Hydrogen absorption properties of Li-Mg-N-H system

Isothermal hydrogen absorption properties of the ball milled mixture of 3Mg(NH2)(2) and 8LiH after dehydrogenation at 200 degrees C under high vacuum were investigated at two different temperatures of 150 and 200 degrees C. The pressure-composition isotherm (PCT) curve at 200 degrees C revealed a two-plateaus-like behavior, while the PCT curve at 150 degrees C showed a single-plateau-like behavior. The hydrogenated phases were composed of LiH and Mg(NH2)(2) under 9 MPa at 200 degrees C, while those were observed as mixed phases of LiH and LiNH2 at 150 degrees C without any trace of Mg(NH2)(2) in XRD measurements. These results indicate that there are two-step hydrogenation processes corresponding to high and low pressures at 200 degrees C, but the kinetics at 150 degrees C is too slow to proceed with the second hydrogenating step at high pressure region. (c) 2005 Elsevier B.V. All rights reserved.