Effects Of Additive Si And Annealing Technology On Hydrogen Storage Performance Of La-Mg-Ni System Alloys

In this dissertation, the La-Mg-Ni system (A₂B₇ type) hydrogen storage alloys were prepared by vacuum induction melting and annealing technology. The phase structures and compositions of the alloys were determined by X-ray diffractionmeter (XRD). The electrochemical performances, high rate discharge capabilities (HRD) and Kinetics characteristic of the alloys were measured by electrochemical measurement system. Hydrogen absorption capacity and kinetics curve of as-cast and annealed alloys were measured by P-C-T curve tester. The investigation results have reliable theoretical basis for further improving the synthetically electrochemical performance of the La-Mg-Ni system electrode alloy, and helpful guides to solve the question of the cyclic stability of La-Mg-Ni system hydrogen storage alloy.Si was selected as an additive element in La_0.75Mg_0.25Ni_3.4Co_0.2Si_x(x=0-0.2) alloys, the effects of Si chemical element content on the structure and electrochemical properties of hydrogen storage alloys were investigated in detail. The obtained results show that the alloys are multi-phase structure and are composed of the LaNi5 type phases and the LaNi3 type phases. The amount of the LaNi5 type phases gradually increases with the increase of Si content, but the amount of the LaNi3 type phases correspondingly decreases. The addition of Si enhances the cycle stability of the alloys, but is harmful to the discharge potential characteristics. The addition of Si enhances the high rate discharge capability, when x was 0.15, the alloy exhibited the best high rate discharge stability, limiting current density, and H-diffusion coefficient which show the best Kinetics characteristic. The gaseous hydrogen absorption capacity of the La-Mg-Ni systemLa_0.75Mg_0.25Ni_3.4Co_0.2Si_x(x=0-0.2) alloys was investigated. The hydrogen absorption rate is well, and the temperature has the higher effect to the hydrogen absorption than the pressure. The addition of Si leads to it decrease the hydrogen absorption capacity, it is harmful to the hydrogen absorption of the alloy.The effects of annealing technology on the microstructure and electrochemical performances of the La-Mg-Ni system La_0.75Mg_0.25Ni_3.4Co_0.2Si_x(x=0-0.2) alloys were studied. For La_0.75Mg_0.25Ni_3.4Co_0.2Si_x(x=0-0.2) alloys, after annealing, the LaNi5 type phases become increased, and LaNi3 type phases get reduced. After annealing the discharge capacity of the alloys are well, and the cyclic stability gets improved. When the annealing temperature is 1123K, the alloys show the best electrochemical properties. The annealing improves the high-rate discharge ability, while at the low annealed temperature the alloys exhibit well kinetics characteristic.