Effect of vanadium on hydrogenation of mechanically treated zirconium-containing alloys

Abstract

UDC 053.082.75Mechanical treatment of powders with additions of nickel to serve as a catalyst of the chemical adsorption of hydrogen is used to activate the hydrogenation of zirconium-containing alloys. Polarization curves are plotted to study the kinetics of electrochemical release and adsorption of hydrogen on zirconium alloys in which aluminum is replaced by vanadium. It is shown that the replacement is efficient and the maximum hydrogen capacity depends on the optimum concentration of the catalyst in the alloy.Zirconium-based alloys of AB 2 type (Laves phases) are promising materials for negative electrodes of nickel-metal-hydride accumulators. However, these alloys have numerous drawbacks that restrict their widespread use [1]. The major drawbacks include a need for additional treatment and activation of the alloys commonly covered with a thin film of oxides and hydroxides that prevent the chemical adsorption of hydrogen on their surface.To activate zirconium-based alloys, we used mechanical treatment (high-energy grinding) with nickel powder additions to activate the chemical adsorption of hydrogen in the hydrogenation process. To form a multicomponent material (effective hydrogen accumulator), the optimal concentration of a catalyst needs to be determined for hydrogen to reach the maximum concentration in the sample over a specific period of time. In addition, the sample should have a microstructure to ensure the maximum alloy-catalyst interface. To this end, zirconium-based alloy powder was ground using a DDR-GM 9458 vibrator ball mill for 15 min and then for 1 h with nickel additions (10, 20, and 50% of the electrode weight). The total weight of the active alloy component was 0.1 g.Electrochemical analyses of the samples were carried out at 25°C in a glass three-electrode cell with cathode and anode chambers separated in 30% KOH solution using a PI-50-1.1 potentiostat at a potential sweep rate of 2 mV/sec. The samples were cold-pressed from pallets (8 mm in diameter) in a nickel mesh. All potentials in this paper relate to a reference oxide-mercury electrode.Electrodes made of zirconium-based alloy with additions of chromium, manganese, and aluminum or vanadium were charged with a current of 200 mA for 5 h and discharged in nonequilibrium conditions with a current from 10 to 0.5 mA to reach a potential of 0.6 V.For a detailed analysis, we chose two alloys that slightly differed in chromium concentrations, one alloy containing aluminum and the other vanadium (Table 1). In both cases, nickel forms additional phases with zirconium [1]. The main phase component is a C 15 cubic structure of MgCu 2 type. Along with this phase, the test samples contain a substantial amount of a C 14 hexagonal phase of MgZn 2 type and secondary phases such as Zr 7 Ni 10 and Zr 9 Ni 11 intermetallides, which agrees with the phase diagram provided in [2].After the electrodes made of alloys 1 and 2 were ground and pressed, respective polarization curves were plotted to assess their electrochemical characteristics in situ and select...