Formation, composition and stability of Mg–Co compounds

Abstract

The existence and stability of Mg2Co and MgCo is still a controversial issue. Even though none of these compounds are included in the last assessed Mg–Co phase diagrams, some authors have claimed their existence. In this paper we propose that only one compound with more than 40 at.% Mg exists, and determine its composition, formation and stability using mainly XRD and DSC. We explore different synthesis methods: beta-Mg2CoH5 dehydriding (prepared both by reactive mechanical alloying and by sintering), mechanical alloying of Mg and Co under Ar, mechanical alloying followed by a heat treatment, and Mg–Co solid-state reaction. We conclude that MgCo is a stable compound, whose formation process can be greatly influenced by kinetic factors that may suppress its presence in favor of MgCo2, the only well-known stable Mg–Co compound.