Papers by Author: Jae Hyeok Shim

Abstract: The interactions of a dislocation with commonly observed irradiation induced defects such as a stacking fault tetrahedron (SFT) and a void are studied using molecular dynamics (MD) simulation methods. The simulation of an SFT interacting with a dislocation in face centered cubic (FCC) copper (Cu) reveals that an SFT is a strong obstacle against a dislocation motion, with dislocation detachment often involving an Orowan like mechanism. The resulting SFT generally involves a shear step, although partial absorption is also observed in some specific interaction geometries. Dislocation interaction with a void has been studied in body centered cubic (BCC) molybdenum (Mo). The dislocation locally annihilates upon contact with the void and then re-nucleates on the void surface as the dislocation glides past the void. The interaction results in the simple shear of the void by one Burger’s vector. The obstacle strength of the void is measured using conjugate gradient molecular statics (MS) method as a function of void size. A large increase in the obstacle strength is observed for a void size greater than 3 nm in diameter.

Abstract: Fine Ti5Si3 powder has been synthesized from a mixture of elemental Ti and Si powders using a mechanochemical method. It shows a good catalytic effect on NaAlH4 by reducing the dehydrogenation temperature and improving the dehydrogenation kinetics. Although the catalytic effect of Ti5Si3 is not better than that of TiCl3, the Ti5Si3 catalyst has an advantage over TiCl3 in terms of hydrogen capacity by releasing more hydrogen than TiCl3 during dehydrogenation. NaAlH4 catalyzed with Ti5Si3 shows reversible hydrogen storage by being hydrogenated at moderate conditions, although the hydrogenation kinetics is rather slow.