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Rust is an
iron oxide Iron oxides are chemical compounds composed of iron and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, ...

iron oxide
, a usually reddish-brown
oxide An oxide () is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...
formed by the reaction of
iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

iron
and
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
in the
catalytic that utilizes a low-temperature oxidation catalyst to convert carbon monoxide to less toxic carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules ...
presence of
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
or
air moisture (99.9839 °C) , - , Boiling point The boiling point of a substance is the temperature at which the vapor pressure of a liquid equals the pressure surrounding the liquid and the liquid changes into a vapor. The boiling point of a liqui ...
. Rust consists of hydrous iron(III) oxides (Fe2O3·nH2O) and
iron(III) oxide-hydroxide Iron(III) oxide-hydroxide or ferric oxyhydroxideA. L. Mackay (1960): "β-Ferric Oxyhydroxide". ''Mineralogical Magazine'' (''Journal of the Mineralogical Society''), volume 32, issue 250, pages 545-557. is the chemical compound of iron Iron ...
(FeO(OH), Fe(OH)3), and is typically associated with the
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide An oxide () is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecu ...

corrosion
of
refined iron Pig iron, also known as crude iron, is an intermediate product Intermediate goods, producer goods or semi-finished products are goods In economics Economics () is the social science that studies how people interact with value; in parti ...
. 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
friable Friability ( ), the condition of being friable, describes the tendency of a solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and c ...
, and provides no passivational protection to the underlying iron, unlike the formation of
patina Patina (or ) is a thin layer that variously forms on the surface of , , and similar ( produced by oxidation or other chemical processes), or certain s, and wooden (sheen produced by age, wear, and polishing), or any similar acquired change ...

patina
on copper surfaces. ''Rusting'' is the common term for
corrosion Corrosion is a natural process that converts a refined metal into a more chemically stable form such as oxide An oxide () is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecu ...

corrosion
of elemental iron and its alloys such as
steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appe ...

steel
. Many other
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
s undergo similar corrosion, but the resulting oxides are not commonly called "rust". Several forms of rust are distinguishable both visually and by
spectroscopy Spectroscopy is the study of the interaction Interaction is a kind of action that occurs as two or more objects have an effect upon one another. The idea of a two-way effect is essential in the concept of interaction, as opposed to a one-way ...

spectroscopy
, and form under different circumstances. Other forms of rust include the result of reactions between iron and
chloride The chloride ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects th ...

chloride
in an environment deprived of oxygen.
Rebar Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel bar or mesh of steel wires used as a tension device in reinforced concrete and reinforced masonry structures to strengthen and aid the con ...
used in underwater
concrete Concrete is a composite material A composite material (also called a composition material or shortened to composite, which is the common name) is a material Material is a substance Substance may refer to: * Substance (Jainism), a ter ...

concrete
pillars A column or pillar in architecture and structural engineering is a structural element that transmits, through compression (physical), compression, the weight of the structure above to other structural elements below. In other words, a column is ...

pillars
, which generates
green rust Green rust is a generic name for various green crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal latti ...
, 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, and if kept in low relative humidity, makes the "stable" layer protective to the iron below, but not to the extent of other oxides such as
aluminium oxide Aluminium oxide is a chemical compound of aluminium and oxygen with the chemical formula 23. It is the most commonly occurring of several Aluminium oxide (compounds), aluminium oxides, and specifically identified as aluminium(III) oxide. It is ...

aluminium oxide
on
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
.


Chemical reactions

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. Over time, the oxygen combines with the metal forming new compounds collectively called rust. 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
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s or increased oxidation state, as part of a
reaction Reaction may refer to a process or to a response to an action, event, or exposure: Physics and chemistry *Chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformat ...

reaction
. The best-known of these reactions involve
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
, hence the name "oxidation". The terms "rust" and "rusting" only mean oxidation of iron and its resulting products. Many other
oxidation reaction (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and permanganate, . It is a purplish-black crystalline salt, th ...
s exist which do not involve iron or produce rust. But only iron or alloys that contain iron can rust. However, other
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
s can corrode in similar ways. The main catalyst for the rusting process is water. Iron or steel structures might appear to be solid, but water molecules can penetrate the microscopic 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. As the atoms combine, they weaken the metal, making the structure brittle and crumbly.


Oxidation of iron

When iron is in contact with water and oxygen, it rusts. If
salt Salt is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure fo ...

salt
is present, for example in
seawater Seawater, or salt water, is water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for al ...

seawater
or
salt spray Salt is a mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is ...
, 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 layer, protects the bulk iron from further oxidation. The conversion of the passivating
ferrous oxide Iron(II) oxide or ferrous oxide is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition ...
layer to rust results from the combined action of two agents, usually oxygen and water. Other degrading solutions are
sulfur dioxide Sulfur dioxide (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the autho ...
in water and
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
in water. Under these corrosive conditions,
iron hydroxide Iron oxides are chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemica ...
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. 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'' for more details.


Associated reactions

The rusting of iron is an electrochemical process that begins with the transfer of
electron The electron is a subatomic particle (denoted by the symbol or ) whose electric charge is negative one elementary charge. Electrons belong to the first generation (particle physics), generation of the lepton particle family, and are general ...

electron
s from iron to oxygen. 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 An electrolyte is a medium containing ions that is electrically conducting Electrical resistivity (also called specific electrical resistance or volume resistivity) is a fundamental property of a material that quantifies how strongly it resis ...

electrolyte
s, as illustrated by the effects of
road salt Sodium chloride , commonly known as salt (although sea salt also contains other chemical salt (chemistry), salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With Molar mass, mola ...
on the corrosion of automobiles. The key reaction is the reduction of oxygen: :O2 + 4  + 2  → 4  Because it forms
hydroxide Hydroxide is a diatomic anion with chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other sym ...
ion An ion () is an atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ...
s, this process is strongly affected by the presence of acid. Likewise, the corrosion of most metals by oxygen is accelerated at low
pH
pH
. Providing the electrons for the above reaction is the oxidation of iron that may be described as follows: :Fe → Fe2+ + 2  The following
redox reaction (mild reducing agent) are added to powdered potassium permanganate (strong oxidizing agent), a violent redox reaction accompanied by self-ignition starts. Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction in whi ...

redox reaction
also occurs in the presence of water and is crucial to the formation of rust: :4 Fe2+ + O2 → 4 Fe3+ + 2 O2− In addition, the following multistep
acid–base reaction An acid–base reaction is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general che ...
s affect the course of rust formation: :Fe2+ + 2 H2O ⇌ Fe(OH)2 + 2  :Fe3+ + 3 H2O ⇌ Fe(OH)3 + 3  as do the following
dehydration In physiology, dehydration is a lack of total body water In physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology Biology is the natural science that studie ...
equilibria: :
Fe
Fe
(OH)2 ⇌ FeO + :
Fe
Fe
(OH)3 ⇌ FeO(OH) + :2 FeO(OH) ⇌ Fe2O3 + 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
FeO
FeO
and black
lodestone of the Smithsonian Image:Lodestone (black).jpg, Lodestone attracting small bits of iron A lodestone is a naturally magnetized piece of the mineral magnetite Magnetite is a mineral and one of the main iron ore Iron ores are rocks and min ...
or
magnetite Magnetite is a mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure for ...

magnetite
(Fe3O4). High oxygen concentrations favour
ferric In chemistry, iron(III) refers to the chemical element, element iron in its +3 oxidation number, oxidation state. In salt (chemistry), ionic compounds (salts), such an atom may occur as a separate cation (positive ion) denoted by Fe3+. The adject ...

ferric
materials with the nominal formulae Fe(OH)3−''x''O. The nature of rust changes with time, reflecting the slow rates of the reactions of solids. Furthermore, these complex processes are affected by the presence of other ions, such as , which serve as electrolytes which accelerate rust formation, or combine with the
hydroxide Hydroxide is a diatomic anion with chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other sym ...
s and
oxide An oxide () is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by che ...
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 Fe2+ ions and hydroxyl ions. Formation of Fe2+ ions and hydroxyl ions are indicated by blue and pink patches respectively.


Prevention

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. Rust is
permeable Permeability, permeable, and semipermeable may refer to: Chemistry *Semipermeable membrane, a membrane which will allow certain molecules or ions to pass through it by diffusion *Vascular permeability, the movement of fluids and molecules betwee ...
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

Stainless steel forms a passivation layer of
chromium(III) oxide Chromium(III) oxide (or chromia) is an inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition ...
. Similar passivation behavior occurs with
magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

magnesium
,
titanium Titanium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical ele ...

titanium
,
zinc Zinc is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

zinc
,
zinc oxide Zinc oxide is an inorganic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior ...

zinc oxide
s,
aluminium Aluminium (aluminum in and ) is a with the  Al and  13. Aluminium has a density lower than those of other common , at approximately one third that of . It has a great affinity towards , and of on the surface when exposed to air ...

aluminium
,
polyaniline Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. Although the compound itself was discovered over 150 years ago, only since the early 1980s has polyaniline captured the intense attention of the scientific commun ...
, and other electroactive conductive polymers. Special "
weathering steel Weathering steel – '' Fulcrum'' (1987) by Richard Serra in the Broadgate office estate, London">Broadgate.html" ;"title="Richard Serra in the Broadgate">Richard Serra in the Broadgate office estate, London Weathering steel, often referred ...
" 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.


Galvanization

Galvanization consists of an application on the object to be protected of a layer of metallic
zinc Zinc is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical element ...

zinc
by either
hot-dip galvanizing Hot-dip galvanization is a form of galvanization Galvanization or galvanizing ( also spelled galvanisation or galvanising) is the process of applying a protective zinc Zinc is a chemical element with the Symbol (chemistry), symbol Zn ...
or
electroplating Electroplating is a general name for processes that produce a metal coating on a solid substrate through the redox, reduction of cations of that metal by means of a direct current, direct electric current. The part to be coated acts as the cathode ...
. Zinc is traditionally used because it is cheap, adheres well to steel, and provides
cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be reca ...
to the steel surface in case of damage of the zinc layer. In more corrosive environments (such as salt water),
cadmium Cadmium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical eleme ...

cadmium
plating is preferred. Galvanization often fails at seams, holes, and joints where there are gaps in the coating. In these cases, the coating still provides some partial cathodic protection to iron, by acting as a
galvanic anode A galvanic anode, or sacrificial anode, is the main component of a galvanic cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode A cathode is the electrode fro ...
and corroding itself 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 A galvanic anode, or sacrificial anode, is the main component of a galvanic cathodic protection Cathodic protection (CP; ) is a technique used to control the corrosion of a metal surface by making it the cathode A cathode is the electrode fro ...

sacrificial anode
as in traditional galvanized coatings. In some cases, such as very aggressive environments or long design life, both zinc and a
coating A coating is a covering that is applied to the surface of an object, usually referred to as the Substrate (materials science), substrate. The purpose of applying the coating may be decorative, functional, or both. Paints and lacquers are 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  µm zinc coating. Under normal weather conditions, this will deteriorate at a rate of 1 µm per year, giving approximately 85 years of protection.


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 In electrochemistry, electrode potential is the electromotive force In electromagnetism and electronics, electromotive force (emf, denoted \mathcal and measured in volts) is the electrical action produced by a non-electrical source. Devices (kno ...
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.


Coatings and painting

Rust formation can be controlled with coatings, such as
paint Paint is any pigmented liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned wi ...

paint
,
lacquer Lacquer is a type of hard and potentially shiny coating A coating is a covering that is applied to the surface of an object, usually referred to as the substrate Substrate may refer to: Physical layers *Substrate (biology), the natural e ...

lacquer
,
varnish Varnish is a clear transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal uses ...

varnish
, or wax tapes that isolate the iron from the environment. 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 In chemistry, an alkali (; from ar, القلوي ''al-qaly'' "ashes of the saltwort") is a base (chemistry), basic, ionic compound, ionic salt (chemistry), salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as ...

alkaline
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. As a closely related example, iron clamps were used to join
marble Marble is a metamorphic rock , a type of metamorphic rock Metamorphic rocks arise from the transformation of existing rock (geology), rock to new types of rock, in a process called metamorphism upright=1.35, Schematic representation of ...

marble
blocks during a restoration attempt of the
Parthenon The Parthenon (; grc, Παρθενών, , ; ell, Παρθενώνας, , ) is a former temple A temple (from the Latin ) is a building reserved for spiritual rituals and activities such as prayer and sacrifice. Religions which erect te ...

Parthenon
in
Athens, Greece , image_skyline = File:Athens Montage L.png, center, 275px, alt=Athens montage. Clicking on an image in the picture causes the browser to load the appropriate article. rect 15 15 985 460 Acropolis of Athens The Acropo ...
, 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 Lead is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elements ...

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. When only temporary protection is needed for storage or transport, a thin layer of oil, grease or a special mixture such as
Cosmoline Cosmoline is the genericized trademark for a common class of brown wax-like petroleum, petroleum-based corrosion inhibitors, typically conforming to United States Military Standard MIL-C-11796C Class 3. They are viscosity, viscous when freshly ap ...
can be applied to an iron surface. Such treatments are extensively used when " 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.


Bluing

Bluing is a technique that can provide limited 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.


Inhibitors

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

Rust can be avoided by controlling the moisture in the atmosphere. An example of this is the use of
silica gel Silica gel is an amorphous In condensed matter physics Condensed matter physics is the field of physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), ...

silica gel
packets to control humidity in equipment shipped by sea.


Treatment

Rust removal from small iron or steel objects by
electrolysis In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in ...

electrolysis
can be done in a home workshop using simple materials such as a plastic bucket filled with an electrolyte consisting of
washing soda Washing is a method of cleaning Cleaning is the process of removing unwanted substances, such as dirt, infectious agents, and other impurities, from an object or environment. Cleaning occurs in many different contexts, and uses many different m ...

washing soda
dissolved in
tap water Tap water (also known as faucet water, running water, or municipal water) is water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substanc ...

tap water
, a length of
rebar Rebar (short for reinforcing bar), known when massed as reinforcing steel or reinforcement steel, is a steel Steel is an alloy An alloy is an admixture of metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', ...
suspended vertically in the solution to act as an
anode An anode is an electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductiv ...

anode
, another laid across the top of the bucket to act as a support for suspending the object,
baling wireImage:Walmart employee placing bale wire on boxes.jpg, Baling wire in use Baling wire, otherwise known as bale wire, farm wire, or soft wire, is a type of wire used in agriculture and industry for everything from mending fences to manually binding re ...
to suspend the object in the solution from the horizontal rebar, and a
battery charger A battery charger, or recharger, is a device used to put energy into a secondary cell or rechargeable battery A rechargeable battery, storage battery, or secondary cell, (or archaically accumulator) is a type of electrical battery A ...
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 A cathode is the from which a leaves a polarized electrical device. This definition can be recalled by using the ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in which positive charges move. Electrons ha ...
. Rust may be treated with commercial products known as rust converter which contain
tannic acid Tannic acid is a specific form of tannin Tannins (or tannoids) are a class of , ic s that bind to and s and various other organic compounds including s and s. The term ''tannin'' (from ''tanner'', from ''tannāre'', from ''tannum'' ...

tannic acid
or
phosphoric acid Phosphoric acid, also known as orthophosphoric acid or phosphoric(V) acid, is a weak acid with the chemical formula . The pure compound is a colorless solid. All three hydrogens are acidic to varying degrees and can be lost from the molecule ...

phosphoric acid
which combines with rust; removed with organic acids like
citric acid Citric acid is an organic compound In , organic compounds are generally any s that contain - . Due to carbon's ability to (form chains with other carbon s), millions of organic compounds are known. The study of the properties, reactions, ...

citric acid
and
vinegar Vinegar is an aqueous solution of acetic acid and trace compounds that may include flavorings. Vinegar typically contains 5–8% acetic acid by volume. Usually, the acetic acid is produced by a double fermentation; converting simple sugars to eth ...

vinegar
or the stronger
hydrochloric acid Hydrochloric acid +(aq) Cl−(aq) or H3O+ Cl− also known as muriatic acid, is an aqueous solution An aqueous solution is a solution Solution may refer to: * Solution (chemistry) Image:SaltInWaterSolutionLiquid.jpg, upMaking a salin ...

hydrochloric acid
; or removed with chelating agents as in some commercial formulations or even a solution of
molasses Molasses () or black treacle Treacle () is any uncrystallised syrup In cooking, a syrup or sirup (from ar, شراب; ''sharāb'', beverage, wine and la, sirupus) is a condiment that is a thick, viscous The viscosity of a fluid ...

molasses
.


Economic effect

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 — a phenomenon sometimes known as "rust packing". It was the cause of the collapse of the
Mianus river bridge The Mianus River Bridge is a span that carries Interstate 95 Interstate 95 (I-95) is the main north–south Interstate Highway System, Interstate Highway on the East Coast of the United States, running from U.S. Route 1 in Florida, U.S. R ...
in 1983, when the bearings rusted internally and pushed one corner of the road slab off its support. Rust was an important factor in the
Silver Bridge The Silver Bridge was an eyebar-chain suspension bridge built in 1928 and named for the color of its aluminium, aluminum paint. The bridge carried U.S. Route 35 over the Ohio River, connecting Point Pleasant, West Virginia, and Gallipolis, Ohi ...
disaster of 1967 in
West Virginia West Virginia () is a U.S. state, state in the Appalachian region, Appalachian, Mid-Atlantic (United States), Mid-Atlantic and Southeastern United States, Southeastern regions of the United States.The United States Census Bureau, Census Burea ...
, when a steel
suspension bridge A suspension bridge is a type of bridge in which the deck (the load-bearing portion) is hung below suspension cables on vertical suspenders. The first modern examples of this type of bridge were built in the early 1800s. Simple suspension br ...

suspension bridge
collapsed in less than a minute, killing 46 drivers and passengers on the bridge at the time. The
Kinzua Bridge The Kinzua Bridge or the Kinzua Viaduct (, ) was a Rail transport in the United States, railroad Trestle bridge, trestle that spanned Kinzua Creek in McKean County, Pennsylvania, McKean County in the U.S. state of Pennsylvania. The bridge was ta ...
in
Pennsylvania Pennsylvania ( , elsewhere ; pdc, Pennsilfaani), officially the Commonwealth of Pennsylvania, is a landlocked A landlocked country is a country that does not have territory connected to an ocean or whose coastlines lie on endorheic basi ...

Pennsylvania
was blown down by a
tornado A tornado is a violently rotating column of air File:Atmosphere gas proportions.svg, Composition of Earth's atmosphere by volume, excluding water vapor. Lower pie represents trace gases that together compose about 0.043391% of the atmos ...

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 Reinforced concrete (RC), also called reinforced cement concrete (RCC), is a composite material in which concrete's relatively low ultimate tensile strength, tensile strength and ductility are compensated for by the inclusion of reinforcement h ...
is also vulnerable to rust damage. Internal pressure caused by expanding corrosion of concrete-covered steel and iron can cause the concrete to
spall Spall are fragments of a material that are broken off a larger solid physical object, body. It can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressur ...

spall
, creating severe structural problems. It is one of the most common failure modes of reinforced concrete
bridge A bridge is a structure A structure is an arrangement and organization of interrelated elements in a material object or system A system is a group of Interaction, interacting or interrelated elements that act according to a set of rules t ...

bridge
s and buildings. File:Silver Bridge collapsed, Ohio side.jpg, The collapsed
Silver Bridge The Silver Bridge was an eyebar-chain suspension bridge built in 1928 and named for the color of its aluminium, aluminum paint. The bridge carried U.S. Route 35 over the Ohio River, connecting Point Pleasant, West Virginia, and Gallipolis, Ohi ...
, as seen from the
Ohio Ohio () is a state State may refer to: Arts, entertainment, and media Literature * ''State Magazine'', a monthly magazine published by the U.S. Department of State * The State (newspaper), ''The State'' (newspaper), a daily newspaper in Co ...

Ohio
side File:Collapsed Kinzua Bridge.jpg, The
Kinzua Bridge The Kinzua Bridge or the Kinzua Viaduct (, ) was a Rail transport in the United States, railroad Trestle bridge, trestle that spanned Kinzua Creek in McKean County, Pennsylvania, McKean County in the U.S. state of Pennsylvania. The bridge was ta ...
after it collapsed


Cultural symbolism

Rust is a commonly used
metaphor A metaphor is a figure of speech A figure of speech or rhetorical figure is a word or phrase that entails an intentional deviation from ordinary language use in order to produce a rhetoric Rhetoric () is the Art (skill), art of ...
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 The Midwestern United States, also referred to as the Midwest or the American Midwest, is one of four census regions of the United States Census Bureau The United States Census Bureau (USCB), officially the Bureau of the Census, is a princ ...
and
American Northeast The northeastern United States (also referred to as the American Northeast, the Northeast, and the East Coast) is a geographical region In geography, regions are areas that are broadly divided by physical characteristics ( physical geography), ...
, once dominated by steel foundries, the
automotive industry The automotive industry comprises a wide range of and s involved in the , , , , and of s. It is one of the world's largest by . The automotive industry does not include industries dedicated to the of following delivery to the end-user, such ...
, and other manufacturers, has experienced harsh economic cutbacks that have caused the region to be dubbed the "
Rust Belt The Rust Belt is a region of the Northeastern The points of the compass are the Euclidean vector, vectors by which planet-based directions are conventionally defined. A compass rose is primarily composed of four cardinal directions—north, e ...
". In music, literature, and art, rust is associated with images of faded glory, neglect, decay, and ruin.


Gallery

File:Nandu River Iron Bridge corrosion - 03.jpg, Rusted and pitted struts of the 70-year-old Nandu River Iron Bridge File:Rustpatterns.jpg, Concentric rust patterns breaking through a painted surface Mk 2 handgrenade.JPG, A rusted but otherwise intact Pineapple grenade that was previously buried in the ground near
Opheusden Opheusden is a town in the Dutch province of Gelderland Gelderland (), also known as Guelders () in English, is a province of the Netherlands, occupying the centre-east of the country. With a total area of of which is water, it is the largest ...
,
Netherlands ) , national_anthem = ( en, "William of Nassau") , image_map = EU-Netherlands.svg , map_caption = , image_map2 = BES islands location map.svg , map_caption2 = , image_map3 ...

Netherlands
File:Rust on iron.jpg, Colors and porous surface texture of rust


See also

*
Corrosion engineeringCorrosion engineering is an engineering specialty that applies scientific, technical, engineering skills, and knowledge of natural laws and physical resources to design and implement materials, structures, devices, systems, and procedures to manage c ...


References


Further reading

* Waldman, J. (2015): ''Rust - the longest war.'' Simon & Schuster, New York. {{Authority control Corrosion Iron