Rust

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(What is rust?)
(What is rust?)
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==What is rust?==
 
==What is rust?==
 
Rust is a kind of corrosion. Corrosion is the decay or breakdown of a material in reaction to its environment.
 
Rust is a kind of corrosion. Corrosion is the decay or breakdown of a material in reaction to its environment.
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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).
  
 
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.
 
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.
  
Chemically, rust is known as Fe<sub>2</sub>O<sub>3</sub>.
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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, this 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. 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.
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Fe2O3 is also known as the mineral hematite: http://en.wikipedia.org/wiki/Hematite .
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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.
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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 also known as the mineral 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 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, forming 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.
  
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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Other metals besides iron 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. However, 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 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 reddish-brown color, that is very different from steel: it's reddish-brown.
  
Water combines with air to form carbonic acid, a good electrolyte.
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There is another iron oxide also known as "rust". It's Fe<sub>3</sub>O<sub>4</sub>. This is also known as "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>. Black oxide itself doesn't offer much protection against corrosion, so it's typically covered up (often with [[epoxy primer]]). Black oxide ''(also known as blueing?)'' 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.
  
Seawater and salt spray make better electrolytes, so they increase rust.
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Rust happens more quickly with salt in the air, because salted air is a better electrolyte.
  
 
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.
 
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.

Revision as of 13:09, 4 August 2007

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