Microstructure and hydrogen desorption characteristics of hydrogenated ScH_2-MB_n (M = Mg and Ga) systems synthesized by mechanical milling

摘要

The mixtures of scandium hydride ScH_2 and metal boride MB_n, which is MgB_2 or CaB_6, were hydrogenated by mechanical milling under hydrogen pressure at room temperature. ScH_2-MgB_2 and ScH_2-CaB_6 desorbed 3.4 and 2.3 mass% of H_2, respectively, with peaks below 300 ℃. The results of synchrotron radiation X-ray powder diffraction and X-ray absorption spectroscopy at the Sc K-edge indicated that ScB_2 was produced by milling. Fourier-transform infrared spectroscopy suggested that hydrogen was stored as B-H bonds in the as-milled samples. Nuclear magnetic resonance spectroscopy clarified the presence of metal borohydrides M(BH_4)_2 (M = Mg and Ca) in the as-milled ScH_2-MB_n mixtures. These results indicate that M(BH_4)_2 is synthesized by milling the ScH_2-MB_n mixtures under hydrogen pressure at room temperature, and hydrogen was desorbed from M(BH_4)_2. The by-products of M(BH_4)_2 are MgH_2 in the M = Mg case, which was observed by transmission electron microscopy, and ScB_2 in both cases.