Direct synthesis of MgH2 nanofibers at different hydrogen pressures

Abstract

ABSTRACT: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.

Chemical equilibrium analysis for hydrolysis of magnesium hydride to generate hydrogen

“…It is an especially promising material owing to its quite high hydrogen capacity of 7.6 mass% and relatively low production cost. Saita et al, demonstrated that MgH 2 can be produced by hydriding chemical vapor deposition (HCVD) in which the MgH 2 absorbs and desorbs as much as 7.6 mass% hydrogen without any activation treatments [18][19][20], and clarified that the total exergy loss of metal hydride production process without activation treatment is smaller than conventional process [21].…”

In situ transmission electron microscopy observation of the decomposition of MgH2 nanofiber

“…the HCVD method, as described elsewhere. [8,9,11] 10 g of commercially available Mg powder (purity: 99%; particle size: < 75 µm) was placed in an Inconel tube and heated to vaporize in an H 2 atmosphere (purity: 99.99999%) at 4.0 MPa and at a temperature of 600 ºC for 20 hours. The reactants, namely, the H 2 and Mg in vapor form, were deposited on the cooled Inconel flange substrate of the reactor at a temperature of 400 ~ 500 ºC to form MgH 2 nanofibers.…”

“…Another solution is to reduce the size of the Mg/Mg-based materials to the nano-scale. In order to manufacture micro/nano-structured Mg or MgH 2 and their composites many processes, such as high-energy ball milling of MgH 2 or MgH 2 -based composites [3][4][5], magnetron sputtering for Mg thin films, [6] physical vapor-transport deposition (PVD) of Mg nanowires, [7] and hydriding chemical vapor deposition (HCVD) of MgH 2 nanofibers, [8][9][10] have been used. The as-prepared Mg nanowires by the PVD method having diameters ranging from 30 to 170 nm exhibit enhanced hydrogen adsorption kinetics.…”

Ultrasonic irradiation on hydrolysis of magnesium hydride to enhance hydrogen generation

“…Two commercially available, (a) large MgH 2 particles and (b) small MgH 2 particles with (average size, purity) = (60 m, 99 mass%) and (2 m, 90 mass%), were prepared by carrying out a gas-solid reaction (GSR) under specified conditions of temperature and pressure. Further, we produced (c) an MgH 2 nanofiber, having a diameter of 500 nm and length of several tens of microns by using hydriding chemical vapor deposition (HCVD) [24][25][26]. During HCVD, magnesium hydride was deposited on the inconel substrate via a gas phase reaction between magnesium vapor and high-pressure hydrogen.…”

“…During HCVD, magnesium hydride was deposited on the inconel substrate via a gas phase reaction between magnesium vapor and high-pressure hydrogen. The detailed procedure is described elsewhere [24][25][26]. Table 1 gives the physical characteristics of the abovementioned three samples; these characteristics were determined using X-ray diffraction with Cu-Kα radiation (XRD, Miniflex, Rigaku Co., Ltd.), a scanning electron microscope (SEM, Japan Electron Co., Pty.…”