Low-temperature hydrogenation of Mg-Ni-Nb2O5 alloy processed by high-pressure torsion

Powder mixtures with a nominal composition Mg-5 wt%Ni-2 wt%Nb2O5 are used to produce ultrafine-grained bulk material by high-pressure torsion (HPT) processing. Samples subjected to 10 and 20 revolutions in torsion under a pressure of 3 GPa developed an ultrafine grain size, mainly in the 100-200 nm range. The hydrogenation properties of these HPT-processed materials have been characterized at temperatures in the interval of 373-723 K. The hydrogenation experiments clearly show faster kinetics of hydrogenation and higher storage capacities in the HPT materials compared to the initial mild-milled powder mixture. The storage capacities have been limited to about 5.5 wt% H-2 by the formation of a substantial amount of MgO in the materials after several hydrogenation cycles. However, as a matter of practical relevance, the production of bulk pieces of the Mg-Ni-Nb2O5 alloy having an ultrafine grain structure allows handling of the material without special precautions against ignition, as well as its storage in contact with air for several months with no evident deterioration of its fast activation in posterior hydrogenation treatments. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

Bulk materials of the Mg-Ni-Nb2O5 alloy with ultrafine grain structure produced by high-pressure torsion (HPT) processing exhibit faster hydrogenation kinetics and higher storage capacities compared to initial mild-milled powder mixtures. However, the storage capacities are limited by the formation of MgO after several hydrogenation cycles. Despite this limitation, the material can be handled and stored without special precautions and maintains its fast activation in posterior hydrogenation treatments for several months.