| Because of its excellent hydrogen storage properties and safety characteristics,ZrCo alloy has been selected as an important candidate material for rapid storage and delivery of hydrogen isotopes by the ITER team.However,since the hydrogen-induecd disproportionation of ZrCo during the hydrogen absorption/desorption processes will cause serious degradation of hydrogen storage properties,disproportionation is considered to be the biggest obstacle on the way of its wide application.Besides,the hydrogen storage kinetics of ZrCo is slower than that of DU,which is also a crictical factor hindering its wide application.Although the substitution of Ti element has improved the anti-disproportionation property of ZrCo effectively,the comprehensive hydrogen storage properties of Zr0.8Ti0.2Co still can not fully meet the needs of practical application,Therefore,it is of great significance to further improve the anti-disproportionation property and kinetic hydrogen storage properties of ZrCo-based alloys.The modifications of microstructure and kinetics of hydrogen absorption/desorption have been focused in this study.Thus,the method of mechanical ball milling has been introduced into the property modifications of ZrCo alloy and Zr0.8Ti0.2Co alloy.Firstly,ZrCo alloy and Zr0.8Ti0.2Co alloy powders have been prepared by ball milling.Subsequently,the effects of ball milling on the hydrogen absorption/desorption kinetics and microstructures of ZrCo alloy and Zr0.8Ti0.2Co alloy have been specifically studied.Meanwhile,the disproportionation kinetics mechanisms of ball milled ZrCo alloy and Zr0.8Tio.2Co alloy have been discussed through kinetic model analysis.This study can provide valuable considerations for further improving the hydrogen storage properties of ZrCo-based alloys.The main contents of this study are summarized as follows:1.The effects of ball milling on the hydrogen sorption kinetics and microstructure of ZrCo alloyKinetic measurements show that the hydrogen absorption rate as well as capacity decreases and the hydrogen desorption rate increases for ZrCo by increasing the ball milling time.After ball milling,the disproportionation rate of ZrCo is enhanced,whereas the disproportionation extent is reduced.It is found from XRD results that the lattice parameter of ZrCo gradually decreases from 3.197 A to 3.188 A when the ball milling time extends from 0 h to 8 h,which is mainly responsible for the disproportionation behavior.Meanwhile,SEM and FIB images demonstrate that the morphology of ZrCo obviously changed after ball milling,which is closely related to the hydrogen sorption kinetics.Furthermore,EDS results reveal that the distribution of Zr and Co elements plays an important role in the disproportionation rate as well as the kinetic mechanism.Kinetic model analysis suggests that the disproportionation of ZrCo should be homogeneous nucleation and one dimensional growth controlled by diffusion.However,the detailed rate limiting modes for nucleation and growth processes may vary according to different ball milling time.This work suggests reduced lattice parameter and uniform distribution of Zr and Co elements should be favorable to improve the anti-disproportionation property of ZrCo.2.The effects of ball milling on the hydrogen sorption kinetics and microstructure of Zr0.8Ti0.2Co alloyKinetic measurements show that the hydrogenation rate and capacity of Zr0.8Ti0.2Co decrease with increasing the ball milling time.However,the dehydrogenation rate accelerates as the ball milling time increases.Meanwhile,reacting at 500 ? for 400 min,the disproportionation rate and extent of Zr0.8Ti0.2Co are enhanced with increasing the ball milling time.Besides,the disproportionation kinetics is clearly inclined to be linear with time at 500 ?.It is found from XRD results that the lattice parameter of Zr0.8Ti0.2Co gradually decreases from 3.164 A to 3.153 A when the ball milling time extends from 0 h to 8 h,which is mainly responsible for the hydrogen absorption/desorption behaviors.In addition,SEM images demonstrate that the morphology of Zr0.8Ti0.2Co has obviously changed after ball milling,which is closely related to the hydrogen absorption kinetics.Meanwhile,HRTEM images show that a large number of disordered microstructures including amorphous regions and defects exist after ball milling,which also plays an important role in hydrogen sorption performances.Furthermore,EDS results reveal that the distribution of elements on the surface of Zr0.8Tio.2Co affects obviously the disproportionation rate as well as the kinetic mechanism.Kinetic model analysis suggests that the initial stage of disproportionation of Zr0.8Ti0.2Co should be a surface step controlling reaction.This work suggests that if Zr0.sTi0.2Co is expected to not only own fast hydrogen sorption kinetics but also have good anti-disproportionation,it may be a good way to prepare Zr0.8Ti0.2Co as fine powder with smaller lattice parameter,uniform element distribution and orderly microstructure. |
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