How Does Metal Rust?

Rust is the result of a chemical reaction between metal, typically iron, and oxygen in the presence of moisture. This process, known as oxidation, transforms the metal into a new compound, iron oxide, which we commonly recognize as rust. The presence of water and oxygen is crucial for rust to form, and this is why metals left exposed to the elements, especially in humid or wet environments, are more prone to rusting.

The rusting process begins when iron reacts with water and oxygen. Initially, the iron dissolves in the acidic solution created by moisture and carbon dioxide in the air, forming ferrous iron and releasing hydrogen. This is the first step in the rusting process. The presence of water acts as a medium that facilitates the transfer of electrons, which is essential for the oxidation reaction to occur. Without moisture, the rusting process would be significantly slower or might not occur at all.

Once the iron has dissolved, the next step involves the oxidation of ferrous iron by oxygen in the air, leading to the formation of hydrated ferric oxide, which is the reddish-brown substance we identify as rust. This transformation involves the iron losing electrons to oxygen, a process that is accelerated by the presence of salts and acids. These substances act as catalysts, speeding up the reaction and making the metal more susceptible to rusting.

Interestingly, the rust that forms on the surface of the metal can sometimes act as a protective layer, preventing further corrosion. However, if this layer is removed or damaged, the underlying metal is exposed again, and the rusting process continues. Some metals naturally resist corrosion better than others, and various treatments like coating, painting, or galvanizing can be applied to protect metals from rusting. These methods create a barrier that prevents moisture and oxygen from reaching the metal surface.