MECHANO-CHEMICAL SYNTHESIS OF NANOSTRUCTURED HYDRIDE COMPOSITES BASED ON Li-Al-N-Mg FOR SOLID STATE HYDROGEN STORAGE

It is observed that large quantities of hydrogen (H2) are released at ambient temperatures during the mechano-chemical synthesis of the Li-Al-N-Mg-based hydride composites using an energetic ball milling in a unique magneto-mill. For the (nLiAlH4+LiNH2; n=1, 3, 11.5, 30) composite, at the molar ratio n=1, the LiNH2 constituent destabilizes LiAlH4 and enhances its decomposition to Li3AlH6, Al and H2, and subsequently Li3AlH6 to LiH, Al and H2. LiNH2 ceases to destabilize LiAlH4 in the composites with increasing molar content of LiAlH4 (n≥3). For the (nLiAlH4+MnCl2; n=1, 3, 8, 13, 30, 63) composite, XRD phase analysis shows that chemical reaction occurs during ball milling between the hydride and chloride constituent forming either an inverse cubic spinel Li2MnCl4 for n=1 or lithium salt (LiCl) for n>1. Both reactions release hydrogen. For the (LiNH2+nMgH2; n=1, 1.5) composite the pathway of hydride reactions depends on the milling energy and milling time. Under low milling energy up to 25h there is either no reaction (1h) or the reaction products are amorphous Mg(NH2)2 (magnesium amide) and nanocrystalline LiH (lithium hydride) without any release of hydrogen. Under high milling energy a new hydride MgNH (magnesium imide) is formed due to reaction between Mg(NH2)2 and MgH2 which is always associated with the release of H2.