Effect Of Element Substitution On Absorption Properties Of Zr₂Fe Alloy

The recovery of hydrogen isotopes in helium or nitrogen is essential for the continuous operation of fusion reactor-related facilities and the prevention of radioactive material leakage.Zr2Fe getter alloy has a low nitrogen absorption capacity and can efficiently absorb hydrogen in a high-pressure nitrogen environment,making it the most suitable getter alloy for absorbing low concentrations of hydrogen in a nitrogen environment.However,the currently used Zr2Fe alloy also has the problem of high secondary phase content such as Zr and ZrFe2,which leads to an increase in its nitrogen absorption and reduces the efficiency of hydrogen absorption.In order to improve the performance of Zr2Fe alloy absorbing hydrogen and other impurity gases in nitrogen environment,this paper studies the phase change of Zr2Fe by using the element substitution method and its effect on the absorption performance of hydrogen,nitrogen and carbon monoxide.(Zr1-xTix)2Fe and(Zr1-xNbx)2Fe alloys substituted by Ti and Nb at A side and Zr2(Fe1-xNix)alloys substituted by Ni at B side were prepared using magnetic levitation melting.The phases and morphologies of the alloys were characterized by SEM and XRD.The hydrogenation PCT curves and the absorption properties of hydrogen,nitrogen and carbon monoxide were measured by a standard Sieverts’type apparatus.The studies found:The phase composition and absorption properties of Zr2Fe alloy are closely related to Zr/Fe content.The main phase of Zr1-xFex(x=0.31,0.33,0.35)alloys is Zr2Fe phase.Zro.67Feo.33 has the highest content of Zr2Fe phase,while Zr0.69Fe0.31 and Zr0.65Fe0.35 have more Zr and ZrFe2 phases,respectively.With the increase of Fe content,the hydrogen absorption capacity of Zr1-xFex alloys decreases from 1.21 H/M to 1.11 H/M at 0.05 MPa,while the carbon monoxide absorption capacity increases about 1.6 times.The Zr0.67Fe0.33 has high absorption capacity of hydrogen and carbon monoxide,and the nitrogen absorption capacity is the smallest,only 55%of that of Zr0.65Fe0.35 alloy.The kinetic analysis shows that the rate-controlling step of hydrogen absorption reaction is nucleation and growth,while that of nitrogen and carbon monoxide absorption reaction is diffusion.(Zr1-xTix)2Fe(x=0.01,0.05,0.1,0.2)and(Zr1-xNbx)2Fe(x=0.01,0.05,0.1,0.2,0.3)alloys were prepared by substituting Ti and Nb on A side of Zr0.67Fe0.33 alloy.The C16 structure Zr2Fe phase in the original Zr0.67Fe0.33 alloy is transformed into cubic(Zr,Ti)2Fe phase,and the C14 structure Zr(Fe,Ti)2 phase appears.With the increase of Ti content,the hydrogen absorption equilibrium pressure of(Zr1-xTix)2Fe alloys increase gradually.Their hydrogen absorption capacity decreases under the same condition,while the absorption capacity of nitrogen and carbon monoxide increases.The nitrogen absorption capacity of(Zr0.8Ti0.2)2Fe alloy at 0.5 MPa is 3.76 mL/g,much higher than that of Zr0.67Fe0.33 alloy(1.12 mL/g),and the carbon monoxide absorption capacity increases nearly 1.4 times.The effect of Nb substitution on Zr0.67Fe0.33 alloy is similar to that of Ti.The main phase of(Zr1xNbx)2Fe also changes to cubic(Zr,Nb)2Fe phase and C14 structure Zr(Fe,Nb)2 phase.Nb substitution increases the hydrogen absorption equilibrium pressure of(Zr1-xNbx)2Fe,decreases the hydrogen absorption capacity under the same conditions,increases the nitrogen absorption capacity,but slightly increase the carbon monoxide absorption capacity.For(Zr0.7Nb0.3)2Fe alloy,the nitrogen absorption capacity reaches 6.94 mL/g,while the carbon monoxide absorption capacity of(Zr0.99Nb0.01)2Fe is the highest,only 20%more than that of Zr0.67Fe0.33 alloy.The kinetic analysis shows that Ti and Nb substitution do not change the mechanism of hydrogen absorption reaction,but make the hydrogen absorption curves appear different stages according to the phase transformation.The rate-controlling step of nitrogen and carbon monoxide absorption reaction is diffusion.Zr2(Fe1-xNix)(x=0,0.05,0.15,0.3,0.5)alloy were prepared by substituting Ni on B side.The results show that Ni substitution can promote the formation of C16 structure Zr2(Fe,Ni)phase and inhibit the formation of ZrFe2 and Zr phases.Zr2(Fe0.7Ni0.3)and Zr2(Fe0.5Ni0.5)alloys are composed of Zr2(Fe,Ni)single phase.With the increase of Ni content,the cell volume of Zr2(Fe,Ni)phase decreases,and the hydrogenation enthalpy gradually decreases from-79.6 kJ/mol of Zr2(Fe0.85Ni0.15)to-67.3 kJ/mol of Zr2(Fe0.5Ni0.5),The hydrogen absorption capacity of Zr2(Fe1-xNix)alloy decreases from 1.18 H/M of Zr2Fe to 1.12 H/M of Zr2(Fe0.5Ni0.5)at 0.05 MPa.With the decrease of the cell volume of Zr2(Fe,Ni)phase and the disappearance of the secondary phase,the absorption capacity of nitrogen and carbon monoxide of Zr2(Fe1-xNix)alloy decreases.Compared with Zr0.67Fe0.33,the absorption capacity of nitrogen and carbon monoxide of Zr2(Fe0.5Ni0.5)alloy decrease by about 40%and 90%,respectively.Ni substitution do not change the rate-controlling steps of hydrogen,nitrogen and carbon monoxide absorption reactions.