Effect of annealing treatment on the anti-pulverization and anti-corrosion properties of La_0.67Mg_0.33Ni_2.5Co_0.5 hydrogen storage alloy

Abstract

The La_0.67Mg_0.33Ni_2.5Co_0.5 hydrogen storage alloy was prepared by the vacuum intermediate frequency induction furnace followed by annealing treatment. The pulverization degree of both the as-cast and annealed alloy powders after gaseous hydriding and dehydriding cycle was investigated and the discovery was that annealing treatment could hardly ameliorate their anti-pulverization ability. The element content of La, Mg, Ni and Co existing in electrolyte before and after the electrochemical cycles by using ICP-AES technology was also analyzed and it showed that a large amount of La and Mg were dissolved in the electrolyte, but the amount of dissolution for La and Mg significantly declined when the alloy was annealed. The XRD analysis revealed that all the alloys consisted of two main phases AB₃ and AB₂ and a residual phase AB₅ while annealing treatment made the AB₂ phase decrease slightly. Furthermore, the anti-corrosion abilities of various elements in different phases of the as-cast and annealed alloy samples were studied by analyzing the element (La, Mg, Ni, Co) change with the corrosion time in phases AB₃ and AB₂ by means of EDS. It turned out that the element of La was mainly corroded out from the phase AB₂ while not easily from the phase AB₃. However, the element of Mg was both easily corroded out from the phases AB₂ and AB₃, but the corrosion was more obvious in the phase AB₃. Therefore, annealing improved the anti-corrosion performances of La and Mg in the phase AB₂.