Novel synthesis of ternary magnesium based transition metal hydrides as potential energy storage materials

Izabela S. Kunce ,  MAREK POLAŃSKI ,  Jerzy Bystrzycki 

Military University of Technology, Faculty of Advanced Technology and Chemistry, Kaliskiego 2, Warszawa 00-908, Poland

Abstract

Ternary magnesium based transition metal hydrides such as Mg2FeH6, Mg2CoH5, Mg2NiH4, etc. are attractive materials for hydrogen or thermal energy storage. Unfortunately, most of them are rather difficult to synthesize. The traditional method for the synthesis of these ternary hydrides is the conventional metallurgical sintering at high temperature (350-550°C) under high hydrogen pressure (2-100 bar). However, in many cases this processing route does not lead to satisfactory results because the yield of the sintering is about 60% and the unreacted elements have to be removed through a complicated process. Therefore to overcome these problems, discovering simple and effective method of their synthesis is needed.

 In our work we present a new method for rapid and effective synthesis of ternary Mg-based Fe, Co and Ni hydrides. The stoichiometric powder mixture of both magnesium hydride and transition metal was mechanically (ball) milled for 1h in a planetary mill under argon. Afterwards unique pressurizing and heating cycle was applied to obtain full phase transformation within no longer than 1,5 hour.

Structural investigations carried out by using X-ray diffraction revealed that almost all initial powder mixture transforms into ternary intermetallic hydride during first several minutes. The yield of the synthesis method is over 90%. However, traces of Fe and Co in the synthesized mixtures were found. Additionally, dehydriding properties of synthesized ternary hydrides were investigated by temperature programmed desorption and differential thermal analysis. The obtained results clearly shown that ternary magnesium based hydrides are formed via direct reaction of magnesium hydride with transition metal and hydrogen. Moreover, our results indicate that significant improvements to the phase transformation and reaction kinetics can be made by mechanical alloying of initial powder mixture due to reducing overall diffusion distances to the nanometer scale.

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Presentation: Poster at E-MRS Fall Meeting 2008, Symposium D, by Izabela S. Kunce
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-12 10:53
Revised:   2009-06-07 00:48
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