Electroplating of alloys

Electrodeposited Me alloys are of great practical importance because of their unconventional electric, magnetic, mechanical and protective properties. The problem of electroplating of alloys is related to the processes of codeposition of metals from multicomponent electrolyte systems. Thermodynamic and kinetic aspects of electrochemical codeposition of metals and the processes of alloy phase formation have been discussed in details by Brenner [6.134], Gorbunova and Polukarov [6.135] and Despic [6.136]. 

It was applied first to describe the electroless deposition of Ni-P alloys, and later for electroplating of alloys of W and Mo with the iron-group metals. 

MEMS). Electroplating of alloys of W and Re with Ni or Co have also gained interest in recent years where high temperature or high abrasion resistance is required. 

Zinc. Supphers of 2inc electroplating chemicals have reported that 2inc electroplating volumes continue to grow. More recendy, electroplated 2inc alloys have been promoted. Zinc was priced at 1.50/kg in eady 1993 (see Zinc and zinc alloys). 

Other Baths. Other forms of 2inc plating are also in use. Immersion 2inc deposits are used as a preparatory step in electroless plating or electroplating of aluminum (146), magnesium (147), and beryUium (148) alloys. Formulations vary with the appHcation typical baths are Hsted in the references cited. 

Electroplating passive alloys Another application of strike baths reverses the case illustrated in the previous example. The strike is used to promote a small amount of cathode corrosion. When the passivation potential of a substrate lies below the cathode potential of a plating bath, deposition occurs onto the passive oxide film, and the coating is non-adherent. Stainless steel plated with nickel in normal baths retains its passive film and the coating is easily peeled off. A special strike bath is used with a low concentration of nickel and a high current density, so that diffusion polarisation (transport overpotential) depresses the potential into the active region. The bath has a much lower pH than normal. The low pH raises the substrate passivation potential E pa, which theoretically follows a relation... 

Koretzky [83] in 1963 published a review of electrodeposited magnetic films, which considers an earlier generation of storage devices. Some magnetic properties of electroplated Co alloys were tabulated by Safranek [84] and by Morral [85]. 

The structures of electroplated hard alloys have been less extensively studied than those of similar electrolessly deposited materials. Sallo and co-workers [118-120] have investigated the relationship between the structure and the magnetic properties of CoP and CoNiP electrodeposits. The structures and domain patterns were different for deposits with different ranges of coercivity. The lower-f/c materials formed lamellar structures with the easy axis of magnetization in the plane of the film. The high-Hc deposits, on the other hand, had a rod-like structure, and shape anisotropy may have contributed to the high coercivity. The platelets and rods are presumed to be isolated by a thin layer of a nonmagnetic material. 

Some common uses are in electrical wiring and components of electronic equipment, roofing, and pipes and plumbing and in the manufacturing of alloys such as brass, bronze, Monel metal, electroplating, jewelry, cooking utensils, insecticides, marine paints, cosmetics, and wood preservatives. 

The subject of alloy electroplating is being dealt with by an ever-increasing number of scientific publications (close to 200 in the last five years in the Journal of the Electrochemical Society alone ). The reason for this seems to be the vastness of the number of possible alloy combinations and the concomitant possible practical applications. 

Nickel salts are used in electroplating, ceramics, pigments, and as catalysts. Sinter nickel oxide is used as charge material in the manufacture of alloy steel and stainless steel. Nickel is also used in alkaline (nickel-cadmium) batteries. 

The nse of complexation to allow codeposition of alloys is well known in electroplating. The best-known example is that of brass (Cu/Zn) plating, where cyanide, which is a stronger complex for Cu than it is for Zn, brings the deposition potentials of the two metals, originally far apart, to almost the same value. There is a direct connection between this effect and the equivalent one for CD. This arises from the fact that, for both CD and electrodeposition of alloys (we in-clnde mixed metal compounds in the term alloy), the effect of the complexant is to lower the concentration of free cations. For CD this affects the deposition throngh the solnbility product, while for electrodeposition it affects the deposition potential through the Nemst equation ... 

Jewelry - [ALUMINUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - CALCINED, TABULAR, AND ALUMINATE CEMENTS] (Vol 2) -antimony m [ANTIMONY AND ANTIMONY ALLOYS] (Vol 3) -electroplating of [ELECTROPLATING] (Vol 9) -electroplating of [ELECTROPLATING] (Vol 9) -gold for [GOLD AND GOLD COMPOUNDS] (Vol 12) -nickel-beryllium alloys m [BERYLLIUM AND BERYLLIUM ALLOYS] (Vol 4)... 

Uses. Much silver is used in the form of alloys. Alloys of copper and silver are much harder than pure silver and equally or more resistant to corrosion. Sterling silver and silver coins are alloys of this type. Small amounts of silver are used in the electroplating of a wide variety of objects, in the silvering of mirrors, and so forth. This metal is of real value in the form of compounds such as silver nitrate (AgN03), commonly known as lunar caustic, which is used in medicine (to cauterize wounds) and in the manufacture of indelible inks. Silver bromide (AgBr) is an extremely important compound because of its use in photography. 

Direct electroplating of metals on water-sensitive substrate materials such as Al, Mg and light alloys with good adherence should be possible using ionic liquids. 

Metal ion electrodeposition potentials are much closer together in ionic liquids compared with water, enabling easier preparation of alloys and the possibility of a much wider range of possible electroplated alloys, which are difficult or impossible in water. 

It appears that in several nonaqueous systems, the difference between the potentials of the A13+/A1 couple and that of other couples, such as Zn2+/Zn, Sn2+/ Sn, Cu2+/Cu, and others is much lower than in aqueous solutions [456-458], Consequently, electroplating of Al alloys from nonaqueous solutions is feasible and may even be advantageous over metallurgical processes of alloy formation [456,459,460], Anodic dissolution of aluminum electrodes has also been investigated [461-465], It appears that reversible behavior of the A13+/A1 couple may be obtained in a number of nonaqueous systems (see next section). 

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