Hydrogenation Properties Of Mg Research Articles

Hydrogenation Properties of Mg-Al-Zn-CaO-Hx Prepared by Hydrogen Induced Mechanical Alloying (HIMA).

Mg and Mg-system alloys are the materials of choice among hydrogen energy storage media due to their high hydrogen storage capacity (7.6 wt.%) and lighter weight (Huot, J., et al., 1999. Structural study and hydrogen sorption kinetics of ball-milled magnesium hydride. Journal of Alloys and Compounds, 293, pp.495-500). However, the formation of hydrogen products at high temperatures, the phenomenon of rapid alloy deterioration, and the low rate of reaction in the hydriding and dehydriding processes have been the main hindrances to commercialization of these alloys for hydrogen storage. In this study, to increase the reaction rate with hydrogen, Mg-Al-Zn-CaO-Hx hydrogen storage alloys were fabricated HIMA (Seok, S., et al., 2005. Evaluations of microstructure and hydrogenation properties on Mg₂NiHx. Transactions of the Korean Hydrogen and New Energy Society, 16(3), pp.238-243). The Alloying times of 72 and 96 h and BCR of 30:1 and 66:1 were used for the HIMA process; the rotation speed was fixed at 200 rpm and the hydrogen pressure was 3 Mpa. SEM was used to confirm the shape of the particles. The crystal structure of the synthesized materials was analyzed by XRD, and BET measurements were performed to determine the correlation between the BCR and specific surface area. The weight change of the composite material was measured by TGA, and the kinetics was evaluated to determine the hydrogen adsorption rate (at 150, 250, and 350 °C).

Composition dependent microstructure evolution, activation and de-/hydrogenation properties of Mg–Ni–La alloys

In this work, in order to elucidate the effect of different alloying elements on the microstructure, activation and the de-/hydrogenation kinetics performance, the Mg–20La, Mg–20Ni and Mg–10Ni–10La (wt.%) alloys have been prepared by near equilibrium solidification combined with high-energy ball milling treatment to realize the internal optimization as well as particle refinement. The results show that the microstructures of the prepared alloys are significantly refined by forming different types and sizes of intermetallic compounds. Meanwhile, the effects of LaH3 and Mg2Ni within the activated samples on de-/hydrogenation kinetics are also discussed. It is observed that the alloy containing LaH3 preserves stable hydrogenation behavior between 573 and 623 K, while the hydrogenation properties of the alloy containing Mg2Ni is susceptible to temperature. A preferable hydrogenation performance is observed in Mg–10Ni–10La alloy, which can absorb as high as 5.86 wt% hydrogen within 15 min at 623 K and 3.0 MPa hydrogen pressure. Moreover, the desorption kinetics and the desorption activation energies are evaluated to illustrate the mechanism based on improved dehydrogenation performance. The addition of proper alloying elements Ni and La in combination with reasonable processing is an effective strategy to improve the de-/hydrogenation performance of Mg-based alloys.

The effects of Si and expanded PTFE substrates on formation and hydrogenation of Mg and Mg–Ti films

In this work, we investigated how DC and pulsed DC Ar gas plasma treatment changes surface topography and chemical composition of silicon and expanded Polytetrafluoroethylene (ePTFE) substrates and how different surface pretreatment techniques can affect the formation and hydrogenation of Mg and Mg–Ti films. It is observed that pre-treating Si and ePTFE substrates with different plasma modes results in significant changes of microstructures of as-deposited Mg and Mg–Ti films. After the hydrogenation of Mg films at 20 bar H2 pressure and 180 °C temperature the formation of crystalline MgH2 phase is observed only for the films deposited on plasma non-treated Si substrates which had the films with smallest dimensions of its columnar structure. It is known that, usually, Ti additives has positive effect on hydrogenation properties of Mg, but in this study independently of the used substrate pre-treatment technique after the hydrogenation of Mg–Ti films their XRD analysis showed no peaks of the crystalline hydride phase. However, depending on the surface properties of the substrate after hydrogenation Mg–Ti films also have several disparities which are discussed and attributed to the potentially related substrate features.

Superior (de)hydrogenation properties of Mg–Ti–Pd trilayer films at room temperature

In this paper, a series of Mg-Ti-Pd trilayer films with various thicknesses of the Ti interlayer were prepared by magnetron sputtering. The trilayer films could be reversibly (de)hydrogenated at room temperature. The relationship between structure and properties of Mg-Ti-Pd trilayer films was comprehensively investigated. Our studies showed that the hydrogen storage properties of Mg-Pd films were significantly improved with the addition of a Ti interlayer. The optimal hydrogenation properties were obtained when the Ti interlayer was 1 nm. The superior hydrogenation properties achieved by introduction of the Ti interlayer could be attributed to several aspects: prevention of Mg-Pd alloying; catalytic dissociation of H(2) molecules and provision of heterogeneous nucleation sites. These results were elucidative for the development of high performance intermetallic hydrogen storage materials and thin film based functional devices.

Effect of rapid solidification on hydrogen solubility in Mg-rich Mg–Ni alloys

The hydrogenation properties of Mg 100− x Ni x alloys ( x = 0.5, 1, 2, 5) produced by melt spinning and subsequent high-energy ball milling were studied. The alloys were crystalline and, in addition to Mg matrix, contained finely dispersed particles of Mg 2Ni and metastable Mg 6Ni intermetallic phases. The alloys exhibited excellent hydrogenation kinetics at 300 °C and reversibly absorbed about 6.5 mass fraction (%) of hydrogen. At the same temperature, the as prepared Mg 99.5Ni 0.5 and Mg 95Ni 5 powders dissolved about 0.6 mass fraction (%) of hydrogen at the pressures lower than the hydrogen pressure corresponding to the bulk Mg–MgH 2 two-phase equilibrium, exhibiting an extended apparent solubility of hydrogen in Mg-based matrix. The hydrogen solubility returned to its equilibrium value after prolonged hydrogenation testing at 300 °C. We discuss this unusually high solubility of hydrogen in Mg-based matrix in terms of ultrafine dispersion of nanometric MgH 2 precipitates of different size and morphology formed on vacancy clusters and dislocation loops quenched-in during rapid solidification.

Improved hydrogenation properties of Mg- x(Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3) composites

Mg- x(Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3)( x=20%, 30%, 40%) (mass fraction) composite powders were prepared by reactive ball milling with hydrogen and their hydrogen storage properties and microstructure were investigated by XRD, SEM and pressure-composition-temperature measurement. The results show that the composites have 3.83%-5.07% hydrogen capacity at 553 K and good hydrogenation kinetics, even at room temperature. Among them, the milled Mg-30%(Ti 0.9Zr 0.2Mn 1.5Cr 0.3) composite has the highest hydrogenation kinetics as it can quickly absorb 2.1% hydrogen at 373 K, 3.5% in 2 000 s at 473 K, even 3.26% in 60 s at 553 K under 3 MPa hydrogen pressure. The improved hydrogenation properties come from the catalytic effect of Ti 0.9 Zr 0.2 Mn 1.5 Cr 0.3 particles dispersed uniformly on the surface of Mg particles.

Influence of Pd on the structure and electrochemical hydrogen storage properties of Mg50Ti50 alloy prepared by ball milling

Abstract High-energy ball milling was used to modify the physico-chemical and the electrochemical hydrogenation properties of Mg 50 Ti 50 alloy via the addition of Pd. This was done by first ball milling Mg and Ti together for (20 − x ) hours. 3.3 at.% Pd was then added and ball milling was resumed for x hours. X-ray diffraction and X-ray photoelectron spectroscopy analyses revealed that the alloying of Pd with pre-milled Mg 50 Ti 50 was initiated after only a few minutes and was completed after 5 h of milling. The maximum discharge capacity of the Mg 50 Ti 50 –3.3 at.% Pd electrode increased significantly with the milling time (from 35 mAh g −1 for 5 min to 480 mAh g −1 for 20 h of milling). The exchange current density increased with the milling time and was directly related to the Pd surface concentration, suggesting that Pd plays a key role in facilitating the charge-transfer reaction. In contrast, the incorporation of Pd had a minor effect on the hydrogen diffusion coefficient. The electrochemical pressure-composition isotherms revealed a significant destabilization of the hydride as the milling time with Pd increased. No significant improvement in the hydrogen storage properties of Mg 50 Ti 50 –Pd electrodes was observed for Pd concentrations higher than 3.3 at.%.

The effects of dynamic structural transformations on hydrogenation properties of Mg and MgNi thin films

Abstract Mg capped with Al and Ti thin layers and Mg x Ni films have been sputter-deposited on quartz substrates and hydrogenated at 600 kPa for 250 °C. A complete fast transformation of metallic into hydride phase is registered for the films, demonstrating the dynamic state of the internal microstructure under hydrogenation. It leads to local and long-range restructuring and the fast hydrogenation rate is attributed to the fast hydrogen uptake and transport along columns and grain boundaries of nanocrystallites. A slow H-loading is observed when the dynamic structural relaxation processes are suppressed by internal and external inhomogeneities such as barrier layers on the surface, new phases in the bulk and impurities. A partial transformation of metallic into hydride phase is registered when the structural formations newly nucleated at the initial stages of hydrogenation suppress dynamic processes and prevent the H-uptake.

Density functional theory studies of the hydrogenation properties of Mg and Ti

Absorption energies of hydrogen in Mg and Ti as a function of the hydrogen concentration were calculated using density functional theory. We investigated hydrogen absorbed in metal hosts with different structures (fcc, hcp, and bct for Mg; hcp and fcc for Ti). The most stable configurations were determined for different hydrogen concentrations. Rutile and fluorite structures are found to be the most stable for Mg and Ti hydrides, respectively. Preference of hydrogen filling up the interstices of the metal hosts, and crystal lattice transformations and distortions were also investigated. Hydrogen atoms prefer to pair up and form clusters in Mg; but hydrogen atoms like to occupy sites which are apart as far as possible in Ti. The differences in the hydrogenation behavior of Mg and Ti were compared and analyzed using the electron density. The hydrogenation behaviors can be related to bonding characteristic of Mg and Ti hydrides. Mg hydride is more ionic than Ti hydride.

Hydrogenation properties of Mg–Al alloys

In this paper the properties of Mg–Al alloys in relation to hydrogen storage are reviewed. The main topics of this paper are materials preparation, hydrogen capacity, thermodynamics of hydride formation, and the kinetics of hydride formation and decomposition. Hydrogenation of Mg–Al leads to disproportionation with the formation of magnesium hydride and metallic aluminum as the final product. Experimental evidence renders this process reversible. It is observed that the enthalpy of hydride formation of magnesium is lowered upon alloying with Al due to a slightly endothermic disproportionation reaction. Further, it is found that the kinetics of hydrogenation, as well dehydrogenation, may be significantly improved by alloying compared to pure Mg. The expense of these improvements of the hydrogenation/dehydrogenation properties is a lower gravimetric hydrogen density in the hydrogenated product.

Investigations on synthesis and hydrogenation properties of Mg–20 wt% Ni–1 wt% TiO 2 composite prepared by reactive mechanical alloying

Reactive mechanical alloying (RMA) was used to prepare Mg–20 wt% Ni–1.0 wt% TiO 2 composite materials. A nanocrystalline composite of MgH 2 and Mg 2NiH 4 formed after 60 h of ball-milling. An increase of the nanocrystalline size was found after 20 hydriding/dehydriding cycles. It absorbed more than 80% of its full capacity in the temperature range of 363–543 K within less than 1 min and desorbed 3.22 mass% of hydrogen at 578 K under a hydrogen pressure of 0.1 MPa in 1 h. DSC analysis shows that the thermodynamic property of Mg-based hydrogen storage alloys do not be changed by the addition of TiO 2 and ball-milled process.

Hydrogen storage properties of preferentially orientated Mg-Ni multilayer film prepared by magnetron sputtering

Mg-Ni multi-layer thin film was deposited on (001) Si wafer by magnetron sputtering with dualtarget. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis reveal that the microstructure of the Mg-Ni multilayer thin film is composed of fine-crystalline Ni layer and crystalline [001] Mg layer. Hydrogenation process of the films were carried out by using the automatic gas reaction controller. The films undergone hydrogenation for different time were analyzed by XRD. The results show that hydrogenation properties of Mg with different preferential orientations are different. (002) diffraction peak of Mg disappears in compensating the appearing of the peaks of Mg 2NiH 4 and MgH 2 in hydrogenation at 533 K, while the (101) peak still remains. The result reveals that the Mg film with (001) preferential orientation absorbs hydrogen at certain temperature easier than that of the Mg film with (101) orientation. This phenomenon can be explained in the view point of the energy change for the nucleation and growth of hydride in different crystal plane.

Synthesis and hydrogenation properties of Mg–3 mol%LaNi 3 composite prepared under an external magnetic field

The Mg–3 mol%LaNi 3 composition was successfully prepared by different techniques, namely, the composite was synthesized by hydrogen combustion synthesis (HCS) with and without an external high magnetic field. The hydrogen storage capacities and hydriding/dehydriding (H/D) rates of the two composites at different temperatures were evaluated and their structures and morphologies were examined. Our main goal in this study is how to control the process of HCS by the external high magnetic field and to investigate its effect on the hydrogenation properties of the composite and analyze these changes from the relationship between the microstructure and crystalline state and the energy injected into the composite from the external high magnetic field.

Synthesis and hydrogenation properties of Mg–La–Ni–H system by reactive mechanical alloying

We have synthesized Mg–30 mass%LaNi 2.28 composite material and investigated its hydrogenation behaviour. The reactive mechanical alloying process of the mixture of Mg and LaNi 2.28 was studied. It is found that a composite of MgH 2 , La 4 H 12.9 and Mg 2 NiH 4 formed after 80 h ball-milling under 3.0 MPa hydrogen. Scanning electron microscopic analysis indicated that these new phases are distributed homogeneously. This composite shows excellent hydriding properties even at moderate temperature. Under 3.0 MPa hydrogen pressure it absorbed more than 80% of its full capacity in the temperature range of 473–553 K within less than 1 min. The maximum hydrogen absorption capacity at 553 K is 5.4 mass%. The enhanced hydriding properties could be attributed to the fine and uniform particles and a synergeticly catalytic effect generated by mechanical milling.

The hydrogen absorption–desorption performances of Mg–Co– X ternary alloys with BCC structure

To improve hydrogenation properties of Mg–Co binary alloys that were developed by the present authors, ternary Mg 50Co 45 X 5 alloys ( X = Fe, Cu and Pd) were synthesized by ball milling. The formation of the BCC phase in the ternary alloys was verified by means of a XRD Rietveld analysis and TEM observation. The BCC lattice parameters of Mg 50Co 45 X 5 ( X = Fe, Cu and Pd) were found to be smaller than that of Mg 50Co 50. Fe addition to Mg 50Co 50 alloy improved the hydrogen absorption capacity to 2.59 mass% at 373 K. The Pd and Cu added alloys showed a desorption isotherm for which the desorption capacity was up to 0.2 mass% at 373 K in the pressure range of 0.01–5.0 MPa. In situ DSC measurements revealed that the hydrogen absorption and desorption reactions of all the ternary alloys studied were reversible at the first thermal cycle. A series of ternary Mg 50Co 50− y Cu y ( y = 5, 7, 9, 10) BCC alloys were synthesized by ball milling. It was found that Mg 50Co 41Cu 9 had the highest hydrogen absorption content (2.0 mass%) among these alloys at 373 K, while it desorbed 0.3 mass% hydrogen at the same temperature under vacuum.

Microstructure and hydrogen sorption properties of Mg–Ni/MmM 5 multi-layer film by magnetron sputtering

To improve the hydrogenation properties of Mg–Ni-base alloys, Mg–Ni/MmM 5 multi-layer film was fabricated by magnetron sputtering. The microstructure and hydrogenation properties of as-deposited film were characterized by X-ray diffraction, scanning electron microscopy and pressure-composition isotherm measurement. It was shown that the Mg–Ni layer is composed of preferred orientational nanocrystalline Mg 2Ni and fine-crystalline Mg, while the MmM 5 layer is in amorphous structure. PCI curve of Mg–Ni/MmM 5 multi-layer film at 523 K is composed of two plateaus, which correspond to the hydriding and dehydriding reactions of Mg and Mg 2Ni, respectively; A maximum hydrogen absorption content of 5.0 mass % is obtained at 523 K . The hydrogenation properties of Mg–Ni/MmM 5 multi-layer film are greatly improved than that of the corresponding Mg–Ni alloy target, which is attributed to the nanocrystalline structure of the Mg–Ni layer and catalytic role of the amorphous MmM 5 layer. However, the hydrogenation properties of Mg–Ni/MmM 5 multi-layer film are deteriorated after several cycles.

Fabrication of Mg−Ni hydrogen storage alloys by rotation-cylinder method

For many years, the Mg−Ni alloys have been studied as good lightweight hydrogen storage materials, however, the alloys present strong difficulties in the fabrication process of mass products. The rotation-cylinder method (RCM) has been developed for magnesium based composites with moderate rotation under a normal atmosphere. In this study, the Mg-3, 6, 9, 12 mass% Ni alloys were easily manufactured by RCM and their hydrogenation properties were evaluated with a Sieverts-type automatic pressure-composition-isotherm (PCI) apparatus at 523, 573 and 623K. The evolution of the microstructure of as-cast specimens appeared to be a typical hypoeutectic structure. From the results of the backscattered electron image (BEI) and energy dispersive spectrometry (EDS), the difference between the composition of the α-Mg and Ni-rich eutectic regions was distinguished clearly. The hydrogenation properties of Mg−Ni alloys depended on the behavior of the nickel compositions. Especially, the hydrogen kinetics of Mg-9 mass% Ni was more excellent than the others.