Editing Rust (section)

== 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, the prevention or slowing 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>
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=== 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.