Hydriding and dehydriding behavior of the product in hydriding combustion synthesis of Mg2NiH4

The hydriding and dehydriding behavior of the product of hydriding combustion synthesis of Mg,NM, was investigated by TG-DTA. During seven heating (dehydriding) and cooling (hydriding) cycles at a rate of 0.1 K/s, the TG-DTA curves of the combustion synthesis product were measured in 1.0 MPa hydrogen atmosphere. Behavior such as activation within the first four hydriding and dehydriding cycles was observed. The hydriding and dehydriding reactions gradually became more rapid from the first to the fourth cycle, and became almost constant after the fourth cycle. This behavior is likely an activation process. It is much easier with the present hydriding combustion synthesis than with the conventional ingot process. The splitting and overlapping of the peaks of the DTA curves for the dehydriding reaction provide information on the existence of two pairs of modifications of Mg2NiH4. (C) 1999 Elsevier Science S.A. All rights reserved.