Aluminum coatings electroplated

Like aluminumtrialkyls, alkylaluminumhalogenides are quite widely used as components of catalytic systems during polymerisation. To polymerise unsaturated compounds, it is preferable to use alkylaluminumchlo-rides with titanium tetrachloride. Alkylaluminumhalogenides, and ethy-laluminumbromides in particular, are also efficient catalysts for the alkylation of ethylbenzene and cyclohexene. Besides, alkylaluminumhalogenides, like aluminumtrialkyls, are used to spray metal aluminum on various surfaces and to make electroplate aluminum coatings. 

In comparing electrolytic aluminum coating with conventional aqueous plating processes, it turns out that both proceed via the following process steps to afford electroplated pieces ... 

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]. 

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. 

After the application of the aluminum coating to the steel substrate, a heat treatment is often applied. Coatings resulting from vacuum deposition, electroplating, electrophoretic application, cladding, or powder coating techniques are annealed to provide adhesion by diffusion alloying [125],... 

Batch coating of steel hardware with aluminum to form aluminum-iron alloy coatings is also done by hot dipping or cementation. Pure aluminum coatings are applied on a batch basis by thermal spray, ion plating, and electroplating from nonaqueous solvents. 

Finishes for aluminum products can be both decorative and useful. Processes in use include anodic oxidation, chemical conversion coating, electrochemical graining, electroplating (qv), thin film deposition, porcelain enameling, and painting. Some alloys respond better than others to such treatments. 

Typically, coatings most often in use as intermediate layers are silver, nickel, copper, and gold however, silver is used by far the most often. This is so because of the low dissociation temperature of silver oxide, making it relatively easy to obtain clean surfaces. Also, the typical thickness range of electroplates used, in practice, for diffusion welding is about 15 to 40/rm, but thicknesses as great as 130 )um must sometimes be used. A considerable variety of steel types as well as aluminum and a host of other difficult-to-join metals and even beryllium have been and continue to be diffusion bonded with the use of electroplated intermediate layers. 

Metal Coatings. Tellurium chlorides, as well as tellurium dioxide in hydrochloric acid solution, impart permanent and attractive black antique finish to silverware, aluminum, and brass. Anodized aluminum is colored dark gold by tellurium electro deposition. A solution containing sodium tellurate and copper ions forms a black or blue-black coating on ferrous and nonferrous metals and alloys. Addition of sodium tellurite improves the corrosion resistance of electroplated nickel. Tellurium diethyldithiocarbamate is an additive in bright copper electroplating (see Electroplating). 

Turbine blades of jet engines are coated with a protective layer of platinum aluminide to impart high temperature corrosion resistance. Platinum is electroplated onto the blade using P-salt or Q-salt electroplating solutions (28,29). The platinum is then diffusion-treated with aluminum vapor to form platinum aluminide. Standards for the inspection and maintenance of turbine blades have become more stringent. Blades are therefore being recoated several times during their lifetime. 

Aluminum, chromium, titanium, and several other metals can be colored by an electrochemical process called anodizing. Unlike electroplating, in which a metal ion in the electrolyte is reduced and the metal is coated onto the surface of the cathode, anodizing oxidizes a metal anode to yield a metal oxide coat. In the oxidation of aluminum, for instance, the electrode reactions are... 

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