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| | =What causes rust?= | | =What causes rust?= |
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| − | ==What is rust?==
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| − | Rust is a kind of corrosion -- a decay or breakdown of a material in reaction to its environment. Specifically, 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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| − | For rust 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). The more conductive the electrolyte, the quicker rust will occur. For this reason, humid air, salty air, or salty water will accelerate the formation of rust.
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| − | Iron, with the chemical symbol of Fe, combines with oxygen, O, to form Fe<sub>2</sub>O<sub>3</sub>, the chemical formula for common reddish-brown rust. In its mineral form, Fe<sub>2</sub>O<sub>3</sub> is known as hematite.
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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 (like nitrous oxide, N<sub>2</sub>O). Oxides are typically formed when elements come into contact with air, through a process known as oxidation. Oxides are common, comprising most of the earth's crust. Elements can have multiple oxides. For example, there are sixteen known iron oxides. Thus, it's more accurate to say that rust is '''an''' iron oxide, rather than saying that rust '''is''' iron oxide.
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| − | Other metals besides iron oxidize, but their oxidation is not referred to as rust. For example, when aluminum oxidizes, it forms a protective, corrosion-resistant coating that is similar in appearance to un-oxidized aluminum. Zinc oxidizes similarly, which is why it is used for galvanizing. Only the oxidation of iron and steel is known as "rust". Why? Because iron oxide takes up more physical space than iron. It's bigger. So, when iron and air combine to make Fe<sub>2</sub>O<sub>3</sub>, it "puffs out", exposing even more of the original steel to the elements.
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| − | There is another iron oxide also referred to as "rust". It's Fe<sub>3</sub>O<sub>4</sub>, commonly called "black oxide", or, in mineral form, magnetite. This is the stuff that's left over after using certain products to "convert" rust. Black oxide takes up the same amount of space as iron, so it doesn't bulge it out, like reddish-brown rust, Fe<sub>2</sub>O<sub>3</sub>. Since black oxide itself doesn't offer much protection against corrosion, it's typically covered up (often with [[epoxy primer]]). Black oxide is an example of a conversion coating, a metal coating where part of the surface is converted into the coating itself, by a chemical or electrochemical process. ''(Is this the same thing as blueing?)''
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| − | ===Why do older cars rust more than newer cars?===
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| − | *Cars are more aggressively coated these days. Galvanizing (explain).
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| − | *Steel used in cars is of a higher quality these days.
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| − | *More salt is used on roads these days.
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| | =Rust assessment= | | =Rust assessment= |
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