Solid-State Synthesis of Hydrogen Storage Mg<SUB>2</SUB>Co Alloys <I>via</I> Bulk Mechanical Alloying

Abstract

Mg-Co system is employed to investigate the solid-state reactivity of Mg 2 Co from the elemental powder mixture of magnesium and cobalt and to describe the hydrogenation and de-hydrogenation processes of Mg 2 Co. Mg 2 Co is successfully solid-state synthesized as a non-equilibrium phase compound by the bulk mechanical alloying. This solid-state reactivity is controlled by the repeated plastic flow of ductile elements in the powder mixture. This non-equilibrium phase, Mg 2 Co is stable up to 833 K. Its hydrogenation and de-hydrogenation processes are described by DSC, PCT and XRD. These processes take place in multi-step with strong dependency on the holding temperature. Hydrogenation process from Mg 2 Co is composed of two steps to Mg 2 CoH 5 and dehydrogenation from Mg 2 CoH 5 , one step to Mg 2 Co, at 633 K. Maximum hydrogen absorption capacity at 633 K is still limited to 2.03 mass% since hydrogenation and de-hydrogenation steps, working at higher temperature, are never activated without chemical modification to original Mg 2 Co.