Rust
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==What is rust?== | ==What is rust?== | ||
| − | Rust | + | Rust is a kind of corrosion. Corrosion is the decay or breakdown of a material in reaction to its environment. |
| − | Rust is iron | + | Rust is an electro-chemical corrosion that occurs in the presence of iron, oxygen, and water. Oxygen and water are available in the open air, and iron is the principal ingredient in steel. |
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| + | Rust is commonly referred to as ''iron oxide''. An oxide is a type of chemical compound that contains oxygen and other elements. Iron, with the chemical symbol of Fe, combines with oxygen, O, to produce sixteen known iron oxides. ''(What's the exact definition of an oxide here?)'' . Oxides are typically formed when elements come into contact with air, through a process known as oxidation. Oxides are common, forming most of the earth's crust. When iron (or steel, which contains mostly iron) is exposed to air, it combines with the oxygen in the air, and forms the iron oxide known as rust. | ||
Other metals oxidize, but their oxidation is not referred to as rust. For example, when aluminum oxidates, it forms a protective, corrosion-resistant coating that looks a lot like un-oxidized aluminum. Zinc's oxide is similar, which is why it is used for galvanizing. | Other metals oxidize, but their oxidation is not referred to as rust. For example, when aluminum oxidates, it forms a protective, corrosion-resistant coating that looks a lot like un-oxidized aluminum. Zinc's oxide is similar, which is why it is used for galvanizing. | ||
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Only the oxidation of iron and steel (iron oxide) is known as "rust". Why? Because iron oxide takes up more physical space than iron. It's bigger. So, when iron pulls oxygen atoms from the air, to make iron oxide, it "puffs out", exposing even more of the original steel to the elements. And, it has a distinct color, that is very different from steel: it's reddish-brown. | Only the oxidation of iron and steel (iron oxide) is known as "rust". Why? Because iron oxide takes up more physical space than iron. It's bigger. So, when iron pulls oxygen atoms from the air, to make iron oxide, it "puffs out", exposing even more of the original steel to the elements. And, it has a distinct color, that is very different from steel: it's reddish-brown. | ||
| − | + | Iron has 16 known oxides: http://en.wikipedia.org/wiki/Iron_oxide .For example, rust is one of iron's oxides: FE2O3. Two iron atoms and 3 oxygen atoms. Iron has another oxide: FE3O4. 3 iron atoms and 4 oxygen atoms. FE3O4 is also known as "black oxide". It's the stuff that's left behind after you "convert" rust. It's magnetite: http://en.wikipedia.org/wiki/Magnetite . Black oxide takes up the same amount of space as iron, so it doesn't bulge it out. It itself doesn't offer much protection against corrosion. This is also called bluing (confirm). This is a "conversion coating", a metal coating where part of the surface is converted into the coating itself, with a chemical or electrochemical process: http://en.wikipedia.org/wiki/Conversion_coating . | |
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Rust is an example of corrosion -- deterioration of a material from reaction with its environment. Rust is electrochemical corrosion. For it to occur, it needs an anode (a piece of metal that gives up electrons), an electrolyte (a liquid that helps transport electrons), and a cathode (a piece of metal that accepts electrons). | Rust is an example of corrosion -- deterioration of a material from reaction with its environment. Rust is electrochemical corrosion. For it to occur, it needs an anode (a piece of metal that gives up electrons), an electrolyte (a liquid that helps transport electrons), and a cathode (a piece of metal that accepts electrons). | ||
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