Hydrogen absorption and desorption by quasicrystalline and related approximant powders produced by mechanical alloying in the Mg-Al-Zn system

Icosahedral quasicrystalline (i-phase) Mg44Al15Zn41 and related Frank-Kaspe r(cubic approximant) phase powders, which were produced by mechanical alloy ing from the elemental powder mixture and subsequent heat treatment, respec tively, have been hydrogenated with hydrogen gas at a temperature of 573 K and a hydrogen pressure of 4.2 MPa. The hydrogen solubility limit for both powders is almost the same and was estimated to be about 16 at%, and no cry stallographic structural dependence was found for the hydrogen solubility. The approximant phase powder was structurally stable after hydrogenation bu t the i-phase powder decomposed into the approximant and MgZn2 intermetalli c phases. Hydrogen desorption occurred at temperatures above about 600 K fo r both powders and was accompanied by the evaporation of zinc. The kinetics of the hydrogen desorption as well as the zinc evaporation were slightly d ifferent in each powder because of the formation of the MgZn2 phase in the i-phase powder after hydrogenation.