Hydriding properties of Mg2Ni nanocomposites obtained by low energy mechanical alloying

F. C. GENNARI; M. R. ESQUIVEL

Río de Janeiro, Brasil

Workshop; Nanomat 2006, III Workshop on Metastable and Nanostructured Materials; 2006

COPPE-UFRJ

Intermetallic Mg2Ni is an interesting material for hydrogen storage (3.6 wt %), with better hydrogen absorption/desorption kinetics than MgH2. Since Mg2Ni is traditionally produced by melting, a high quality intermetallic is difficult to obtain because of the large differences in the melting point and vapor pressure between Mg and Ni. An alternative for synthesizing Mg2Ni is the use of the mechanical alloying (MA) process. This technique allows the production of nanostructures, is applicable to all classes of metals and has the possibility of scaling up to production of tonnage quantities. In the present work, the effect of milling time of the 2Mg-Ni mixture on the structure, microstructure and hydriding properties of Mg2Ni nanocomposites was investigated. The formation of an amorphous precursor as well as nanocrystalline Mg2Ni was detected as a function of the milling time. Two Mg2Ni nanocomposite samples were selected to analyze their reactivity with hydrogen, one obtained after 100 h of MA (MN100) and the second one after 200 h of MA (MN200). The pressure-composition isotherms showed different hydrogen storage capacities and plateau slopes after the first cycle. In addition, the low temperature Mg2NiH4 (LT) formed from MN100 h decomposes at 190 °C, whereas this hydride produced from MN200 first transforms to the high temperature Mg2NiH4 and then decomposes at about 255 °C. The differences in the hydriding properties of MN100 and MN200 were associated with the microstructure and structure of the phases formed during heating under argon/hydrogen.