The activation characteristics of a Zr-based hydrogen storage alloy electrode surface-modified by ball-milling process

摘要

In order to improve the activation properties of theZr-based hydrogen storage alloy electrode, the ball-milling processis applied to the Zr-based alloy using the Ti-based alloy powder asa surface modifier. While the Zr-based alloy electrode is not fullyactivated before 50 cycles, the ball-milled Zr-based alloy electrodeusing Ti-based alloy as a surface modifier is fully activated withinonly 4 cycles. In order to analyze the strikingly improved activationcharacteristics after ball-milling, the microstructure of ball-milledalloy is examined by TEM, SEM and EDS. It is observed that thereis a surface alloying region at the contact points between the twoalloy powders from the TEM bright-field image. Furthermore, thelocal quantitative analysis by EDS clearly reveals that the atomicconcentration of the constituting elements in the surface alloyingregion is gradually changed between the two alloy powders. Fromthe above results, it is suggested that the high kinetic energyapplied in the ball-milling process causes cold-welding or surfacealloying at the points of impact where Zr-based alloy particlescollide with Ti-based alloy particles by the action of steel balls athigh speed. The SEM analysis demonstrates that the particle size isdecreased as the ball-milling time increases, which implies anincrease in the surface area of Zr-based alloy particles touching Ti-based alloy particles. Eventually, it can be suggested that Ti-alloypowder serves as a window for hydrogen to penetrate into the Zr-based alloy, which leads to easy absorption-desorption of hydrogenand also to improvement in the activation properties of the Zr-based alloy electrode.