Formation reaction of Mg2FeH6: effect of hydrogen absorption/desorption kinetics

• Autor(a) principal: Asselli,Alexandre Augusto Cesario
• Data de Publicação: 2013
• Outros Autores: Botta,Walter José, Huot,Jacques
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Materials research (São Carlos. Online)
• Texto Completo: http://old.scielo.br/scielo.php?script=sci_arttext&pid=S1516-14392013000600023
• topic: metal hydrides; high-energy ball milling; kinetics

In this paper we address some aspects of the kinetics of hydrogen absorption and desorption of Mg2FeH6 nanocomposite powder. The Mg2FeH6 material was prepared from a 2Mg-Fe composition by reactive milling under H2 pressure at room temperature. After mechano-chemical processing, the material was mainly constituted of Mg2FeH6 having a hydrogen gravimetric capacity corresponding to 94% of the theoretical capacity. The kinetics of hydrogen absorption at constant temperature and the transformation of phases during this process were studied. The kinetics of hydrogen absorption presented a two-step behaviour. First, β-MgH2 was formed with faster kinetics than Mg2FeH6 under constant temperature and H2 pressure. Then, β-MgH2 reacted with α-Fe forming Mg2FeH6 in a much slower reaction. Unexpectedly, reaction of hydrogen desorption showed an one-step kinetics, even if Mg2FeH6 and β-MgH2 phases were previously present in the powder.