Investigation On Hydrogen Storage Properties Of Mg-Ni-Based Alloys

In this paper,alloys of Mg₇₆Ti₁₂Fe_8-xNi₄Al_x(x=1,2,3,4)and Mg_76-xTi₁₂Fe₈Ni₄B_x (x=0,4,8,12)were prepared by mechanical alloying and the hydrogen storage properties were investigated systematically.The study of these systems has used all tools available to materials science research,including X-ray diffraction,test of pressure-composition isotherms,thermodynamic performances test and analysis of scanning electron microscopy.It is showed that the main binary alloy phases of Mg₇₆Ti₁₂Fe_8-xNi₄Al_x alloys are Mg₂Ni,Al_1.1Ni_0.9and AlMg.For Mg₇₆Ti₁₂Fe_8-xNi₄Al_x(x=1,2,3,4)alloys,the hydrogen storage capacity is 2.20,3.19,2.90 and 3.01wt%,respectively.No evident influence to hydrogen absorption-desorption rate is observed when Aluminum element is added. However,with the amount of substitution Al for Fe increasing the decomposition rate of metallic hydrides decreases and the hysteresis between absorption and desorption increases.With ball mill time increasing,the rates of hydrogen absorption-desorption increase,the onset temperature of hydrides decomposition decrease,the hysteresis between hydrogen absorption and desorption become lower,the hydrides decomposition degree become higher,but the hydrogen storage capacity will be influenced.The main alloy phases of Mg_76-xTi₁₂Fe₈Ni₄B_x(x=0,4,8,12)hydrides are MgH₂, TiH₂,Mg₂NiH,Mg₂NiH₄ and HFeTi.Process of hydrogen absorption will promote the formation of Mg₂Ni,Fe₂B and FeTi.Mechanically milled alloys have relative high hydrogen storage capacity.The temperature of hydrogen desorption reaction degrades with the milling time,and the hysteresis between absorption and desorption decreases.The hydrides of Mg_76-xTi₁₂Fe₈Ni₄B_x(x=0,4,8,12)alloys can decompose at 523K completely.For Mg₆₈Ti₁₂Ni₄Fe₈B₈ alloy,the highest hydrogen storage capacity emerge when milled after 40 hours.