Rust: What It Is, How It Forms & Why It’s a Problem

by Joost Nusselder | Last Updated:  May 27, 2022

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Rust is an iron oxide, usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable both visually and by spectroscopy, and form under different circumstances.

It’s a very complex process, but we’ll look at all the factors that contribute to it. Plus, I’ll share some tips on how to prevent it.

What is rust

What in the World is Rust?

Rust is a term commonly used to describe the oxidation of iron or steel caused by exposure to moisture and oxygen. Technically, rust is an iron oxide, specifically a hydrous iron(III) oxide or iron(III) oxide-hydroxide. It is formed when iron reacts with oxygen in the presence of water or air moisture, resulting in a reddish-brown flaky coat on the metal.

Causes of Rust

Rust occurs when iron or steel is exposed to moisture and oxygen. The presence of water or air moisture acts as a catalyst, increasing the speed of the reaction between iron and oxygen. Some factors that contribute to rusting include:

  • Geographical location: Areas with high humidity, rainfall, or wind can contribute to the spread of rust.
  • Exposure to salt: Salt can speed up the rusting process, making it worse in heavily salted areas.
  • Lack of protection: Unprotected steels are more susceptible to rusting than those that are coated or painted.

Prevention and Treatment of Rust

Preventing rust is a good way to protect metal from the inevitable effects of oxidation. Some ways to prevent rust include:

  • Coating or painting the metal surface to protect it from exposure to moisture and oxygen.
  • Keeping the metal dry and free from moisture.
  • Using stainless steel or other rust-resistant metals in areas where rust is a concern.

Treating rust can be a bit more challenging, but some methods include:

  • Sanding or wire-brushing the rusted area to remove the rust.
  • Applying a rust converter to the affected area to chemically change the rust into a more stable compound.
  • Filling in any pitting or cavities with a metal filler to restore the structural integrity of the metal.

The Science Behind Rust: Exploring the Chemical Reactions

Rust is a result of a chemical reaction that occurs when iron is exposed to oxygen and moisture. The main chemical reaction that causes rusting is the oxidation of iron, which can be represented by the following equation:

4Fe + 3O2 → 2Fe2O3

This means that four atoms of iron combine with three molecules of oxygen to produce two molecules of iron oxide.

The Role of Water and Oxygen in Rusting

Water and oxygen are the two key elements required for rusting to occur. When iron is exposed to water and oxygen, the process of rusting begins. Water acts as a medium that carries the oxygen molecules to the iron surface, while oxygen provides the electrons that are required for the oxidation process.

The Effects of Moisture and Dryness on Rusting

Moisture plays a crucial role in the rusting process. When iron is exposed to moisture, it forms iron hydroxide, which is a compound that contains both iron and water molecules. This compound is unstable and easily breaks down, forming iron oxide and releasing water molecules. This process causes the iron to flake and form a scale, which can eventually lead to the complete breakdown of the metal. On the other hand, dryness can slow down or even prevent the rusting process from occurring.

The Complex Nature of Rusting

Rusting is a complex process that involves a vast number of chemical reactions. It begins with the oxidation of iron, which is then combined with water molecules to form iron hydroxide. This compound then breaks down to form iron oxide and release water molecules. The resulting iron oxide forms a protective layer on the surface of the metal, but this layer can eventually flake off and expose fresh metal to the elements, causing the rusting process to continue.

The Similarities and Differences Between Rusting and Corrosion

Rusting and corrosion are often used interchangeably, but they are not the same thing. Rusting is a specific type of corrosion that occurs when iron is exposed to oxygen and moisture. Corrosion, on the other hand, is a general term that describes the process of metals reacting with their environment to form compounds. Corrosion can occur in many different forms, including rusting, but it can also occur in other ways, such as when metals are exposed to salt or acid.

The Key Factors That Influence Rusting

Several factors can influence the rusting process, including:

  • The presence of water and oxygen
  • The presence of salt or other electrolytes
  • The purity of the metal
  • The structure of the metal
  • The temperature and humidity of the environment

Understanding these factors is crucial for preventing rusting and preserving metal objects in everyday life.

Stop Rust in its Tracks: Tips for Preventing Corrosion

When it comes to preventing rust, the type of metal you choose can make a big difference. Some metals are naturally more resistant to corrosion than others. For example, stainless steel is a popular choice for outdoor furniture and appliances because it contains chromium, which forms a protective layer on the surface of the metal. Other metals, like aluminum and copper, are also relatively resistant to corrosion. If you’re working on a project that will be exposed to the elements, consider using one of these metals.

Use a Corrosion Inhibitor

One of the most effective ways to prevent rust is to use a corrosion inhibitor. These chemical compounds work by decreasing the corrosion rate of a metal or alloy that comes into contact with a liquid or gas. Corrosion inhibitors can be added to a variety of substances, including water, oil, and fuel. They work by forming a protective barrier on the surface of the metal, which prevents moisture and other corrosive agents from reaching the metal itself. Some common types of corrosion inhibitors include:

  • Zinc phosphate
  • Sodium nitrite
  • Sodium benzoate
  • Calcium nitrate

Keep it Dry

Moisture is one of the main culprits when it comes to rust and corrosion. If you want to prevent rust from forming on your metal surfaces, it’s important to keep them as dry as possible. This means storing metal objects in a dry place, wiping them down after use, and avoiding exposing them to moisture whenever possible.

Apply a Protective Coating

Another effective way to prevent rust is to apply a protective coating to your metal surfaces. There are a variety of coatings available, including paint, epoxy, and polyurethane. These coatings work by forming a barrier between the metal and the environment, preventing moisture and other corrosive agents from reaching the metal surface.

Regular Maintenance

Finally, one of the best ways to prevent rust is to stay on top of regular maintenance. This means inspecting your metal surfaces regularly for signs of corrosion, cleaning them as needed, and applying any necessary protective coatings or corrosion inhibitors. By staying vigilant and taking proactive steps to prevent rust, you can keep your metal surfaces looking great for years to come.

Getting Rid of Rust: Treatment Options

When it comes to treating rust, there are a variety of options available. Here are some of the most common types of rust converters:

  • Tannic acid-based converters: These solutions contain tannic acid, which chemically converts rust into a stable, inert layer of ferric tannate. This layer provides a protective barrier against further rusting. Tannic acid-based converters are a great option for household decorations and small metal items. Ferprime and Qconvert are some examples of tannic acid-based converters.
  • Phosphoric acid-based converters: These solutions contain phosphoric acid, which converts rust into an oxide that is inert and stable. Phosphoric acid-based converters are a great option for larger pieces of metal that need to be treated quickly. They are also commonly used in conjunction with painting or epoxy to create a strong, rust-resistant surface. Some examples of phosphoric acid-based converters include Rust-Oleum Rust Reformer and KBS Coatings RustSeal.
  • Polymer-based converters: These solutions contain an active ingredient that converts rust into a polymer that creates a strong, protective layer. Polymer-based converters are a great option for items that will be exposed to harsh conditions, such as outdoor furniture or vehicles. They are also easy to apply, as they can be sprayed directly onto the rusty surface. Some examples of polymer-based converters include POR-15 Rust Preventive Coating and Rust-Oleum Rust Reformer.

Choosing the Right Rust Converter

When selecting a rust converter, it’s important to consider the following factors:

  • The type of metal you are treating
  • The size of the item you are treating
  • The type of rust converter you prefer (tannic acid-based, phosphoric acid-based, or polymer-based)
  • The method of application (aerosol, sprayable, or quart/gallon)
  • The time required for the converter to dry and cure

Additional Tips for Rust Treatment

Here are some additional tips to keep in mind when treating rust:

  • Make sure the surface is clean and dry before applying the converter.
  • If the rust is particularly stubborn, you may need to remove it mechanically (with a wire brush or sandpaper) before applying the converter.
  • Always wear protective gloves and eyewear when working with rust converters.
  • If you are using a phosphoric acid-based converter, you may want to lower the pH of the solution by wetting the surface with an acid (such as vinegar) before applying the converter. This can speed up the reaction and provide additional support for the oxide layer.
  • If you are using a polymer-based converter, make sure to select a converter that contains a solvent (such as glycol monobutyl ether) that acts as a wetting agent. This will help the converter penetrate the rust and provide a strong, stable layer.


So, rust is a chemical reaction that occurs when iron comes into contact with oxygen and moisture. 

It’s important to know how to prevent rust and treat it when it occurs. So, don’t be afraid to ask questions if you’re not sure about something. Just remember to always be careful with rust and to use protective coatings.

Joost Nusselder, the founder of Lakeside Smokers is a content marketer, dad and loves trying out new food with BBQ Smoking (& Japanese food!) at the heart of his passion, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with recipes and cooking tips.