Zinc electroplating, applications

Cadmium and zinc electroplating provides galvanic corrosion protection when coated on steel. Deposit thickness can vary between 5 and 25 p,m (0.2 and 1 mil), and typical applications for both coatings are found in Table 10. Cadmium is preferred for the protection of steel in marine environments, whereas zinc is preferred in industrial environments. Cadmium is also preferred for fastening hardware and connectors because its coefficient of friction is less than zinc. Cadmium is toxic and should not be used in parts that will have contact with food. Precautions for minimizing hydrogen embrittlement should be taken because cadmium plating is more susceptible to such embrittlement than any other plated metal. 

Concentrated, aqueous solutions of ZnCla dissolve starch, cellulose (and therefore cannot be filtered through paper ), and silk. Commercially ZnCla is one of the important compounds of zinc. It has applications in textile processing and, because when fused it readily dissolves other oxides, it is used in a number of metallurgical fluxes as well as in the manufacture of magnesia cements in dental fillings. Cadmium halides are used in the preparation of electroplating baths and in the production of pigments. 

Electroplating Cadmium is usually electroplated from a cyanide solution. Zinc is also deposited from cyanide electrolyte, but for some applications mildly acidic and alkaline non-cyanide electrolytes are increasingly being used. Typical cyanide-based electrolyte formulations for both metals taken from Specifications DTD 903 and 904 are given in Table 13.6. 

In addition to the metals listed above, many alloys are commercially electroplated brass, bronze, many gold alloys, lead—tin, nickel—iron, nickel—cobalt, nickel—phosphorus, tin—nickel, tin—zinc, zinc—nickel, zinc—cobalt, and zinc—iron. Electroplated alloys in lesser use include lead—indium, nickel—manganese, nickel—tungsten, palladium alloys, silver alloys, and zinc—manganese. Whereas tertiary and many other alloys can feasibly be electroplated, these have not found commercial applications. 

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

Cadmium is found in low concentrations in most soils and waters. It is produced as a by-product of zinc and lead mining and smeltering. Industrial use of cadmium has led to a dramatic increase in environmental problems caused by this element. Cadmium is used in semiconductors, nickel-cadmium batteries, electroplating, polyvinyl chloride (PVC) manufacturing, and control rods for nuclear reactors. The most important sources for aquatic contamination are active and inactive lead-zinc mines, land application of sewage sludge, zinc-cadmium smelters, effluents from plastic and steel production, and wastewaters from the production of nickel-cadmium batteries and electroplating (Zuiderveen, 1994). 

Enriched in many zinc ores, hlack shales, phosphatic shales. Can he enriched in soils, sediments, and waters affected hy emissions from smelters, power plants agricultural applications of sewage sludge mining and industrial wastes and hy-products industrial wastes, hy-products, and trash (i.e., battery production, leather tanning, electroplating, cement use). 

Many electrochemical applications, such as the electroplating of chrome, zinc or nickel, suffer from unwanted side-effects related to gas production on electrodes. In other processes gas formation is the only aim. 

The process has been continuously improved [71] but so far a breakthrough in the application of electroplated aluminum is still pending. The problem is the price, compared to zinc coatings. Electroplated aluminum is more expensive than zinc by a factor of 3 to 5. Therefore, electroplated aluminum is restricted to some high-tech applications, for example, special optical surfaces. As a corrosion-protective coating, the material is not yet an alternative to the established systems. 

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