Effect of α-Al_2O_3 particles on the electrochemical codeposition of Co-Ni alloys from sulfamate electrolytes

摘要

The effect of α-Al_2O_3 particles on the electrochemical codeposition behaviour of Co-Ni alloys from sulfamate electrolyte was investigated by codeposition experiments, zeta potential and electrochemical methods. The results indicate that the presence of Al_2O_3 particles in Co-Ni sulfamate electrolytes contributes to the preferential codeposition of Co. Moreover, increasing Co~(2+) concentration also can enhance the codeposition of Al_2O_3 particles in Co-Ni alloy matrix. Zeta potential measurements confirm that Co~(2+) has a stronger tendency to adsorb on Al_2O_3 particles surface than Ni~(2+) does in sulfamate electrolytes. Steady-state polarization and electrochemical impedance spec-troscopy (EIS) show that the effect of Al_2O_3 particles on electrochemical codeposition behaviour of Co-Ni alloy in different Co~(2+)/Ni~(2+) ratio electrolytes (1:5 and 5:1) is quite contrary. In nickel-rich electrolytes (Co~(2+)/Ni~(2+) = 1:5), the Al_2O_3 particles cause a negative shift in reduction potential and an increase of charge transfer resistance. However, in cobalt-rich electrolytes (Co~(2+)/Ni~(2+) = 5:1), Al_2O_3 particles lead to a positive shift of reduction potential and reduce the charge transfer resistance. Moreover, in EIS, besides one capacitive loop at high frequency and one inductive loop at low frequency, the introduction of Al_2O_3 particles leads to a further inductive loop at low frequency. According to simulated results of EIS, an electrochemical codeposition mechanism of Al_2O_3 particles with Co-Ni alloys is presented and in good agreement with the experimental results.