Thermal conductivity and specific heat measurements of metal hydrides

There are extensive efforts underway worldwide to develop inexpensive and practical hydrogen storage materials for the implementation of a hydrogen-based energy economy. Metal hydrides are leading candidates for hydrogen storage applications because they are solid at room temperature and release hydrogen on demand when heated. HSM systems Inc. has developed a practical hydrogen storage system in which the metal hydride is housed in a sealed stainless-steel vessel. Hydrogen is generated by simply heating the enclosed metal hydride. It is important to understand the thermal response of the metal hydride as it is heated to determine when and at what rate the hydrogen will be released. Heat transfer can be modeled with the appropriate knowledge of the vessel's geometry, composition and intrinsic thermal characteristics (i.e. thermal conductivity and specific heat). Although the thermal properties of stainless steel are well known, those of metal hydrides are poorly characterized. This paper presents a simple and efficient measurement technique for determining the thermal conductivity and the specific heat of metal hydrides. Since practical hydrogen storage applications will likely involve the use of compacted powders, the thermal conductivity of both powdered and pressed pellets of select metal hydrides have been determined; namely: NaAlH4 powder/compressed pellet NaAlH4 + 2% TiCl3 powder/compressed pellet LiAlH4 powder/compressed pellet LiNH2+2LiH powder/compressed pellet 7:1 MgH2:LiBH4 + 1 % TiCl3 powder/compressed pellet The thermal conductivity of each sample has been measured via the modified transient plane source technique. Specific heat measurements have been made using differential scanning calorimetry (DSC).