Effects and mechanism of Ti, Ni, Sc, Fe substitution on the thermal stability of zirconium cobalt–hydrogen system

• Crystallographic parameters of ZrCo alloys and their hydrides with Ti, Sc, Ni, Fe substituted were investigated.
• Thermodynamic parameters were calculated for ZrCo alloys with Ti, Sc, Ni, Fe substituted.
• Kinetics of disproportionation of ZrCo alloys with Ti, Sc, Ni, Fe substitution were studied.
• Explained the increasing ability of anti-disproportionation of ZrCo with Ti substituted.

ZrCo alloys with Ti, Sc, Ni, Fe substitution (Zr0.8Ti0.2Co, Zr0.8Sc0.2Co, ZrCo0.8Ni0.2, ZrCo0.8Fe0.2) were prepared via arc-melting method, and then products before and after hydrogenation were characterized by X-ray diffraction. Results showed that the crystal structure of ZrCo alloys substituted with Ti, Sc, Ni and Fe substitution formed cubic phase, and the lattice parameters of ZrCo alloys and these hydrides decreased with Ti substituted, while increased with Sc, Ni, Fe substitution. The dehydrogenation pressure composition isotherms for all these alloys were obtained in the temperature range between 523 K and 623 K, and it was found that desorption plateau pressure increased in order of ZrCo0.8Fe0.2 < ZrCo < Zr0.8Sc0.2C < ZrCo0.8Ni0.2 < Zr0.8Ti0.2Co. Meanwhile, the enthalpy and entropy change for hydrogen desorption were calculated. And the kinetics of hydrogen-induced disproportionation in desorption mode for all these alloys was also investigated. Results demonstrated that the rate and extent of disproportionation of ZrCo alloys decreased with Ti substitution, while increased with Sc, Ni and Fe substitution. Thermal analytical method (DSC) was carried out to investigate the mechanism of thermal stability change of ZrCo alloys after Ti, Sc, Ni, Fe substitution. It could be inferred that the effect of element substitution on disproportionation of ZrCo alloys was caused by the radius change of hole sizes of hydrogen occupation sites.