Synthesis of nanocomposite hydrides for solid-state hydrogen storage by controlled mechanical milling techniques

The following composite hydride systems: NaBH4–MgH2, MgH2–LiAlH4, MgH2–VH0.81 and MgH2–NaAlH4, were synthesized in a wide range of compositions by controlled reactive/mechanical (ball) milling in a magneto-mill. In effect, composites having nanometric grain sizes of the constituent phases (nanocomposites) were produced. It is shown that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems such as NaBH4 + MgH2, MgH2 + VH0.81 and MgH2 + LiAlH4 substantially decreases linearly with increasing volume fraction of the constituent having lower desorption temperature according to the well-known composite rule-of-mixtures (ROM). It is also shown that the ROM behavior can break down due to an ineffective milling of a composite. The composite system MgH2 + NaAlH4 does not obey the ROM behavior.