Improvement of the Reaction Rates of Mg with H2 by the Addition of TaF5 via Reactive Mechanical Grinding

Abstract

A sample with a composition of 90 wt% Mg-10 wt% TaF5 (named Mg-10TaF5) was prepared by reactive mechanical grinding, and its hydriding and dehydriding properties were examined. The activation of Mg-10TaF5 was not required. At n=1, the sample absorbed 3.63 wt% H for 5 min, 4.03 wt% H for 10 min, and 4.53 wt% H for 30 min at 593 K under 12 bar H2. At n=1, the sample desorbed 0.59 wt% H for 5 min, 1.46 wt% H for 10 min, 3.42 wt% H for 30 min, and 4.24 wt% H for 60 min at 593 K under 1.0 bar H2. Mg-10TaF5 after reactive mechanical grinding contained MgH2, Mg, and very small amounts of MgF2 and Ta2H. The XRD pattern of Mg-10TaF5 dehydrided at n=3 revealed Mg, MgH2, a small amount of MgO, and very small amounts of MgF2 and Ta2H phases. Mg-10Fe2O3 and Mg-10MnO were reported to have quite high hydriding rate and dehydriding rates, respectively. Mg-10TaF5 had a larger initial hydriding rate but a lower quantity of hydrogen absorbed for 60 min than Mg-10Fe2O3. However, Mg-10TaF5 had a higher initial dehydriding rate (after the incubation period) and a larger quantity of hydrogen desorbed for 60 min than Mg-10MnO. †(Received April 29, 2013)