Effect of additional catalytic phases imposed by sintering on the hydrogen absorption behavior of AB2 type Zr-based alloys

The effect of microsegregated secondary phases of the Zr–Ni system on the electrochemical hydrogen absorption of a Laves phase AB2 type alloy of composition Zr0.9Ti0.1(Ni0.5Mn0.25Cr0.20V0.05)2 is studied. The activation process and discharge capacity of electrodes containing this alloy in both as-melted and annealed conditions are monitored in alkaline media along charge–discharge cycling. The as-melted material, containing microsegregated secondary phases formed during solidification, shows a higher discharge capacity and lower charging–discharging overpotentials than the annealed material. This effect is ascribed to the solubilization of the secondary catalytic phases due to the thermal treatment. To study the possibility of customizing the electrochemical properties of alloys by imposing secondary catalytic phases in a controlled way, similar tests are also carried out on a sintered composite material elaborated from powder of the annealed alloy, mixed with powder of a separately melted alloy of the Zr–Ni system, containing secondary catalytic phases, mainly Zr7Ni10 and Zr9Ni11. A sintered composite based on an alloy with low secondary catalytic phase content is also elaborated and tested for comparison. The selected base alloy is Zr(Cr0.5Ni0.5)2 in annealed condition, where a major AB2 phase with a minimum content of secondary catalytic phases is expected. The hydrogen absorption–desorption behavior for the different cases is discussed and correlated with the metallurgical characterization of the materials.