What is rust primarily composed of?

Rust is primarily composed of iron oxide, which is formed when iron reacts with oxygen in the presence of moisture. This chemical reaction typically occurs in environments where oxygen and water are available, leading to the corrosion of iron and its alloys. The process can be represented by the chemical reaction:

4 Fe + 3 O2 + 6 H2O → 4 Fe(OH)3

As the iron(III) hydroxide dehydrates, it forms iron(III) oxide (Fe2O3), commonly known as rust. This material is usually reddish-brown in color and is indicative of the deterioration of iron. Understanding rust as iron oxide is essential because it highlights the need for protective measures against corrosion, such as painting, galvanizing, or using stainless steel.