Abstract:The formation conditions of MgB₂ in 2LiBH₄ + MgH₂ system during dehydrogenation were investigated and its mechanism was discussed. The results show that direct decomposition of LiBH₄ is suppressed under relative higher initial dehydrogenation pressure of 4.0×10⁵ Pa, wherein LiBH₄ reacts with Mg to yield MgB₂, and 9.16% (mass fraction) hydrogen is released within 9.6 h at 450 °C. However, under relatively lower initial dehydrogenation pressure of 1.0×10² Pa, LiBH₄ decomposes independently instead of reacting with Mg, resulting in no formation of MgB₂, and 7.91% hydrogen is desorbed within 5.2 h at 450 °C. It is found that the dehydrogenation of 2LiBH₄ + MgH₂ system proceeds more completely and more hydrogen desorption amount can be obtained within a definite time by forming MgB₂. Furthermore, it is proposed that the formation process of MgB₂ includes incubation period and nucleus growth process. Experimental results show that the formation process of MgB₂, especially the incubation period, is promoted by increasing initial dehydrogenation pressure at constant temperature, and the incubation period is also influenced greatly by dehydrogenation temperature.

Key words: complex hydride; LiBH₄; MgB₂; hydrogen storage; formation mechanism