Hydrogen desorption process in Mg$_{2}$Ni hydrides

Abstract

One of the most interesting intermetallic compounds investigated for energy storage purposes has been the Mg$_{2}$Ni alloy which was prepared by mechanical alloying. Hence it was used here for hydriding-dehydriding implied mechanisms studies. Hydrogenation of milling prepared Mg$_{2}$Ni alloy samples under a 1 MPa H$_{2}$ flux at 473K for 5 min allowed the formation of two Mg$_{2}$Ni-hydrides which were identified by the empirical formulae Mg$_{2}$NiH$_{4}$ and Mg$_{2}$NiH$_{0.3}$ [1]. Dehydriding behavior along the temperature range from 298 to 623K was recorded by Thermo Gravimetric Analysis (TGA). TGA spectrum exhibited two weight decrease peaks. The maximum hydrogen amount desorbed was 3.95 $\pm $ 0.01 wt%. Isotherms between 470 and 600K, every 30K, were obtained by using the same technique, showing a discontinuity which might be associated with a dehydriding process taking place in two steps. Approximately 40-50% of the total H$_{2}$ content seems to be desorbed in the first faster step. The present results might confirm that the two hydrides formed present a differentiated desorption outline.