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Fig. 3 Potentiodynamic stripping voltammograms of a zinc film electrodeposited from electrolyte containing 0.2 m ZnSO, + 0.5 Mm Na,SO, at pH 2.5 at different rotation speeds

Figure 3 Potentiodynamic stripping voltammograms of a zinc film electrodeposited from electrolyte containing 0.2 m ZnSO, + 0.5 Mm Na,SO, at pH 2.5 at different rotation speeds

Related Figures (14)

During alloy deposition at high current densities, the pH near the electrode surface is much higher than at the bulk due to the parasitic hydrogen evolution reaction.® Hence, a study of the equilibrium formation of various hydroxide species in the bath was carried out in order to identify the different com- ponents that exist in a solution at different pH levels. The
During alloy deposition at high current densities, the pH near the electrode surface is much higher than at the bulk due to the parasitic hydrogen evolution reaction.® Hence, a study of the equilibrium formation of various hydroxide species in the bath was carried out in order to identify the different com- ponents that exist in a solution at different pH levels. The
Fig. 2 Solution equilibrium concentrations of a Zn—Ni plating bath as a function of pH
Fig. 2 Solution equilibrium concentrations of a Zn—Ni plating bath as a function of pH
Fig. 4 Potentiodynamic stripping voltammograms of nickel film electrodeposited from electrolyte containing 0.5 mM NiSO,+0.5 M Na,SO,, pH 2.5, v = 30 mV s~ at different rotation speeds
Fig. 4 Potentiodynamic stripping voltammograms of nickel film electrodeposited from electrolyte containing 0.5 mM NiSO,+0.5 M Na,SO,, pH 2.5, v = 30 mV s~ at different rotation speeds
Fig. 5 Potentiodynamic stripping voltammograms recorded on a fixed disc electrode from electrolytes containing 0.5 M NiSO, + 0.2 M ZnSO, + 0.5 M Na,SO,, pH 2.5 at different sweep rates
Fig. 5 Potentiodynamic stripping voltammograms recorded on a fixed disc electrode from electrolytes containing 0.5 M NiSO, + 0.2 M ZnSO, + 0.5 M Na,SO,, pH 2.5 at different sweep rates
Fig. 6 Potentiodynamic stripping voltammograms obtained in the same electrolyte as in Fig. 5 for different rotation speeds, v = 30 mV ev7l Zn). The second peak which occurs at — 0.575 V us. SCE cor- responds to dissolution of zinc from the y phase (zinc content varies between 76 and 87%). The small difference in the chemical potential of zinc in the two phases is due to the small difference in the nickel content in the alloy. Since the electro- deposition of zinc is under mass transfer control??-?’ one can expect that at a constant sweep rate, an alloy rich in zinc will be electrodeposited and subsequently stripped at higher rota- tion rates. Indeed this phenomenon was observed in Fig. 6
Fig. 6 Potentiodynamic stripping voltammograms obtained in the same electrolyte as in Fig. 5 for different rotation speeds, v = 30 mV ev7l Zn). The second peak which occurs at — 0.575 V us. SCE cor- responds to dissolution of zinc from the y phase (zinc content varies between 76 and 87%). The small difference in the chemical potential of zinc in the two phases is due to the small difference in the nickel content in the alloy. Since the electro- deposition of zinc is under mass transfer control??-?’ one can expect that at a constant sweep rate, an alloy rich in zinc will be electrodeposited and subsequently stripped at higher rota- tion rates. Indeed this phenomenon was observed in Fig. 6
Fig. 7 Composition of a dc plated Zn—-Ni alloy from the same elec- trolyte as in Fig. 5 as a function of the applied current density at several electrode rotation speeds (wt.%) Fig. 8 shows the composition of zinc—nickel films plated on the rotating disc electrodes as a function of the average current density for different rotation speeds in the pc mode. The deposition was carried out using pulse plating with a duty cycle of 0.5 and frequency of 80 Hz at 50°C. The composition of the electrolyte was the same as in Fig. 7. At lower average current densities, the zinc deposition is under kinetic control
Fig. 7 Composition of a dc plated Zn—-Ni alloy from the same elec- trolyte as in Fig. 5 as a function of the applied current density at several electrode rotation speeds (wt.%) Fig. 8 shows the composition of zinc—nickel films plated on the rotating disc electrodes as a function of the average current density for different rotation speeds in the pc mode. The deposition was carried out using pulse plating with a duty cycle of 0.5 and frequency of 80 Hz at 50°C. The composition of the electrolyte was the same as in Fig. 7. At lower average current densities, the zinc deposition is under kinetic control
Fig. 8 Zinc composition profiles as a function of current density at various rotation speeds for pc mode
Fig. 8 Zinc composition profiles as a function of current density at various rotation speeds for pc mode
Fig.9 Zinc composition profiles as a function of current density at various rotation speeds for pr mode
Fig.9 Zinc composition profiles as a function of current density at various rotation speeds for pr mode
Fig. 10 Effect of nonyl phenyl polyethylene oxide on the alloy com- position tial to be extended in either a cathodic or anodic direction without creating conditions for concentration depletion of the electroactive species at the interface. This is clearly seen in Fig. 10, where for the pc mode, the hump of the zinc concentration profile shifts to a more cathodic current indicating that the mass transfer limitations for zinc reduction are delayed. For the pr mode, the presence of 2 g 17! of nonyl phenyl poly- ethylene oxide in the electrolyte reduces the zinc content in the alloy due to the additive surface-coverage effect. In this case the hydrogen ion concentration is less depleted during ¢,,, because of the reduction in available surface area for hydro- gen evolution reaction. Higher proton concentration during the t,¢, period and a smaller surface reaction area decrease the rate of the hydrogen oxidation reaction which causes, for a specific applied average current density, the electrode to be
Fig. 10 Effect of nonyl phenyl polyethylene oxide on the alloy com- position tial to be extended in either a cathodic or anodic direction without creating conditions for concentration depletion of the electroactive species at the interface. This is clearly seen in Fig. 10, where for the pc mode, the hump of the zinc concentration profile shifts to a more cathodic current indicating that the mass transfer limitations for zinc reduction are delayed. For the pr mode, the presence of 2 g 17! of nonyl phenyl poly- ethylene oxide in the electrolyte reduces the zinc content in the alloy due to the additive surface-coverage effect. In this case the hydrogen ion concentration is less depleted during ¢,,, because of the reduction in available surface area for hydro- gen evolution reaction. Higher proton concentration during the t,¢, period and a smaller surface reaction area decrease the rate of the hydrogen oxidation reaction which causes, for a specific applied average current density, the electrode to be
Fig. 11 Pulse potential responses at different applied current den- sities during t,, To study the influence of rotation speed of the electrode on the morphology of the electrodeposited zinc-nickel alloys,
Fig. 11 Pulse potential responses at different applied current den- sities during t,, To study the influence of rotation speed of the electrode on the morphology of the electrodeposited zinc-nickel alloys,
Fig. 12 EDS spectrum of samples taken at an average current density of 50 A dm~? on a rotating copper disc electrode and at rota- tion speeds of (a) 100 and (b) 1200 rpm
Fig. 12 EDS spectrum of samples taken at an average current density of 50 A dm~? on a rotating copper disc electrode and at rota- tion speeds of (a) 100 and (b) 1200 rpm
Fig. 13 Metallographic pictures of the electrodeposited Zn-Ni alloy, magnification x 100. (a) Dendritic growth in the absence of nonyl phenyl polyethylene oxide, I = 12 A dm~?; (b) morphology of depos- ited zinc-nickel alloy in the presence of 2 g 1~' nonyl phenyl poly- ethylene oxide, J = 12 A dm ?; (c) interference metallographic picture of the same place as in Fig. 13(b); (d) interference metallographic picture obtained at optimal plating conditions using a current density of I= 15 Adm? and 2 g1"‘ nonyl phenyl polyethylene oxide. The influence of the organic additive on the morphology of the electrodeposited zinc-nickel alloys was studied using inci- dent light microscopy and incident interference microscopy. The zinc-nickel alloy was deposited using the sulfate electrolyte + 2 g1~1 nonyl phenyl polyethylene oxide, pH 2.5 and T = 50°C. The results obtained for zinc—nickel electro- deposition are summarized in Fig. 13. The zinc—nickel alloy shows dendritic crystal growth when electrodeposited from
Fig. 13 Metallographic pictures of the electrodeposited Zn-Ni alloy, magnification x 100. (a) Dendritic growth in the absence of nonyl phenyl polyethylene oxide, I = 12 A dm~?; (b) morphology of depos- ited zinc-nickel alloy in the presence of 2 g 1~' nonyl phenyl poly- ethylene oxide, J = 12 A dm ?; (c) interference metallographic picture of the same place as in Fig. 13(b); (d) interference metallographic picture obtained at optimal plating conditions using a current density of I= 15 Adm? and 2 g1"‘ nonyl phenyl polyethylene oxide. The influence of the organic additive on the morphology of the electrodeposited zinc-nickel alloys was studied using inci- dent light microscopy and incident interference microscopy. The zinc-nickel alloy was deposited using the sulfate electrolyte + 2 g1~1 nonyl phenyl polyethylene oxide, pH 2.5 and T = 50°C. The results obtained for zinc—nickel electro- deposition are summarized in Fig. 13. The zinc—nickel alloy shows dendritic crystal growth when electrodeposited from
Fig. 14 SEMs of an alloy deposited from a bath containing 0.5 M NiSO, + 0.2 M ZnSO, + 0.5 M Na,SO, + 2 g17! nonyl phenyl poly- ethylene oxide, pH 2.5, T = 50°C (a) using the galvanostatic pulse technique, average current density I,, = —60 A dm~? at w = 500 rpm; (b) using the galvanostatic pulse technique, average current density I,, = —40 A dm~?, (c) using the galvanostatic pulse reverse technique, I,, = —60 A dm~, i, = 12 A dm~? at w = 500 rpm; and ({d) using the galvanostatic pulse reverse technique, J,,= —40 A dm~?,i,= 8 Adm? at w = 500 rpm
Fig. 14 SEMs of an alloy deposited from a bath containing 0.5 M NiSO, + 0.2 M ZnSO, + 0.5 M Na,SO, + 2 g17! nonyl phenyl poly- ethylene oxide, pH 2.5, T = 50°C (a) using the galvanostatic pulse technique, average current density I,, = —60 A dm~? at w = 500 rpm; (b) using the galvanostatic pulse technique, average current density I,, = —40 A dm~?, (c) using the galvanostatic pulse reverse technique, I,, = —60 A dm~, i, = 12 A dm~? at w = 500 rpm; and ({d) using the galvanostatic pulse reverse technique, J,,= —40 A dm~?,i,= 8 Adm? at w = 500 rpm
Fig. 15 SEM spectrum of an alloy deposited using the pulse reverse technique from a bath containing 0.5 M NiSO, + 0.2 M ZnSO, + 0.5 M Na,SO,, pH 2.5, T = 50°C, w = 500 rpm; (a) in the absence of nonyl phenyl polyethylene oxide, average current density J, = —-40 A dm~?, i, = 8 A dm~? and (b) in the presence of 2 g 17+ nonyl phenyl polyethylene oxide, average current density, 1, = —40 A dm~?, i, = 8 A dm~
Fig. 15 SEM spectrum of an alloy deposited using the pulse reverse technique from a bath containing 0.5 M NiSO, + 0.2 M ZnSO, + 0.5 M Na,SO,, pH 2.5, T = 50°C, w = 500 rpm; (a) in the absence of nonyl phenyl polyethylene oxide, average current density J, = —-40 A dm~?, i, = 8 A dm~? and (b) in the presence of 2 g 17+ nonyl phenyl polyethylene oxide, average current density, 1, = —40 A dm~?, i, = 8 A dm~
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