Copper protective oxide coating

Iron can also form a protective oxide coating. However, this oxide is not a very effective shield against corrosion, because it scales off easily, exposing new metal surfaces to oxidation. Under normal atmospheric conditions, copper forms an external layer of greenish copper sulfate or carbonate called patina. Silver tarnish is silver sulfide, Ag2S, which in thin layers gives the silver surface a richer appearance. Gold shows no appreciable corrosion in air. 

Mainly on aluminum. Mirror coatings are used to protect the thin metal surface (silver, copper) of metal-coated glass against oxidation or reaction with H2S or S02. 

Where the corrosion resistance of a coating depends upon its passivity, it is common to follow plating with a conversion coating process to strengthen the passive film. Zinc, cadmium and tin in particular are treated with chromate solutions which thicken their protective oxides and also incorporate in it complex chromates (see Section 1S.3). There are many proprietary processes, especially for zinc and cadmium. Simple immersion processes are used for all three coatings, while electrolytic passivation is us on tinplate lines. Chromate immersion processes are known to benefit copper, brass and silver electrodeposits, and electrolytic chromate treatments improve the performance of nickel and chromium coatings, but they are not used to the extent common for the three first named. 

Immersion tin is a thin coating of pure tin, typically 0.6 to 1.2 /tm thick, which protects the underlying copper from oxidation and provides a highly solderable surface. Tin is deposited using a galvanic displacement process and can be applied in vertical or conveyorized equipment. Tin boards are used primarily for solderability and have very good compliant pin connector functionality. 

Non-ferrous metals may form a protective oxide layer, providing a barrier against further deterioration. The coating of aluminum, magnesium, copper, chromium, cadmimn and tin may be required, nevertheless, to protect the surface from deterioration other than oxidation, or a clear coat may be used to preserve the appearance of the virgin metal from oxidation. Zinc surfaces may require a chemical pre-treatment prior to the application of the primer and top coat, depending on the condition of the surface and type of primer used. Lead and lead alloy surfaces are easily coated with a linseed oil based primer and a compatible top coat. 

Immersion tin is another relatively new board finish, although it has been utilized in the industry in other forms for many years. Immersion tin rehes on a relatively thin (0.1 to 0.5 pm) coating of tin deposited from an immersion-tin process directly over copper. The tin protects the copper from oxidation during storage. As tin is not readily deposited onto copper by an immersion process, chemical enhancing agents known as catalysts must be utilized to enhance the tin... 

When the operating temperature exceeds ca 93°C, the catalytic effects of metals become an important factor in promoting oil oxidation. Inhibitors that reduce this catalytic effect usually react with the surfaces of the metals to form protective coatings (see Metal surface treatments). Typical metal deactivators are the zinc dithiophosphates which also decompose hydroperoxides at temperatures above 93°C. Other metal deactivators include triazole and thiodiazole derivatives. Some copper salts intentionally put into lubricants counteract or reduce the catalytic effect of metals. 

Flame spray metallising is widely used for the protection of metal against corrosion, especially for in situ protection of stmctural members. The principal metal used for spraying of plastics is sine. Aluminum and copper are also used. If the distance from the part is too great, the zinc solidifies before it touches the part and adhesion is extremely poor. If the molten zinc oxidizes, conductivity and adhesion are poor. If the distance is too short, the zinc is too hot and the plastic warps or degrades. These coatings are not as dense as electrically deposited coatings because of numerous pores, oxide inclusions, and discontinuities where particles have incompletely coalesced. 

Paint is one of the most common and widely used materials in home and building constmction and decoration (see Building materials). Its broad use comes from its abiHty to provide not only improved appearance and decoration but also protection of a substrate to which it is appHed. Evidence of the historical uses of paint goes back over 25,000 years to cave paintings found in Europe. The Bible describes pitch being used to coat and protect Noah s Ark. Over 10,000 years ago in the Middle East, various minerals and metals such as lime, siHca, copper and iron oxides, and chalk were mixed and reacted to produce many colors. Resins from plant sap and casein were also used. Over 2000 years ago in Asia, resins refined from insect secretions and sap from trees were used to make clear lacquers and varnishes (2). 

Molten tin wets and adheres readily to clean iron, steel, copper, and copper-base alloys, and the coating is bright. It provides protection against oxidation of the coated metal and aids in subsequent fabrication because it is ductile and solderable. Tin coatings can be appHed to most metals by electro deposition (see Electroplating). 

Ultramodern techniques are being applied to the study of corrosion thus a very recent initiative at Sandia Laboratories in America studied the corrosion of copper in air spiked with hydrogen sulphide by a form of combinatorial test, in which a protective coat of copper oxide was varied in thickness, and in parallel, the density of defects in the copper provoked by irradiation was also varied. Defects proved to be more influential than the thickness of the protective layer. This conclusion is valuable in preventing corrosion of copper conductors in advanced microcircuits. This set of experiments is typical of modern materials science, in that quite diverse themes... combinatorial methods, corrosion kinetics and irradiation damage... are simultaneously exploited. 

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