Rust

rustingferruginouscorrosioniron oxiderust stainrustsaccelerating corrosioncorrosivityoxidationoxidative rusting
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.wikipedia
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Iron

FeFe 2+ Fe(III)
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.
Fresh iron surfaces appear lustrous silvery-gray, but oxidize in normal air to give hydrated iron oxides, commonly known as rust.

Corrosion

corrosion resistancecorrodecorrosive
Rusting is the common term for corrosion of iron and its alloys, such as steel.
Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion.

Iron(III) oxide

ferric oxideFe 2 O 3 iron oxide
Rust consists of hydrated iron(III) oxides Fe 2 O 3 ·nH 2 O and iron(III) oxide-hydroxide (FeO(OH), Fe(OH) 3 ).
Iron(III) oxide is often called rust, and to some extent this label is useful, because rust shares several properties and has a similar composition.

Oxide

oxidesmetal oxideO
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.

Iron(III) oxide-hydroxide

iron(III) hydroxideferric hydroxidehydrated iron oxide
Rust consists of hydrated iron(III) oxides Fe 2 O 3 ·nH 2 O and iron(III) oxide-hydroxide (FeO(OH), Fe(OH) 3 ).
The γ polymorph lepidocrocite is commonly encountered as rust on the inside of steel water pipes and tanks.

Metal

metalsmetal ionsmetal ion
Many other metals undergo similar corrosion, but the resulting oxides are not commonly called rust.
Most will react with oxygen in the air to form oxides over various timescales (potassium burns in seconds while iron rusts over years).

Redox

oxidationreductionoxidized
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.
The reaction can occur relatively slowly, as with the formation of rust, or more quickly, in the case of fire.

Rebar

reinforcing steelrebarsreinforcing bar
Rebar used in underwater concrete pillars, which generates green rust, is an example. 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, tap water, lengths of rebar, washing soda, baling wire, and a battery charger.
Common rebar is made of unfinished tempered steel, making it susceptible to rusting.

Iron oxide

iron oxidesferruginousiron hydroxide
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.
Common rust is a form of iron(III) oxide.

Ferric

Fe 3+ iron(III)ferric iron
High oxygen concentrations favour ferric materials with the nominal formulae Fe(OH) 3−x O x⁄2.
Iron(III) is usually the most stable form of iron in air, as illustrated by the pervasiveness of rust, an insoluble iron(III)-containing material.

Iron(II) oxide

ferrous ironferrous oxideFeO
The conversion of the passivating ferrous oxide layer to rust results from the combined action of two agents, usually oxygen and water.
One of several iron oxides, it is a black-colored powder that is sometimes confused with rust, the latter of which consists of hydrated iron(III) oxide (ferric oxide).

Weathering steel

Cor-Ten steelcorten steelCor-Ten
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.
Weathering steel, often referred to by the genericized trademark COR-TEN steel and sometimes written without the hyphen as corten steel, 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.

Oxygen

OO 2 molecular oxygen
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.
Oxygen is present in the atmosphere in trace quantities in the form of carbon dioxide . The Earth's crustal rock is composed in large part of oxides of silicon (silica, as found in granite and quartz), aluminium (aluminium oxide, in bauxite and corundum), iron (iron(III) oxide, in hematite and rust), and calcium carbonate (in limestone).

Green rust

Rebar used in underwater concrete pillars, which generates green rust, is an example.
They are believed to be intermediates in the oxidative corrosion of iron to form iron(III) oxyhydroxides (ordinary brown rust).

Electrochemistry

electrochemicalelectrochemistelectrochemical reaction
If salt is present, for example in seawater or salt spray, the iron tends to rust more quickly, as a result of electrochemical reactions.
Corrosion is an electrochemical process, which reveals itself in rust or tarnish on metals like iron or copper and their respective alloys, steel and brass.

Passivation (chemistry)

passivationpassivatingpassivation layer
As with other metals, like aluminium, a tightly adhering oxide coating, a passivation layer, protects the bulk iron from further oxidation.
The passivation process removes exogenous iron, creates/restores a passive oxide layer that prevents further oxidation (rust), and cleans the parts of dirt, scale, or other welding-generated compounds (e.g. oxides).

Rust converter

corrosion treatmentsrust remover
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 the stronger hydrochloric acid; or removed with chelating agents as in some commercial formulations or even a solution of molasses.
Rust converters are chemical solutions or primers that can be applied directly to an iron or iron alloy surface to convert iron oxides (rust) into a protective chemical barrier.

Ferroxyl indicator solution

Onset of rusting can also be detected in laboratory with the use of ferroxyl indicator solution.
It is often used to detect rusting in various situations.

Electrolysis

electrolyticelectrolyzedelectrolyze
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, tap water, lengths of rebar, washing soda, baling wire, and a battery charger.
Because the process separates the non-metallic particles from the metallic ones, it is very useful for cleaning a wide variety of metallic objects, from old coins to even larger objects including rusted cast iron cylinder blocks and heads when rebuilding automobile engines.

Mianus River Bridge

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.
Rust formed within the bearing of the pin, exerting a force on the hanger which was beyond design limits for the retaining clamps.

Reinforced concrete

ferro-concreteferroconcretesteel-reinforced concrete
Reinforced concrete is also vulnerable to rust damage.
When rebar corrodes, the oxidation products (rust) expand and tends to flake, cracking the concrete and unbonding the rebar from the concrete.

Water

H 2 Oliquid wateraqueous
Rust is an iron oxide, a usually red oxide formed by the redox reaction of iron and oxygen in the presence of water or air moisture.

Spectroscopy

spectroscopiclaser spectroscopyspectroscopist
Several forms of rust are distinguishable both visually and by spectroscopy, and form under different circumstances.

Friability

friableinduratedbleeding
friable, and it provides no protection to the underlying iron, unlike the formation of patina on copper surfaces.

Patina

patinatedpatinationpatinas
friable, and it provides no protection to the underlying iron, unlike the formation of patina on copper surfaces.