If salt is present, for example in seawater or salt spray, the iron tends to rust more quickly, as a result of chemical reactions. When iron is in contact with water and oxygen, it rusts. As the atoms combine, they weaken the metal, making the structure brittle and crumbly. Meanwhile, the oxygen atoms combine with metallic atoms to form the destructive oxide compound. If chloride ions are present, as is the case with saltwater, the corrosion is likely to occur more quickly. The hydrogen atoms present in water molecules can combine with other elements to form acids, which will eventually cause more metal to be exposed. Iron or steel structures might appear to be solid, but water molecules can penetrate the microscopic pits and cracks in any exposed metal. The main catalyst for the rusting process is water. However, other metals can corrode in similar ways. But only iron or alloys that contain iron can rust. Many other oxidation reactions exist which do not involve iron or produce rust. The terms "rust" and "rusting" only mean oxidation of iron and its resulting products. The best-known of these reactions involve oxygen, hence the name "oxidation". Although rust may generally be termed as "oxidation", that term is much more general and describes a vast number of processes involving the loss of electrons or increased oxidation state, as part of a reaction. Over time, the oxygen combines with the metal forming new compounds collectively called rust. Rust is a general name for a complex of oxides and hydroxides of iron, which occur when iron or some alloys that contain iron are exposed to oxygen and moisture for a long period of time. Rapid oxidation occurs when heated steel is exposed to air Rust scale forming and flaking off from a steel bar heated to its forging temperature of 1200☌. 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 aluminium oxide on aluminium. 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. Rebar used in underwater concrete pillars, which generates green rust, is an example. Other forms of rust include the result of reactions between iron and chloride in an environment deprived of oxygen. Several forms of rust are distinguishable both visually and by spectroscopy, and form under different circumstances. Many other metals undergo similar corrosion, but the resulting oxides are not commonly called "rust". Rusting is the common term for corrosion of elemental iron and its alloys such as steel. Surface rust is commonly flaky and friable, and provides no passivational protection to the underlying iron, unlike the formation of patina on copper surfaces. Given sufficient time, any iron mass, in the presence of water and oxygen, could eventually convert entirely to rust. nH 2O) and iron(III) oxide-hydroxide (FeO(OH), Fe(OH) 3), and is typically associated with the corrosion of refined iron.Rust consists of hydrous iron(III) oxides (Fe 2O 3 Rust is an iron oxide, a usually reddish-brown oxide formed by the reaction of iron and oxygen in the catalytic presence of water or air moisture. Colors and porous surface texture of rust Steels
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