Effect of α-Al 2O 3 particles on the electrochemical codeposition of Co–Ni alloys from sulfamate electrolytes

Abstract

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 spectroscopy (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.