LYCOS RETRIEVER 
Corrosion
built 204 days ago
Corrosion is breaking down of essential properties in a material due to reactions with its surroundings. In the most common use of the word, this means a loss of an electron of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a well-known example of electrochemical corrosion. This is commonly known as rust. This type of damage usually affects metallic materials, and typically produces oxide(s) and/or salt(s) of the original metal. Corrosion ... includes the dissolution of ceramic materials and can refer to discoloration and weakening of polymers by the sun's ultraviolet light.
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Corrosion Coupons are the most common method for monitoring corrosion rates. Coupons are metal strips that are ½ wide, 1/16 inches thick, and 3 inches long. Coupons are available in any alloy commonly found in aqueous systems. Common alloys used to monitor cooling water are 1010 mild steel and copper.
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Corrosion (oxidation of metal) can only occur if some other chemical is present to be reduced. In most environments, the chemical that is reduced is either dissolved oxygen or hydrogen ions in acids. In anaerobic conditions (no oxygen or air present), some bacteria (anaerobic bacteria) can thrive. These bacteria can provide the reducible chemicals that allow corrosion to occur. That's how the limited corrosion that was found on the hull of the Titanic occurred. The picture below shows a "rusticle" removed from the hull of Titanic.
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Corrosion inhibitors are often added to paints. A pigment with anticorrosive properties is zinc phosphate. Compounds derived from tannic acid (e.g. Kelate) or zinc salts of organonitrogens (e.g. Alcophor 827) can be used together with anticorrosive pigments. Other corrosion inhibitors are Anticor 70, Albaex, Ferrophos, and Molywhite MZAP.
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Corrosion of zinc is lowest in the pH range from about 5.5 to 12.5. However, the corrosion of zinc in water is accelerated largely by the impurities present in the water and rarely is natural water pure. Even rainwater, which is distilled by nature, contains nitrogen, oxygen, carbon dioxide, as well as acquired airborne impurities such as dust or smoke.
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Corrosion