Rust

Rust is an <a href="/facts/Iron_oxide/KDo8hLWn">iron oxide</a>, a usually reddish-brown <a href="/facts/Oxide/DXtoVe1C">oxide</a> formed by the reaction of <a href="/facts/Iron/QK1JYy8E">iron</a> and <a href="/facts/Oxygen/acyn6o8r">oxygen</a> in the <a href="/facts/Catalytic/LPBS7TQC">catalytic</a> presence of <a href="/facts/Water/0lkXnJPK">water</a> or <a href="/facts/Air_moisture/DX5IUFG0">air moisture</a>. Rust consists of <a href="/facts/Hydrous_ferric_oxides/oo4Lsf9M">hydrous iron(III) oxides</a> (Fe2O3·nH2O) and <a href="/facts/Iron(III)_oxide-hydroxide/YpW6aAAS">iron(III) oxide-hydroxide</a> (FeO(OH), Fe(OH)3), and is typically associated with the <a href="/facts/Corrosion/lIC7H4we">corrosion</a> of <a href="/facts/Refined_iron/bxLL2NaR">refined iron</a>.
Given sufficient time, any iron mass, in the presence of water and oxygen, could eventually convert entirely to rust. Surface rust is commonly flaky and <a href="/facts/Friable/bkPTPxqQ">friable</a>, and provides no <a href="/facts/Passivation_(chemistry)/tPADJj5G">passivational</a> protection to the underlying iron, unlike the formation of <a href="/facts/Patina/IVQsrSMM">patina</a> on copper surfaces. Rusting is the common term for <a href="/facts/Corrosion/lIC7H4we">corrosion</a> of elemental iron and <a href="/facts/Ferroalloy/0NfDFfQE">its alloys</a> such as <a href="/facts/Steel/aN6qWo4H">steel</a>. Many other <a href="/facts/Metal/PT8hNX6R">metals</a> undergo similar corrosion, but the resulting oxides are not commonly called "rust".
Several forms of rust are distinguishable both visually and by <a href="/facts/Spectroscopy/mj71FuNK">spectroscopy</a>, and form under different circumstances. Other forms of rust include the result of reactions between iron and <a href="/facts/Chloride/m9NUaUDR">chloride</a> in an environment deprived of oxygen. <a href="/facts/Rebar/qm27fUbk">Rebar</a> used in underwater <a href="/facts/Concrete/K6whGVNx">concrete</a> <a href="/facts/Column/NDtghP75">pillars</a>, which generates <a href="/facts/Green_rust/nGtySEbh">green rust</a>, is an example. Although rusting is generally a negative aspect of iron, a particular form of rusting, known as stable rust, causes the object to have a thin coating of rust over the top. If kept in low relative humidity, it makes the "stable" layer protective to the iron below, but not to the extent of other oxides such as <a href="/facts/Aluminium_oxide/wXM9P6pI">aluminium oxide</a> on <a href="/facts/Aluminium/7wmR8jYE">aluminium</a>.

Rust open-in-new

Rust