| Hydrogen is one of the best energy choices,and how to realize efficient hydrogen storage is the key.TiFe alloy is a kind of high capacity room temperature hydrogen storage alloy,which has the advantages of low cost and good hydrogen absorption and desorption cycle performance.The activation process of the alloy was severely restricted for the first time.In this thesis,Sm and La elements are used to partially replace TiFin Ti22Fe16Mn3Cr alloy,and Ti22-xSmxFe16Mn3Cr as cast alloy with different Sm and La elements is prepared by medium frequency vacuum melting furnace.The effects of Sm and La substitution on the phase composition,microstructure,hydrogen absorption activation,hydrogen storage kinetics and hydrogen storage thermodynamic properties of TiFe alloys were studied.The as-cast Ti22-xSmxFe16Mn3Cr（x=0,0.1,0.2,0.3,0.4）alloys are composed of main phase TiFe phase and a small amount of second phase Ti2Fe and Sm phase.The cell volume V and lattice constant a of TiFe phase decrease with the increase of Sm content.After hydrogen absorption,the phase group of the alloy becomes TiFe H,TiFe H2and TiFH phase,and Sm3H7phase appears with the increase of Sm substitution.The grain size of the alloy becomes finer with the increase of Sm addition,resulting in more phase boundaries and nanocrystalline boundaries.The alloy can be activated rapidly under 3 MPa hydrogen pressure and 403 K temperature.With the increase of Sm addition,the first hydrogen absorption incubation period of the alloy is significantly reduced and the activation cycle is greatly shortened.With the increase of Sm content,the hydrogen storage capacity of the alloy first increases slightly,while after Sm content is 0.1,the hydrogen storage capacity decreases gradually.The maximum hydrogen capacity of Sm0.1alloy at 323 K is 1.633wt.%.In addition,the addition of Sm also improves the hydrogen storage kinetic properties of the alloy.The plateau pressure increases with the increase of Sm substitution.Sm0.2alloy shows the change of minimum hydrogenation enthalpyΔH.It means that the thermal stability of hydride is reduced.The maximum hydrogen storage capacity of x=0,0.1,0.2,0.3 and 0.4 alloys are 1.621,1.633,1.54,1.532 and 1.328 wt.%,respectively.The increase of Sm increases the platform pressure of TiFe on TiFe H.In addition,the enthalpy and entropy changes of hydrogenation/dehydrogenation reaction at different temperatures were calculated by van’t Hoff equation.The hydrogen absorption enthalpyΔHabof x=0,0.1,0.2,0.3 and 0.4 alloys are-30.11,-31.67,-26.97,-27.71,and-27.4 k J mol-1H2,respectively.The phase structure of as-cast Ti22-xLaxFe16Mn3Cr（x=0,0.1,0.2,0.3,0.4）alloys is TiFe main phase and a small amount of second phase Ti2Fe.After hydrogen absorption,there are TiFe H0.06,TiFe H,and TiFe H2phases in the alloy.When the content of La reaches0.4,La H3phase appears in the alloy.La substitution promotes the generation of micro defects（such as dislocations and grain boundaries）,which is conducive to hydrogen diffusion.The alloy added with La shows excellent activation ability,and the alloy can absorb and release hydrogen normally and reversibly in only one cycle.With the increase of La content,the hydrogen storage capacity of the alloy first increases slightly,while after La content is 0.1,the hydrogen storage capacity decreases gradually.The maximum hydrogen storage capacity of the alloy at 323 K and 3 MPa is 1.80 wt.%.In addition,the addition of La also improves the hydrogen storage kinetics of the alloy.The plateau pressure increases with the increase of La content.Enthalpy change of hydrogen absorption|ΔH|increases first and then decreases with the increase of La content.La0.1alloy shows the maximum absolute value of hydrogenation enthalpy change|ΔH|and it is25.23 k J/mol,which means the hydride of La0.1alloy is unstable. |
