Hydrogen absorption/desorption properties of MmNi4.5Cr0.5-xZrx alloys

Hydrogen absorption/desorption properties of MmNi(4.5)Cr(0.5-x)Zr(x) alloys ( x = 0, 0.05, 0.1) were investigated in the present work. The Pressure-Composition ( PC) isotherms and absorption kinetics were measured in the temperature range of 273 <= T <= 303 K by the volumetric method. XRD patterns showed that the as-annealed MmNi(4.5)Cr(0.5-x)Zr(x) alloys had CaCu5 type hexagonal structure and could keep the same single phase after 16 cycles of absorption/desorption. It was found that with the increase of x in MmNi(4.5)Cr(0.5-x)Zr(x) alloys, the dissociation plateau pressure increased, the hysteresis was diminished, the hydrogen uptake capacity was reduced and the absorption kinetics was improved. The absorption plateau pressure increased when x was increased to 0.05, but decreased when x increased to 0.1. It was also found that the dissociation plateau pressure increased linearly with increasing cell volume V and the lattice parameter a, and the hydrogen uptake capacity decreased linearly with increasing Zr content. (c) 2008 Elsevier B.V. All rights reserved.