Electroplated hard chromium

For the protection of aluminum parts, a wide range of surface layers stand ready. Price and applicability strongly depend on the application. PVD coatings are less expensive than ion implantation layers but set strict limits on part dimensions and batch sizes. Electroplated hard chromium layers can be used for corrosion protection in combination with other layer types. 

Ihble 11 Compares the Taber abrasion resistance of electroplated nickel, electroless nickel, and electroplated hard chromium... 

Electroplating. Chromium is electroplated onto various substrates in order to realize a more decorative and corrosion- or wear-resistant surface (24—32). About 80% of the chromium employed in metal treatment is used for chromium plating over 50% is for decorative chromium plating (see Metal surface treatments). Hard chromium plating differs from decorative plating mostiy in terms of thickness. Hard chromium plate may be 10 to several 100 p.m thick, whereas the chromium layers in a decorative plate may be as thin as 0.25 p.m, which corresponds to about two grams Cr per square meter of surface. 

National Emission Standards for Coke Oven Batteries National Perchloroethylene Air Emission Standards for Dry Cleaning Facilities National Emission Standards for Chromium Emissions from Hard and Decorative Chromium Electroplating and Chromium Anodizing Tanks Ethylene Oxide Emissions Standards for Sterilization Facilities... 

This process is suitable both for the production of metallic chromium and for the coating of objects with thin, decorative or thicker hard chromium layers (chromium electroplating). 

Most chromium is used in three basic industries chemical, metallurgical and refractory (heat-resistant) (Barceloux 1999), with the metal industry using the majority. Ferrochrome, an iron/chromium alloy, is used as an additive to produce chromium-steels which are stainless and hard. Chromic acid solutions are employed in electroplating of chromium on other metals to imPart corrosion resistance and for decorative purposes. The refractory industry has... 

EPA Federal Register (1995) National Emission Standards for Chromium emissions from hard and decorative chromium electroplating and chromium anodizing tanks, vol 60. Research Triangle Park, pp 4547 993... 

Fig. 8.12 Examples of hard chromium electroplating for engineering applications, (a) A printing roll following grinding and polishing, a smooth and highly reflecting surface finish is possible, (b) An injection moulding tool used to produce plastic water tanks (Photographs courtesy Ionic Surface Treatments Plating by Hilton and Tuck Division, Manchester.)...

Chromium electroplating is also used as decorative and hard coatings. Colored and tarnish-resistant chromium decorative coatings are produced over a base deposit of copper and/or nickel for applications such as those noted above for nickel. Hard chromium coatings are used for hydraulic pistons and cylinders, piston rings, aircraft engine parts, and plastic molds, where resistance to wear, heat abrasion, and/or corrosion are required. 

To obtain hardness value comparable to hard chromium coatings, NC (15 to 20 nm grain size) electroplated Ni-Co alloys were considered, as they exhibit... 

Chromium is a hard metal with excellent corrosion and oxidation resistance. Its properties are summarized in Table 6.3. Chromium coatings are usually produced by electroplating or sputtering, but CVD is being investigated for several applications. 

Industry also uses electroplating for many applications. Chromium, an extremely hard surface metal, is commonly electroplated over steel cores for heavy duty applications. Worn or damaged metal machine parts may be restored by re-plating the worn sections. 

Chromium is a hard, brittle metal that, with difficulty, can be forged, rolled, and drawn, unless it is in a very pure form, in which case the chromium is easier to work with. It is an excellent alloying metal with iron. Its bright, silvery property makes it an appropriate metal to provide a reflective, non-corrosive attractive finish for electroplating. 

Copper(l) cyanide is used in copper plating of nickel, chromium, zinc alloys, steel, and other metals or alloys. Such copper plating imparts brightness, smoothness, hardness, and strength. The cyanide solution employed for copper electroplating consists of copper cyanide and sodium cyanide. Other apph-cations of this compound are as an insecticide, a catalyst in polmerization, and as an antifouling agent in marine paints. 

In addition to its use in making steels, chromium is widely used to electroplate metallic objects with an attractive, protective coating (Section 18.12). Chromium is hard and lustrous, takes a high polish, and resists corrosion because an invisible, microscopic film of chromium(III) oxide shields the surface from further oxidation. 

Chromium is a white, hard, lustrous, and brittle metal (mp 1903 10°C). It is extremely resistant to ordinary corrosive agents, which accounts for its extensive use as an electroplated protective coating. The metal dissolves fairly readily in nonoxidizing mineral acids, for example, hydrochloric and sulfuric acids, but not in cold aqua regia or nitric acid, either concentrated or dilute. The last two reagents passivate the metal in a manner that is not well understood. The electrode potentials of the metal are... 

Chromium is often electroplated onto a softer metal to improve its hardness, stability, and appearance. Chrome bumpers and trim can be found on many vintage cars. ... 

Pure nickel was first isolated in 1751. Like cobalt, nickel was used to color glass, though nickel compounds turn glass and other substances green rather than blue. Because nickel is resistant to corrosion, it is often combined with other metals to form alloys that resist oxidation. A process known as electroplating uses nickel to coat the surface of metals that are vulnerable to corrosion, like iron or steel. Stainless steel is an example of a product made from nickel almost half the nickel that is mined each year is used to manufacture it. Also composed of chromium, stainless steel is extremely resistant to corrosion. Another nickel alloy is monel, which is made with copper. Monel is hard and resistant to corrosion, making it ideal for commercial marine applications such as the manufacture of boat propellers. The heating parts in toasters and electric ovens are made from an alloy called nichrome, which is another metal, made from chromium and nickel. 

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