Papers by Author: R.A. Varin

Abstract: In this work oxidized and oxide-free amorphous boron (a-B) powder and elemental Mg were used in an attempt to directly synthesize the Mg(BH4)2 complex hydride by controlled reactive mechanical alloying (CRMA) under hydrogen in a magneto-mill up to 200h. The particle size was refined to the 100-200nm range. Nanocrystalline MgH2 (~6nm crystallite size) was formed within the particles when an oxidized a-B is used. In contrast, a mixture of MgB2 and an amorphous hydride MgHx was formed when an oxide-free a-B was used. Differential scanning calorimetry (DSC) test up to 500°C produced a single endothermic heat event at 357.7°C due to hydrogen desorption. In addition, desorption conducted in a Sieverts-type apparatus revealed ~1.4wt.% of hydrogen release. The X-ray diffraction pattern after DSC test of the 200h milled sample made with oxide-free boron showed the presence of MgB2.

Abstract: The paper presents the results of studies of the hydrogen sorption properties of nanocrystalline Mg2Ni intermetallic prepared by mechanical (ball) milling under controlled shearing/impact mode. The pre-alloyed intermetallic powders were subjected to ball milling under various controlled milling conditions such as shearing, high-energy shearing and impact in a magnetic Uni-Ball-Mill 5. The hydriding properties were evaluated by monitoring the absorption PC isotherms by the conventional constant-volume method using Sieverts semi-automatic apparatus. Changes of structure during processing and hydriding properties of nanostructured Mg2Ni intermetallic powders are shown and discussed.