Rust
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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. | 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. | ||
| − | 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. | + | 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?=== | ||
| + | *Cars are more aggressively coated these days. Galvanizing (explain). | ||
| + | *Steel used in cars is of a higher quality these days. | ||
| + | *More salt is used on roads these days. | ||
=Rust assessment= | =Rust assessment= | ||
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