Study On Hydrogen Storage Properties And Preparation Of Mg-Al-Li Alloys

The Mg-Al-Li ternary hydrogen storage alloys were prepared by combining heat treating with modern nano technology. And the effects on hydrogen storage properties of preparation process and catalytic doping on Mg-Al-Li ternary alloys were discussed in this paper.Firstly, the Mg5Al3Li2 alloy was prepared by combining different heat treating with solid state chemical mechanical milling process and the effects on hydrogen storage properties of Mg5Al3Li2 alloys which were prepared by combining heat treating(such as free cooling, quenching) with solid state chemical mechanical milling and solid state chemical mechanical milling respectively were discussed. Then it found that the sample prepared by combining heat treating with solid state chemical mechanical milling was mainly composed of Mg17Al12 and Mg17Li3, but the sample prepared by directly solid state chemical mechanical milling was composed of Mg17Li3 and AlLi. The hydrogenation/dehydrogenation thermodynamics and dynamics performance could not be improved by free cooling and quenching, but also the hydrogen amount of alloy was reduced. The Mg5Al3Li2 alloy prepared by solid state chemical mechanical milling had better hydrogen storage properties, and with the increasing of milling time, the hydrogen storage properties of Mg5Al3Li2 alloy had been significantly improved. When the milling time increased to 60h, the materials showed the best hydrogen storage properties, but with a further increasing of the milling time, the hydrogen storage capacity and the kinetics of hydrogen performance were decreased.Secondly, Mg5AlAlxLi2(x=2,3,4) and Mg5Al3Lix(x=1,2,3) alloys were prepared by mechanical alloying, and the effects of Al content and Li content on the hydrogen storage properties of Mg-Al-Li ternary alloy system were studied. It found that increasing molar amount of Al could reduce the generation of intermediate Mg2Al3, promote fully hydrogenated, improve alloy hydrogenation dynamics performance, reduce the dehydrogenation temperature from 300 ℃ (x=2) to 280℃(x=4), improve alloy dehydrogenation kinetics and thermodynamic properties, shift the dehydrogenation reaction from two steps to one step, but it would lead to decrease the hydrogen amount of alloy. While increasing the molar amount of Li in the Mg-Al-Li alloy, the hydrogen content was decreased from 3.75wt%(x=1) to 2.23wt%(x=3), the initial dehydrogenation temperature was increased from 285 ℃(x=1) to 300℃(x=3), and the thermodynamic properties and the kinetic properties of the hydrogenation/dehydrogenation of the alloy were decreased, because Li is soft and easy to be coated on the surface of Mg-Al particles.Then, substituting for partial Al of Mg-Al-Li alloy by Ti, it found that the Mg10Al7-xLi2Tix(x=1,2,3) alloys which were prepared by mechanical alloying in argon atmosphere were composed of Mg17Li3, Al and Ti. However, after hydrogenation/dehydrogenation reaction, the phase structure of the alloy was changed. Three alloys hydrogenation reaction paths were different. For example, the dehydrogenation products of Mg10Al6Li2Ti alloy hydrogenated were Mg17Al12, dehydrogenation products of Mg10Al5Li2Ti2 alloy hydrogenated were Mg17Al12 and Mg17Li3, and dehydrogenation products of Mg10Al4Li2Ti3 alloy hydride were Mg17Li3 and Mg2Al3. It showed that changing the Ti and Al molar amounts could control the reaction path of the alloy. Comparing with Mg5Al3Li alloy, the initial hydrogenation temperature of Mg-Al-Li alloy was reduced from 150℃ to 125℃(x=2), the initial dehydrogenation temperature of Mg-Al-Li alloy was reduced from 285 ℃ to 200 ℃ (x=2), the hydrogen amount of alloy was increased from 3.66wt% to 4.08wt%(x=1) and hydrogenation/ dehydrogenation kinetics performance was improved by adding proper amount of Ti to Mg-Al-Li alloy.