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You have probably seen rust on old cars or buildings and other metal surfaces and wondered what it is. Many people generally think that rust is simply oxidation and don’t really know what causes it. So, what causes rust?

What Creates Rust?

Rust is an iron oxide, a product of the reaction between iron and oxygen in the presence of water or air moisture. The oxygen reacts with the iron to form iron oxide, which is also known as rust. The water helps the oxygen to react with the iron by providing a source of moisture.

Rusted bolts and locks

Rust is a major problem for many industries because it can cause metal surfaces to deteriorate and break down. It can also be very difficult to remove once it has formed. Rust can cause serious problems for buildings, structures, cars, and other valuable metal products.

It is essential to understand what creates rust to prevent it from forming in the first place. Industries and other organizations that use metal objects need to take measures to protect their assets from rust and other forms of corrosion as much as possible.

Rust Formation Processes

Rust is iron oxide, which forms when iron or an alloy that contains iron is exposed to oxygen and moisture for a long time. The resulting reddish-brown appearance is due to hydrated iron(III) oxide formation.

Rusting is an electrochemical process that begins with transferring electrons from the metal to oxygen. This creates an electron deficiency in the metal, which must be filled by the flow of electrons from a more electronegative substance.

Three things must be present for rusting to occur: iron, oxygen, and water. Rust forms when these three elements combine and create an electrochemical reaction.  iron + water + oxygen → hydrated iron(III) oxide. It is the hydrated part that makes rust brown instead of red.

Factors Influencing the Rate of Rusting

When it comes to rust, not all metals are created equal. The rate of rusting depends on the various factors that can be summarized as follows:

The Type of Metal

Some metals rust more easily than others. For example, iron and steel rust more readily than aluminum or stainless steel. The difference is due to the electrochemical potential of the metal. Pure metals are usually more reactive and therefore more prone to rusting.

Stainless steel alloys contain at least 10.5% chromium. The chromium forms a thin layer of oxide on the surface of the steel that protects it from further rusting. If your appliances are rusting, it may be due to the fact that they’re made with a less corrosion-resistant steel alloy.

Car weathered with rust

The Presence of Moisture

Rust can’t form without water. The reason why iron pipes often rust from the inside is that water vapor condenses on the metal. The presence of moisture speeds up the rusting process because it provides the electrolyte needed for the reaction to occur.

Non-alloyed metals are particularly susceptible to rusting in humid environments. That’s why you’ll often see galvanized steel or wrought iron rusting faster than other types of metal.

The Presence of Oxygen

Rust can only form in the presence of oxygen. If you live in a dry climate, your metal surfaces may be less likely to rust. This is because oxygen is required for the reaction to occur, and it’s more readily available in the humid air.

What you need to remember is that not only oxygen is found in water or humid areas. Carbon dioxide in the air can also provide the oxygen necessary for rusting. In the presence of water, carbon dioxide reacts to form carbonic acid. This electrolyte can speed up the rusting process and cause corrosion.

Therefore, even if you don’t live in a humid climate, your metal surfaces may still rust if they’re exposed to carbon dioxide and water.

The Presence of Other Chemicals

Rust can also form when other chemicals are present. For example, salt accelerates the rusting process by corroding the metal. This is why you’ll often see iron railings and fences rust more quickly near the ocean.

Acids can also speed up the rusting process. This is because they break down the oxide layer that forms on the surface of the metal, exposing the metal to oxygen and water hence accelerating the rusting process.

Bases can also promote rusting. This is because they neutralize the acids that form on the surface of the metal, exposing it to oxygen and water. Therefore, if you live in an area with high pollution levels, your metal surfaces may be more likely to rust.

The Temperature

The temperature can also influence the rate of rusting. In general, the higher the temperature, the faster the rusting process. This is because the molecules of water and oxygen are more active at higher temperatures, and they can more easily penetrate the metal surface and react with the iron.

Wire brush removing rust from wheel

How to Prevent Rust

Preventing rust is a never-ending battle because there are so many ways that metal can become exposed to oxygen and moisture. The following are some general tips for preventing rust:

  • Keep metal clean and dry. Whenever metal becomes wet, wipe it dry as soon as possible to prevent rust from forming. Metals such as car engines and industrial parts washer should be cleaned religiously.
  • Apply a rust-resistant coating. This can be a paint, powder coating, oil, or wax. The key is to make sure the metal is completely covered so that oxygen and moisture can’t reach it.
  • Store metal in a cool, dry place. Store metal in a climate-controlled environment to prevent rust from forming.
  • Check for rust regularly. Inspect metal regularly for any signs of rust and remove it immediately. You can use degreasers after the initial cleaning.
  • Use rust-resistant fasteners. When attaching metal to other metal, use fasteners made from a rust-resistant material such as stainless steel.

Related Questions

What Will Produce Rust When Wet?

Hydrogen peroxide, also known as H2O2, is what will produce rust when wet. It does this by oxidizing the metal, which then creates rust.

How Can I Remove Rust?

Yes! There are a few ways to remove rust, including sanding, using a chemical rust remover, using a quality degreaser, or using an electrolytic process and then repainting the metal.


Rust can be a costly affair that often goes unnoticed. It is important to take measures to prevent rust from developing and address it early on when it does occur. Ensure that your home or office is well ventilated and that any areas prone to dampness are properly insulated.

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