Glossary

Oxidation is a chemical reaction in which a material—typically a metal—loses electrons when it comes into contact with oxygen or another oxidizing agent, often forming an oxide layer on its surface. In simple terms, it’s the process that causes metals like iron to rust, copper to develop a green patina, or aluminum to form a thin protective film.

When a metal is exposed to air or moisture, oxygen molecules react with the atoms on its surface, creating metal oxides. For example, when iron reacts with oxygen and water, it forms iron oxide (rust), which is porous and flaky, allowing the corrosion to continue deeper into the metal. In contrast, metals such as aluminum, chromium, and titanium form stable, tightly adherent oxide layers that protect the underlying metal from further oxidation—this property is called passivation.

Oxidation doesn’t always cause damage; in many cases, it’s intentionally used to enhance corrosion resistance or surface appearance (as in anodizing aluminum or black oxide coatings on steel). However, uncontrolled oxidation can weaken materials, reduce conductivity, and lead to structural failure over time.