CONICET | Buscador de Institutos y Recursos Humanos

Mechanical milling/alloying is a powerful technique used for the refining/synthesis of different materials, in particular alloys and intermetallic compounds. Cold welding and fracturing mechanisms allow the formation of homogeneous alloys and intermetallics from metals with very different melting point, which are hard to produce by the traditional metallurgical processes. MgCo is the only stable intermetallic compound reported in the Mg- 2 Co system [1]. However, both a deep analysis of the literature and additional experimental evidence [2] corroborated the existence of MgCo intermetallic in the Mg-rich zone. Although the MgCo compound was not formed during milling of the Mg-Co mixtures, further heating of as-milled mixtures leads to the formation of MgCo by solid-state diffusion [2,3]. The synthesis of the MgCo is a key issue related with the formation of Mg-Co hydrides, such as Mg CoH and Mg Co H , with promising properties for hydrogen storage applications. The Mg-Co mixture was milled using a low energy mill during 200 h under argon and then submitted to thermal treatment. The mechanical milling (MM) of Mg-Co mixture leads to microstructural refinement reducing the diffusion distances and then favouring the kinetics of solid-state reaction. As a consequence, the formation of MgCo compound occurs at temperatures of 623 K, which is lower than previously reported. As-milled sample ( with Mg and Co phases) and as-milled plus heated sample (with MgCo compound) were non-isothermally heated under hydrogen pressure using highpressure differential scanning calorimetric equipment. The presence of MgCo intermetallic compound improves the reactivity with hydrogen, reducing both hydrogen absorption and desorption temperature, as well as increasing the total hydrogen storage capacity up to 573 K. An analysis of the interplay of hydride phases as a function of the starting samples and experimental conditions is presented.

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