H-sorption behaviour of mechanically activated Mg–Zn powders

We report here on powder mixtures, with nominal compositions Mg7Zn and Mg7Zn3, which were ball milled (i) at room temperature in an inert Ar atmosphere, (ii) at liquid nitrogen temperature (cryomilling), and (iii) at room temperature in a reactive H2 atmosphere (reactive milling). In all cases, ball milling results in the formation of an amorphous Mg–Zn phase with a likely composition of about Mg45Zn55. A fraction of Mg is left unreacted and transforms to MgH2 if ball milling is carried out in a reactive H2 atmosphere. Hydrogen-absorption (H-absorption) in a Sievert-type apparatus for the powders ball milled in Ar results in the partial conversion of the Mg into MgH2. The amorphous Mg–Zn phase appears not to play any significant role in the hydrogen-sorption (H-sorption) behaviour and crystallizes into Mg21Zn25. The latter partially decomposes into MgH2 and MgZn2, provided the hydrogenation reaction is extended for sufficiently long times.