Factors affecting electrodeposition

There are several important system variables that control the electrodeposition of a coating. These include the chemistry of both the aqueous and organic phases, the applied voltage and electrode geometry, coating time and bath temperature. 

The most important aqueous-phase parameters appear to be conductivity and acidity. Likely effects of variation of these parameters are an alteration of micelle migration rate (due to changes in surface charge) and control of the electrolysis of water, which may have significant implications for the interfacial microstructure of the final coating and therefore film adhesion. Typical conductivities are in the (2-8) X 10 S m range. 

Both constant-voltage and constant-current coating methods have been employed, the latter eliminating large current spikes that can occur on switching on the voltage and can cause problems with some resists at the beginning of electrodeposition. 

Other important variables are the chemical and physical natures of the surface to be coated. Changes in the origin and pre-clean treatment of the conductive substrate can have profound effects on both the thickness and performance of electrodeposited coatings. 

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Electrodeposition technique is a suitable way to get open and porous structure because it is very easy to control number, size and distribution of holes by the choice of appropriate electrodeposition conditions [19]. Factors affecting number, size, and distribution of holes are ... 

Sibottier, E., Sayen, S., Gaboriaud, F., and Walcarius, A. (2006) Factors affecting the preparation and properties of electrodeposited silica thin films functionalized with amine or thiol groups. Langmuir, 22, 8366-8373. 

In addition, the nanopore filling and nanotube formation mechanism of both polymers and metals is analyzed in detail. The results indicate that many factors affect the deposition morphology including electrochemical bath pH, pore-anchoring agents, nanopore geometry, nanoelectrode morphology, pore-wall functionalization, active ion concentration, as well as electrodeposition potential and/or current density. 

Most solutions used in electrodeposition of metals and alloys contain one or more inorganic or organic additives that have specific functions in the deposition process. These additives affect deposition and crystal-building processes as adsorbates at the surface of the cathode. Thus, in this chapter we first describe adsorption and the factors that determine adsorbate-surface interaction. There are two sets of factors that determine adsorption substrate and adsorbate factors. Substrate factors include electron density, d-band location, and the shape of substrate electronic orbitals. Adsorbate factors include electronegativity and the shape of adsorbate orbitals. 

As in any electrode process, the potential applied to the electrode determines the reaction rate. In electrodeposition, we expect that it affects the rate of deposition and thence the structure of the deposit a low overpotential signifies more time available to form an electrodeposit of perfectly crystalline structure. This can be observed experimentally (Fig. 15.7). Another factor arises from differences in current density between different parts of the electrode owing to electrode shape, which affects mass transport and thus accessibility to the cations to be deposited. Generally, it is best to apply a potential corresponding to the formation of poly crystalline deposits. A more perfect crystalline structure would be desirable, but the low rate of electrodeposition does not compensate for using such low overpotentials. 

Electrodeposition has the ability to produce a relatively uniform distribution of metal upon a cathode of irregular shape. Though the uniformity depends on the distribution of electric fields inside the electrolyte toward the surface of the electrode, other important factors have to be considered. The addition of agents (additives) to the electrolyte, for example, can affect the microscopic mechanism of electrodeposition, reducing the roughness of the deposit and producing a visual effect known as brightening. 

The key factors that control the rate of electrodeposition and the structure, physical properties, uniformity, and composition of electrodeposited metals and alloys are (1) thermodynamics (where the electric potential is based on the standard electromotive series) (2) electrode kinetics (which may vary with the structure of the electrodeposit) and (3) mass transport (which is important at high current densities, where the delivery of reactant to the cathode surface affects the local deposition rate and the structure of the deposit). 

Two-dimensional experiments with optical microscopy are also affected by other negative factors. Laser confocal microscopy has a relatively slow imaging speed and is not suitable for real-time electrodeposition studies. Furthermore, hydrogen bubbles interfere with optical microimaging making it difficult to observe their effects. Why, then, have two-dimensional studies so far dominated this domain The answer is that they are considerably simpler than those in 3D since they are not affected by complications like convection and, indeed, hydrogen bubbles. It is time,... 

The need to prepare very thin sample sources for counting necessitates a lengthy radiochemical separation procedure to remove bulk elements efficiently, as well as alpha emitters that will interfere with the spectra (Table 1). Radiochemical procedures and sample mounting onto a planchet are variable in efficiency and can be affected by sample-related factors. It is therefore imperative to use a yield monitor for the procedure if quantitation is required. After radiochemical separation the solution is prepared for alpha counting using electrodeposition, co-precipitation and filtration as a thin source, direct evaporation, electrospraying, or vacuum sublimation. If the planchet is contaminated with polonium, the planchet is heated to remove the volatile polonium. 

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