Optimization of microencapsulating and compacting conditions for hydrogen storage alloy

Thermophysical properties and cycling strength of a compact of copper-microencapsulated magnesium-nickel alloy have been studied for different fabrication conditions. In preparing the compact, the conditions of copper content (film thickness), loading pressure, loading hold time and pressing method were changed to assess their effect on thermal conductivity/diffusivity and strength against hydrogen absorption-desorption cycling. Thermal conductivity of the Cu-coated compact was shown to increase significantly compared with the Cu-free one; however, very significantly, thermal conductivity did not depend on copper content of the compact at all. Heavy loading pressure for compacting also increased thermal diffusivity due to an increase of contacted area among particles within the compact. However, the compact showed viscoelastic behavior; namely, it took as long as 1.8 ks until thermal diffusivity reached a constant value under a fixed loading pressure. Upon hydrogen absorption-desorption cycling the Cu-coated compacts did not crack, even after 200 cycles, while the Cu-free compacts broke easily within 100 cycles. These results show the possibility for the practical use of hydrogen storage alloy compacts with less copper microencapsulation.