Rust
(→What is rust?) |
(→What is rust?) |
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==What is rust?== | ==What is rust?== | ||
Rust is the common name for iron oxide. An oxide is a chemical compound containing an oxygen atom and other elements. Oxides are 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 iron oxide -- rust. | Rust is the common name for iron oxide. An oxide is a chemical compound containing an oxygen atom and other elements. Oxides are 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 iron oxide -- rust. | ||
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| + | Rust is iron plus oxygen. | ||
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 red. | 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 red. | ||
| − | Iron is FE, although it rarely exists in pure form. Oxygen is O2. They combine to form FE2O3: iron | + | Iron is FE, although it rarely exists in pure form. Oxygen is O2. They combine to form FE2O3: one of 16 possible known iron oxides. |
| − | Elements can have multiple oxides. The original element can combine with the oxygen in different proportions. 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. | + | Elements can have multiple oxides. The original element can combine with the oxygen in different proportions. 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. 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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Seawater and salt spray make better electrolytes, so they increase rust. | Seawater and salt spray make better electrolytes, so they increase rust. | ||
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| + | The notion that, after you "encapsulate" rust, it still "lives underneath", is generally correct. There is mobile oxygen in the metal, living beneath the surface, causing more rust. | ||
=Rust assessment= | =Rust assessment= | ||
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