Direct synthesis of MgH_2 nanofibers at different hydrogen pressures

摘要

This paper describes the direct synthesis of magnesium hydride (MgH_2) nanofibers by hydriding chemical vapor deposition (HCVD), in which the effect of hydrogen pressure on the production rate, the composition and the shape of products obtained were examined by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET). The XRD patterns showed that the main product in each case was MgH_2; in particular, the products formed at 2, 3 and 4 MPa were highly pure. In contrast, at a hydrogen pressure of 1 MPa, unhydrided Mg was deposited along with MgH_2. The SEM images also revealed orientation of the as-deposited products; higher pressures of 3 and 4 MPa caused the formation of straight and curved nanofibers, and lower ones of 1 and 2 MPa, highly curved nanofibers and nanorods with a few straight nanofibers. With pressurizing hydrogen, not only the BET specific surface areas of the products but also the production rate increased. The results also appealed that HCVD could control the shape/ size of MgH_2 nanofibers by changing the pressure via only a single operation.