Papers by Keyword: Magnesium Hydride

Abstract: The structure of MgH₂ samples has been investigated by the neutron diffraction method at room temperature and 5 K. Samples of MgH₂ have been prepared with vacuum extraction technique at high temperature. Obtained neutron data demonstrated that samples contain coexisting Mg and MgH₂ phases in different rate. The distribution of hydrogen atoms in the structure of the samples is comparable at both temperatures. Collected neutron data and results of X-ray analysis show that microstructure of the samples is different at room and at low temperature. Non-stability of partly desorbed MgH₂ samples after low temperature treatment has been discussed on basis of different diffusion of hydrogen atoms in varied microstructure.

Abstract: The structure of partly desorbed and quenched samples of MgH₂ has been investigated by the neutron diffraction method. In ambient conditions a partly desorbed sample demonstrates high stability, while the same sample quenched at low temperature decomposed into Mg after several days. Obtained neutron data showed that all studied samples contain coexisting Mg and MgH₂ phases. Hydrogen distribution for both quenched and non-quenched samples is similar. Hydrogen atoms occupied sites predominantly in the MgH₂ lattice, whereas Mg lattice is free of the hydrogen.

Abstract: Samples of partly desorbed MgH₂ have been studied by the X-ray diffraction method. All samples contained two phases (Mg and MgH₂) and were stable at ambient condition for several months. After fast quenching in liquid nitrogen the samples became unstable and transformed after several days into Mg. The rate of decomposition depends on the amount ratio of Mg and MgH₂ phases in the sample. Destabilization of the hydride phase observed in quenched samples can be explained on the basis of different diffusion of disordered and ordered hydrogen atoms.

Abstract: We report on the preparation and hydrogen desorption/absorption kinetics of nanocrystalline magnesium hydride (MgH₂) added commercial Ti by high-energy ball milling. The phase and composition of the as-milled powders are characterized by X-ray diffraction (XRD). The results show that the milled sample contained MgH₂ phase, Ti phase and small amount of MgO phase. When the milling time is 30 h, the hydrogen desorption property of MgH₂ has been investigated and found that the sample releases 0.43, 0.86 and 0.90 wt% H₂ in 200 minutes at 280, 290 and 300 ^oC , respectively. Moreover, the sample absorbs 0.48, 0.0.58 and 0.61 wt% H₂ in 15 minutes at 280, 290 and 300 ^oC , respectively. It can be seen that the kinetics of hydrogen desorption/absorption of MgH₂-Ti composite has been greatly enhanced compared to the pure MgH₂.

Abstract: Recently, Magnesium hydride MgH₂ is one of the attractive hydrogen storage materials because it reaches a high hydrogen capacity. However, the reaction kinetics is too slow and needs high temperature for progressing hydrogen absorption and desorption reactions, which hinders the process of practical applications and it is necessary to improve the hydrogen storage propesties. In this paper, most used or under research methods (Doping with metal and compound) of improving on the hydrogen storage of magnesium hydride are reviewed, in particular to elements substitution, addition of transition metal oxides or fluorine and so on. The advantages and disadvantages of vaious methods of improving on the hydrogen storage of magnesium hydride are compared. The trend of the methods of improving is also introduced.

Abstract: We report on the preparation and hydrogen desorption/absorption kinetics of nanocrystalline magnesium hydride (MgH₂) added commercial TiO₂ by high-energy ball milling. The phase and composition of the as-milled powders are characterized by X-ray diffraction (XRD). The results show that the milled sample contained MgH₂ phase, small amount of Mg and various phases of TiO₂ such as tetragonal and orthorhombic structure. The effect of the milling time (10, 20 and 30 h) on the hydrogen desorption property of MgH₂ has been investigated and found that the milling time of 20 h has excellent dehydrogenation properties, which can release 3.3 wt% H₂ within 60 min at 300 ^oC, which indicates that the kinetics of hydrogen desorption of MgH₂-TiO₂ composite has been greatly enhanced compared to the pure MgH₂. Moreover, hydrogen absorption kinetics of the sample milled 20 h has been studied and the hydrogen content is 0.7, 0.8 and 1.2 wt% H₂ at 250, 280 and 300 ^oC within 60 min, respectively.

Abstract: In this study, 9 wt% V and 1 wt% Al were co-milled with MgH₂ at different milling times to produce nanostructured composite powders. The effect of milling time and additives on the hydrogen desorption properties of obtained powders was evaluated by thermal analyzer method and compared with pure MgH₂. The phase constituents and grain size of powders were characterized by X-ray diffractometry method. As the milling time was increased, both the grain size and hydrogen desorption temperature were decreased. An improved dehydrogenation temperature was achieved by alloying of MgH₂ with V and Al. The effect of the V and Al addition on improvement of the dehydrogenation properties was discussed.

Abstract: The crystal structure of magnesium hydride affects the properties of magnesium for hydrogen storage. The crystal phase and dehydriding temperature of magnesium hydride from magnesium by high-energy ball milling under hydrogen atmosphere with anthracite carbon, which was prepared from anthracite coal by demineralization and carbonization, as milling aid was investigated. The HRTEM observation and XRD characterization showed that the Mg hydrided into nanocrystalline β-MgH₂ of tetrahedral crystal structure and γ-MgH₂ of orthorhombic crystal structure during milling under 1 MPa of hydrogen, and the γ-MgH₂ increased with the extension of milling time. The DSC analysis showed that the endothermic peak of γ-MgH₂ was 53 °C lower than that of β-MgH₂ in the material from 10 h of milling.

Abstract: In this paper, magnesium hydride was used to react with water using a new design of control strategy to produce maximized on-demand hydrogen generation from the hydrolysis reaction. Magnesium hydride is the chemical compound MgH2, which contains 7.66% by weight of hydrogen and as a potential hydrogen source. Although the concept of reacting chemical hydride with water to produce hydrogen is not new, there have been a number of recent published papers which might be employed as on site generation of hydrogen for fuel cell applications. Under room temperature, the hydrolytic reaction between magnesium hydride and water to form a thin-layer of magnesium hydroxide on the outer surface impedes water from coming into direct contact with the magnesium hydride. The key to continual removal of this coherent magnesium hydroxide layer can induce the reaction of magnesium hydride with water near room temperature by the addition of citric acids. These additions act to disrupt the magnesium hydroxide layer on the magnesium hydride. This concept of using the magnesium hydride reaction with water to produce hydrogen has the following conclusions. This study presents a maximized on-demand hydrogen gas generator capable of producing hydrogen at an almost-constant H2 rate, which using this approach can reach the 6.4% by weight of hydrogen. In addition, based on the kinetics of magnesium hydride-water reaction, it does not need any noble-metals catalysts to meet the minimum hydrogen flow rate for fuel cell power systems. Finally, the cost of producing hydrogen from magnesium hydride-water approach would cost approximately $15 per kg hydrogen.

Abstract: In this paper, magnesium hydride was used to react with water to produce the hydrogen gas. Magnesium hydride is the chemical compound MgH2, which contains 7.66% by weight of hydrogen. Although the concept of reacting chemical hydride with water to produce hydrogen is not new, there have been a number of recent published papers which might be employed to power fuel cell devices for portable applications. Under the room temperature, the hydrolytic reaction between magnesium hydride and water to form a thin-layer of magnesium hydroxide on the outer surface impedes water from coming into direct contact with the magnesium hydride. The key to continual removal of the coherent magnesium hydroxide layer by adding a citric acid has the following conclusions. First, using this approach can reach the 6.4wt% of hydrogen. Finally, the cost of producing hydrogen from magnesium hydride-water hydrogen generation approach would cost approximately $15 per kg hydrogen.