The Reserch On Hydrogen Storage Properties Of Magnesium-based Alloys Prepared By Mechanically Ball-milling

In this paper, previous research works on sorts of hydrogen storage alloys have been extensively reviewed.And then Mg-based hydrogen storage materials were slected as the subject for study.The purpose was to prepare the Mg-Ti binary alloys and the Mg-Sc-Ti ternary alloys and analysed the hydrogen storage properties.The emphases was put on analysing the influence of composition and the ball-milling technological parameter for the alloy structure, find out the relations between the structure and the hydrogen storage properties by means of X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, TG/DSC and other means of different techniques.The MgxTi100-x (x=35,50,65,80) alloys were prepared by planetary ball milling and high-speed vibratory ball milling under different ball milling conditions.In the Planetary ball milling process, the powder was felt together seriously. The XRD patterns showed that simple substance exists, meanwhile the HCP and FCC structures was found at x=80,65. when x=50 and 35, the BCC structure of alloy was synthesized.In the high-speed vibration ball milling process, the powders felt together at x=80,65, the mixed phases with HCP and FCC structures were obtained; when x=50,35, the sticking was mitigated. Respectively, the single FCC phase and the single BCC phase was successfully synthesized. The SEM pictures indicated that the alloys particle size was nonuniform (1～25μm) at x=80,65,50, and relatively well-proportioned while x=35, less than 5μm; The composition analysis indicated that the real composition was error from the theory composition designed,and the comparative Mg content was somewhat lower. The TEM pictures showed that it was tended to form nanometer crystals or amorphous crystal when the magnesium content was higher, and the unit crystal when the magnesium content was lower.The hydrogen storage test indicated that the alloys with HCP or FCC structure reveals a bad the hydrogen dynamics performance and the hydrogen storage capacity was less thanl.5wt% at 300℃. Comparatively, the alloy Mg35Ti65 with BCC structure has high hydrogen storage the capacity (3.88wt%) and fast hydrogen absorbing speed at 300℃, nearly maximal in 4 minutes.however, Moreover, The alloy with BCC structure still keep stably after hydrogenation 2 hours at 200℃, and the grain size increased; after hydrogenation at 300℃, besides Mg-Ti-H FCC structure, the MgH2 and TiH2 hydride appeared, That means the BCC structure of the alloy starts to decompose at 300℃.Mg4Sc alloy was synthesized by planetary ball milling, and different elements (Ti, Y, Al) took the part place of Mg or Sc elements during the ball milling process. According to hydrogen absorption tests, It showed that the components of the hydrogen absorption properties at 300℃adding Ti element was the best, and adding Al element the worst.Then studyed the influence of different content of Ti elements on the alloy structure and hydrogen storage properties. The studies on Mg4Sc1-xTix (x=0.3,0.5,0.8,1.0) alloys have shown that changing the content of Ti elements has little effect on alloy structure; hydrogen absorption tests showed that after activation at high temperature,the Sc content higher the hydrogen storage capacity better (x=0.7, the maximum hydrogen storage capacity was 3.75wt%). The reversible hydrogen absorption properties at a high temperature is superior than the binary Mg-Ti alloy.