roest

Roest is the oxidation of iron and its alloys that occurs when exposed to moisture and oxygen. The resulting compound is commonly iron oxide hydrated, known in English as rust, typically appearing as a reddish‑brown, flaky coating that weakens the metal over time. The most common form is iron(III) oxide hydrate, which can be described as ferric oxide hydrated with water.

Rust forms more quickly in the presence of electrolytes, such as salt, and under fluctuating temperatures that promote repeated wetting and drying. The electrochemical nature of corrosion causes iron to lose electrons at the metal surface and to react with oxygen and water, producing corrosion products that occupy a larger volume than the original metal and can cause cracking or spalling.

Rust is more likely on unprotected iron and steel. The process can be slowed or halted by removing moisture, applying protective coatings (paints, oils, varnishes), or by reducing the metal's exposure to oxygen and water. Common preventive methods include galvanizing (zinc coating), applying protective paints, using stainless steel or other alloys, and employing cathodic protection.

Removing rust can involve mechanical abrasion, chemical rust removers (for example acids or chelating solutions), or electrochemical cleaning. In many applications, ongoing protection and maintenance are essential to preserve structural integrity.