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, three groups of Mg-based alloys(Mg-Ni,Mg-Ni-Co, and Mg-Ni-Zr) were prepared by induction melting, and three groups of alloys (Mg-Ni, Mg-Ni-Zr and Mg-Ni-Co) were synthesized by mechanical alloying which were milling by agate ball. These alloys were subjected to detailed examinations, including XRD, SEM analysis, gaseous hydrogen- storage-property testing. Moreover, the thesis has discussed how to improve the process of mechanical alloying. the results showed that:â‘ Mg₂Ni,Mg₂Ni_0.8M_0.2(M=Co,Zr) and Mg₂Ni_0.6M_0.4(M=Co,Zr) were prepared by induction melting. The chemical constitution analysis of these alloys showed that Co were dissolved into Mg₂Ni successfully, but it was difficult for the Zr to be dissolved into Mg₂Ni. XRD results showed that All of the samples prepared by induction melting contained the phase of Mg₂Ni and Mg except the sample Mg₂Ni which had no phase of Mg in。Because of the exisiting of Mg, the alloys had a good hydrogen absorption capacity, especially Mg₂Ni_0.6Zr_0.4 reached 5.27% in a short time.â‘¡The alloys prepared by induction melting after milling improved the temperature of hydrogen absorption and desorption and decreased the time of hydrogen absorption, but it had slightly the capacity of hydrogen absorption decreased; As hydrogen desorption as concerned, it decreased the temperature.â‘¢Mg₂Ni_1-yZr_y(y=0.2, 0.4)å’ŒMg₂Ni_1-yCo_y(y=0, 0.1, 0.2, 0.4) were synthesized by mechanical alloying. All of them had the main phase Mg₂Ni which transformed to the hydride of Mg₂NiH4 after absorbing hydrogen. Besides, it was found Co₂Mg which had ability of hydrogen absorption in Mg₂Ni1-yCoy and Ni7Zr2 in Mg₂Ni_1-yZr_y.It did not have the ability of hydrogen absorption. So they reduced the ability of hydrogen absorption, which was the reason that the alloys prepared by induction melting were better than the alloys synthesized by mechanical alloying.â‘£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.