Rusted bolt

A blacksmith removing rust with sand prior to welding

Rust damage in automobiles can create hidden dangers.

Rusting can completely eat away iron. Note the galvanization on the unrusted portions.

Rust is a general term for iron oxides formed by the reaction of iron with oxygen. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances.^[1] The chemical composition of rust is typically hydrated iron(III) oxide (Fe₂O₃.nH₂O), and under wet conditions may include iron(III) oxide-hydroxide (FeO(OH)). Rusting is the common term for corrosion of iron and its alloys, such as steel. Although oxidation of other metals is equivalent, these oxides are not commonly called rust. Iron oxide pigment There are a number of iron oxides: Iron oxides Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites. ... For other uses, see Iron (disambiguation). ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... Animation of the dispersion of light as it travels through a triangular prism. ... Iron(III) oxide — also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust — is one of the several oxide compounds of iron, and has paramagnetic properties. ... Iron(III) oxide-hydroxide (FeO(OH)), also called hydrated iron oxide and yellow iron oxide, is an oxide-hydroxide of iron. ... For the hazard, see corrosive. ... For other uses, see Steel (disambiguation). ...

As rust has higher volume than the originating mass of iron, its buildup may force apart adjacent parts - a phenomenon known as rust smacking.

Chemistry

The rusting of iron is one of the more widely used examples of corrosion. This electrochemical process requires the presence of water, oxygen and an electrolyte and leads to the formation of hydrated iron oxides. For the hazard, see corrosive. ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... General Name, symbol, number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, period, block 16, 2, p Appearance colorless (gas) pale blue (liquid) Standard atomic weight 15. ... An electrolyte is a substance containing free ions that behaves as an electrically conductive medium. ...

Net reactions

The overall outcome of rust formation involves reaction of iron with varying amounts of oxygen and water.

• 2Fe + O₂ + 2H₂O → 2Fe(OH)₂
• 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃
• 4Fe + 3O₂ + 2H₂O → 2Fe₂O₃•H₂O
• 6Fe + 4O₂ → 2Fe₃O₄

Mechanism

Pure, solid iron oxidizes in water:

Fe(s) → Fe²⁺(aq) + 2e^-

These electrons will quickly react with the disassociated hydrogen ions (in H₃O⁺(aq) form) and the dissolved oxygen in the water (O₂(aq)):

4e^-(aq) + 4H₃O⁺(aq) + O₂(aq) → 6H₂O(l)

Therefore, as seen from the above equation, the more acidic the water, the greater will be the rate of corrosion (since the concentration of H₃O⁺(aq) will be greater.) At extremely low pH’s, the hydrogen ions will react with the electrons producing hydrogen gas instead: For the hazard, see corrosive. ... For other uses, see PH (disambiguation). ... This article is about the chemistry of hydrogen. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ...

2H⁺(aq) + 2e^-(aq) → H₂(g)

Thus, as seen from the above equations, the pH of the solution (whether it is pure water or water containing electrolytes) rises. This leads to the formation of OH^- ions (in cases where the body of water is significantly large, the pH does not rise as sharply, but this is of no consequence since OH^- ions are always present, even in pure water.) The cations then react with the OH^- or even the H⁺ ions and dissolved oxygen to form a variety of compounds, which constitute rust: For other uses, see PH (disambiguation). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... An ion is an atom or group of atoms with a net electric charge. ...

Fe²⁺(aq) + 2OH^-(aq) → Fe(OH)₂(s)

4Fe²⁺(aq) + 4H⁺(aq) + O₂(aq) → 4Fe³⁺(aq) + 2H₂O(l)

Fe³⁺(aq) + 3OH^-(aq) → Fe(OH)₃(s)

From the above equations, it is seen that the pH and amount of dissolved oxygen can affect the outcome of the reactions. In water with limited dissolved oxygen Fe₃O₄(s) is formed, which is a black solid and commonly called lodestone: Magnetite Lodestone or loadstone refers to either: Magnetite, a magnetic mineral form of iron(II), iron(III) oxide Fe3O4, one of several iron oxides. ...

6Fe²⁺(aq) + O₂(aq) + 12OH^-(aq) → 2Fe₃O₄(s) + 6H₂O(l)

The porous Fe(OH)₃ rust can slowly disintegrate into a crystallized form, which is the familiar red-brown rust:

2Fe(OH)₃(s) → Fe₂O₃•H₂O(s) + 2H₂O(l)

Iron oxide (FeO) can also be formed. The presence of other ions, such as calcium or calcium carbonates reacts with the iron hydroxides and iron oxides to form a variety of precipitates. Other metals corrode via similar chemical processes. For other uses, see Iron (disambiguation). ... For other uses, see Calcium (disambiguation). ... Hydroxide is a functional group consisting of oxygen and hydrogen: -O−H It has a charge of 1-. The term hydroxyl group is used when the functional group -OH is counted as a substituent of an organic compound. ... For alternative meanings see metal (disambiguation). ...

Rust prevention

Hydrated rust is permeable to air and water, allowing the metal to continue to corrode - internally - even after a surface layer of rust has formed. Given sufficient hydration, the iron mass can eventually convert entirely to rust and disintegrate. Corrosion of aluminium is different from steel or iron, in that aluminium oxide formed on the surface of aluminum metal forms a protective, corrosion resistant coating, a process known as passivation. Stainless steel similarly resists rusting by forming a passivation layer of chromium(III) oxide. This is also true of magnesium, copper, titanium, and zinc. Aluminum redirects here. ... For other uses, see Steel (disambiguation). ... For other uses, see Iron (disambiguation). ... Alumina redirects here. ... Passivation is the process of making a material passive in relation to another material prior to using the materials together. ... The 630 foot high, stainless-clad (type 304L) Gateway Arch defines St. ... Passivation is the process of making a material passive in relation to another material prior to using the materials together. ... Chromium(III) oxide, also known as chromium sesquioxide or chromia, is one of four oxides of chromium, chemical formula Cr2O3. ... General Name, symbol, number magnesium, Mg, 12 Chemical series alkaline earth metals Group, period, block 2, 3, s Appearance silvery white solid at room temp Standard atomic weight 24. ... Copper has played a significant part in the history of mankind, which has used the easily accessible uncompounded metal for nearly 10,000 years. ... General Name, symbol, number titanium, Ti, 22 Chemical series transition metals Group, period, block 4, 4, d Appearance silvery metallic Standard atomic weight 47. ... General Name, symbol, number zinc, Zn, 30 Chemical series transition metals Group, period, block 12, 4, d Appearance bluish pale gray Standard atomic weight 65. ...

Galvanization consists of coating metal with a thin layer of another such metal. Typically, zinc is applied by either hot-dip galvanizing or electroplating. Zinc is traditionally used because it is cheap, easy to refine and adheres well to steel. In more corrosive environments (such as at sea) cadmium may be used. Galvanization often fails at seams, holes and joints, where the coating is pierced. In these cases the coating provides cathodic protection to metal, where it acts as a galvanic anode rusting in preference. Galvanization or galvanisation refers to any of several electrochemical processes named after the Italian scientist Luigi Galvani. ... Hot-dip galvanizing is a form of galvanization. ... Electroplating is the process of using Davd lloyd current to coat an electrically conductive object with a relatively thin layer of metal. ... General Name, Symbol, Number cadmium, Cd, 48 Chemical series transition metals Group, Period, Block 12, 5, d Appearance silvery gray metallic Standard atomic weight 112. ... Aluminium anodes mounted on a steel jacket structure Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. ...

More modern coatings add aluminium to the coating as zinc-alume, aluminium will migrate to cover scratches and thus provide protection for longer. These rely on the aluminium and zinc oxides protecting the once-scratched surface rather than oxidizing as a sacrificial anode. A sacrificial anode, or sacrificial rod, is a metallic anode used in an electrochemical process where it is intended to be dissolved to protect other metallic components. ...

There are several other methods available to control corrosion and prevent the formation of rust, colloquially termed rustproofing. Rustproofing is the process whereby the rate at which objects made of iron and/or steel begin to rust can be made so slowly that the places in which they are are rusting can be spotted in time and repaired. ...

• Cathodic protection makes the iron a cathode in a battery formed whenever water contacts the iron and also a sacrificial anode made from something with a more negative electrode potential, commonly zinc or magnesium. The electrode itself doesn't react in water, but only provides electrons to prevent the iron rusting.

• Bluing is a technique that can provide limited resistance to rusting for small steel items, such as firearms; for it to be successful, water-displacing oil must be rubbed onto the blued steel.

• Corrosion control can be done using a coating to isolate the metal from the environment, such as paint. Large structures with enclosed box sections, such as ships and modern automobiles, often have a wax-based product (technically a slushing oil) injected into these sections. This may contain rust inhibiting chemicals as well as forming a barrier. Covering steel with concrete provides protection to steel by the high pH environment at the steel-concrete interface. However, if concrete covered steel does corrode, the rust formed can cause the concrete to spall and fall apart. This creates structural problems.

To prevent rust corrosion on automobiles, they should be kept cleaned and waxed. The underbody should be sprayed to make sure it is free of dirt and debris that could trap moisture. After a car is washed, it is best to let it sit in the sun for a few hours to let it air dry. In winter, or in salty conditions, cars should be washed more regularly as road salt (calcium chloride) can accelerate the rusting process. Aluminium anodes mounted on a steel jacket structure Cathodic protection (CP) is a technique to control the corrosion of a metal surface by making that surface the cathode of an electrochemical cell. ... This article may be too technical for most readers to understand. ... Bluing is a passivation process in which steel is partially protected against rust, and is named after the blue-black appearance of the resulting protective finish. ... A coating is a covering that is applied to an object to protect it or change its appearance. ... For other uses, see Paint (disambiguation). ... Very high speed photography of a small projectile impacting a thin aluminium plate at 7000 m/s. ...

References

1. ^ Interview, David Des Marais.

See also

Wikimedia Commons has media related to:

Rust

• WD-40
• Cosmoline
• Weathering steel

Image File history File links Commons-logo. ... WD-40 is the trademark of a widely used penetrating oil (cleaner, lubricant and anti-corrosive solution) spray. ... Cosmoline: A yellowish or light-amber colored ointment like mass, having a slight fluorescence, petroleum like odor and taste (do not taste it please). ... Cor-Ten steel - Fulcrum (1987) by Richard Serra Weathering steel, best-known under the trademark Cor-Ten steel, is a group of steel alloys which were developed to obviate the need for painting, and form a stable rust-like appearance if exposed to the weather for several years. ...

External links

• A Primer on Rust, thorough rust prevention and removal information
• Rust Removal and Prevention Articles