View source for Rust

{{Short description|Type of iron oxide}}
{{About|the chemical compound|other uses|Rust (disambiguation)}}

[[File:Rust on iron.jpg|thumb|upright=1.35|Colors and porous surface texture of rust]]
{{Steels}}
'''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]]. Rust consists of [[hydrous ferric oxides|hydrous iron(III) oxide]]s (Fe<sub>2</sub>O<sub>3</sub>·nH<sub>2</sub>O) and [[iron(III) oxide-hydroxide]] (FeO(OH), Fe(OH)<sub>3</sub>), and is typically associated with the [[corrosion]] of [[refined iron]].

Given sufficient time, any iron mass in the presence of water and oxygen, will form rust and could eventually convert entirely to rust. Surface rust is commonly flaky and [[friable]], and provides no [[passivation (chemistry)|passivation]]al protection to the underlying iron unlike other metals such as aluminum, [[copper]], and [[tin]] which form stable oxide layers. ''Rusting'' is the common term for [[corrosion]] of elemental iron and [[ferroalloy|its alloy]]s such as [[steel]]. Many other [[metal]]s undergo similar corrosion, but the resulting oxides are not commonly called "rust".<ref>{{cite web |title=Rust, n.1 and adj. |url=https://www.oed.com/view/Entry/169112 |website=OED Online |publisher=Oxford University Press |access-date=7 July 2018 |language=en |date=June 2018}}</ref>

Several forms of rust are distinguishable both visually and by [[spectroscopy]], and form under different circumstances.<ref>{{cite web|url=http://nasa.gov/centers/ames/multimedia/audio/MER/mer13.html|title=Interview, David Des Marais|work=NASA|date=2003|url-status=live|archive-url=https://web.archive.org/web/20071113202732/http://nasa.gov/centers/ames/multimedia/audio/MER/mer13.html|archive-date=2007-11-13}}</ref> Other forms of rust include the result of reactions between iron and [[chloride]] in an environment deprived of oxygen. [[Rebar]] used in underwater [[concrete]] [[column|pillars]], which generates [[green rust]], 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; this results from reaction with atmospheric oxygen. If kept free of moisture, it makes the "stable" layer protective to the iron below, albeit not to the extent of other oxides such as [[aluminium oxide]] on [[aluminium]].<ref>{{Cite web|url=http://www.depotwijzer.be/sites/default/files/files/rust_never_sleeps.pdf|title=Rust Never Sleeps: Recognizing Metals and Their Corrosion Products|last1=Ankersmit|last2=Griesser-Stermscheg|last3=Selwyn|last4=Sutherland|first1=Bart|first2=Martina|first3=Lindsie|first4=Susanne|website=depotwijzer|publisher=Parks Canada|access-date=23 July 2016|url-status=live|archive-url=https://web.archive.org/web/20160809005011/http://www.depotwijzer.be/sites/default/files/files/rust_never_sleeps.pdf|archive-date=9 August 2016}}</ref>

== Chemical reactions ==
[[File:RustyChainEdit1.jpg|thumb|Heavy rust on the links of a chain near the [[Golden Gate Bridge]] in [[San Francisco]]; it was continuously exposed to moisture and [[salt spray]], causing surface breakdown, cracking, and flaking of the metal. The chain was replaced in 2023.]]
[[File:Trabajando una pieza de metal al rojo sobre un yunque.jpg|thumb|Rust scale forming and flaking off from a steel bar heated to its [[forging]] temperature of 1200°C. Rapid oxidation occurs when heated steel is exposed to air.]]

Rust is a general name for a complex of oxides and hydroxides of iron,<ref>{{Cite book|url=https://books.google.com/books?id=lH8GRXstqQEC&q=Rust+is+another+name+for+iron+oxide|title=Accent on science|last1=Sund|first1=Robert B.|last2=Bishop|first2=Jeanne|date=1980|publisher=C.E. Merrill|isbn=9780675075695|language=en|url-status=live|archive-url=https://web.archive.org/web/20171130151505/https://books.google.com/books?id=lH8GRXstqQEC&q=Rust+is+another+name+for+iron+oxide&dq=Rust+is+another+name+for+iron+oxide&hl=en&sa=X&ved=0ahUKEwiEp8Lzj8DUAhVM82MKHUJnBIsQ6AEILTAB|archive-date=2017-11-30}}</ref> which occur when iron or some alloys that contain iron are exposed to oxygen and moisture for a long period of time. Over time, the oxygen combines with the metal, forming new compounds collectively called rust, in a process called rusting.  Rusting is an [[redox|oxidation]] reaction specifically occurring with iron.  Other metals also corrode via similar oxidation, but such corrosion is not called rusting.

The main [[Catalysis|catalyst]] for the rusting process is water. Iron or steel structures might appear to be solid, but water molecules can penetrate the microscopic [[Pitting corrosion|pits]] and cracks in any exposed metal. The hydrogen atoms present in water molecules can combine with other elements to form acids, which will eventually cause more metal to be exposed. If chloride ions are present, as is the case with saltwater, the corrosion is likely to occur more quickly. Meanwhile, the oxygen atoms combine with metallic atoms to form the destructive oxide compound. These iron compounds are brittle and crumbly and replace strong metallic iron, reducing the strength of the object.

===Oxidation of iron===

When iron is in contact with water and oxygen, it rusts.<ref name="Bodner">{{cite web|url=https://chemed.chem.purdue.edu/genchem/topicreview/bp/ch19/oxred_1.php|publisher=Bodner Research Web|access-date=28 April 2020|title=Oxidation Reduction Reactions}}</ref> If [[salt]] is present, for example in [[seawater]] or [[salt spray]], the iron tends to rust more quickly, as a result of chemical reactions. Iron metal is relatively unaffected by pure water or by dry oxygen. As with other metals, like aluminium, a tightly adhering oxide coating, a [[Passivation (chemistry)|passivation layer]], protects the bulk iron from further oxidation. The conversion of the passivating [[ferrous oxide]] layer to rust results from the combined action of two agents, usually oxygen and water.

Other degrading solutions are [[sulfur dioxide]] in water and [[carbon dioxide]] in water. Under these corrosive conditions, [[iron hydroxide]] species are formed. Unlike ferrous oxides, the hydroxides do not adhere to the bulk metal. As they form and flake off from the surface, fresh iron is exposed, and the corrosion process continues until either all of the iron is consumed or all of the oxygen, water, carbon dioxide or sulfur dioxide in the system are removed or consumed.<ref>{{cite book|last1=Holleman|first1=A. F.|last2=Wiberg|first2=E.|title=Inorganic Chemistry|publisher=Academic Press|location=San Diego|date=2001|isbn=0-12-352651-5}}</ref>

When iron rusts, the oxides take up more volume than the original metal; this expansion can generate enormous forces, damaging structures made with iron.  See ''[[#Economic effect|economic effect]]'' for more details.

=== Associated reactions ===

The rusting of iron is an electrochemical process that begins with the transfer of [[electron]]s from iron to oxygen.<ref>{{Cite encyclopedia | last1 = Gräfen | first1 = H. | last2 = Horn | first2 = E. M. | last3 = Schlecker | first3 = H. | last4 = Schindler | first4 = H. | year = 2000 | chapter = Corrosion | encyclopedia = Ullmann's Encyclopedia of Industrial Chemistry| publisher= Wiley-VCH | doi = 10.1002/14356007.b01_08 | isbn = 3527306730 }}</ref> The iron is the reducing agent (gives up electrons) while the oxygen is the oxidizing agent (gains electrons). The rate of corrosion is affected by water and accelerated by [[electrolyte]]s, as illustrated by the effects of [[road salt]] on the corrosion of automobiles. The key reaction is the reduction of oxygen:
:O<sub>2</sub> + 4&nbsp;{{e-}} + 2&nbsp;{{H2O}} → 4&nbsp;{{OH-}}
Because it forms [[hydroxide]] [[ion]]s, this process is strongly affected by the presence of acid. Likewise, the corrosion of most metals by oxygen is accelerated at low [[pH]]. Providing the electrons for the above reaction is the oxidation of iron that may be described as follows:
:Fe → Fe<sup>2+</sup> + 2&nbsp;{{e-}}

The following [[redox reaction]] also occurs in the presence of water and is crucial to the formation of rust:
:4&nbsp;Fe<sup>2+</sup> + O<sub>2</sub> → 4&nbsp;Fe<sup>3+</sup> + 2&nbsp;O<sup>2−</sup>

In addition, the following multistep [[acid–base reaction]]s affect the course of rust formation:

:Fe<sup>2+</sup> + 2&nbsp;{{hsp}}H<sub>2</sub>O ⇌ Fe(OH)<sub>2</sub> + 2&nbsp;{{H+}}
:Fe<sup>3+</sup> + 3&nbsp;{{hsp}}H<sub>2</sub>O ⇌ Fe(OH)<sub>3</sub> + 3&nbsp;{{H+}}

as do the following [[Dehydration reaction|dehydration]] equilibria:
:[[Iron|Fe]](OH)<sub>2</sub> ⇌ FeO + {{H2O}}
:[[Iron|Fe]](OH)<sub>3</sub> ⇌ FeO(OH) + {{H2O}}
:2&nbsp;FeO(OH) ⇌ Fe<sub>2</sub>O<sub>3</sub> + {{H2O}}

From the above equations, it is also seen that the corrosion products are dictated by the availability of water and oxygen. With limited dissolved oxygen, iron(II)-containing materials are favoured, including [[iron(II) oxide|FeO]] and black [[lodestone]] or [[magnetite]] (Fe<sub>3</sub>O<sub>4</sub>). High oxygen concentrations favour [[ferric]] materials with the nominal formulae Fe(OH)<sub>3−''x''</sub>O<sub>{{frac|''x''|2}}</sub>. The nature of rust changes with time, reflecting the slow rates of the reactions of solids.<ref name="Bodner"/>

Furthermore, these complex processes are affected by the presence of other ions, such as [[calcium|Ca<sup>2+</sup>]], which serve as electrolytes which accelerate rust formation, or combine with the [[hydroxide]]s and [[oxide]]s of iron to precipitate a variety of Ca, Fe, O, OH species.

The onset of rusting can also be detected in the laboratory with the use of [[ferroxyl indicator solution]]. The solution detects both Fe<sup>2+</sup> ions and hydroxyl ions. Formation of Fe<sup>2+</sup> ions and hydroxyl ions are indicated by blue and pink patches respectively.

== Prevention  ==
[[File:Uithuizermeeden de Boer 02.JPG|thumb|upright|[[Weathering steel|Cor-Ten]] is a group of steel alloys which were developed to eliminate the need for painting, and form a stable rust-like appearance after several years' exposure to weather.]]

Because of the widespread use and importance of iron and steel products, and because rusting severely compromises the strength, functionality and the appearance of such products, the prevention and control of rust is the basis of major economic activities in a number of specialized technologies. A brief overview of methods is presented here; for detailed coverage, see the cross-referenced articles.
<!-- TO BE ADDED: Estimates of annual economic damage due to rust, and annual expenditures to prevent rust -->

Rust is [[Permeation|permeable]] to air and water, therefore the interior metallic iron beneath a rust layer continues to corrode. Rust prevention thus requires coatings that preclude rust formation.

=== Rust-resistant alloys ===
{{See also|Stainless steel|Weathering steel}}

[[File:Rust-AH-2022.jpg|thumb|left|Cor-Ten sheet with rust coating]]
Stainless steel forms a [[Passivation (chemistry)|passivation]] layer of [[chromium(III) oxide]].<ref>{{Cite book|url=https://books.google.com/books?id=h4zLBQAAQBAJ&q=Stainless+steel+forms+a+passivation+layer+of+chromium%28III%29+oxide&pg=PA142|title=Ohmic Heating in Food Processing|last1=Ramaswamy|first1=Hosahalli S.|last2=Marcotte|first2=Michele|last3=Sastry|first3=Sudhir|last4=Abdelrahim|first4=Khalid|date=2014-02-14|publisher=CRC Press|isbn=9781420071092|language=en|url-status=live|archive-url=https://web.archive.org/web/20180502013026/https://books.google.com/books?id=h4zLBQAAQBAJ&pg=PA142&dq=Stainless+steel+forms+a+passivation+layer+of+chromium(III)+oxide&hl=en&sa=X&ved=0ahUKEwinp83KkefXAhXD5lQKHYSACKAQ6AEIJjAA#v=onepage&q=Stainless%20steel%20forms%20a%20passivation%20layer%20of%20chromium(III)%20oxide&f=false|archive-date=2018-05-02}}</ref><ref>{{Cite web|url=http://www.homofaciens.de/technics-electrochemistry-corrosion-prevention_en.htm|title=Corrosion prevention - HomoFaciens|last=Heinz|first=Norbert|website=www.homofaciens.de|access-date=2017-11-30|url-status=live|archive-url=https://web.archive.org/web/20171201030421/http://www.homofaciens.de/technics-electrochemistry-corrosion-prevention_en.htm|archive-date=2017-12-01}}</ref> Similar passivation behavior occurs with [[magnesium]], [[titanium]], [[zinc]], [[zinc oxide]]s, [[aluminium]], [[polyaniline]], and other electroactive conductive polymers.<ref>{{Cite journal |title=Formation of stable passive film on stainless steel by electrochemical deposition of polypyrrole |url=https://www.researchgate.net/publication/244152652 |journal=Electrochimica Acta}}</ref>

Special "[[weathering steel]]" alloys such as Cor-Ten rust at a much slower rate than normal, because the rust adheres to the surface of the metal in a protective layer. Designs using this material must include measures that avoid worst-case exposures since the material still continues to rust slowly even under near-ideal conditions.<ref>{{cite web |url= https://www.azom.com/article.aspx?ArticleID=12974|title= Weathering Steel|author=<!--Not stated--> |date= 28 June 2016|website= azom.com|publisher= AZoM|access-date= 2022-09-13|quote=The steel is allowed to rust and because of its alloy composition rusts more slowly than conventional steel and the rust forms a protective coating slowing the rate of future corrosion}}</ref>
{{clear}}

=== Galvanization ===
{{main|Galvanization}}
[[Image:Rust from bathtub in Kyiv.jpg|thumb|Interior rust in old galvanized iron water pipes can result in brown and black water.]]

Galvanization consists of an application on the object to be protected of a layer of metallic [[zinc]] by either [[hot-dip galvanizing]] or [[electroplating]]. Zinc is traditionally used because it is cheap, adheres well to steel, and provides [[cathodic protection]] to the steel surface in case of damage of the zinc layer. In more corrosive environments (such as salt water), [[cadmium]] plating is preferred instead of the underlying protected metal. The protective zinc layer is consumed by this action, and thus galvanization provides protection only for a limited period of time.

More modern coatings add aluminium to the coating as ''zinc-alume''; aluminium will migrate to cover scratches and thus provide protection for a longer period. These approaches rely on the aluminium and zinc oxides protecting a once-scratched surface, rather than oxidizing as a [[sacrificial anode]] as in traditional galvanized coatings. In some cases, such as very aggressive environments or long design life, both zinc and a [[coating]] are applied to provide enhanced corrosion protection.

Typical galvanization of steel products that are to be subjected to normal day-to-day weathering in an outside environment consists of a hot-dipped 85&nbsp;[[μm]] zinc coating. Under normal weather conditions, this will deteriorate at a rate of 1&nbsp;μm per year, giving approximately 85 years of protection.<ref>{{cite web |url= https://www.greenspec.co.uk/building-design/steel-corrosion-protection/|title= Steel corrosion protection - Durability - Structural steel|author=<!--Not stated--> |date= |website= greenspec.co.uk|publisher= greenspec|access-date= 2022-09-13|quote=For atmospheric corrosion, refer to the Galvanizers Association Millennium Map of average zinc corrosion rates. About 50% of England and Wales has a rate of under 1&nbsp;μm/year}}</ref>

=== Cathodic protection ===
{{main|Cathodic protection}}

Cathodic protection is a technique used to inhibit corrosion on buried or immersed structures by supplying an electrical charge that suppresses the electrochemical reaction. If correctly applied, corrosion can be stopped completely. In its simplest form, it is achieved by attaching a sacrificial anode, thereby making the iron or steel the cathode in the cell formed. The sacrificial anode must be made from something with a more negative [[electrode potential]] than the iron or steel, commonly zinc, aluminium, or magnesium. The sacrificial anode will eventually corrode away, ceasing its protective action unless it is replaced in a timely manner.

Cathodic protection can also be provided by using an applied electrical current. This would then be known as ICCP Impressed Current Cathodic Protection.<ref>{{Cite news|url=http://www.matcor.com/resources/cathodic-protection-systems/|title=Cathodic Protection Systems - Matcor, Inc.|work=Matcor, Inc.|access-date=2017-03-29|language=en-US|url-status=live|archive-url=https://web.archive.org/web/20170330083432/http://www.matcor.com/resources/cathodic-protection-systems/|archive-date=2017-03-30}}</ref>

=== Coatings and painting ===
{{main|Rustproofing}}
[[Image:Flaking paint on rusting metal.jpg|thumb|upright|left|Flaking paint, exposing a patch of surface rust on sheet metal]]

Rust formation can be controlled with coatings, such as [[paint]], [[lacquer]], [[varnish]], or wax tapes<ref>{{cite web |url=https://trentoncorp.com/wp-content/uploads/2016/01/20000e_trenton_corporation_wax-tape_systems_brochure_rev10.pdf |title=Wax-Tape Anticorrosion Wrap Systems |publisher=Trenton Corporation |access-date=2018-03-22 |url-status=dead |archive-url=https://web.archive.org/web/20180323092310/https://trentoncorp.com/wp-content/uploads/2016/01/20000e_trenton_corporation_wax-tape_systems_brochure_rev10.pdf |archive-date=2018-03-23 }}</ref> that isolate the iron from the environment.<ref>{{Cite book |last=Schweitzer |first=Philip A |url=http://www.crcnetbase.com/isbn/9780849382451 |title=Corrosion engineering handbook. |date=2007 |publisher=CRC Press |isbn=978-0-8493-8246-8 |location=Boca Raton |language=English |oclc=137248977}}</ref> 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. Such treatments usually also contain rust inhibitors. Covering steel with concrete can provide some protection to steel because of the [[alkaline]] [[pH]] environment at the steel–concrete interface. However, rusting of steel in concrete can still be a problem, as expanding rust can fracture concrete from within.<ref>{{cite web |title=Corrosion of Embedded Metals |url=https://www.cement.org/learn/concrete-technology/durability/corrosion-of-embedded-materials |website=cement.org |publisher=Portland Cement Association |access-date=9 July 2021}}</ref><ref>{{cite web |title=Rust Wedge: Expanding rust is a force strong enough to shatter concrete |url=https://www.exploratorium.edu/exhibits/rust-wedge |website=exploratorium.edu |date=17 April 2018 |access-date=9 July 2021}}</ref>

As a closely related example, iron clamps were used to join [[marble]] blocks during a restoration attempt of the [[Parthenon]] in [[Athens, Greece]], in 1898, but caused extensive damage to the marble by the rusting and swelling of unprotected iron. The ancient Greek builders had used a similar fastening system for the marble blocks during construction, however, they also poured molten [[lead]] over the iron joints for protection from seismic shocks as well as from corrosion. This method was successful for the 2500-year-old structure, but in less than a century the crude repairs were in imminent danger of collapse.<ref>{{cite web |last1=Hadingham |first1=Evan |title=Unlocking Mysteries of the Parthenon |url=https://www.smithsonianmag.com/history/unlocking-mysteries-of-the-parthenon-16621015/ |website=smithsonianmag.com |access-date=9 July 2021}}</ref>
When only temporary protection is needed for storage or transport, a thin layer of oil, grease or a special mixture such as [[Cosmoline]] can be applied to an iron surface. Such treatments are extensively used when "[[Reserve fleet|mothballing]]" a steel ship, automobile, or other equipment for long-term storage.

Special anti-seize lubricant mixtures are available and are applied to metallic threads and other precision machined surfaces to protect them from rust. These compounds usually contain grease mixed with copper, zinc, or aluminium powder, and other proprietary ingredients.<ref>{{cite web |title=Anti-seize Compounds Information |url=https://www.globalspec.com/learnmore/materials_chemicals_adhesives/industrial_oils_fluids/anti_seize_compounds |website=globalspec.com |publisher=Engineering 360 |access-date=9 July 2021}}</ref>

=== Bluing ===
{{main|Bluing (steel)}}

Bluing is a technique that can provide limited  {{Citation needed|reason=permanent|date=July 2023}} resistance to rusting for small steel items, such as firearms; for it to be successful, a water-displacing oil is rubbed onto the blued steel and other steel.{{Citation needed|date=July 2023}}

=== Inhibitors ===
{{main|Corrosion inhibitor}}

Corrosion inhibitors, such as gas-phase or volatile inhibitors, can be used to prevent corrosion inside sealed systems. They are not effective when air circulation disperses them, and brings in fresh oxygen and moisture.

=== Humidity control ===
{{See also|Dehumidifier|Desiccant}}

Rust can be avoided by controlling the moisture in the atmosphere.<ref>{{Cite book|url=https://books.google.com/books?id=vn7E49c8CGQC&q=Rust+can+be+avoided+by+controlling+the+moisture+in+the+atmosphere&pg=PA28|title=Young Scientist Series ICSE Chemistry 7|last1=Mirza|first1=Lorraine |first2=Krishnakali |last2=Gupta|publisher=Pearson Education India|isbn=9788131756591|language=en|url-status=live|archive-url=https://web.archive.org/web/20171130151505/https://books.google.com/books?id=vn7E49c8CGQC&pg=PA28&dq=Rust+can+be+avoided+by+controlling+the+moisture+in+the+atmosphere&hl=en&sa=X&ved=0ahUKEwiBgbqXy-bXAhXHyVQKHemzAdIQ6AEILTAB#v=onepage&q=Rust%20can%20be%20avoided%20by%20controlling%20the%20moisture%20in%20the%20atmosphere&f=false|archive-date=2017-11-30}}</ref> An example of this is the use of [[silica gel]] packets to control humidity in equipment shipped by sea.

== Treatment ==

Rust removal from small iron or steel objects by [[electrolysis]] can be done in a home workshop using simple materials such as a plastic bucket filled with an electrolyte consisting of [[Sodium carbonate|washing soda]] dissolved in [[tap water]], a length of [[rebar]] suspended vertically in the solution to act as an [[anode]], another laid across the top of the bucket to act as a support for suspending the object, [[baling wire]] to suspend the object in the solution from the horizontal rebar, and a [[battery charger]] as a power source in which the positive terminal is clamped to the anode and the negative terminal is clamped to the object to be treated which becomes the [[cathode]].<ref name=antique-engines>{{cite web|title=Rust Removal using Electrolysis|url=http://antique-engines.com/electrol.asp|website=antique-engines.com|access-date=April 1, 2015|url-status=usurped|archive-url=https://web.archive.org/web/20150330211904/http://www.antique-engines.com/electrol.asp|archive-date=March 30, 2015}}</ref> Hydrogen and oxygen gases are produced at the cathode and anode respectively. This mixture is flammable/explosive.<ref>{{cite web |last1=Smith |first1=Paul |title=Exploding Hydrogen Balloons with Different Amounts of Oxygen |url=https://www.youtube.com/watch?v=J6zRbDfgYAc |website=Youtube |date=24 June 2022 |access-date=2023-12-29}}</ref> Care should also be taken to avoid [[hydrogen embrittlement]]. Overvoltage also produces small amounts of ozone, which is highly toxic, so a low voltage phone charger is a far safer source of DC current.  The effects of hydrogen on global warming have also recently come under scrutiny.<ref>{{cite journal |last1=Derwent |first1=Richard |title=Global warming potential (GWP) for hydrogen: Sensitivities, uncertainties and meta-analysis |url=https://www.sciencedirect.com/science/article/abs/pii/S0360319922055380 |journal=International Journal of Hydrogen Energy |date=2023 |volume=48 |issue=22 |pages=8328–8341 |doi=10.1016/j.ijhydene.2022.11.219 |bibcode=2023IJHE...48.8328D |access-date=December 9, 2023|url-access=subscription }}</ref>

Rust may be treated with commercial products known as [[rust converter]] which contain [[tannic acid]] or [[phosphoric acid]] which combines with rust; removed with organic acids like [[citric acid]] and [[vinegar]] or removed with [[chelation|chelating]] agents as in some commercial formulations or even a solution of [[molasses]].<ref name=practical-machinist>{{cite web|title=Rust Removal with Molasses|date=6 July 2005 |url=http://www.practicalmachinist.com/vb/general-archive/rust-removal-using-molasses-90452/|access-date=November 29, 2017|url-status=live|archive-url=https://web.archive.org/web/20160925094819/http://www.practicalmachinist.com/vb/general-archive/rust-removal-using-molasses-90452/|archive-date=September 25, 2016}}</ref>

== Economic effect ==
{{anchor|Economic effect}}
{{Main|Corrosion}}

[[File:Rust wedge.jpg|thumb|upright=.6|Outdoor ''Rust Wedge'' at the [[Exploratorium]] showing the expansion of rusting iron]]
Rust is associated with the degradation of iron-based tools and structures. As rust has a much higher volume than the originating mass of iron, its buildup can also cause failure by forcing apart adjacent parts phenomenon sometimes known as "rust packing". It was the cause of the collapse of the [[Mianus river bridge]] in 1983, when the bearings rusted internally and pushed one corner of the road slab off its support.

 [[Silver Bridge]] disaster of 1967 in [[West Virginia]], when a steel [[suspension bridge]] collapsed in less than a minute, killing 46 drivers and passengers on the bridge at the time. The [[Kinzua Bridge]] in [[Pennsylvania]] was blown down by a [[tornado]] in 2003, largely because the central base bolts holding the structure to the ground had rusted away, leaving the bridge anchored by gravity alone.

[[Reinforced concrete]] is also vulnerable to rust damage. Internal pressure caused by expanding corrosion of concrete-covered steel and iron can cause the concrete to [[spall]], creating severe structural problems. It is one of the most common failure modes of reinforced concrete [[bridge]]s and buildings.

<gallery class="center" mode="packed" caption="Structural failures caused by rust">
File:Silver Bridge collapsed, Ohio side.jpg|The collapsed [[Silver Bridge]], as seen from the [[Ohio]] side
File:Collapsed Kinzua Bridge.jpg|The [[Kinzua Bridge]] after it collapsed
File:Nandu River Iron Bridge corrosion - 03.jpg|Rusted and [[Pitting corrosion|pitted]] struts of the 70-year-old [[Nandu River Iron Bridge]]
File:Qew bruecke nf beton kaputt 23 von 46.jpg|Rusting [[rebar]] has expanded and [[spall]]ed concrete off the surface of this [[reinforced concrete]] support.
</gallery>

== Cultural symbolism ==

Rust is a commonly used [[metaphor]] for slow decay due to neglect, since it gradually converts robust iron and steel metal into a soft crumbling powder. A wide section of the industrialized [[American Midwest]] and [[American Northeast]], once dominated by [[steelmaking|steel foundries]], the [[automotive industry]], and other manufacturers, has experienced harsh economic cutbacks that have caused the region to be dubbed the "[[Rust Belt]]".

In music, literature, and art, rust is associated with images of faded glory, neglect, decay, and ruin.
<!-- EXAMPLES: "Rust Never Sleeps", "Diamonds and Rust", "Kingdom of Rust", "Carnival of Rust", "Rust Belt Music", "Rust in Peace", etc. -->

==See also==
* [[Corrosion engineering]]

== References ==

{{Reflist}}

== Further reading ==
* [[Jonathan Waldman|Waldman, J.]] (2015): ''Rust – the longest war.'' Simon & Schuster, New York. {{ISBN|978-1-4516-9159-7}}
* {{Cite book |last=Schweitzer |first=Philip A. |title=Corrosion engineering handbook. Fundamentals of metallic corrosion : atmospheric and media corrosion of metals |date=2007 |publisher=CRC Press |isbn=978-0-8493-8244-4 |edition=2 |location=Boca Raton |oclc=137248972}}
* {{Cite book|title=Corrosion of reinforcement in concrete construction|date=1996|publisher=Royal Society of Chemistry, Information Services|others=C. L. Page, P. B. Bamforth, J. W. Figg, International Symposium on Corrosion of Reinforcement in Concrete Construction|isbn=0-85404-731-X|location=Cambridge|oclc=35233292}}
* Corrosion – 2nd Edition ([[Elsevier|''elsevier.com'']]) Volume 1and 2; Editor: L L Shreir {{ISBN|9781483164106}}

{{Commons category}}
{{wiktionary}}


{{Authority control}}

[[Category:Corrosion]]
[[Category:Iron]]