발간논문

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MgH2 was employed as a starting material instead of Mg in this work. A sample with a composition of 94 wt% MgH2-6 wt% Ni (called MgH2-6Ni) was prepared by reactive mechanical grinding. The hydriding and dehydriding properties were then examined. An MgH2-Ni hydrogen storage alloy that does not require an activation process was developed. The alloy was prepared in a planetary ball mill by grinding for 4 h at a ball disc revolution speed of 250 rpm under a hydrogen pressure of about 12 bar. The sample absorbed 3.74 wt% H for 5 min, 4.07 wt% H for 10 min, and 4.41 wt% H for 60 min at 573 K under 12 bar H2, and desorbed 0.93 wt% H for 10 min, 1.99 wt% H for 30 min, and 3.16 wt% H for 60 min at 573 K under 1.0 bar H2. MgH2-6Ni after reactive mechanical grinding contained β-MgH2 (a room temperature form of MgH2), Ni, γ-MgH2 (a high pressure form of MgH2), and a very small amount of MgO. Reactive mechanical grinding of Mg with Ni is considered to facilitate nucleation, and to reduce the particle size of Mg. Mg2Ni formed during reactive mechanical grinding also increases the hydriding and dehydriding rates of the sample.

keyword : hydrogen absorbing materials, mechanical alloying/milling; microstructure, X-ray diffraction, starting material MgH2

To increase the hydrogen storage capacity of Mg-based materials, a sample with a composition of 69.7 wt% MgH2 + 30.3 wt% LiBH4 was prepared by planetary ball milling under hydrogen. The absorption and desorption properties of unmilled MgH2, unmilled LiBH4, and 69.7 wt% MgH2 + 30.3 wt% LiBH4 were examined. At 648 K the unmilled MgH2 desorbed 5.70 wt% for 60 min. The unmilled LiBH4 desorbed 6.40 wt% H for 780 min at 673 K. The 69.7 wt% MgH2 + 30.3 wt% LiBH4 sample desorbed 3.10 wt% H for 50 min, and 3.32 wt% H for 300 min at 623 K at the second cycle.

keyword : hydrogen absorbing materials, mechanical alloying/milling, microstructure, X-ray diffraction, MgH2 + LiBH4

Nano-sized Co and Al2O3 powders were successfully synthesized from 3/4Co3O4 and 2Al by highenergy ball milling. A dense nanocrystalline 2.25Co-Al2O3 composite was consolidated from mechanically synthesized powders by the pulsed current activated sintering (PCAS) method within 2 min. Consolidation was accomplished under the combined effects of a pulsed current and mechanical pressure. A dense 2.25 Co-Al2O3 with relative density of up to 95% was produced under simultaneous application of a 80 MPa pressure and a pulsed current of 2800 A. The fracture toughness and hardness of the 2.25Co-Al2O3 composite were 8 MPa · m1/2, 870 kg/mm2, respectively.

keyword : rapid sintering, composite materials, nanomaterials, mechanical properties