Synthesis And Research Of Mg-based Hydrogen Storage Alloys

Having the advantage of high storage capacity, low density, pollution-free and a relatively low cost, the Mg-based alloys is a promising choice used for hydrogen storage materials. However, there's still a long way for Mg-based alloys to be used as an ideal carrier of hydrogen because of its bad thermodynamics and kinetics properties in hydrogen absorption and desorption. The reactions occurring during the process of hydrogen storage require a high temperature and the velocity of these reactions is too slow. So a great amount of work focus on overcoming the weakness of Mg-based alloys mentioned above.In this thesis, four groups of Mg-based alloys(Mg-Ni,Mg-Ni-Co, Mg-Ni-Cu and Mg-Ni-Zr) were prepared by induction melting, and three groups of alloys (Mg-Ni, Mg-Al-Ni and Mg-Ni-Cu) were synthesized by mechanical alloying. These alloys were subjected to detailed examinations, including XRD, SEM analysis, gaseous hydrogen- storage-property testing and electrochemical-property testing. Moreover, the thesis has discussed how to improve the process of mechanical alloying.Mg2Ni,Mg2Ni0.8M0.2(M=Co, Cu, Zr) and Mg2Ni0.6M0.4(M=Co, Cu, Zr) were prepared by induction melting. The chemical constitution analysis of these alloys showed that Co and Cu were dissolved into Mg2Ni successfully, but it was difficult for the Zr to be dissolved into Mg2Ni. All of the samples prepared by induction melting contained the phase of Mg2Ni except the sample, Mg2Ni0.8Cu0.2, which had the phase CuMg2 as its main hydrogen storage phase. Furthermore, the alloy partly substituted by Co, Cu and Zr contained a compound phase, Mg-Ni-M (M= Co, Cu or Zr), of which the ingredient and microstructure needed to be studied in depth.Mg2-xAlxNi(x=0, 0.1, 0.3) and Mg2Ni1-yCuy(y=0, 0.1, 0.2, 0.3) were synthesized by mechanical alloying. All of them had the main phase Mg2Ni which transformed to the hydride of Mg2NiH4 after absorbing hydrogen. The alloy partly substituted by Al contained another hydrogen storage phase Mg3AlNi2 and the alloy samples partly substituted by Cu contained a phase Cu11Mg10Ni9. Moreover, the thesis used the process of synthesizing sample, Mg1.8Al0.2Ni, as an example to illustrate that the method of mechanical alloying can synthesize hydrogen-storage alloys with satisfactory performances in very short time, after properly reducing the effect of bonding on the materials during the ball milling. Compared with the samples prepared by induction melting, the samples prepared by mechanical alloying had better kinetics properties and lower temperature for hydrogen absorption and desorption. For the samples prepared by induction melting, the hydrogen storage properties improved as the times of cycle increased. In contrast, for the samples prepared by mechanical alloying, the first cycle had the best hydrogen storage properties. For all the samples prepared by both the two methods, the plateau pressure of the sample Mg2Ni was higher than any samples partly substituted by other elements except for the situation of Cu.