Synthesis and hydriding properties of Mg-based nanocomposites

Tony Spassov 1Zlatina Zlatanova 1Tsveta Himitliiska 1Stanislava Todorova 1Stoyan Bliznakov 

1. University of Sofia, Faculty of Chemistry, 1 J. Bourchier Avenue, Sofia 1164, Bulgaria

Abstract

Mg/AB5, Mg/AB and Mg/C nanocomposites were synthesized by mechanical milling in planetary type ball mills. The milling conditions were varied with the aim to produce composites with different morphology and microstructure, characterized by electron microscopy and x-ray diffraction. Continuous milling results in grain size refinement and in some cases to amorphization of the material. Milling under hydrogen gas atmosphere results in substantially finer particle size of the Mg/AB5 and Mg/AB composites compared to the materials milled under argon.

 The hydriding and dehydriding of the composites were carried out in a hydrogen gas phase as well as electrochemically. It was proved that the morphology and microstructure of the nanocomposites has an influence on their hydrogen capacity and hydriding/dehydriding kinetics. Finer particle and grain size improves markedly the kinetics of hydriding/dehydriding. Smaller nanocrystallites size generally results in an increase of the electrochemical capacity as well.

The hydrogen sorption kinetics of Mg/AB5 and Mg/AB nanocomposites with different microstructure has been studied and the mechanism of the absorption process has been determined. A low-temperature (near room temperature) hydrogen absorption has been detected for the Mg/AB5 nanocomposites. A small difference in the nanocrystalls size of the nanocomposites results also in noticeable difference in the electrochemical behavior (hydrogen capacity and stability at hydrogen charge/discharge cycling).

 The hydrogen capacity, hydrogen desorption temperature and absorption/desorption kinetics of MgH2 mechanically milled with different carbon additives were found to be dependent on the amount of the additives as well as on the milling duration. Considerable decrease of the hydrogen desorption temperature has been obtained for the MgH2/C nanocomposites. The electrochemical hydriding/dehydriding behavior of  Mg/C nanocomposites was also investigated.

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Presentation: Oral at E-MRS Fall Meeting 2009, Symposium I, by Tony Spassov
See On-line Journal of E-MRS Fall Meeting 2009

Submitted: 2009-05-10 15:30
Revised:   2009-06-07 00:48
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