corrosion is an electro chemical process

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NACE

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Corrosion protection

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Plating

From Wikipedia, the free encyclopedia

This article is in need of attention from an expert on the subject. WikiProject Chemistry or theChemistry Portal may be able to help recruit one. (November 2008)

For other uses, see Plate.

Plating describes surface-covering where a metal is deposited on a conductive surface. Plating has been done for hundreds of years, but it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, to alter conductivity, for radiation shielding, and for other purposes. Jewelry typically uses plating to give a silver or gold finish. Thin-film deposition has plated objects as small as an atom, therefore some plating isnanotechnology.

There are several plating methods, and many variations. In one method, a solid surface is covered with a metal sheet, and then heat and pressure are applied to fuse them (a version of this is Sheffield plate). Other plating techniques include vapor deposition under vacuum andsputter deposition. Recently, plating often refers to using liquids. Metallizing refers to coating metal on non-metallic objects.

Contents  [hide] 1 Electroplating 2 Electroless plating 3 Specific cases 3.1 Gold plating 3.2 Silver plating 3.3 Rhodium plating 3.4 Chrome plating 3.5 Zinc plating 3.6 Tin plating 3.7 Alloy plating 3.8 Composite plating 3.9 Cadmium plating 3.10 Nickel plating 4 See also 5 References

the basics of Plating

blackodizing

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Passivation

From Wikipedia, the free encyclopedia

This article includes a list of references or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (February 2009)

Passivation is the process of making a material "passive" in relation to another material prior to using the materials together. For example, prior to storing hydrogen peroxide in an aluminium container, the container can be passivated by rinsing it with a dilute solution of nitric acid and peroxide alternating with deionized water. The nitric acid and peroxide oxidizes and dissolves any impurities on the inner surface of the container, and the deionized water rinses away the acid and oxidized impurities. Another typical passivation process of cleaning stainless steel tanks involves cleaning with sodium hydroxide and citric acid followed by nitric acid (up to 20% at 120 °F) and a complete water rinse. This process will restore the film, remove metal particles, dirt, and welding generated compounds (e.g. oxides).

In the context of corrosion, passivation is the spontaneous formation of a hard non-reactive surface film that inhibits further corrosion. This layer is usually an oxide or nitride that is a few atoms thick.

Contents  [hide] 1 Mechanisms of passivation 2 Electrochemical passivation processes 3 Passivation of specific materials 4 Terminology for assorted passivation processes 5 Rationale for passivating aluminium 6 See also 7 References 7.1 Notes 7.2 Bibiography 8 Further reading