Rust
(→What is rust?) |
(→What is rust?) |
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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. | + | 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. In mineral form, 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 . |
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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