Hydrogen storage characteristics of Ti₄₅Zr₃₈Ni _17-xCo_x (x = 4, 8) alloy and quasicrystal powders produced by mechanical alloying

The effect of substitution of Co for Ni on hydrogen storage characteristics of Ti-Zr-Ni/Co powders (Ti₄₅Zr₃₈Ni_{17- x}Co_x (x = 4, 8)) produced by mechanical alloying (MA) was investigated. The final product after MA was amorphous for all the powders, but subsequent annealing caused the formation of the icosahedral quasicrystal (i) phase with a Ti₂Ni type crystal and a C14 like Laves phases. The amount of i-phase decreased, and reversely those of Ti₂Ni and the Laves phases increased with increasing the amount of Co. After hydrogenation at 573 K and at an initial hydrogen pressure of 3.8 MPa, the maximum hydrogen concentration for the annealed powders reached was about 58 at%, and all the phases in the powders transformed to metallic hydrides ((Zr,Ti)H₂, Ni(Zr,Ti)H₃ and Co(Zr,Ti)H₃). Because of the formation of several hydrides, accelerated hydrogen desorption occurred at several temperatures. The activation energies for hydrogen desorption varied from about 70 kJ/mol to 180 kJ/mol.