Composite plating, electrolyte

The metallic substrate, clean and rinsed, is immersed wet in the plating cell. The base metals which are usually plated present an essentially metallic surface to the electrolyte, and the slight corrosive action of the rinse water in preventing the formation of any substantial oxide film is important. A critical balance of corrosion processes in the initial stages is vital to successful electroplating, and for this reason there is a severe restriction on the composition of the electroplating bath which may be used for a particular substrate. This will be discussed later. The substrate is made the cathode of the cell it may be immersed without applied potential ( dead entry) or may be already part of a circuit which is completed as soon as the substrate touches the electrolyte ( live entry). Live entry reduces the tendency for the plating electrolyte to corrode the substrate in the period before the surface... 

SOFC electrodes are commonly produced in two layers an anode or cathode functional layer (AFL or CFL), and a current collector layer that can also serve as a mechanical or structural support layer or gas diffusion layer. The support layer is often an anode composite plate for planar SOFCs and a cathode composite tube for tubular SOFCs. Typically the functional layers are produced with a higher surface area and finer microstructure to maximize the electrochemical activity of the layer nearest the electrolyte where the reaction takes place. A coarser structure is generally used near the electrode surface in contact with the current collector or interconnect to allow more rapid diffusion of reactant gases to, and product gases from, the reaction sites. A typical microstructure of an SOFC cross-section showing both an anode support layer and an AFL is shown in Figure 6.4 [24],... 

J. P. Cells, J. R. Roos, C. Buelens, and J. Fransaer, Mechanism of Electrolytic Composite Plating Survey and Trends, Trans. Inst. Metal Finish., 69, No. 4, 133-139 (1991). 

Tab. 11 Composition and working conditions of a silver plating electrolyte...

The incorporation of dimethylamine borane complex (BH3NH(CH3)2) and zinc sulphate into a nickel plating electrolyte results in co-deposition of boron (B) and zinc (Zn). Table 2 presents the chemical composition of Ni-B and Ni-B-Zn alloy coatings. It can be noticed that both boron (B) and Zinc (Zn) have been successfully co-deposited with nickel forming Ni-B and Ni-B-Zn alloy coatings on the surface of the steel substrate. The addition of zinc into Ni-B matrix resnlts in change in metallic luster and chemical composition. These findings are consistent with previous studies [26]. 

The co-deposition of microparticles with metal ions in an electrolytic bath under the influence of electric field to form a composite plating coating containing those microparticles. 

Langford, K. and Parker, J.E. (1971) Analysis of Electroplating and Related Solutions, R. Draper LTD, Teddington. Zhukov, B.D., Borodikhina, L.I., Shchekochikhin, V.M, Poddubny, N.P, and Bek, R.Y. (1973) Study of dec-trodeposition of copper horn cyanide electrolytes. The composition of the cyanide copper plating electrolyte. Izv. 

Metallic particles such as chromium can be introduced into a metal plating electrolyte (for example, nickel and cobalt), and the deposited composite can be subsequently heat treated to form high-temperature oxidation-resistant alloys. MCrAlY composites have been made by depositing 10 p,m CrAlY powder in a cobalt or nickel matrix. Heat treatment bonds... 

The most developed application of UDD is their use for strengthening composite electrochemical chromium-based coatings. Ultradisperse diamond is introduced into the standard chromium-plating electrolyte usually as suspension. The... 

Electroless plating on metal substrates can be improved by addition of pentaerythritol, either to a photosensitive composition of a noble metal salt (99), or with glycerine to nickel plating solutions (100). Both resolution and covering power of the electrolyte are improved. 

Fig. 2. Multilayer printed circuit board composite. Constmction is multiple layers of epoxy—glass and foil copper. Foil copper outermost layer and drilled through-holes are sequentially plated with electroless copper, electrolytic copper, electroless nickel, and electroless gold.

Electrochemical processes (e.g., electrolysis, electroplating, electromachirring, crrnetrt generation, and corrosion [Plate 8]) are distinguished by their occturence in a boundary region between an electrolyte (liqtrid or solid) and an electrode. The corrrse of these processes is strongly dependent on the potential at the electrode surface, the composition and stmcture of the electrode, the composition of the electrolyte, and the microstmcture of the electrolyte in the boundary layer near the electrode surface. In certain applications, the pore size and coimectivity of the electrode can also be important. 

Actually, it is recognized that two different mechanisms may be involved in the above process. One is related to the reaction of a first deposited metal layer with chalcogen molecules diffusing through the double layer at the interface. The other is related to the precipitation of metal ions on the electrode during the reduction of sulfur. In the first case, after a monolayer of the compound has been plated, the deposition proceeds further according to the second mechanism. However, several factors affect the mechanism of the process, hence the corresponding composition and quality of the produced films. These factors are associated mainly to the com-plexation effect of the metal ions by the solvent, probable adsorption of electrolyte anions on the electrode surface, and solvent electrolysis. 

Several binary alloys of technological importance are known to form by way of an underpotential co-deposition mechanism. The abnormal composition-potential relationship observed in Cu-Zn alloys deposited from cyanide-based electrolytes, one of the most widely used commercial alloy plating processes, is attributed to the underpotential co-deposition of Zn [64]. The UPD of Zn is also known to occur on Co and Fe and has been included in treatments focusing on the anomalous co-deposition of Co-Zn [65] and Ni-Zn alloys [66-68]. Alloys of Cu-Cd have been shown to incorporate Cd at underpotentials when deposited from ethylene diamine solution [69-71]. 

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