Study On The Microstructure And Storage Hydrogen Properties Of Ti_22-xCe_xFe₁₆Mn₃Cr（x=0⁰.4） Alloys

Traditional energy is unrenewable,and environmental pollution problems caused by fossil fuel combustion are everywhere.Therefore,hydrogen energy,as an alternative clean energy,has attracted a huge mass of exploration.There are still multitudes of problems to be handdled in hydrogen storage.It is vital to study excellent hydrogen storage alloys.TiFe alloy has attracted extensive attention because of its rich raw materials and large hydrogen storage capacity.The activated TiFe alloy can operate at room temperature.However,its poor activation performance has always been the main reason limiting its large-scale industrial application.Our objiect is to improve the activation properties of TiFe alloy and enhance the comprehensive hydrogen storage properties of TiFe alloy.The as cast alloy is composed of main phase TiFe phase,a handful of second phase Ti₂Fe phase,[Fe,Cr]phase and rare earth phase.After hydrogenation,the TiFe phase is formed into TiFe H_0.06,TiFe H and TiFe H₂hydrides.Ti_22-xCe_xFe₁₆Mn₃Cr（x=0,0.1,0.2,0.3,0.4）alloy was prepared by vacuum induction melting under the protection of helium.The microstructure and hydrogen storage properties of as cast and ball milled alloys were studied in detail.The main results are as follows:The as cast alloy is composed of main phase TiFe phase,a small amount of second phase Ti₂Fe phase,[Fe,Cr]phase and rare earth phase.After hydrogen absorption,the TiFe phase changes to TiFe H_0.06.TiFe H and TiFe H₂hydrides.The higher the temperature,the less the first hydrogen absorption of the alloy and the shorter the activation incubation period.At the initial hydrogen pressure of 4 MPa and the temperature of 443 K,the activation properties of Ti_21.7Ce_0.3Fe₁₆Mn₃Cr alloy are excellent.Simultaneously,the hydrogen absorption and desorption rate of the samples are also enhanced.After adding Ce,the hydrogen absorption and desorption rate is markedly higher than that of TiFe alloy.Furthermore,the addition of Ce exaltes the generation of micro defects（such as dislocations and grain boundaries）,which is adminsters to hydrogen diffusion.When the hydrogen absorption equilibrium is reached at 303K under the initial hydrogen pressure of 3.5 MPa,the maximum hydrogen absorption capacity of Ti_22-xCe_xFe₁₆Mn₃Cr（x=0,0.1,0.2,0.3,0.4）is 1.28 wt.%,respectively 1.56wt.%,1.60wt.%,1.58wt.%,1.57wt.%.When the alloys has added of Ce,the hydrogen absorption first increases and then declines.After thermodynamic calculation,the absolute values of hydrogenation enthalpy change of x=0,0.1,0.2,0.3 and 0.4 alloys are obtained.and|ΔH|are 25.37,24.89,23.22,22.35 and 23.12 k J/mol respectively.As cast Ti_21.7Ce_0.3Fe₁₆Mn₃Cr alloy was ball milled in argon atmosphere for 0 min,15 min,30 min,45 min and 60 min.The function of ball milling process on the phase structure and hydrogen storage properties of the samples were explored.It’s result shows that the XRD diffraction peak of the alloy widened with the extension of ball milling time.In terms of the activation properties of the alloy after ball milling,it is found that the first hydrogen absorption incubation period of the alloy first decreases and then increases with the increase of ball milling time.The activation time is the shortest when ball milling for 30min,and the incubation period of hydrogen absorption is 150 s.At 303 K,the alloy has the best dynamic hydrogen absorption performance after ball milling for 30 min,and the maximum hydrogen absorption capacity is1.30wt%.Compared with that without ball milling,ball milling Ti_21.7Ce_0.3Fe₁₆Mn₃Cr alloy has different effects on enthalpy and entropy change at different time.The minimum enthalpy of formation is 20.21 k J/mol when ball milling for 30 min.