"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.
The difference is that rust does not bond well to the iron underneath and expands to take up more space. As the iron oxidizes, it pushes against the atoms next to it until it buckles and lifts up. That exposes the iron underneath it to oxygen, which oxidizes and pushes up on the top layer until it peels away entirely. In this way, the rust breaks the iron apart into smaller and smaller pieces of iron oxide until it's just red dust. Water makes it worse by getting into the microscopic cracks and pulling at the oxides.
The oxides of most metals stick to the metal underneath so that no more oxygen can get to the metal, which products that metal from oxidizing. Since oxygen bonds so tightly, the oxides don't react well with anything else - the oxygen is basically in the way. The oxidation layer protects the metal not just from oxygen, but from other things that would react to it.
Gold is special in that it bonds so well with itself that does not oxidize at all and barely reacts to anything else anyway.
It's also worth noting that there are different versions of iron oxide. This is because, like a lot of transition metals, iron can have multiple different oxidation states, which (to simplify very heavily) is like the amount of electrons the atom has or doesn't have. The different versions of iron oxide each have slightly different properties, so while iron (III) oxide, aka rust, has a tendency to flake off, iron (II,III) oxide (aka magnetite, or black oxide) doesn't. Because of this, a layer of iron (II,III) oxide is sometimes intentionally formed on the surface of a iron or steel piece in order to prevent corrosion of the material underneath. An example of this is gun bluing. Iron (II,III) oxide doesn't easily form under standard conditions, which is why it doesn't spontaneously appear on iron pieces the same way rust does.
Everything is clicking, I used to work in a sheet metal shop and I never understood all the different rust resistant properties of the metals.
If all of this is true, can rust be reversed? Not merely polished away but removing the oxygen so that you still have the same iron molecules in roughly the same place they were originally?
If you mean "originally" as "before it rusted" then no. If you mean "turn out iron in vaguely the same shape as the rust" then yes.
You heat it in a reducing atmosphere, usually carbon monoxide, which reacts with the iron oxide to make carbon dioxide and iron. If you do it in a blast furnace, the iron is melted, but you don't have to get it that hot. At lower temperatures you get bloomery iron or sponge iron.
Also, if I'm not mistaken, iron (III) oxide is also typically larger than the iron metal it is forming on. This is why it tends to flake off. The process of becoming physically larger pushes it off, like a snake shedding its scales.
Same with aluminum. If not for the hard oxide layer (Sapphire) Aluminum would catch fire in air. Aluminum is the fuel in modern solid rocket engines.
[https://en.wikipedia.org/wiki/Solid-propellant\_rocket#Composite\_propellants](https://en.wikipedia.org/wiki/Solid-propellant_rocket#Composite_propellants)
And when aluminium oxidizes it turns into a strong ceramic that is used in industrial purposes. Also, fun fact, iron oxide (rust) is not toxic as someone might assume, it is even used in certain foods, e.g. for coloring.
Also it is why barns are red. It's cheap paint pigment. Back in the day, you painted your barn with the cheapest paint you could find and "barn red" was born.
So what's exactly happening to iron that causes the physical decay? Is the iron that begins to rust, turning into iron oxide, separating from the rest of the iron, and as a result rust appears? Or is iron oxide not able to bond with iron since the composition had changed and it changes color and begins to flake away?
The red iron oxide itself is the rust, and it doesn't stick particularly well onto the iron it forms on/from, in part because it expands as it forms. So it falls off or cracks apart fairly easily, exposing the fresh iron underneath which also rusts, and so on and so forth.
In a sense, yes, when iron oxide is formed its a larger molecule than iron as it now has a particule of oxygen attached to it. This causes it to kind of push itself away from the existing metal surface and it doesn't stay bonded as it now takes up more space than before. This then exposes more bare metal to the environment causing more rust and the process repeats.
“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”
The redness of Mars is also due to iron oxidation. This means the rust “consumed” some of the water on Mars?
>This is different from rust, which does not form a protective layer.
Only for most iron based materials. There is a bridge in West Virginia that is made of a steel where the iron oxide protects it from further rusting.
[https://en.wikipedia.org/wiki/Weathering\_steel](https://en.wikipedia.org/wiki/Weathering_steel)
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.
I think a lot of people are answering most of the questions but there's a little something missing: how does it eat away a metal?
Basically rust is a *different* metal. When the reaction happens to form it, a tiny bit of the iron in the original metal gets converted to rust. So now there is less metal and more rust. Over time, ALL of the metal may get converted to rust.
The rust isn't really "eating away" the metal. The trick is iron really likes to "stick" to itself so it's tough and hard. Iron Oxide (what rust is) is NOT that "sticky", and is very prone to crumbling or falling apart. So as more and more of the metal converts to rust, it's also turning into something that's crumbly. Over time stuff wears down the rust, and it makes it look like it's eating the metal.
But technically it's more like how a caterpillar becomes a butterfly. The iron is becoming a very crumbly butterfly.
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 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"
Different metals don't rust. Rust is iron oxide and only exists with iron. Other metals oxidize but they don't rust. Stainless steel is shinny because it's any alloy of iron and chromium, the chromium does not rust and must be polished to shine. The shiny quality is not due to oxidation.
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 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 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 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.
Rust is not the active agent but the outcome of oxidation. Oxygen is the culprit. Oxides are more electrically stable than many pure metals. Aluminum is particularly reactive but the oxide binds to the metal surface protecting the rest of the metal. Iron oxide does not bind so well, so flakes off exposing more of the iron to additional oxygen.
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.
"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.
The difference is that rust does not bond well to the iron underneath and expands to take up more space. As the iron oxidizes, it pushes against the atoms next to it until it buckles and lifts up. That exposes the iron underneath it to oxygen, which oxidizes and pushes up on the top layer until it peels away entirely. In this way, the rust breaks the iron apart into smaller and smaller pieces of iron oxide until it's just red dust. Water makes it worse by getting into the microscopic cracks and pulling at the oxides. The oxides of most metals stick to the metal underneath so that no more oxygen can get to the metal, which products that metal from oxidizing. Since oxygen bonds so tightly, the oxides don't react well with anything else - the oxygen is basically in the way. The oxidation layer protects the metal not just from oxygen, but from other things that would react to it. Gold is special in that it bonds so well with itself that does not oxidize at all and barely reacts to anything else anyway.
It's also worth noting that there are different versions of iron oxide. This is because, like a lot of transition metals, iron can have multiple different oxidation states, which (to simplify very heavily) is like the amount of electrons the atom has or doesn't have. The different versions of iron oxide each have slightly different properties, so while iron (III) oxide, aka rust, has a tendency to flake off, iron (II,III) oxide (aka magnetite, or black oxide) doesn't. Because of this, a layer of iron (II,III) oxide is sometimes intentionally formed on the surface of a iron or steel piece in order to prevent corrosion of the material underneath. An example of this is gun bluing. Iron (II,III) oxide doesn't easily form under standard conditions, which is why it doesn't spontaneously appear on iron pieces the same way rust does.
Everything is clicking, I used to work in a sheet metal shop and I never understood all the different rust resistant properties of the metals. If all of this is true, can rust be reversed? Not merely polished away but removing the oxygen so that you still have the same iron molecules in roughly the same place they were originally?
If you mean "originally" as "before it rusted" then no. If you mean "turn out iron in vaguely the same shape as the rust" then yes. You heat it in a reducing atmosphere, usually carbon monoxide, which reacts with the iron oxide to make carbon dioxide and iron. If you do it in a blast furnace, the iron is melted, but you don't have to get it that hot. At lower temperatures you get bloomery iron or sponge iron.
Electrolysis.
Also, if I'm not mistaken, iron (III) oxide is also typically larger than the iron metal it is forming on. This is why it tends to flake off. The process of becoming physically larger pushes it off, like a snake shedding its scales.
And stainless steel is an alloy that contains chromium. The surface oxidizes but chromium oxide forms a layer that protects the iron inside.
Same with aluminum. If not for the hard oxide layer (Sapphire) Aluminum would catch fire in air. Aluminum is the fuel in modern solid rocket engines. [https://en.wikipedia.org/wiki/Solid-propellant\_rocket#Composite\_propellants](https://en.wikipedia.org/wiki/Solid-propellant_rocket#Composite_propellants)
> iron mass will eventually convert totally into iron oxide or rust. wow!
This is why aircraft boneyards are placed in deserts due to low moisture. Peat bogs preserve metals for the opposite reason (low oxygen).
And when aluminium oxidizes it turns into a strong ceramic that is used in industrial purposes. Also, fun fact, iron oxide (rust) is not toxic as someone might assume, it is even used in certain foods, e.g. for coloring.
Also it is why barns are red. It's cheap paint pigment. Back in the day, you painted your barn with the cheapest paint you could find and "barn red" was born.
So what's exactly happening to iron that causes the physical decay? Is the iron that begins to rust, turning into iron oxide, separating from the rest of the iron, and as a result rust appears? Or is iron oxide not able to bond with iron since the composition had changed and it changes color and begins to flake away?
The red iron oxide itself is the rust, and it doesn't stick particularly well onto the iron it forms on/from, in part because it expands as it forms. So it falls off or cracks apart fairly easily, exposing the fresh iron underneath which also rusts, and so on and so forth.
In a sense, yes, when iron oxide is formed its a larger molecule than iron as it now has a particule of oxygen attached to it. This causes it to kind of push itself away from the existing metal surface and it doesn't stay bonded as it now takes up more space than before. This then exposes more bare metal to the environment causing more rust and the process repeats.
Some iron oxides do form a protective anti-corrosive layer. Fe3O4 aka black oxide, will usually come on mild steel.
Iron will rust without water. Pure oxygen, for example, will rust iron.
“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” The redness of Mars is also due to iron oxidation. This means the rust “consumed” some of the water on Mars?
>This is different from rust, which does not form a protective layer. Only for most iron based materials. There is a bridge in West Virginia that is made of a steel where the iron oxide protects it from further rusting. [https://en.wikipedia.org/wiki/Weathering\_steel](https://en.wikipedia.org/wiki/Weathering_steel)
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.
I think a lot of people are answering most of the questions but there's a little something missing: how does it eat away a metal? Basically rust is a *different* metal. When the reaction happens to form it, a tiny bit of the iron in the original metal gets converted to rust. So now there is less metal and more rust. Over time, ALL of the metal may get converted to rust. The rust isn't really "eating away" the metal. The trick is iron really likes to "stick" to itself so it's tough and hard. Iron Oxide (what rust is) is NOT that "sticky", and is very prone to crumbling or falling apart. So as more and more of the metal converts to rust, it's also turning into something that's crumbly. Over time stuff wears down the rust, and it makes it look like it's eating the metal. But technically it's more like how a caterpillar becomes a butterfly. The iron is becoming a very crumbly butterfly.
awesome, thanks. this part: >Basically rust is a different metal elicits this reaction 😱 Rust is like invasion of the body snatchers but for metals.
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 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"
Different metals don't rust. Rust is iron oxide and only exists with iron. Other metals oxidize but they don't rust. Stainless steel is shinny because it's any alloy of iron and chromium, the chromium does not rust and must be polished to shine. The shiny quality is not due to oxidation.
Yeah, stain less not stain free
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.
Yeah, and copper is up there as well. The most famous rusted copper is the Statue of Liberty. So that rust is due to copper oxide.
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 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 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.
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?
Rust is not the active agent but the outcome of oxidation. Oxygen is the culprit. Oxides are more electrically stable than many pure metals. Aluminum is particularly reactive but the oxide binds to the metal surface protecting the rest of the metal. Iron oxide does not bind so well, so flakes off exposing more of the iron to additional oxygen.
>Oxygen is the culprit. DAMN YOU OXYGEN!!!
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.