Composite behaviour of MgH 2 and complex hydride mixtures synthesized by ball milling

Abstract

In the present work, the MgH 2–LiAlH 4 and NaBH 4–MgH 2 hydride composites were synthesized by mechanical ball milling. The phase structure and morphology were investigated by XRD and SEM. The hydrogen desorption characteristics of obtained composites were measured by DSC. It is shown that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems, decreases linearly with increasing volume fraction of the constituent having lower desorption temperature. It is demonstrated that the hydrogen desorption in the hydride composites involves two steps: first, the lower temperature hydride decomposes to metal or complex hydride + metal and H 2 and in a subsequent step, these intermediary compounds, catalyze or thermodynamically change the decomposition of the high temperature hydride. The thermodynamic destabilization can be an effect of solid solution or intermediate intermetallic phase formation. Sometimes both phenomena such catalytic influence and intermetallic phase formation can be observed.