Bright Chrome Plating

The free chromium produced in this reaction is laid down in a thin layer on the surface of another metal, such as steel. The chromium protects the steel from corrosion and gives it a bright, shiny surface. Many kitchen appliances are chrome-plated this way. 

Chrome plate is a widely used electroplated coating and its appearance can be bright, satin, matt or black. It combines resistance to corrosion, wear and heat, use in contact with foodstuffs and decorative qualities. By itself it does not give a high level of protection against corrosion. To obtain a high level of corrosion protection, the chromium is deposited over a coating of nickel. 

Chrome plate, which was extensively used on automotive parts until the introduction of plastics, is actually a three-ply coating. A flash of copper is first laid down, followed by a nickel coating which comprises most of the finished thickness. A thin, hard coating of bright chromium is then applied as the topcoat The total thickness is normally 25 to 50 //m. 

The current technology being used in the automotive industry to satisfy the demand for bright metal appearance has been the use of chrome plating. 

Another example of where ultrasound influences the discharge rate of chromium is in the chromium electroplating of steel plates. When cold-rolled steel plate is elecUo-lytically chromated from a silent aqueous solution containing chromates and dichromates, a chrome coating of 13 mg m is obtained after 1 s, whilst in the presence of ultrasound a coating of 45 mg m is obtained [25] in the same time. The product is also accompanied with an increase in the brightness of the metal. Similar results have been found by other workers [26]. 

Chemicals for electroplating n. Most plastics plated today are finished with a copper/ nickel/chrome electroplate, but many other finishes are possible, such as bright brass antique brass, satin nickel, silver, black chrome, and gold. The actual composition of the electroplate is designed for the particular apphcation of the electroplate. 

Chromium plated parts on automobiles consist of steel substrates with an intermediate layer of nickel, or in some cases, layered deposits of copper and nickel. The thin chromium deposit provides bright appearance and stain free surface while the nickel layer provides the corrosion protection to the steel substrate. With this system it is essential that the nickel cover the steel substrate completely because the iron will be the anode and nickel the cathode. Any breaks or pores in the coating will result in the condition shown in Figure 16.3. This figure illustrates the reason for the corrosion of chrome trim on automobiles after World War II. 

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