Current density electrodeposition

The fundamental basis of the sonoelectrochemical technique to form nanoparticles is massive nucleation using a high current density electrodeposition pulse (ca. 150-300 mA cm ), followed by removal of the deposit from the sonoelectrode by the sonic pulse. Removal of the particles from the electrode before the next current pulse prevents crystal growth. Overall there are many experimental variables involved in sonoelectrochemical deposition electrolyte composition and temperature, electrodeposition conditions including current density (le), pulse-on time (te(on)) and ratio between pulse-on time and pulse-off time (te(off)) (the duty cyde) sonic probe conditions sonic power (Is), sonic pulse parameters, fs(on) and ts(off). 

Schaltin, S., Brooks, N.R., Stappers, L., Van Hecke, K., Van Meervelt, L., Binnemans, K. and Fransaer, J., High current density electrodeposition from silver conplex ionic liquids, Phys. Chem. Chem. Phys. 14 (5), 1706-1715 (2012). 

If the applied current density is reduced when a tin anode has been made passive in alkaline solution with the formation of a brown him and evolution of oxygen, the surface him changes to one of yellow colour and dissolution of tin as stannite ions proceeds freely . This effect is exploited in the electrodeposition of tin from sodium or potassium stannate solutions. 

An electrodeposited coating is never, in practice, completely uniform in thickness. The actual thickness of metal deposited at a particular point in a given time is dependent on the current density (i.e. the current per unit area) at that point, and the current density is not uniform over the whole surface... 

At the start the cathode is invariably a metal different from that to be deposited. Frequently, the aim is to coat a base metal with a more noble one, but it may not be possible to do this in one step. When a metal is immersed in a plating bath it will corrode unless its potential is sufficiently low to suppress its ionisation. Fortunately, a low rate of corrosion is tolerable for a brief initial period. There are cases where even when a cathode is being plated at a high cathodic (nett) current density, the substrate continues to corrode rapidly because the potential (determined by the metal deposited) is too high. No satisfactory coating forms if the substrate dissolves at a high rate concurrently with electrodeposition. This problem can be overcome by one or more of the following procedures ... 

The voltage used is 4-8 V, current density 9-22 A/dm, and temperature 38-43°C. Higher current densities, up to 55 A/dm, are used for thick deposits. A considerable amount of heat is generated during electrodeposition and provision must be made for cooling of the electrolyte during operation. 

Burnt Deposit a rough, poorly coherent, electrodeposit that results from the application of an excessively high current density. 

Electrodeposition of polycrystalline mngsten disulfide (WS2) thin films on TO/glass, from an aqueous solution of tungstic acid and Na2S03 (pH 7.0-9.5), at different current densities ranging from 20 to 60 mA cm , and temperatures 40, 60, and 80 °C, has been reported [155]. Both the 2H and 3R phases of WS2 were found... 

Figure 14.4 (a) Current density vs. potential curves obtained for electrodeposition of Ni-P alloy in the presence (solid curve) and absence (dashed curve) of NaH2P02 (P-source of the alloy). 

The film electrodeposition process was studied by means of linear sweep voltammetry. The rate of electrochemical reaction was determined from current density (current-potential curves). The film deposits were characterized by chemical analysis, IR - spectroscopy, XRD, TG, TGA and SEM methods. 

On the basis of obtained data of cyclic voltammograms for 3d metals oxides electrodeposition the optimal conditions (current density, potential, process time, electrolyte composition, temperature) for dense oxide films (Ni, Cr and Co) deposition on steel foil have been elaborated. Data relating to several best films are summarized in Table 1. 

In addition, EC-ALE offers a way of better understanding compound electrodeposition, a way of breaking it down into its component pieces. It allows compound electrodeposition to be deconvolved into a series of individually controllable steps, resulting in an opportunity to learn more about the mechanisms, and gain a series of new control points for electrodeposition. The main problem with codeposition is that the only control points are the solution composition and the deposition potential, or current density, in most cases. In an EC-ALE process, each reactant has its own solution and deposition potential, and there are generally rinse solutions as well. Each solution can be separately optimized, so that the pH, electrolyte, and additives or complexing agents are tailored to fit the precursor. On the other hand, the solution used in codeposition is a compromise, required to be compatible with all reactants. 

From the research on electrocodeposition to date, a number of variables appear to be influential in the process, which include hydrodynamics, current density, particle characteristics, bath composition, and the particle-bath interaction. The influence that a particular variable has on the process is typically assessed by the change in the amount of particle incorporation obtained when that variable is adjusted. Although the effect of each of these process variables has been reported in the literature, the results are often contradictory. The effects of the process variables, of which many are interrelated, can also vary for different particle-electrolyte systems and electrodeposition cell configurations used. This review will summarize these effects and the contradictions in the literature on electrocodeposition. 

Electroless deposition as we know it today has had many applications, e.g., in corrosion prevention [5-8], and electronics [9]. Although it yields a limited number of metals and alloys compared to electrodeposition, materials with unique properties, such as Ni-P (corrosion resistance) and Co-P (magnetic properties), are readily obtained by electroless deposition. It is in principle easier to obtain coatings of uniform thickness and composition using the electroless process, since one does not have the current density uniformity problem of electrodeposition. However, as we shall see, the practitioner of electroless deposition needs to be aware of the actions of solution additives and dissolved O2 gas on deposition kinetics, which affect deposit thickness and composition uniformity. Nevertheless, electroless deposition is experiencing increased interest in microelectronics, in part due to the need to replace expensive vacuum metallization methods with less expensive and selective deposition methods. The need to find creative deposition methods in the emerging field of nanofabrication is generating much interest in electroless deposition, at the present time more so as a useful process however, than as a subject of serious research. 

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