| dc.description.abstract | The development of materials with high hydrogen storage capacity has thus become important. AB5 alloys are common hydrogen storage material with a reasonable hydrogen storage capacity. However, AB5 alloys consist of a significant portion of rare earth metals (REMs), which are getting more and more expensive. Therefore, AB3 alloys, which use much less REMs but more low-cost metals such as Ca and Mg, may be more cost-effective for hydrogen storage. AB3 alloys have a larger hydrogen storage capacity in addition to the lower working temperature and pressure as compared with the AB5 alloys. Therefore, it is proposed that AB3 alloys can at least partially replace AB5 alloy in some applications. The results in this study show the effect of mixing AB3 and AB5 on the ability to store hydrogen. The main focus of this research is to study the hydrogen storage properties of an AB3 alloy La0.7Ca0.7Mg1.6Ni9 before and after mixing with an AB5 alloy La0.56Ce0.38Ni5; and the effect of heat treatment on these alloys and their composites. Initially, La-Ca-Mg-Ni hydrogen alloy with different elemental ratios was prepared by high-frequency induction heating method, La0.56Ce0.38Ni5 was directly purchased from a Chinese company. Inductively Coupled Plasma (ICP) was used to determine the alloy composition as La0.49Ca1.07Mg1.94Ni9 and La0.56Ce0.38Ni5. To study the effect of heat-treatment on the La-Ca-Mg-Ni/AB5 hydrogen composites, a of AB3 type La–Ca–Mg–Ni-based hydrogen storage alloys have been heat-treated at 800 ℃ for 48 hours under an argon atmosphere. Electron probe microanalysis (EPMA) was used to examine the localized chemical compositions in the samples before and after heat treatment. X-ray diffraction (XRD) and transmission electron microscope (TEM) were used to examine the crystal structure and phase changes of the. The X-ray diffraction analysis reveals the presence of two phases in the alloy, namely the FCC (La,Mg)Ni3 phase and the HCP (LaNi5) phase. Finally, the hydrogen storage properties of the samples were studied by a Sivert’s type equipment, and the Pressure-Composition-Isotherms (PCI) curves of the samples were determined. It was found that AB3 obtained shows a flat pressure plateau, thus suggesting a high homogeneity of the alloy prepared using the heat treatment. The hydrogen capacity of pure AB5 and AB5 after heat treatment was found to be 1.4 wt.% and 1.26 wt.% at 25℃, under a hydrogen charging pressure of 5 MPa. In contrast, the PCI curve of the commercial AB5-type La0.6Ce0.4Ni5 hydrogen storage alloy was found to have a higher plateau pressure, with a bigger hysteresis. The hydrogen storage capacity of the sample with 50 wt.% AB3 and 50 wt.% AB5 alloy was found to increased under the same hydrogen charging conditions, indicating the beneficial effect of the blending of the two alloys.
In conclusion, AB3-type La-Ca-Mg-Ni alloy was successfully fabricated in this study. The phase structure of FCC & HCP have been verified by XRD and TEM. The result EPMA of AB3 alloy after heat treatment only magnesium aggregated, while the rest of the elements distributed evenly. Besides, the crystallinity of AB3 and AB5 increased after heat treatment. The hydrogen storage capacities of La0.49Ca1.07Mg1.94Ni9 alloy were measured to be 1.34 wt.% at 25 ℃. The hydrogen storage capacities of AB5 before and after heaat treatment La0.6Ce0.4Ni5 1.4 wt. % and 1.26 wt. %. PCI curve of AB3 type La-Ca-Mg-Ni and AB5 type La0.56Ce0.38Ni5 alloy mixture before and after heat treatment rearch 1.36 wt.% and 0.93 wt. %, desorption capacity was 1.13 wt.% and 0.78 wt. %.? | en_US |