The Research On Phase Stability And Related Properties Of Magnesium-based Hydrogen Storage Alloys And Mg-Al(Ce) Based Alloys

Among the advanced magnesium alloys materials investigated, heat resistant magnesium alloys have been used in many fields, with excellent room temperature mechanical properties and low cost. However, the use of these magnesium alloys has been limited due to their poor heat resistance. Numerous studies have been carried out in order to improve poor creep property. As a potential good candidates for high-capacity batteries, magnesium-based hydrogen storage alloys have been extensively researched due to their high hydrogen storage capacity, light weight and low cost. However, a slow hydriding and dehydrogenating kinetics and high dissociation temperature(≈250℃) limit its practical application for batteries. In this dissertation, energy, electronic structure, structure stability and relative properties of magnesium hydride (MgH₂) and intermetallic compounds of Mg-Al(Ce) alloy are investigated. Since Mg₂FeH₆ is based on inexpensive metallic elements Mg and Fe, its price in commercial applications should be much lower than other complex hydrides, preparation technology of mechanical alloying 2Mg-Fe mixture powers, small samples of the milled powers at selected times for microstructure, dehydrogenating properties, energy and electronic structure of hydride phase are also investigated. Some new results will be benefit for designing for the advance magnesium-based hydrogen storage alloys and heat resistant magnesium alloys. This work is supported by Ph.D Programs Foundation of Ministry of Education of China (20020530012) and Science technology Important Programs Foundation of Ministry of Education of China (104139).In order to design the adavance magnesium-based hydrogen storage alloys, the energy and electronic structure of magnesium hydride (MgH₂) alloyed by 3d transition metal and Ge, Nb,Ca elements are investigated from the alloy energy view. From the relaxation study, it is noted that the alloying elements (except for Cu) mainly influence the position of the matrix atoms in their vicinity: i.e., only the positions of the nearest neighbor H3 atoms are significantly changed. As far as 3d transition metal elements are concerned, the influence of alloying elements on the position of the H3 atoms increases in the order of Sc,Zn,Ti,V,Fe,Mn,Co,Ni,Cr, while non-transition metal elements, the increasing order is Nb, Ge, Ca. Through calculations of the negative heat of formation of magnesium hydride alloyed by X (X denotes 3d transition metal or Ge, Nb,Ca) element, it is found that...