Cooperative effects at formation and decomposition of magnesium hydride in powders
Résumé
The detailed kinetic analysis of formation and decomposition of powder magnesium hydride has shown that in contrast to conventional coarse-grained magnesium in which particles seem to react independently from each other, contacts between particles are important at hydriding of nanostructural magnesium because it facilitates the nucleation process hampered in nano-sized particles. The cooperative effects have been revealed also at decomposition of powder magnesium hydride. Being limited by recombination and desorption of hydrogen, the reaction of decomposition of magnesium hydride starts on the particles containing metal impurities or being in contact with the metal surface of container. The nuclei of metallic magnesium formed in these particles initiate the nucleation in the neighboring particles being in contact with them. Nucleation propagates like a chain process. Separation of particles by dilution of the sample by inert additive leads to considerable decrease of the reaction rate.