TEM analysis of high-energy ball-milled MgH2 powders

Presenter: Mohsen Danaie

 

 

Our main focus in this research is gaining deeper understanding of the milled microstructure of MgH2 powder, using cryogenic transmission electron microscopy (TEM). We milled MgH2 powder in inert environment, with half of the milled batch being subsequently annealed under pressurized hydrogen for 2 and 16hrs. We observed a substantial decrease in desorption temperature after ball-milling. Upon annealing for 2hrs, this enhancement was reduced and then completely vanished after 16hrs. Milling induced a significant amount of strain in the hydride phase, reduced the grain size and modified the particle size distribution to multi-modal. Annealing eliminated the microstrain, increased the grain size close to initial value and smoothed the particle size distribution. TEM analysis of the ball-milled powder showed large population of nano-scale twins in the hydride microstructure. Subsequent annealing drastically reduced the density of the twins. We discuss the potential influence of milling-induced strain and nano-twins on the desorption kinetics.