Electrodeposition baths

Compared with the CBD technique, electrodeposition requires some additional capital equipment (i.e., suitable power supplies and electrodes). Major advantages of the electrodeposition process include the insignificant amount of waste generation. The electrodeposition bath can be reused for an unlimited number of cycle times when salts are replenished in the bath. The major drawback for electrodeposition is that it requires conductive substrates, which limits the application of this process in several key technologies. 

The electrodeposited Bi2Sr2CaiCu2Ox (BSCCO) precursor films were obtained by co-electrodeposition of the constituent metals using nitrate salts dissolved in DMSO solvent. The electrodeposition was performed in a closed-cell configuration at room temperature ( 24°C). The cation ratios of the electrodeposition bath were adjusted systematically to obtain BSCCO precursor compositions. A typical electrolyte-bath composition for the BSCCO films consisted of 2.0-g Bi(N03)3-5H20,1.0-g Sr(N03)2, 0.6-g Ca(N03)2-4H20, and 0.9-g Cu(N03)2-6H20 dissolved in 400 mL of DMSO solvent. The substrates were single-crystal LAO coated with 300 A of Ag. 

GZO films were electrodeposited from an electrodeposition bath containing 0.29-g gadolinium halide and 0.1-g zirconium halide dissolved in a 150-mL electrolyte solution. Electrodeposition was performed at a current density of 1 mA/cm2 and under constant stirring in a vertical two-electrode cell configuration. The average rate of deposition was about 25 nm/min. 

From the foregoing it should be quite clear that in practice it is virtually impossible to obtain and maintain electrodepositing baths free of impurities. This is so even in the setting of a research laboratory. Thus, in research work pertaining to electrode kinetics, for instance, careful and often complex purification procedures are a necessity to remove some key contaminants. Otherwise, no reproducible or reliable results can be obtained. The practical plating shop worker, on the other hand, deals with highly contaminated (from the point of view of the researcher) solutions from a variety of by-and-large unknown sources. It is for this reason that for the most part, technical practice must rely on empirical observations. 

Some spedal instances arise when deposition in an electrodeposition bath would be inappropriate. Small areas can be plated by making a cathodic connection and touching the area with a pad soaked in an electrolyte and in which is located an insoluble anode (often graphite).8 A popular... 

Room-temperature ionic liquids (denoted RTILs) have been studied as novel electrolytes for a half-century since the discovery of the chloroaluminate systems. Recently another system consisting of fluoroanions such as BF4 and PFg , which have good stability in air, has also been extensively investigated. In both systems the nonvolatile, noncombustible, and heat resistance nature of RTILs, which cannot be obtained with conventional solvents, is observed for possible applications in lithium batteries, capacitors, solar cells, and fuel cells. The nonvolatility should contribute to the long-term durability of these devices. The noncombustibility of a safe electrolyte is especially desired for the lithium battery [1]. RTILs have been also studied as an electrodeposition bath [2]. 

All of the coating was carried out on 3 inch X 5 inch, 24-gage zinc-phosphated (Bonderite EP-2), cold rolled steel panels with a deionized rinse. Each panel was immersed in the electrodeposition bath to a constant depth of 10 cm so that a current density or 2.0 ma/cm2 could be used for all coating experiments. 

The compositions of cathodic and anodic electrodeposition baths are given in Table 3.11. The main components are resins, pigments, extenders, some solvent, and neutralization agents. The latter are used to neutralize the charge on the resins so that they become water dispersible. The application data affect the plant and equipment technology (e.g., choice of construction materials, energy consumption, and rectifier design) [3.109], [3.117]. 

Certain components of domestic appliances are also coated with electrodeposition paints. Two-pack polyurethanes are applied if the dimensions of the parts are too large for the electrodeposition bath. These paints dry at ambient temperature to give films with similar properties to stoving acrylic enamels. Solvent-free powder coatings are also used to coat domestic appliances. Nowadays powder coatings and precoated metal (coil coating) are gaining more importance. 

So far we have dealt with reactions in which a solid has been consumed. When a solid surface is built up by a reaction, transport of reactants in the fluid phase is destabilizing, just as is the case during solidification (Seshan, 1975). An example of considerable practical importance is electrodeposition. In this case, instability is normally undesirable because it leads to an irregular surface that does not have the preferred bright appearance. It has been found that instability can sometimes be prevented by including small quantities of certain surface active organic additives in the electrodeposition bath (Edwards, 1964). The additives diffuse to the solid-liquid interface and are either incorporated into the developing deposit or consumed by an electrochemical reaction. Since they are surface active, they adsorb at the interface and produce a decrease in the rate of the electrodeposition reaction, possibly because they block some sites where metal ions would otherwise deposit. 

The question of the oxide content in the electrodeposition bath is critical while it was generally asserted that it should be the lowest possible for the quality of the plates, Christensen et al now claim that the presence of a certain amount of oxide in the melt enhances the crystallinity and the coherence of their deposits [18]. 

Chamelot P., Taxil P. and Lafage B., Voltammetric studies of tantalum electrodeposition baths, (1994), Electrochemica Acta, 39, 2571-75. 

Chamelot P, Taxil P, Lafage B (1994) Voltammetric studies of Tantalum electrodeposition baths. Electrochem Acta 17 2571-2574... 

It must be emphasized that SeS03 ions in the electrodeposition baths are formed by the dissolution of elemental Se in S03 solution. The formation of CdSe can also be explained by the codeposition of Cd and Se, or the initial formation of Se followed by CdSe precipitation onto the electrode surface [54] ... 

The acidic baths usually contain Cd " (from various Cd salts) and Te02 as the sources of Cd and Te, respectively [67-81]. In general, HTe02 is the stable and active species of Te02 in acidic electrodepositing baths. The formation of CdTe via electrodeposition from acidic aqueous baths has been explained by several proposed reactions. One of these reactions is ... 

This mechanism explains why CdTe can be obtained at an electrodepositirai potential that is more positive than the reduction potential of Cd " in the electrodeposition baths. Regardless of which mechanism is adopted, the overall process is a six-electron reductive reaction, as shown in Eq. 13. 

Some complexing agents such as 2,2 -bypyridine and ethylenediamine (en) are introduced to facilitate the electrochemical growth of CdTe. Dergacheva et al. indicated that the introduction of 2,2 -bypyridine makes the reduction potentials of Te(TV) anions and Cd (11) ions closer [94]. Murase et al. used ethylenediamine instead of ammonia in the electrodeposition baths. This allowed the temperature of the electrodeposition baths to be increased to 363 K, resulting in highly crystalline CdTe deposits without any post-treatment [95]. 

By introducing appropriate species (As or Ga) to the electrodepositing baths, n-type or p-type ZnSe thin films can be prepared [106]. 

Commercial Au electrodeposition bath (Orotemp Technic Inc.) deposition at —2.5 V... 

Other evidence of hydrogen formation playing a role includes Fukunaka et al., who were able to observe an increase in Ni nanotube wall thickness when the electrodeposition bath s pH was increased. These nanotubes were produced in an unmodified polycarbonate template. They associate the nanotube formation with the depression of the H2 bubble formation, a schematic of which is found in Figure 10.13. It can be inferred that H2 generation is less at higher pHs resulting in smaller diameter bubble formation and thus thicker-walled nanotubes. Thus, H2 gas bubble formation and/or suppression must be considered as a possible aspect of the metal nanotube formation mechanism. 

In 2006, Xu et al. were able to synthesize Ni nanotubes in AAO utilizing PI 23 as a surfactant in the electrodeposition bath. The surfactant is thought to have a strong affinity for both the AAO and the Ni + ions, thus encouraging deposition along the pore walls leading to nickel nanotube synthesis. An increase in nanotube wall thickness was observed with increased electrodeposition time however, in contrast to the previous kinetics mechanism, they found that increasing the current density also leads to an increase in nanotube wall thickness. Certainly, there may be different mechanism between the unmodified pores and these surfactant modified pores. 

Most electrodeposition baths operate at very low solids with 10-15% being typical. This can cause bath instability problems if the neutralising agent is too volatile and evaporates whilst in the bath. Being relatively high capital cost equipment means that quality performance is required from the coating. 

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