Metal hydride compacts of improved thermal conductivity

Metal hydrides begin as hydride-forming metal alloys with good thermal conductivity. However, undergoing hydriding/dehydriding reactions and subsequently causing large strain changes, they decrepitate and finally form a powder bed. Such a powder bed exhibits poor thermal conductivity (k(eff) similar to 0.1 W/m K) and reduces the heat transfer process to and from the bed that occurs with hydrogen absorption and desorption. A newly developed technique reported here (recompressed expanded graphite technique), that allows one to significantly improve the thermal conductivity of a metal hydride, LaNi5, is presented. The compacts with LaNi5 and recompressed expanded graphite were made and their thermal conductivity measurements were taken. Recompressed expanded graphite is used to allow good heal transfer while providing efficient mass transfer. This study reports that the manufactured metal hydride compact has the thermal conductivity in the range of k(eff) similar to 3-6 W/m K that shows a greater potential in developing high-power metal hydride devices. It should be pointed out that a minute amount of expanded graphite increases the thermal conductivity of metal hydride significantly. (C) 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.