloys can absorb and desorb hydrogen in the pressure range from 0.01 to 1 MPa under ambient temperature, these are one of the desirable methods. The main issues to overcome for the practical applications are cyclic durability and material cost. Therefore, the speaker has investigated the hydrogen storage behavior from the viewpoints of atomic structure and clarified the degradation mechanism in AB5, AB2 and BCC alloys. In this talk, the speaker would like to concentrate on their recent study for local structure change in BCC alloys upon hydrogenation. 

The following results were obtained;

In di-hydride, interatomic distance of hydrogen with the surrounding metal atoms decreased with decreasing the atomic radius of metals indicating that hydrogen position slightly moved toward the smaller atoms and is not at the center of tetrahedral site. 

In mono-hydride, the metal lattice was locally distorted from BCT structure and the local structure was similar to VH0.5–like structure.

Hydrogen storage capacity of V10Ti35Cr55 drastically decreased in the early cycles and this capacity loss had strong correlation with r-dependent peak broadening of PDF patterns suggesting that the dislocations are accumulated upon the cyclic hydrogenation. Therefore, it is most likely that the accumulation of dislocations led degradation of hydrogen storage capacity. 

Biography:Dr. Kouji Sakaki received his Ph. D. in Materials Science from Osaka University in 2004. Then he has been working at National Institute of Advanced Industrial Science and Technology (AIST) and he is a group leader now. He is interested in the development and fundamental research on hydrogen storage materials.