Effects of annealing treatment on phase structures, hydrogen absorption-desorption characteristics and electrochemical properties of a V3TiNi0.56Hf0.24Mn0.15Cr0.1 alloy

The effects of annealing treatment on the phase structures, hydrogen absorp tion-desorption characteristics and electrochemical properties of the V3TiN i0.56Hf0.24Mn0.15Cr0.1 alloy have been studied. It is found that both the a s-cast and annealed alloys consist of a main phase with b.c.c. structure an d a C14-type secondary phase with hexagonal structure. With increasing anne aling temperature, the lattice parameters of two phases decrease and the vo lume fraction of the main phase increases slightly. The present results ind icate that annealing treatment decreases the maximum hydrogen desorption ca pacity, which could be attributed to a decrease in stability of ahoy hydrid e due to the decrease in cell volume of the alloy phases. Furthermore, incr easing annealing temperature decreases the high rate capability and deterio rates the durability of the alloy electrode in the alkaline electrolyte dur ing charging-discharging cycles, which would be associated with the change in composition of the secondary phase and the grain growth of the main phas e. (C) 2000 Elsevier Science S.A. All rights reserved.