A powder metallurgy approach for the production of a MgH2-Al composite material

This research work presents a powder metallurgy (PM) route for the production of a hydrogen storage MgH2-Al composite material. This system has been considered to avoid one of the main problems of bulk materials for chemical hydrogen storage, that is decrepitation. The process involves several steps, like cryomilling of pure Al, mixing with MgH2and compaction of the powder blends by Spark Plasma Sintering (SPS). The first part of the work was focused on the optimization of the aluminum scaffold. Cryomilling of aluminum was carried out in order to reduce the crystallite size to the range of nanometers. Pure aluminum specimens were sintered with two different sets of sintering parameters in order to investigate their effect on the properties of the matrix material after the sintering process. Then, a bulk composite consisting of MgH2 and 20 wt.% Al was produced in order to evaluate the resistance to decrepitation. In spite of the comminution of the MgH2 particle size after three hydrogen absorption/desorption cycles, the overall structure is faultless due to the reinforcement introduced by aluminum. Furthermore, aluminum retained its nanocrystalline character during temperature cycling. However, the sample during absorption/desorption cycling showed a reduced hydrogen storage behavior, caused by the formation of the highly stable intermetallic phase Mg17Al12 as well as by a partial oxidation of Mg.