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

In order to improve the activation properties of the Zr-based hydrogen storage alloy electrode, the ball-milling process is applied to the Zr-based alloy using the Ti-based alloy powder as a surface modifier. While the Zr-based alloy electrode is not fully activated before 50 cycles, the bah-milled Zr-based alloy electrode using Ti-based alloy as a surface modifier is fully activated within only 4 cycles. In order to analyze the strikingly improved activation characteristics after ball-milling, the microstructure of ball-milled alloy is examined by TEM, SEM and EDS. It is observed that there is a surface alloying region at the contact points between the two alloy powders from the TEM bright-field image. Furthermore. the local quantitative analysis by EDS clearly reveals that the atomic concentration of the constituting elements in the surface alloying region is gradually changed between the two alloy powders. From the above results, it is suggested that the high kinetic energy applied in the ball-milling process causes cold-welding or surface alloying at the points of impact where Zr-based alloy particles collide with Ti-based alloy particles by the action of steel balls at high speed. The SEM analysis demonstrates that the particle size is decreased as the ball-milling time increases, which implies an increase in the surface area of Zr-based alloy particles touching Ti-based alloy particles. Eventually, it can be suggested that Ti-alloy powder serves as a window for hydrogen to penetrate into the Zr-based alloy, which lends to easy absorption-desorption of hydrogen and also to improvement in the activation properties of the Zr-based alloy electrode. (C) 1999 Elsevier Science S.A. All rights reserved.