Where does rust come from? How does it begin to form and why only on certain metals?
In: Chemistry
Rust is the result of that metal reacting with oxygen.
It’s the result of ionic interaction, and different metals will “rust” in different ways. Like stainless steel for example, the shiny outside layer is actually how that particular metal “rusts”
Rust is iron oxide. It forms when other ions (often dissolved in water which is why water makes rust) react with the iron (it’s actually a somewhat complex reaction). There’s basically a tier list of metals and the higher up the list it is, the more it rusts. Iron is quite high up.
“Rust” is iron oxide, which is a combination of iron and oxygen. Having these two elements, however, will not cause it to form: it needs the presence of a third substance. That substance (or “catalyst”) is water, either in liquid form or as moisture in the air. Many metals are subject to corrosion of this type, but in general useage only those that contain iron are considered to be rusting.
Some metals, like copper and its alloys (brass and bronze) develop something called a patina instead. The patina protects the body of the metal from further chemical changes. This is different from rust, which does not form a protective layer. Given enough time and the right conditions, any iron mass will eventually convert totally into iron oxide or rust.
Rust is iron oxide, formed when oxygen reacts with iron. The problem with rust is that it’s less waterproof and airtight than regular iron, so once rust forms, it creates an opening for air and water to get deeper into the metal and create even more rust. Some metals either don’t react with oxygen (gold, for example), or they react with oxygen to form an oxide that is waterproof and airtight (creating a patina). This patina prevents oxygen from penetrating further into the metal, and is sometimes even desirable as it may have certain characteristics like strength and chemical resistance that are superior to the original metal.
Rust is a chemical reaction. Oxygen atoms combine with iron atoms to form iron oxide. It doesn’t eat away metal, it *is* the metal, just in a different form. The iron changes properties due to the bond with oxygen, causing it to become flaky and brown etc. This is why there are pits left when rust is cleaned away. The metal that used to be in the pits is the rust that was removed.
Rust is the combination of a metal with oxygen, for example let’s say you have an iron pipe that’s not painted or covered in any way, oxygen in the air will combine with the iron and form iron oxide which we usually know as rust, if there’s nothing interacting with the pipe rust will form a layer on the surface and that’s it, the problem is rust is brittle so if something rubs against it the rust will chip away revealing fresh iron that will again combine with more oxygen, repeat this process for long enough and you end with a hole on the pipe.
Rust is Iron (III) oxide. It can only happen on certain metals because it can only happen when iron is present.
Iron (III) oxide is a much weaker chemical than whatever Iron alloy (like steel) the material was made of, so it very easily chips away. That’s what gives it the “eating away” effect. The oxide can only form very close to the surface, but then that can chip away, so more iron can rust.
Iron (II) oxide is less common, but its stronger, and has a distinct black color, rather than the red of rust.
Other metals also oxidize, but they all have wildly different properties. The Statue of Liberty, for example, is made out of copper, so over time, it has turned the distinct green color of copper oxide, but copper oxide doesn’t chip away like rust does.
Rust forms on metals that contain iron. Iron is a major component of steel, and steel is a very common building material because it is light and strong.
Rust is a special name we give to iron and iron alloys (like steel) that have undergone a process called oxidization. Most metals oxidize, but iron oxidizes in a way that is particularly troublesome for its integrity.
When iron oxidizes, it pulls in water and this results in significant structural changes. When some metals oxidize, they simply combine with oxygen to form a new molecule. For example aluminum oxide is Al2O3. That’s two aluminum atoms and three oxygen atoms. Nice and simple. Aluminum oxidizes, but it does not rust. When aluminum oxidizes, the aluminum oxide forms a thin, stable layer on the metal’s surface. Aluminum oxide is actually very hard, so once a thin layer has formed, the oxidization process can’t reach the pure aluminum underneath. Aluminum’s oxidization process is self-terminating!
Iron, on the other hand, oxidizes differently. Instead of forming a hard surface, iron oxide is loose and not very strong. This allows the corrosive process to follow tiny fissures in the material, burrowing their way into the surface. The result is a flaky mess that we call rust.
Whether or not a metal corrodes like aluminum or iron depends on the specific chemical oxidization process. Most metals are elemental (composed of a single element) or alloys of a single element (mostly a single element with small parts of others), so their corrosive process is distinct to their elemental characteristics. That is why aluminum oxidization is almost unnoticeable, copper oxidization develops a pretty green patina, and iron turns into flakey dust. These are each the result of their elemental uniqueness.
It doesnt eat metal. It iron/steel become rust due to oxygen. Since rust is really weak, it can then flake off exposing more iron to oxygen. This will repeat until all the iron is iron oxide.
Is there a type of paint or coating that combines with rust to form a new substance that stops rust and seals off the rest of the metal underneath?
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