Significant decrease of hydride decomposition enthalpy in ordered Mg-In alloys induced by growing hydrogen concentration

Abstract

Hydrogen sorption in four ball-milled Mg-xIn alloys (with x = 9, 61, 69, and 81 wt.%) was studied. It was found that pressure-concentration isotherms (PCI curves) of hydrogen desorption from disordered alloy (9 wt.% In) showed "ordinary" appearance leading to a constant hydride decomposition enthalpy ΔH close to the value known for pure Mg; however, the plateaus of PCI's obtained for desorption from ordered alloys (x > 9 wt.% In) were significantly upward-curved. Observed values of ΔH in ordered alloys were lower and decreased with increasing x and hydrogen concentration. Results were explained by size effect. K e y w o r d s : hydrogen storage, Mg alloys, ordering, hydrides, ball milling