Aluminum electroplating

Quaternary Salts. Herbicides paraquat (20) and diquat (59) are the quaternary salts of 4,4 -bipyridine (19) and 2,2 -bipyridine with methyl chloride and 1,2-dibromoethane, respectively. Higher alkylpyridinium salts are used in the textile industry as dye ancillaries and spin bath additives. The higher alkylpyridinium salt, hexadecylpytidinium chloride [123-03-5] (67) (cetylpyridinium chloride) is a topical antiseptic. Amprolium (62), a quaternary salt of a-picohne (2), is a coccidiostat. Bisaryl salts of butylpyridinium bromide (or its lower 1-alkyl homologues) with aluminum chloride have been used as battery electrolytes (84), in aluminum electroplating baths (85), as Friedel-Crafts catalysts (86), and for the formylation of toluene by carbon monoxide (87) (see QuaternaryAA ONiUM compounds). 

Electroplated aluminum is growing in acceptance for use in automotive paits, electrical equipment, and appliances and foi pioducts in a marine environment. Markets may be extended as the result of a new galvano-aluminum electroplating process developed by Siemens Research Laboratory (Erlangen, Germany) and described in the Hans reference. 

Hans, R. High-Purity Aluminum Electroplating," Adv. Mat. Proc., 14 (June 1989). 

Extensive work has been devoted to aluminum electroplating in nonaqueous systems. Choosing appropriate bath compositions enables aluminum to be deposited at high efficiency and purity from nonaqueous electrolyte solutions. Comprehensive reviews on this matter have appeared recently in the literature [123,455], This work has led to the development of a number of commercial processes for nonaqueous electroplating of aluminum. The quality of the electroplated aluminum is very similar to that of cast metal. For instance, electrodeposited aluminum can be further anodized in order to obtain hard, corrosion resistive, electrically insulating surfaces. It is also possible to electroplate A1 on a wide variety of metal surfaces, including active metals (e.g., Mg, Al), nonactive metals, and steel. 

The study of molten haloaluminates was initiated because these melts are interesting from a scientific point of view. Practically, these melts are used for aluminum electroplating, as electrolytes in low temperatures batteries (see below) and, likewise, aluminum production by electrolysis of these melts has been tried (see Section II.A.7 Aluminum Chloride Electrolysis ). 

Fig. 19. 15 m aluminum electroplating SEDEC/Schempp und Decker, Berlin). 

The aluminizing process is a clean operation and the final products (Fig. 23), i. e., aluminum-coated metals, pose no environmental threat. We know today that aluminum can to a large extent replace cadmium as a corrosion-protective coating for work pieces [176]. Since cadmium is applied extensively in automobiles, aviation, on- and offshore industries, aluminum coating, i.e. both the aluminum electroplating process and the resulting coated pieces play an important role in environmental protection. The properties of the electrolytically produced aluminum layers on work pieces for aviation and space technology have been tested [183]. 

Thus, the conclusion is that for a preceding dissociation or a following combination, either of the non-rds terms, Jp/v or yffy, can be fractional, but the other must be a whole number. This is an important point that is not otherwise apparent In fact we have found that just such an error has been made in an analysis of the mechanism of the reaction of aluminum electroplating from a hydride hath. This error was found to he due entirely to the mistaken assumption that both anodic and cathodic non-rds terms (i.e., Yp/V and Y//V), of B R s theoretical transfer coefficients [Eqs. (la) and (lb)] could simultaneously give fractional contributions and so account for the transfer coefficients that had been derived from experimental Tafel plots. 

Fodisch et al. [238] deposited palladium by electroplating on a porous alumina layer, which had been obtained by anodic oxidation of aluminum. Electroplating can be seen as an alternative to impregnation. The authors observed a rather inhomogeneous (bimodal) deposition within the pores of the alumina layer palladium was mainly concentrated at the pore mouths and at the end of the pores, whereas no palladium was detected in the middle section of the pores. Possibly as a result of this distribution, the performance of the catalyst was found to be rather poor in comparison with that of a catalyst prepared by impregnation. 

Early in their work on molten salt electrolytes for thermal batteries, the Air Force Academy researchers surveyed the aluminum electroplating literature for electrolyte baths that might be suitable for a battery with an aluminum metal anode and chlorine cathode. They found a 1948 patent describing ionicaUy conductive mixtures ofAlCh and 1-ethylpyridinium halides, mainly bromides [6]. Subsequently the salt 1-butylpyridinium chloride -AICI3 (another complicated pseudo-binary) was found to be better behaved than the earlier mixed halide system, so the chemical and physical properties were measured and published [7]. I would mark this as the start of the modern era for ionic liquids, because for the first time a wider audience of chemists started to take interest in these totally ionic, completely nonaqueous new solvents. 

The most important product of the electrochemical industry in terms of value added was electroplating. The value added by electroplating was almost 75% greater than that added by the second ranked product, aluminum. Electroplating s predominance was due to a high volume of shipments coupled with a value added-shipments ratio of over 70%. Electroplating, itself, accounts for... 

---