Pulse Current Deposition

The electrodeposition process can either occur under potential (potentiostatic deposition) or current (galvanostatic deposition) control. In practice, the common approach is to control the deposition flux (current) in order to obtain the deposit with desired thickness and properties. The electrodeposition under galvanostatic control can be executed as either the constant current process or using some more complex currenttime function profile. In the latter case, the electrodeposition process is commonly called the pulse current deposition and it has been widely used in industrial and academic applications. The typical pulse current function has the simple on/off profile shown in Fig. 11.  

The successful application of this pulse current function is dependent on the proper determination of the pulse time toa, rest time roff and magnitude of the pulse current densityjpuise. The optimum duration of the pulse current stage should be such that no limitations for metal ion transport (A/ ) towards the electrode-electrolyte interface is encountered. Finding these conditions requires the mathematical treatment of the 

The exact mathematical solution of Eq. (16) is somewhat cumbersome, presented in the form of a Fourier series expansion/ For practical application, it is more convenient to consider the approximate solutions that are dependent on the value of the term a t where a is defined as  

The evaluation of this term is dependent on an appropriate estimate of Df m+ and 5 and for many practical applications, these parameters can be estimated or measured experimentally. There are two fimiting situations which define the shape of the approximate solution for Eq. (16). The first one, a t 0.2, the approximate solution for the concentration-time profile of the metal ions at the electrode-solution interface is given as 

In both equations, and stand for the concentration of metal ions in the 

---

Figure 5.15 shows that the corrosion current is one order of magnitude smaller for the pulse current-deposited (pc) Zn-Ni-Cd (7% Cd) sacrificial coatings when compared to the direct current-deposited (dc) Zn-Ni-Cd with 22% Cd in the alloy [36]. The corrosion rates of pulse current-deposited Zn-Ni-Cd sacrificial coatings that contain 7% and 3% Cd were 0.49 and 1.03 mpy, respectively much lower than the 2.87 mpy observed for the direct current-deposited Zn-Ni-Cd alloy with 22% Cd in the alloy. 

Employ pulse current deposition method Maximize amount of zinc electrodeposited from electrolyte solution Need to identify optimal deposition conditions, followed by electrochemical tests to characterize improvements in system efficiency... 

Fig. 15. SEM micrographs of Cu-Al deposits containing 5 a/o A1 that were prepared with different plating techniques at zavg = 0.70 mA in the 60.0 m/o AlCl3-EtMeImCl melt at room temperature (a) DC plating (b) superimposed-pulse current plating, ip = 1.254 mA, ton = 1 s, is = 0.509 mA, ts = 3 s, and (c) reverse-pulse current plating, ip = 1.254 mA, ton = 1 s, ir = 0.43 mA, tr = 0.5 s. The thickness of each deposit is approximately 5 pm based on a compact layer of pure copper. Reproduced from Zhu et al. [103]...

The approaches used for preparation of inorganic nanomaterials can be divided into two broad categories solution-phase colloidal synthesis and gas-phase synthesis. Metal and semiconductor nanoparticles are usually synthesized via solution-phase colloidal techniques,4,913 whereas high-temperature gas-phase processes like chemical vapor deposition (CVD), pulsed laser deposition (PLD), and vapor transfer are widely used for synthesis of high-quality semiconductor nanowires and carbon nanotubes.6,7 Such division reflects only the current research bias, as promising routes to metallic nanoparticles are also available based on vapor condensation14 and colloidal syntheses of high-quality semiconductor nanowires.15... 

Fig. 8.1 The crystallite size dependence of the pulsed current density for gold deposits deposited from a commercial sulfite bath without any additives [29].

Mass transport plays an important role in pulsed metal deposition. On the one hand it limits the maximum rate of deposition and influences the structure and properties of deposits. On the other hand it effects the macrothrowing and microthrowing power. Under dc conditions, the maximum deposition rate is given by the limiting current density, fg, where the metal ion concentration... 

Figure 6.7 Influence of pulse parameters on deposit morphology for copper deposition from a copper sulfete/sulfuric acid electrolyte [6.102]. p pulse current density ipj limiting pulse current density i average current density jj limiting current density under dc conditions.

Electrodeposition using pulsed currents is known as pulse plating. The pulsed currents can be unipolar (on-off) or bipolar (current reversal). Pulses can be used along or be superimposed on a DC feed. By using the bipolar pulse, metal deposition occurs in the cathodic pulse period, with a limited amount of metal being... 

Several studies were published in recent years on electrodeposition of W-Co alloys. Donten and Stojek used pulse electrodeposition to increase the tungsten content in amorphous Co-W alloys. These alloys contained, in addition, small amounts of boron or phosphorous. They showed that, if a symmetrical current pulse was used, the tungsten content in the alloys reached a maximum value of 41.4 at.%, which is higher than in the case of direct current deposition. However, when using any asymmetrical... 

Meyer claimed that both Ni and Co seem to stabilize the presence of ReO4 anions near the cathode. He proposed that there was a catalytic effect of Ni on the decomposition of ReOT. Sadana and Wang studied the effects of bath composition, pH, temperature, stirring, current density and pulsed current on the characteristics of Au-Re deposits, which contained 0.25-63.4 wt.% Re. The solution consisted of citric acid and potassium perrhenate. The Re-content of the deposit was found to increase markedly as a result of stirring, increase in current density, decrease in bath pH and temperature, and the use of pulsed current. In addition, the as-deposited alloys exhibited XRD patterns of supersaturated solid... 

Hydroxyapatite substituted with metabolic elements such as Sr, Mg and Zn were deposited by pulsed current ECD technique (Gopi et al., 2014). The coatings imparted sufficient corrosion resistance to the Ti alloy substrate and showed potential for suitable cell attachment and proliferation. Addition of single-walled carbon nanotubes (SWCTs) to electrochemically deposited hydroxyapatite increased the coating bond strength to 26 MPa, an improvement of about 70% over that of pure hydroxyapatite (Pei et al., 2014). 

---