Rust and Corrosion: What’s the difference?

Understanding the nuances between rust and corrosion is not just an academic exercise; it’s essential for preserving our belongings, ensuring the durability of infrastructure, and prolonging the life of materials in our ever-changing world. The team at Neutrarust have compiled a handy guide on the differences between rust and corrosion, read on to learn more. 

Rust and corrosion are related but distinct terms that are often used interchangeably. Here are the key differences between the two:

Rust 

Is a specific type of corrosion that occurs when iron or iron-based alloys (like steel) react with oxygen and moisture in the presence of certain salts or electrolytes. It results in the formation of iron oxide (usually reddish-brown in colour) on the surface of the metal.

Corrosion 

Is a more general term that encompasses the degradation of metals and materials through various chemical reactions with their environment. Corrosion can affect a wide range of metals and materials, not just iron or steel, and it can take many forms. It may not always resemble the classic reddish-brown rust seen on iron and steel.

What metals are affected by rust and corrosion?

Rust: Rust is specific to iron and iron-based alloys. It does not occur on other metals like aluminium or copper.

Corrosion: Corrosion can affect a wide variety of metals, including iron, steel, aluminium, copper, and many others.

What causes rust?

Rust is primarily caused by the reaction of iron or steel with oxygen and moisture, often accelerated by the presence of salts or electrolytes (e.g. saltwater affecting ships and shipping containers, road salt affecting cars).

Corrosion, on the other hand, can be caused by various chemical reactions, including oxidation, acid-base reactions, and electrochemical processes, depending on the material and the environment.

Examples of Rust

Rust: a car chassis made of steel developing a reddish-brown layer on its surface due to exposure to salt, rain and humidity is a classic illustration of rust. In this scenario, the iron or steel in the car chassis reacts with oxygen and moisture in the presence of atmospheric contaminants, leading to the formation of iron oxide, which is commonly referred to as rust. Rust can weaken the structural integrity of the car chassis over time if not properly treated or maintained. Therefore, it’s important to take steps to treat rust in order to prolong the life of the chassis and ensure the safety and performance of the vehicle.

When thinking of a car, it’s useful to realise that there are different “levels” of rust, depending on how much it has penetrated the surface. These are surface rust, scale rust, and penetrating rust. Surface rust can be considered one of the least damaging types of rust, and while it should be treated before it gets worse, it doesn’t necessarily need immediate attention. Scale rust refers to the areas of rust that have started to penetrate the surface of the metal and cause the underlying surface to become pitted and rough in texture. Penetrating rust is the type that can cause the metal to disintegrate and is usually beyond repair. 

Corrosion: Aluminium corroding and forming white or greyish spots when exposed to acidic substances or saltwater.

In summary, rust is a specific type of corrosion that affects iron and steel, characterised by its reddish-brown appearance, while corrosion is a more general term that encompasses various forms of material degradation caused by chemical reactions with the environment and can affect a wide range of metals and materials.