Additives electrodeposition

O Brien. 1235 Ohmic drop, 811, 1089, 1108 Ohmic resistance, 1175 Ohm s law, 1127. 1172 Open circuit cell, 1350 Open circuit decay method, 1412 Order of electrodic reaction, definition 1187. 1188 cathodic reaction, 1188 anodic reaction, 1188 Organic adsorption. 968. 978. 1339 additives, electrodeposition, 1339 aliphatic molecules, 978, 979 and the almost-null current test. 971 aromatic compounds, 979 charge transfer reaction, 969, 970 chemical potential, 975 as corrosion inhibitors, 968, 1192 electrode properties and, 979 electrolyte properties and, 979 forces involved in, 971, 972 977, 978 free energy, 971 functional groups in, 979 heterogeneity of the electrode, 983, 1195 hydrocarbon chains, 978, 979 hydrogen coadsorption and, 1340 hydrophilicity and, 982 importance, 968 and industrial processes, 968 irreversible. 969. 970 isotherms and, 982, 983... 

Electrodeposition of semiconductors is a low-cost process. The most expensive equipment used in the process is a computerized potentiostat which may cost up to 5,000 compared to techniques like molecular beam epitaxy (MBE) or metal organic vapor phase epitaxy (MOVPE) in which the cost of the machines is in the order of 1 million. In addition, electrodeposition is versatile in application in the sense that many semiconductor materials can be electrodeposited using the same equipment. The only change required is basically the replacement of the deposition electrolyte by the desired one at any time. Evidence of a variety of electrodeposited semiconductors includes CdTe [32-42], CdS [10,32], ZnSe [11], ZnTe [12-14], SnS [17], CuInSea [18-22], CuInGaSe2 [23-27], and nitrides [9,43]. 

Electrochemical codeposition often results in formation of different microstructures and phases. Moreover, electrodeposited binary alloys may or may not be the same in phase structure as those formed by simple melting. In addition, electrodeposited phases are not always in the thermodynamic equilibrium and can... 

Only about 10 elements, ie, Cr, Ni, Zn, Sn, In, Ag, Cd, Au, Pb, and Rh, are commercially deposited from aqueous solutions, though alloy deposition such as Cu—Zn (brass), Cu—Sn (bronze), Pb—Sn (solder), Au—Co, Sn—Ni, and Ni—Fe (permalloy) raise this number somewhat. In addition, 10—15 other elements are electrodeposited ia small-scale specialty appHcations. Typically, electrodeposited materials are crystalline, but amorphous metal alloys may also be deposited. One such amorphous alloy is Ni—Cr—P. In some cases, chemical compounds can be electrodeposited at the cathode. For example, black chrome and black molybdenum electrodeposits, both metal oxide particles ia a metallic matrix, are used for decorative purposes and as selective solar thermal absorbers (19). 

Electrodeposition of Metals. Citric acid and its salts are used as sequestrants to control deposition rates in both electroplating and electroless plating of metals (153—171). The addition of citric acid to an electroless nickel plating bath results in a smooth, hard, nonporous metal finish. 

The early history of ionic liquid research was dominated by their application as electrochemical solvents. One of the first recognized uses of ionic liquids was as a solvent system for the room-temperature electrodeposition of aluminium [1]. In addition, much of the initial development of ionic liquids was focused on their use as electrolytes for battery and capacitor applications. Electrochemical studies in the ionic liquids have until recently been dominated by work in the room-temperature haloaluminate molten salts. This work has been extensively reviewed [2-9]. Development of non-haloaluminate ionic liquids over the past ten years has resulted in an explosion of research in these systems. However, recent reviews have provided only a cursory look at the application of these new ionic liquids as electrochemical solvents [10, 11]. 

It was quite recently reported that La can be electrodeposited from chloroaluminate ionic liquids [25]. Whereas only AlLa alloys can be obtained from the pure liquid, the addition of excess LiCl and small quantities of thionyl chloride (SOCI2) to a LaCl3-sat-urated melt allows the deposition of elemental La, but the electrodissolution seems to be somewhat Idnetically hindered. This result could perhaps be interesting for coating purposes, as elemental La can normally only be deposited in high-temperature molten salts, which require much more difficult experimental or technical conditions. Furthermore, La and Ce electrodeposition would be important, as their oxides have interesting catalytic activity as, for instance, oxidation catalysts. A controlled deposition of thin metal layers followed by selective oxidation could perhaps produce cat-alytically active thin layers interesting for fuel cells or waste gas treatment. 

Nickel is also widely used as an electrodeposited underlay to chromium on chromium-plated articles, reinforcing the protection against corrosion provided by the thin chromium surface layer. Additionally the production of articles of complex shape to close dimensional tolerances in nickel by electroforming —a high-speed electrodeposition process —has attracted considerable interest. Electrodeposition of nickel and the properties of electro-deposited coatings containing nickel are dealt with in greater detail in Section 14.7. 

In addition to the alloys in Table 4.21, Ni-Sn and Ni-Ti alloys also possess useful corrosion resistance. Ni-Sn alloys are extremely brittle and, because of this, are used only as electrodeposited coatings. Ni-Ti alloys over a wide range of compositions have been studied, of which perhaps the intermetallic compound NiTi (55 06Ni-44-94Ti) has attracted the most interest. 

Annealing of electrodeposited copper reduces the mechanical properties. As an example, the tensile strength has been reported to decrease from 275-330 MN/m to 180-255 MN/m on heating at above 300°C while the hardness of deposits obtained in the presence of addition agents may drop from as high a value as 300 HV to 80 HV after annealing at 200° C. 

Despite the large differences in respect of other mechanical properties, it has been established that the wear resistance of copper deposits, which is markedly inferior to, for example, that of electrodeposited nickel, is not significantly affected by either type of bath or addition agents. 

A wide range of applications for hard, wear-resistant coatings of electroless nickel containing silicon carbide particles have been discussed by Weissenberger . The solution is basically for nickel-phosphorus coatings, but contains an addition of 5-15 g/1 silicon carbide. Hiibner and Ostermann have published a comparison between electroless nickel-silicon carbide, electrodeposited nickel-silicon carbide, and hard chromium engineering coatings. 

Electroless nickel coatings containing PTFE particles have been discussed by Tulsi, and non-stick coatings of electrodeposited nickel containing 30% by volume PTFE particles are described by Naito and Otaka . They found that the addition of organic additives to increase the hardness of the nickel matrix to 500-600 Hy reduced the incorporation of the PTFE to 10-15% by volume. 

Addition Agent a substance added to an electroplating solution to produce a desired change in the physical properties of the electrodeposit. 

Anti-pitting Agent an addition agent (q.v.) which is used to prevent the formation of pits or large pores in an electrodeposit. 

Brightener an addition agent used specifically to produce an electrodeposit of high specular reflectivity. 

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