Synthesis of B2-structured Mg alloys by mechanical alloying, and their hydriding properties

Binary B2-structured magnesium alloys were produced by ball milling magnesium with silver, lanthanum or palladium elemental powder in equiatomic quantities. MgLa showed the best hydrogen absorption characteristics among the as-milled alloys. Magnesium-lanthanide alloys have recently attracted much attention due to their optical switching and metal to semi-conductor transitional properties with hydrogen absorption, and hence, hydriding behaviour of MgLa is of a great interest. Pressure-composition-temperature (PCT) and X-ray diffraction measurements showed that MgLa dissociates upon hydriding between 300 and 400degreesC. Lanthanum hydride was formed initially at very low hydrogen pressure (< 10(-5) MPa) and then magnesium hydride was formed. Van't Hoff plot showed that pressure plateaus observed at various temperatures corresponded to that of magnesium. MgAg and MgPd intermetallic alloys were observed to form at a rapid rate during milling, consistent with their high negative enthalpy of formation. However, these alloys absorbed practically no hydrogen. Adding ternary elements such as titanium, vanadium and palladium to MgAg showed some improvement in hydrogen absorption.