Study On Microstructure And Properties Of ZrCo Based Hydrogen Storage Alloy

In the International Thermonuclear Experimental Reactor（ITER）and the hydrogen isotope Storage and Supply System（SDS）,ZrCo is regarded as one of the most promising candidate materials to replace uranium（U）for hydrogen isotope storage,transportation and supply.Its outstanding advantages include nonradioactivity,low pyrophoricity,low equilibrium hydrogen pressure at room temperature(～10^-3 Pa),high hydrogen capacity（～1.9 wt.%）and the ability of trapping ³He.Nevertheless,ZrCo exhibits some shortcomings.Element doping is currently the main way to improve the kinetics,hydrogen absorption/desorption cycle stability and anti-disproportionation performance of ZrCo alloy.To improve the above problems,V,Ti,Hf and Cr-doped alloys were prepared by vacuum arc melting in this paper.ZrCo-based hydrogen storage alloys were characterized by X-ray diffraction（XRD）,scanning electron microscope（SEM）,energy dispersive spectrometer（EDX）,differential scanning calorimeter（DSC）,transmission electron microscope（TEM）and a customized Sievert type hydrogen storage material testing apparatus.Effects of V,Ti,Hf and Cr doping on the microstructure,activation properties,hydrogen desorption properties,thermodynamic properties,cycling stability and anti-disproportionation properties of ZrCo-based hydrogen storage alloys were investigated systematically.The mechanism of action is analyzed and studied.The relevant research results can provide technical support for the application of ZrCo-based alloys in the hydrogen isotope storage and supply system of the ITER project.The main research results are as follows:1.Zr_50-xV_xCo₅₀（x=2.5,3.5,5.0）alloys are composed of CsCl-type cubic phase ZrCo and brittle Zr V_0.24Co_1.76 second phase.The lattice constant and cell volume decrease with the increase of V content.V doping effectively improves the initial activation properties of ZrCo alloy.Moreover,the incubation period and activation time of the alloy are greatly reduced due to the generation of the second phase Zr V_0.24Co_1.76 with catalytic effect.The hydrogen absorption plateau pressure of ZrCo alloy increases and the hydrogen absorption formation enthalpy（35）H reduces,which effectively improves the hydrogenation performance of ZrCo alloy.The cycle stability and anti-disproportionation performance of ZrCo alloy are improves after doping V.2.Zr_0.8Ti_0.2Cr_xCo_1-x（x=0,0.05,0.1,0.15）samples consist of ZrCo and two laves phases（Co Zr₂ and Ti Cr₂ phases）.The lattice constant and cell volume of Zr_0.8Ti_0.2Co alloy increase with the increase of Cr content.Moreover,Cr doping produces a Ti Cr₂ phase that strongly catalyzes the conversion of H₂ to H,so the activation performance of Zr_0.8Ti_0.2Co alloy is improved.The hydrogen absorption/desorption time is shortened and the dehydrogenation activation energy is reduced.However,the dehydrogenation capacity of Cr-doped samples decreases since the addition of Cr increases the hydrogen residue in the hydride.In addition,Cr doping has little effect on the anti-disproportionation property of Zr_0.8Ti_0.2Co alloy.3.Zr_0.8Hf_xTi_0.2-xCo（x=0,0.05,0.1,0.15）alloys consist of ZrCo and Hf Co phases.The lattice constant and cell volume increase after Hf doping.Hf doping can coordinate hydrogen diffusion to accelerate the dissociation of hydrogen molecules into hydrogen atoms,so the initial activation kinetics is enhanced and the dehydrogenation time is shortened.What’s more,the dehydrogenation activation energy is reduced after doping Hf.The cyclic stability of Hf-doped samples is enhanced on the basis of maintaining the anti-disproportionation property of Zr_0.8Ti_0.2Co alloy.