Rust
(→What is rust?) |
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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. | 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. | ||
| − | + | There is another iron oxide also referred to 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 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?)'' | |
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. | 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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